This study examines the effect of the UK COVID-19 lockdown on nitrogen dioxide road traffic emissions and the potential change in carbon dioxide air traffic emissions based on airport usage. In doing so, it compares air quality in specific areas of Greater London and the Scottish Highlands, allowing insight into possible ways that lockdown can change damaging environmental impacts as restrictions relax and beyond. Data collected prior to and during lockdown from urban and suburban air quality monitoring systems allow opportunities to compare findings with emissions targets set by UK governmental bodies and the Paris Agreement. Data collection methods include the use of chemiluminescence, retrieving airport data, and questionnaires. Investigations reveal that some of the more densely populated areas examined have reached air pollution targets over the lockdown period. Nitrogen dioxide concentrations have halved in all the urban areas and suburban areas examined. The findings are interesting as the decrease is not solely due to the enforced lockdown; the prior rapid spread of the first UK COVID-19 cases resulted in a steep decline in air pollution. Lockdown has helped to prolong these lower concentrations but there is concern that these could return to pre-lockdown levels as restrictions end. Citizens are keen to continue lockdown routines post-lockdown, however, almost half indicate that this will not be possible.
This unique study compares the early 2020 air quality of the Greater London region with the Scottish Highlands. These UK regions are chosen for comparison due to their contrasting geographical location, environmental status and urban contrasts.
It should be noted that Greater London’s Air Quality Focus Areas monitor the region’s most highly polluted areas. However, this study focuses on the effect of decreased movement on traffic nitrogen dioxide emissions by specifically examining a cross-section sample of three Air Quality Monitoring Areas in the Greater London agglomeration as these offer a more comparative examination against the two urban and rural environments within the Highland Council area. It is considered that the specific locations targeted within these areas will provide a more balanced representation of both regions.
Greater London is a highly urbanised region of south-eastern England. Statistics for 2019 show a population of 8,961,989 within an area of 607 square miles (1572 km2), giving a population density of 14,764 per square mile (5,701 per km2). Vehicle licencing data for that period records 3,058,800 vehicles throughout the 32 Boroughs and the City of London which comprise the Greater London region. Heathrow airport, in the London Borough of Hillingdon, is the sole provider of international flights in the Greater London agglomeration.
The Highlands is a sparsely populated, remote area of northern Scotland. Statistics for 2019 indicate a population of 235,830 within an area of 9,905 square miles (25,654 km2), giving a population density of 24 per square mile (9 per km2). Vehicle licencing for 2019 records 158,000 vehicles throughout the Highland Council area. Inverness Airport, part of the Highlands and Islands Airports Limited group, is located 8 miles north-east of the city of Inverness and is the only commercially scheduled flight hub in the area.
Both regions are ultimately under generalised UK agreements and governance.
The Greater London region incorporates 32 Boroughs, each with designated local government powers and responsibilities whereas the City of London, at the centre of the Greater London region, falls under the authority of the City of London Corporation. However, the Greater London Authority (GLA) encompasses all 33 subdivisions at a next-tier level.
The Highland Council has authority at local government level but it is ultimately under the jurisdiction of the Scottish Government where devolved authority is granted by the UK Government.
Air Quality Legislation and Transport Strategies:
European Parliament Directives necessitate annual UK governmental response to show compliance with the Council Directive on ambient air quality and cleaner air for Europe and the Fourth Daughter Directive under the Air Quality Framework Directive.
With compliance to European Directives, the UK Government forms legislative air quality and transport policy on the basis of the independent advice to the Department for Environment, Food & Rural Affairs (DEFRA) by the Air Quality Expert Group who provide specialist knowledge of the levels, sources and characteristics of UK air pollutants. Nationwide legislation within DEFRA’s Clean Air Strategy then cascades to the formulation of more specific and regional air quality, transport and emissions policies. In accordance with EU directives the UK government’s strategy sets out targets to ensure that nitrogen dioxide concentrations never exceed more than a 200μg/m3 hourly mean limit in any area on more than eighteen occasions a year and remain within the annual mean limit value of 40 μg/m3.
A Scotland-wide air quality policy outlining the nation’s plan to further develop future air quality improvements ’Cleaner Air for Scotland – The Road to a Healthier Future’ is administered by the devolved powers of the Scottish government, with a regional action plan at local government level in the case of the Highland Council area. Transport Scotland further supports governmental policy by ensuring environmental and economic sustainability throughout Scotland’s land, air and water transport networks. Similarly, for the Greater London region of England, the GLA’s London Environment Strategy (2018) outlines present and long-term plans to address the persistent climate change, air quality and transport challenges presented by such a dense urban environment. Transport for London operate under the instruction of the GLA to monitor, maintain and improve all aspects of road, rail and bus transportation in the region.
Inverness Airport is targeting emissions, air quality and ecological issues within its Environmental Strategy 2020-2030 and Heathrow Airport’s Carbon Neutral Growth Roadmap sets out similar plans towards a target of carbon neutrality by 2050.
As transmission of the virus is via close proximity to respiratory droplets, it rapidly reached pandemic status as defined by the World Health Organisation. This resulted in trans-global governmental action to slow transmission and save lives. In an attempt to protect citizens, world leaders imposed lockdown conditions to restrict human contact and movement, forcing some of the strictest bans on everyday activities since the Second World War. Globally, the most vulnerable citizens were instructed to stay at home due to the consequential risk of serious infection.
In the UK, the implementation of these stringent lockdown measures resulted in a sudden and dramatic decrease in human circulation in all settlements. Unless deemed absolutely necessary, all workplaces and educational establishments closed, and citizens began to establish new work and study routines from home. Recreational and leisure activities were also prohibited although daily exercise was encouraged due to the physical and mental health benefits. This generated increased interest and unexpected opportunities to walk or cycle although some citizens remained sceptical through fear of transmission. The decrease in human circulation resulted in a substantial decline in road traffic. Demand for public transport diminished, partly due to social distancing and transmission concerns. Domestic and international flights were grounded and airports closed too.
Air Quality & Public Health:
Nitrogen dioxide, produced mainly by vehicle engines, is statistically one of the most harmful pollutants causing a significant long-term threat to public health and ecosystems. Over decades, the rapid global increase in air pollution has exacerbated the triggers for respiratory problems even when present in small concentrations. Exposure can also be problematic to citizens in less densely populated cities. However, recent studies of worldwide lockdown have shown significant reductions of up to 70% of such pollutants in Asian countries, albeit less in Europe.
The Paris Agreement and The European Commission’s 2030 Energy & Climate Framework:
Variations in environmental air quality can be assessed by investigating the concentration of air pollutants over the lockdown period. It is further necessary to examine the efficacy of the Paris Agreement in reducing harmful emissions and explore the potential of the European Commission’s 2030 Energy & Climate Framework in its aim to mitigate rapidly increasing global temperatures by reducing carbon dioxide emissions by 40% of 1990 levels by 2030. There is no doubt that the COVID-19 pandemic alone will have limited positive impact on the long-term threat of climate change; it is in the exit strategy where more ground can be gained.
Prior to the COVID-19 pandemic, environmental and ecological studies have highlighted the urgent requirement for global action to reduce pollutants to protect citizens and habitats. Previous projects and recent outcomes have called for communities to adapt attitudes and behaviours towards domestic and industrial travel, and import and export migration in relation to the ecology of the local region. More recent studies of world lockdowns have focused mainly on larger cities with specific attention to industrial behaviours. Further urban studies found that lockdown measures drastically mitigated emissions with air quality improving dramatically.
Aims & Hypotheses:
Enforced habit changes and unprecedented travel restrictions may significantly affect UK air pollutant concentrations in all areas. Diverse environments may need to be addressed separately with specific localised attention to establish how the concentration of emissions may evolve.
Primarily, this study analyses the effect of mobility restrictions on air quality with focussed attention to the pollution caused by road and air traffic in areas of Greater London compared to the Scottish Highlands. It aims to investigate the overall significance of any potential air quality divergence by comparing the levels of nitrogen dioxide in specific locations and examining the historic carbon emissions of Heathrow Airport and Inverness Airport from currently available data. It examines whether the concentration of these air pollutants in the selected sectors meet the overall targets for mitigating air pollution and climate change or if more work is required. In 2019, the Highland Council area (Non-agglomeration Zone: UK0039) was compliant for both hourly and annual limits for nitrogen dioxide pollutants whereas Greater London (Agglomeration Zone: UK0001) satisfied the hourly limit values but exceeded the annual limit values.
It is hypothesised that this study will find that the sudden reduction in road and air traffic activity during lockdown could beneficially affect air quality across urban and suburban environments. However, as this has clearly been demonstrated in numerous earlier papers, this study asks whether enforced lockdowns were the sole contributory factor or if there are further considerations.
Investigation outcomes are recorded in the results section where the facts and trends of all datasets are reported. A discussion and conclusion follow in which the significance of the findings describe how an unprecedented change in behaviour and activity over lockdown may result in a change in air quality. It further explores how changes in air traffic pollution compare to multi-source targets set by the European Directives and makes recommendations for retaining any potential air quality benefits.
To capture pertinent and real-time data it is necessary to undertake this study during the COVID-19 lockdown period – specifically March to July 2020. Therefore, investigative methods of data collection include:
- the use of chemiluminescence within targeted urban and suburban nitrogen dioxide monitoring systems,
- retrieval of statistical carbon dioxide emissions and terminal footfall data from specific airports,
- a worldwide public opinion, habit and movement survey.
Nitrogen Dioxide Monitoring Systems:
Met Office integrated data systems (MIDAS) were not selected for data analysis as the location of their monitors in Highland would not offer valid comparison. Therefore, data is examined from selected governmental urban roadside and suburban background air quality monitoring systems in Greater London and the Scottish Highlands, namely:
- Greater London – Borough of Camden, Euston Road (CD009): an Inner London area with an urban traffic environment,
- Greater London – Royal Borough of Greenwich, Eltham (LON6): an Outer London area with a more suburban background environment,
- Greater London – Royal Borough of Kensington & Chelsea, Cromwell Road (KC2): an Inner London area with an urban background environment,
- Highland Council area – Inverness, Academy Street (INV03): a city centre area with an urban traffic environment,
- Highland Council area – Fort William (FW): a suburban background environment surrounded by mountains and lochs.
Daily mean nitrogen dioxide concentrations are calculated from hourly data held in Scottish Air Quality and Air Quality England data repositories. This hourly data is robust as it derives from the chemiluminescence technique used by each of the targeted automatic monitoring systems. Chemiluminescence offers an effective analysis of air quality by determining very low concentrations of nitrogen dioxide in hourly intervals with an accuracy of greater than 99% for the full air sample investigated.
Nitrogen dioxide concentrations are also calculated for the period January to July 2020 to examine how implementation or removal of lockdown measures affects air pollution levels. The results from the specified nitrogen dioxide air quality monitoring systems are compared to overall UK environmental targets to see whether or not each area investigated makes a positive contribution to those targets.
Air Traffic Carbon Dioxide Emissions Data:
Unlike nitrogen dioxide, corresponding carbon dioxide emissions data are not accessible on a real-time basis as higher frequency data collection systems are currently unavailable for 2020 data collection.
Historical data showing annual carbon dioxide emissions is available but such annual data reporting will not give a statistically accurate representation of how lockdown affects carbon dioxide emissions for that specific period. Generally, carbon dioxide emissions data are released years after collection despite the push for mitigating climate change related issues. Consequently, only predictions can be made for present and long-term carbon dioxide emissions. However, statistical evidence of terminal and air passenger usage at London Heathrow Airport and Inverness Airport is recorded in the Civil Aviation Authority’s database. For comparison, this study examines the 2018 and 2019 data to identify any significant change in the number of airport terminal passengers in the 2020 lockdown period. The 2018 and 2019 data act as a control to show a pre-established trend, therefore no mean calculations are necessary.
Habit and Mobility Survey:
In April 2020, a worldwide online public survey was used to ascertain whether citizens felt motivated to retain newly developed lockdown habits and routines once a post-lockdown normality is established. The results from anonymous respondents in England and Scotland may not guarantee an accurate representation of the people of Greater London and the Scottish Highlands, however, the findings illustrate a general consensus.
Figure 1 identifies the AQMA in Academy Street, Inverness, the capital city of the Scottish Highlands. Academy Street is ranked the fourth most nitrogen dioxide polluted road in Scotland and thus requires special attention to reduce the effects of pollutants. The AQMA highlighted in the map is located in the centre of Academy Street where concentrations of nitrogen dioxide are predictably high due to a high concentration of vehicles and insufficient space for pollutants to escape the dense urban city centre confines.
Areas highlighted in green and yellow in Figure 2 indicate the AQMAs of Greater London. This indicates that individual boroughs have plans in place to reduce air pollution in areas of their local governance.
Figure 1: Inverness City Centre showing the Air Quality Management Area (AQMA). (The Highland Council/Europa 2021). Copyright Via Europa @ 2020 Europa Technologies Ltd. All rights reserved.
Figure 2: Greater London showing the AQMAs highlighted in green and yellow to indicate all that monitor nitrogen dioxide (DEFRA 2020) (contains public sector information licensed under the Open Government Licence v2.0).
Figure 3 illustrates a marginal rise in mean nitrogen dioxide concentrations in the urban areas of Euston Road (London Borough of Camden) and Academy Street (Inverness, Highland) after the first UK COVID-19 cases were confirmed, followed by a steep and significant decrease prior to lockdown being officially imposed. This decrease continued bilaterally during lockdown but less dramatically in Inverness. The trends then levelled before gradually increasing as lockdown restrictions relaxed and the UK economy began to reboot. Notably, there was a delay in the trend’s increase in Inverness compared to Camden as lockdown restrictions remained in place for an additional three weeks in Scotland.
Figure 3: Comparison of mean nitrogen dioxide concentrations in London Camden (Euston Road) and Highland, Inverness (Academy Street) from 01/01/2020 – 01/07/2020 (Air Quality England 2020) and (Scottish Air Quality 2020).
Figure 4 illustrates the change in mean nitrogen dioxide concentrations in the suburban background areas of Eltham (Royal Borough of Greenwich, London) and Fort William (Highland). These areas demonstrated similar trends in concentrations over the period. The trendline shows that data for Fort William reached a 2020 maximum of 6μg/m3 soon after the announcement of the first UK COVID-19 case in England and decreased by approximately 3μg/m3 throughout the lockdown period. The trend continued to decrease even after restrictions began to ease. Conversely, the trendline for Eltham illustrates a more significant change in nitrogen dioxide concentrations as a maximum concentration of 18μg/m3 was observed prior to the arrival of the first COVID-19 case in the UK reducing by around 6μg/m3 throughout early lockdown. Again, the trend continued to decrease even after restrictions began to ease.
Figure 4: Comparison of mean nitrogen dioxide concentrations in London Eltham and Fort William, Highland, from 01/01/2020 – 29/07/2020 (Air Quality England 2020) and (Scottish Air Quality 2020).
Table 1 demonstrates that nitrogen dioxide concentrations in the urban areas of Euston Road and Academy Street decreased by 37% and 50% respectively during lockdown compared to pre-lockdown concentrations. Nitrogen dioxide concentrations began to increase in Euston Road as lockdown restrictions eased but continued to decline in Academy Street although both changes were negligible. A 5% and 48% reduction in mean nitrogen dioxide concentrations were observed from pre-lockdown to enforced lockdown in the suburban areas of Eltham and Fort William respectively. Mean concentrations in both of these areas continued to fall even when restrictions began to ease.
Table 1: Mean nitrogen dioxide concentrations in targeted urban and suburban areas over specific periods of 2020 (Air Quality England 2020) and (Scottish Air Quality 2020).
|Time Period||Mean Nitrogen Dioxide Concentration (μg/m3)|
Environment: Urban traffic
Environment: Urban traffic
|Prior to first UK COVID-19 case (01/01/20 – 30/01/20)||61.6||32.0||18.4||5.8|
|Prior to start of UK Lockdown
(31/01/20 – 25/03/20)
|UK Lockdown Restrictions
(26/03/20 – 10/05/20)
|Easing of UK Lockdown Restrictions (11/05/20 – 02/07/20)||37.2||15.6||10.7||2.5|
Figure 5 shows that the number of air terminal passengers at Inverness Airport fell by 49% in March 2020 compared to March 2019 figures. Passenger numbers then decreased to zero throughout April and May before gradually beginning to increase in June and July although passengers still remained at 88% – 99% fewer than the same time the previous year. There are historically fewer terminal passengers at Inverness Airport during winter months. Data for 2018 and 2019 were included to demonstrate that the COVID-19 lockdown has markedly reduced the number of terminal passengers from the standard pattern.
Figure 5: Number of terminal passengers at Inverness Airport from January 2018 to July 2020 (Civil Aviation Authority 2020).
Figure 6 illustrates that lockdown has resulted in a dramatic decrease in air terminal passengers at London Heathrow Airport. Terminal passengers fell by 52% in March compared to March 2019 figures. Passenger numbers then decreased drastically throughout April and May showing a 97% decrease on the same months in 2019. Passenger numbers were slow to return in June and July staying at between 89% – 95% down on the same period in 2019. There are historically fewer terminal passengers at Heathrow Airport during winter months. Data for 2018 and 2019 were included to demonstrate that the COVID-19 lockdown has markedly reduced the number of terminal passengers from the standard pattern. Figures 5 & 6 illustrate similar seasonal and lockdown trends.
Figure 6: Number of terminal passengers at London Heathrow Airport from January 2018 to July 2020 (Civil Aviation Authority 2020).
Figure 7 uses anonymous questionnaire responses to suggest that people in Scotland were marginally more inclined to continue to implement their lockdown routines post-lockdown if circumstances would allow. It should be noted that the data corresponds to the general population of Scotland rather than just the Highlands. Figure 8 uses anonymous questionnaire responses to suggest that people in England were more inclined to continue to implement lockdown routines post-lockdown if circumstances would allow. It should be noted that the data corresponds to the general population of England rather than just Greater London.
Figure 7: Number of survey respondents in Scotland who say they will or will not continue to enforce lockdown routines once lockdown ends (Campbell 2020, Unpublished results).
Figure 8: Number of survey respondents in England who say they will or will not continue to enforce lockdown routines once lockdown ends (Campbell 2020, Unpublished results).
Table 2 records the annual mean nitrogen dioxide concentrations and percentage changes from Cromwell Road, London and Academy Street, Inverness in order to compare changes in concentrations in recent years against the first seven months of 2020 for both urban settlements. It also provided the opportunity for comparison against the targets set by the Paris Agreement. It should be noted that the 2020 figures deviated from the norm due to a significant period of lockdown in the spring and part-year reporting.
Table 3 illustrates transport carbon dioxide emissions from 1990-2019 including road transport, domestic aviation, railways and domestic shipping. This UK wide data was examined in the absence of specific carbon dioxide data collection devices in the targeted locations. It allows for comparison of carbon dioxide impacts from a 1990 baseline with associated percentage changes. Data for 2019 is provisional and 2020 carbon dioxide emissions data have yet to be released. However, the study by Le Quéré et al. 2020 offers calculation of global carbon dioxide emissions across all sources for the lockdown periods.
Table 2: Mean annual/part-annual nitrogen dioxide concentrations and percentage changes recorded at Cromwell Road, London and Academy Street, Inverness, Highland from 2017 to July 2020 inclusive (Air Quality England 2017-2020) and (Scottish Air Quality 2017-2020).
|Year||Annual Mean NO2 Concentration (μg/m3)
Royal Borough of Kensington & Chelsea:
|Change from Previous Annual NO2 Mean (%)
Royal Borough of Kensington & Chelsea:
|Annual Mean NO2 Concentration (μg/m3)
|Change from Previous Annual NO2 Mean (%)
Table 3: UK Transport Carbon Dioxide Emissions 1990-2019. (DBEIS 2018:2, 2019:2 & 2020:2 2020:3).
CO2 Emissions (MtCO2e)
|Change from Previous
5-Year Traffic CO2 Emissions (%)
|Change from Previous
Annual Traffic CO2 Emissions (%)
|Change from 1990 Traffic CO2 Emissions (%)|
Nitrogen Dioxide Concentrations:
Figure 3 offers a comparison of the change in nitrogen dioxide concentrations associated with the lockdown in the selected urban areas of London Camden (Euston Road) and Inverness (Academy Street). As nitrogen dioxide is one of the main air pollutants emitted from vehicle engines the decrease in nitrogen dioxide concentrations shown in Figure 3 suggests that the number of vehicular journeys may have decreased in both areas. This is interesting as it can be realised that it was not solely the implementation of the UK COVID-19 lockdown confinements that caused citizens to reduce vehicular journeys; voluntary changes in population behaviour prior to enforced lockdown could also have been a contributory factor.
The apparent three-week delay in the increase in nitrogen dioxide concentrations in Inverness compared to London Camden could be attributed to the first COVID-19 cases being reported on 31st January in England and 2nd March in Scotland and the resultant extended lockdown period imposed on Scotland’s citizens. Therefore, Figure 3 could further suggest that Scotland has approximately three weeks to monitor how England’s air quality evolves as it leaves lockdown. Consequently, Scotland’s citizens could learn from England’s roadmap out of lockdown in terms of air quality and be prudent regarding unnecessary travel and use more economical means of transport such as walking and cycling.
Table 2 examines the mean annual nitrogen dioxide concentrations recorded over three and a half years for London’s Cromwell Road and Academy Street in Inverness, both urbanised areas. Data comparisons show that, in 2019, both sites exceed the annual mean limit values set by the Paris Agreement of 40μg/m3. The 2020 concentrations are within the target values at both locations as the mean concentration for 2020 is 29μg/m3 for Cromwell Road and 24μg/m3 for Academy Street at the end of July. These figures are 28% and 40% under the specified limit respectively. Cromwell Road has made significant progress in achieving the targets in the two preceding years although historical data since site monitoring began in 1998 shows that the area has consistently struggled to control air pollution. Academy Street figures have been static since the monitoring system was installed in late 2016 but rise significantly in 2019. Concentrations for the early segment of 2020 show percentage decreases from 2019 levels of 34% (Cromwell Road) and 44% (Academy Street). Clearly, these are within limit values, but this data is not yet robust due to part-year reporting.
Figure 4 offers a comparison of the change in nitrogen dioxide concentrations associated with the lockdown in the selected suburban areas of London Eltham and Fort William. Fort William is a town of approximately ten thousand citizens with relatively low town activity per se. The change in inhabitants\’ behaviour there from pre-lockdown to during lockdown is noticeable but has a less consequential impact on habitually low nitrogen dioxide concentrations. This change in Eltham is not huge in comparison to more urban areas but it could mark a less significant change in human activity from pre-lockdown to during lockdown.
The cancellation of international flights could proffer an explanation of any recognised increase in nitrogen dioxide concentrations in suburban areas over the summer months as citizens opt for a staycation in the countryside. Movement around the country and a rise in road traffic could result in increases in vehicular emissions as lockdown measures further relax.
Table 1 illustrates that suburban areas predictably have lower concentrations of nitrogen dioxide than urban roadside areas. Inverness (urban), Fort William (suburban), and London Eltham (suburban) have successfully remained under the UK government’s nitrogen dioxide target limit of an annual mean of 40μg/m3 both prior to and during lockdown. Urban Inverness comfortably remained under this target prior to lockdown but the implementation of lockdown and a possible subsequent decrease in travel has significantly improved the ability to remain under the target with nitrogen dioxide concentrations halving over recent months. Suburban areas have also remained under the target prior to and during lockdown. It is particularly interesting that the COVID-19 lockdown has enabled the more urban areas of high population within Central London, like Camden, to fall below the target limits. Although the figures account for a shorter portion of the year, this area of Central London has seen a decrease of 37% in nitrogen dioxide concentrations from pre-lockdown to during lockdown and before the first easing of restrictions. However, there is concern that a possible increase in nitrogen dioxide concentrations could follow in the near future as lockdown restrictions further relax. With Central London precariously falling short of the proposed target limits and increased traffic expected in the near future, these concentrations could soar by returning to levels similar to those seen prior to lockdown. The trendline in Figure 3 also illustrates that nitrogen dioxide concentrations are beginning to increase in both urban areas of Euston Road and Academy Street. This suggests the need for immediate measures to remain within the target limit for nitrogen dioxide emissions.
Figures 7&8 illustrate relatively balanced ideologies as citizens are keen to retain their lockdown routines post-lockdown but approximately half the anonymous survey respondents believed they will be unable to sustain newly developed routines and habits. One respondent from an urban area of England stated they wished to maintain some of the silver linings associated with lockdown but that “it is very much going to be in the hands of employers”. They do not envisage that businesses will allow continued or increased flexibility in the workplace and consequently employees could feel forced to return as restrictions ease. Another respondent who resides in a more remote area with poor access to public transport stated that all the village shops were closed, therefore “using the car for shopping is an essential”. These responses suggest that citizens in both urban and suburban areas could travel more post-lockdown leading to increased vehicular emissions similar to pre-lockdown levels. Nitrogen dioxide concentrations could return to 2019 levels where the area investigated on Cromwell Road (Royal Borough of Kensington & Chelsea) in Greater London was close to meeting the 40μg/m3 annual mean limit value, recording 44μg/m3. A sudden and prolonged surge in nitrogen dioxide emissions could place the area at substantial risk of, again, failing to meet the target for mitigating nitrogen dioxide emissions.
Actions Authorities are taking to Reduce Traffic Air Pollution:
Table 1 records mean nitrogen dioxide concentrations for four areas at specific timescales. The data examined shows that 1st February had the highest mean nitrogen dioxide concentration in Academy Street in the first half of 2020 with readings reaching 144.6μg/m3. This demonstrates that the Highland Council has successfully met the hourly mean nitrogen dioxide concentration limit throughout the first six months of 2020. The government also outlines UK targets to ensure that the annual mean nitrogen dioxide concentration does not surpass 40μg/m3 in any area. The Highland Council has successfully monitored and controlled these levels throughout the first six months of 2020 with a daily mean nitrogen dioxide concentration 23.5μg/m3 as of 1st July; 41% below the target limit although this is not a prediction of an annual outcome.
The Highland Council collaborates with HITRANS, a transport company for the Highlands and Islands, in the £3-6million project, ‘Accessing Inverness’. The project aims to provide more city centre space for pedestrians and cyclists by sacrificing road space for pedestrianised areas and strives to beautify the city centre by adding greenery to make the environment more ecologically friendly. The introduction of more roadside greenery could mitigate nitrogen dioxide concentration by absorbing pollutants thus leading to a possible cleaner atmosphere. These proposals could see a further reduction in nitrogen dioxide emissions resulting from a dramatic decrease in city centre vehicles, citizens using more economical means of travelling or choosing to walk. Improved access to Inverness Railway Station and the Eastgate Shopping Centre could result in a reduced need for public transport. In line with the Climate Change (Scotland) Act, the Highland Council has additional plans to mitigate climate change and improve air quality which aim to:
- Reduce greenhouse gases,
- Implement measures to adapt to the changing climate,
- Work in a sustainable way,
- Implement the Carbon CLEVER project,
- Implement and strengthen the Highland Climate Change Adaptation Initiative,
- Monitor Air Quality Management Areas,
- Promote smarter travel choices,
- Promote low emissions vehicles and supporting infrastructure,
- Assess and improve traffic management,
- Implement the ‘Safer Routes to School’ campaign,
- Implement the ‘Go For It’ walking and cycling incentive,
- Encourage low carbon travel and transport wherever possible.
Figure 3 data was collected from air quality monitoring systems in Inverness, Highland, and Euston Road in the London Borough of Camden. Euston Road is adjacent to Euston Station, ranked the sixth most used UK train station and predicted to become busier with the development of the HS2 rail links. As a major transport hub, it is reasonable to assume that there are high concentrations of nitrogen dioxide here due to heavy vehicular traffic around the area and ambient rail transport emissions. However, nitrogen dioxide concentrations in Euston Road have never surpassed the target limit in 2020 with a maximum hourly mean concentration of 150.1μg/m3 on 16th February. This is slightly higher than concentrations in Inverness but is to be expected as London is a more urbanised, highly populated city. Data used to plot Figure 3 indicates that the mean nitrogen dioxide concentration for the first half of 2020 in Euston Road is 46.1μg/m3 which is 6.1μg/m3 (15%) greater than the target limit. This suggests that authorities in Camden are not addressing the air pollution issues rigorously enough. However, the period of data collection from January to June means that significant changes to nitrogen dioxide concentrations could take place throughout the year thus possibly lowering the annual mean, but with nitrogen dioxide concentrations on the rise, this may not happen.
Like Inverness, Greater London strives to improve ambient air quality. The London Borough of Camden is partnering with thirty additional London boroughs in the project ‘Idling Action’ which was introduced in 2016 to reduce vehicular emissions from idling road traffic. Traffic congestion and idling is a major problem in densely populated urban areas as increased road traffic can result in higher concentrations of air pollutants. Taller buildings can create a concentrated corridor of air pollution which can significantly affect the health of the population, particularly those already affected by respiratory illness. The GLA is taking additional action across all boroughs under the terms of the London Environment Strategy. This aims to implement, monitor and build on existing air quality strategies including:
- London Local Air Quality Management (LLAQM),
- Central London Ultra Low Emission Zone (ULEZ),
- Plans for a London-wide Low Emissions Zone,
- ‘Green screens’ and ‘school streets’,
- Low Emissions Bus Zones,
- Low Emissions Neighbourhoods (LENs),
- London Electric Vehicle Infrastructure Delivery Plan / ‘Go Ultra Low City’,
- ‘Breathe London’ project,
- Urban Greening,
- London Climate Change Partnership.
Carbon Dioxide Emissions & Air Transport:
Statistics show that the transport sector accounted for approximately a third of total UK carbon dioxide emissions in 2017 overtaking the energy sector, whereas this share had been just a fifth in 1990. Other sectors have cut emissions more effectively, however a steady general decrease in traffic emissions is contributing to the overall required reduction.
Table 3 analyses transport related carbon dioxide emissions across the whole of the UK from 1990 to 2019 although 2019 figures remain provisional. Although the data reveals only a 4.5% reduction in carbon dioxide emissions over the nineteen-year span, there has been a 41% decrease in carbon dioxide emissions across all sources over that period which is in line with the EU’s 2030 Climate & Energy Framework target to reduce greenhouse gas emissions by at least 40% of 1990 levels by 2030.
Figures 5 and 6 illustrate the change in the number of passenger flights at Inverness Airport and London Heathrow Airport respectively. Both figures demonstrate a significant and unprecedented decrease in the number of passengers from February 2020 onwards. This corresponds to the time when the first UK COVID-19 cases were reported, suggesting that airlines and airports had been advised to cancel flights to avoid transmission of the disease. This sharp decrease in air passengers and fewer flights suggests a significant decrease in traffic air pollution although figures have yet to be released. There were no passengers in the Inverness Airport terminal in April and May 2020 suggesting that all commercial flights were cancelled and that any airborne flights were for emergencies or for the transportation of cargo. Figures for both airports also illustrate a significant decrease in the number of passengers flying during winter months possibly further contributing to decreased traffic air pollution. However, an even more significant decrease in the number of passengers at both airports may have been evident had the COVID-19 lockdown related decrease happened during warmer months when the number of passengers travelling had been habitually higher. Fewer operational aircraft could have led to a more significant improvement in air quality due to a greater reduction in the emission of air pollutants. One study found a decrease of 60% of carbon dioxide emissions (a decrease of around 1.7 MtCO2d⁻¹) over the lockdown period in the aircraft industry alone.
As lockdown restrictions ease and passenger demand increases, some airlines are resuming internal flights and selected international flights. Routes from Inverness Airport have started to reopen with the popular British Airways route from Inverness Airport to London Heathrow Airport back in operation. This suggests that as lockdown restrictions ease, more routes will return resulting in a significant increase in air traffic emissions.
Existing Global Legislation & Potential Climatic Impact of a Return to High Emissions:
Since the late 19th century, global mean temperatures have risen by nearly 0.8℃ and have risen by approximately 0.2℃ per decade over the past 25 years. The Paris Agreement aims to mitigate air pollution on a global scale to help slow the rate at which temperatures increase. The European Commission contributes to this under their 2030 Climate & Energy Framework by setting targets to reduce greenhouse gas emissions by 40% of 1990 concentrations by 2030.
The UN Intergovernmental Panel on Climate Change (IPCC) examine the impact of climate change and the effect of greenhouse gas emissions. UK emissions are dominated by carbon dioxide which accounted for approximately 81% of greenhouse gas emissions in 2018. Carbon budgets were introduced in the UK under the 2008 Climate Change Act with each carbon budget setting 5-year targets. In 2019 the target was set at achieving net zero emissions by 2050. The government aims for UK wide net zero road transport emissions by 2050 as outlined in its Road to Zero strategy and consequently will ban sales of combustion vehicle engines from 2030.
Analysis of 2020 data for all areas examined suggest that the COVID-19 lockdown has enabled those urban and suburban settlements to secure a solid position within the Paris Agreement targets for mean annual nitrogen dioxide concentration a decade in advance. However, with such an unprecedented year, and data accounting for only seven months of the year, these levels may be unsustainable going forward.
Table 3 illustrates a 4.5% decrease in UK traffic related carbon dioxide emissions between 1990 and 2019. This helps the UK to meet the European Commission’s 2030 Climate & Energy Framework overall target of reducing greenhouse gas emissions, across all sources, by 2030. As traffic related nitrogen dioxide concentrations have significantly reduced during the early part of 2020, then the same could apply to carbon dioxide emissions. These could decrease further as a result of the lockdown and come confidently within the target a decade in advance. One study discovered a 17% daily decrease in worldwide carbon dioxide emissions by 7th April 2020 in comparison to average emissions in 2019. Almost half of the decrease could have been attributed to the reduction in traffic. It should be noted that this does not apply solely to the UK, but it is a prediction of emissions worldwide.
In June 2019, the UK became a global leader by becoming the first major economy to legislate an end to its contribution to global climate change by 2050. However, with a potential increase in air pollutants to levels seen prior to lockdown, the planet’s atmosphere could continue to warm possibly leading to the detrimental impacts of climate change over coming decades. Higher nitrogen dioxide concentrations, particularly in suburban and rural areas, could cause rain to become acidic causing farmland soil to become infertile and potentially destroy crops and harm wildlife. If the planet continues to warm, Arctic and Antarctic ice sheets will continue to melt rapidly thereby increasing sea levels if this is not carefully monitored. Rising sea levels could cause countries like the Netherlands and cities like New York to flood or become entirely submerged as these areas are close to sea level. Therefore, it is vital to maintain these lower concentrations of nitrogen dioxide.
The efforts of governments and authorities in improving air quality can be noticed relatively quickly at local and national level. Comparatively, improvements in climate change will take generations of effort on a global scale.
The Challenges and Dilemmas of a Post-Lockdown Roadmap:
The enforced change in population activity implies that citizens would travel less frequently. This is perhaps more evident in built up areas and city centres where the population density is greater than in suburban areas and where there may have been a greater change in activity from pre-lockdown to during lockdown. However, a significant fall in new daily COVID-19 cases, fewer deaths, and easing of UK lockdown restrictions, could see citizens gradually return to normal activity thus increasing vehicular journeys and pollutants.
The government’s discouragement of the use of shared transport to help slow the spread of the virus is a further contributory factor to a potential increase in nitrogen dioxide as many citizens no longer car-share or use forms of public transport thus increasing personal vehicular activity.
Research Outcomes of Previous Studies & Consequent Examination of Hypotheses:
The COVID-19 pandemic has undoubtedly halted the world in its tracks. This study is grateful to the academic insight of others and concurs with the evidence examined. Countless studies are emerging which examine many aspects and outcomes: some comparative like this study of Greater London and the Scottish Highlands, and similar examples who provide cross-border analyses.
Across the globe, vulnerable groups are at risk of severe illness if infected by the virus in airborne droplets. Ettema et al. and De Vos acknowledge the necessity for social distancing to become the global norm but express concern regarding the emotional and psychological damage this could cause but welcome inter-governmental encouragement for citizens to take exercise. Encouragement of citizens to walk or cycle wherever possible provides opportunities for exercise but also results in a significant fall in emissions as people travel less. Public transport demands also decrease and Troko et al. note that many passengers avoid this method due to social distancing and virus transmission concerns.
It is evident that the COVID-19 pandemic has resulted in very similar trends worldwide. Dantas (Brazil), Collivignarelli et al. (Italy), Bao & Zhang (China), Menut et al. (Western Europe) and Tobias et al. (Spain) all report benefits in terms of reduced emissions due to confinements and restrictions on mobility. Muhammad et al. calculate that half the world’s population have experienced lockdown with mobility reducing by up to 90% and a resultant reduction of environmental pollutants of up to 30% in epicentres. In the UK, the investigation by Higham et al. reports substantial reductions in vehicular traffic. These findings support the points raised in this study regarding the importance of maintaining safe forms of mobility.
Holgate is one of many pre-covid studies to have called for action on the life-long impact on air quality. Deng et al., Mi et al. and Bignal et al. have highlighted the threat to ecological environments and populations from pollutants.
Unsurprisingly, many studies have recently examined ambient air quality, emissions and environmental legislation. Peters et al. and Figueres et al. have examined climate policies in comparison to previous rising emissions and acknowledge the need for all sectors and agencies to do more. Liu et al. and Le Quéré et al. estimate a predicted fall in Carbon emissions due to the pandemic and Forster et al. acknowledge a potential short-term cooling since January but warn of possible off-sets. This evidence within this study supports these earlier findings.
The results support the hypothesis: the sudden reduction in road and air traffic activity during lockdown has beneficially affected air quality across urban and suburban environments. However, as society leaves lockdown it is highly probable that activity and travel will increase thereby increasing nitrogen dioxide and carbon dioxide emissions.
However, by far the most interesting observation emerging from this study is the power of human influence and desire to change. This is equally influential at local and global levels. This power emerges in the observations of Figure 3, Figure 4 and Table 1 where it is evident that a significant reduction in emissions occurs before lockdown is enforced. This shows that the reduced emissions levels are not solely as a result of government restrictions on activity and movement. A survey by Statista found that 48% of British citizens were afraid of becoming infected prior to lockdown. It is notable that citizens instinctively adapt their habits and inhibit mobility when faced with a potential threat to the health of themselves and their loved ones. This in-built desire for human preservation is arguably more powerful and effective than government enforcement and is an important element as we move forward with further plans to mitigate climate change. This is highly relevant as global citizens have the greatest power to voluntarily make the change, not documents and statistics which the common man struggles to comprehend. Doukas et al. also note this in their examination of the effectiveness and challenges of the Paris Agreement and supporting legislation, by highlighting the importance of factoring in the human element in any future decision making processes. This human element has also emerged in a positive light in studies by Taylor & Ampt and Budd & Ison. Taylor & Ampt outline Australia’s Voluntary Behaviour Change Program and Budd & Ison introduce the Responsible Travel concept, both aimed to encourage citizens to make sensible choices towards the future of the planet.
There can be no doubt that the decrease in atmospheric nitrogen dioxide concentrations is a welcomed result of lockdown. The nationwide effect of lockdown has resulted in a significant reduction in traffic air pollution levels which has the potential to reduce respiratory symptoms, environmental damage and improve the planet’s health. There is a risk that these air pollution levels could return to pre-lockdown levels as lockdown restrictions are relaxed so immediate action must be taken by governments and citizens to maintain these lower levels of traffic air pollution. However, the 2008-2009 Financial Crisis resulted in a decrease in carbon dioxide emissions but saw an increase in nitrogen dioxide emissions by almost four-fold in 2010. Authorities must act immediately to maintain the beneficial lower concentration rates of nitrogen dioxide to prevent a similar catastrophe post COVID-19.
Climate change and poor air quality are examined and legislated separately at present despite the fact that they are interrelated. It is necessary to streamline this to avoid any resulting trade-offs which could outweigh potential benefits. For example, DEFRA’s Clean Air Strategy 2019 aims to reduce the use of heavily polluting vehicles and move to zero emission transport over the coming decades. One planned implementation is to encourage citizens to switch to electric vehicles. As a result, they foresee a reduction in nitrogen dioxide emissions, particularly in roadside areas. This is commendable but risks environmental damage as a consequence as the resultant high demand for power at electric vehicle charging stations means that a reliable electricity supply must be obtained on a larger scale. Renewable energy sources like wind turbines and solar panels will be grossly inadequate in supplying sufficient power for the influx of electric vehicles over the coming decades. Currently, more than half of global electricity is generated from coal and gas plants. Potentially these could generate sufficient electricity to supply electric vehicles, but such intensive electricity production could lead to a huge increase in air pollution caused by the burning of fossil fuels. This suggests that electric vehicles are not necessarily a more ecological or environmentally friendly alternative to regular petrol and diesel engine vehicles as the electricity must be obtained from somewhere. Authorities may wish to extend existing pilot projects such as Heathrow Airport’s investigation into new sustainable fuels like converting household waste into aviation fuel.
Councils must undertake alternative zero emission projects including encouraging and accommodating pedestrians and cyclists in preference to promoting electric vehicles, particularly in city centres where air pollution is generally higher. New York, Paris and Berlin have dedicated entire roads to pedestrians and cyclists to enable citizens to travel safely as they socially distance. Some of these implementations are said to be fully integrated into urban areas so the UK can learn from them and develop this.
Increased, safe use of public transport should be encouraged with the removal of fares or the implementation of reduced fares to encourage commuters to switch to public transport. The arrival of HS2 rail links, providing they are affordable, can also potentially benefit air quality and contribute to climate change goals in the long term as this will allow for passenger and freight transportation via much more environmentally friendly methods than existing air, road and rail services.
There has been a significant decrease in the number of aircraft operating due to the dramatic fall in passenger demand. Some airports have closed entirely, operating solely for emergency aviation transport. This increase in grounded flights suggests a significant decrease in air pollutants. As lockdown restrictions relax an increase in aircraft activity is likely as demand increases for internal flights to resume across the UK. Further lifting of restrictions could see additional airlines reopen and international routes restart. This potential increase in operating aircraft could result in a significant increase in the concentration of air pollutants. The effects of this could surpass pre-lockdown levels particularly if citizens return to foreign travel for leisure where passenger demand could soar past previous levels. This could significantly pollute areas surrounding the airports and could be detrimental to cities where the airport is located in highly populated areas.
Citizens may wish to further exercise their lockdown routines, habits and newly developed skills. More than half the people surveyed stated they will continue to travel less which would result in fewer emissions and could maintain lower concentrations of air pollutants. Conversely, the remainder stated they may return to their pre-lockdown habits through choice or necessity. Some may be forced to commute as lockdown travel restrictions relax. Rush hour commuters in more urban areas such as Central London could return in greater numbers similar to pre-lockdown levels resulting in increased traffic congestion and the mass build-up of air pollutants as car engines idle. This will see a significant surge in air pollution levels. Governments and authorities must actively work with businesses to enable changes which allow employees to work from home, thus relieving vehicular congestion and reducing traffic related air pollution. Despite the unexpected difficulty and massive change to education systems, many students coped extremely well with online learning during lockdown. Where feasible, this should continue in order to alleviate rush hour traffic and minimise the number of idling vehicles around schools, colleges and universities.
Councils and environmental bodies should work collaboratively with agencies on projects to greenify areas to help improve the ecology and reduce the impact of high emissions in urban areas. These proposals could help maintain the lower concentrations achieved by the implementation of a nationwide lockdown. If governmental bodies continued to enforce these measures with adaptations where and when necessary, there could be a further decrease in air pollution which could positively impact the planet’s health and that of its citizens. For example, the restoration and expansion of peatland would remove carbon from the air and provide a natural habitat for biodiversity. If maintained over a significantly longer period of time, the rate at which climate change and global warming occurs could reduce substantially, possibly resulting in less habitat loss and fewer endangered species. Action must occur now in order to preserve and maintain the benefits of these lower air pollution concentrations.
The more suburban areas of this study illustrate a less significant decrease in the concentration of air pollutants caused by traffic prior to and during lockdown. This is possibly due to an insignificant decrease in activity around those specific areas and the fact that suburban areas may habitually have less traffic. As citizens become more comfortable with the easing of movement restrictions, emissions could increase in all areas due to a population desire to enjoy new freedoms. Consequently, rural and suburban areas may see increased travel negatively affecting the biodiversity of those areas due to possible increased traffic emissions and noise pollution. Governments could consider the economic and atmospheric benefits of promoting and incentivising UK ‘low emissions’ holiday and lifestyle opportunities.
Increased air pollution concentrations can be harmful to nature and habitats. Leaf damage results in a reduction of the rate of photosynthesis as leaf surface area reduces. This issue could be highly prevalent in greener areas in Central London such as Hyde Park. If these issues are sustained over a longer period of time, crop yield in agriculture could significantly reduce risking food insecurity. A decrease in greenery in urban areas could lead to a significant reduction in biodiversity as more species are forced to leave the area.
The impact of increased air pollution levels is detrimental to the environment and its people. The potential air pollution rebound resulting from a possible increase in post-lockdown vehicular traffic could result in significant health problems in those who live in highly populated and dense areas, city centres and urban hubs. The potential significant increase in nitrogen dioxide concentrations could be a substantial problem for those living in Central London, risking increased morbidity and mortality as citizens suffer from infections, the prolonged effects of damage to windpipes and lung function. Those diagnosed with asthma, sleep apnoea and chronic obstructive pulmonary disease (COPD) could similarly be significantly affected. A survey respondent remarked “having COPD and asthma, the air quality has been a marked improvement. Walking is so much easier”. This suggests that the decreased concentration of air pollutants has made challenging tasks more manageable for those with underlying health conditions. Higher concentrations could result in a higher frequency of asthma attacks. On average, asthma attacks result in three fatalities per day in the UK suggesting that a change to air pollution levels can reduce annual deaths caused by asthma by almost 1100. The increased risk of other respiratory symptoms could heighten the effects of COVID-19 and result in more fatalities as NHS care systems may be unable to cope with a surge in COVID-19 cases.
This study observes that the COVID-19 lockdown has contributed to a significant decrease in the concentration of traffic air pollutants in the more urban areas of Inverness and Central London. It is particularly interesting that the concentration of air pollutants has generally decreased as a result of the first COVID-19 cases reaching the UK. It can be hypothesised that the arrival of the virus induced fear resulting in citizens voluntarily staying at home to protect themselves and others. From the data, it can be concluded that the COVID-19 lockdown has generally strengthened and significantly prolonged this effect by placing restrictions on movement and social contact.
The ‘fear factor’ is a powerful communicator and it could form the basis of a new governmental approach to address climate change and air quality issues. Citizens may more readily and effectively identify with saving their loved ones and descendants rather than focusing on saving the planet. Such actions and changes would have the same overall result but would be derived from an entirely different approach.
1. LG Inform. 2019. lginform.local.gov.uk. https://lginform.local.gov.uk/reports/lgastandard?mod-metric=176&mod-area=E12000007&mod-group=S12000017&mod-type=area.
2. Department for Transport. 2019. “VEH0105.” gov.uk. https://www.gov.uk/government/statistics/vehicle-licensing-statistics-2019
3. European Parliament. 2008. “Directive 2008/50/EC of the European Parliament and of the Council of 21 May 2008 on ambient air quality and cleaner air for Europe.” OJ L 152, (6), 1. https://eur-lex.europa.eu/legal-content/EN/TXT/PDF/?uri=CELEX:02008L0050-20150918&from=EN.
4. European Parliament. 2005. “Directive 2004/107/EC of the European Parliament and of the Council of 15 December 2004 relating to arsenic, cadmium, mercury, nickel and polycyclic aromatic hydrocarbons in ambient air. (Fourth Daughter Directive) (2004).” OJ L 23, (1), 3. https://eur-lex.europa.eu/legal-content/EN/TXT/PDF/?uri=CELEX:02004L0107-20150918&from=EN.
5. European Council. 1996. “Council Directive 96/62/EC of 27 September 1996 on ambient air quality assessment and management. (1996).” OJ L 296, (11), 55. https://eur-lex.europa.eu/legal-content/EN/TXT/PDF/?uri=CELEX:01996L0062-20080611&from=EN.
6. Department for the Environment, Food & Rural Affairs. 2019. “Clean Air Strategy (PB 14554).” gov.uk/defra. https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/770715/clean-air-strategy-2019.pdf.
7. Scottish Government. 2015. “Cleaner Air for Scotland – The Road to a Healthier Future (PPDAS49541).” gov.scot. https://www.gov.scot/binaries/content/documents/govscot/publications/strategy-plan/2015/11/cleaner-air-scotland-road-healthier-future/documents/00488493-pdf/00488493-pdf/govscot%3Adocument/00488493.pdf?forceDownload=true.
8. Greater London Authority. 2018, 2019. “London Environment Strategy.” london.gov.uk. https://www.london.gov.uk/sites/default/files/london_environment_strategy_0.pdf, https://www.london.gov.uk/sites/default/files/les_one_year_on_2019_0.pdf.
9. Highlands and Islands Airports Limited. 2019. “Environmental Strategy 2020-2030.” hial.co.uk. https://www.hial.co.uk/wp-content/uploads/2019/07/HIAL-Environmental-Strategy-2020-2030-Intentions-and-Targets.pdf.
10. Heathrow Airport Limited. 2018. “Carbon Neutral Growth Roadmap.” heathrow.com. https://www.heathrow.com/content/dam/heathrow/web/common/documents/company/heathrow-2-0-sustainability/futher-reading/Carbon-Neutral-Growth-Roadmap.pdf.
11.World Health Organisation. 2019. “Coronavirus.” who.int/health. https://www.who.int/health-topics/coronavirus.
12. Higham, J. E., M. A. Green, and C. A. Ramirez. 2020. “UK COVID-19 Lockdown: What are the impacts on air pollution.” https://arxiv.org/pdf/2006.10785.pdf.
13. Huang, C., Y. Wang, X. Li, L. Ren, J. Zhao, Y. Hu, L. Zhang, et al. 2020. “Clinical features of patients infected with 2019 novel coronavirus in Wuhan, China.” The Lancet 395 (10223):497-506. https://doi.org/10.1016/S0140-6736(20)30183-5.
14. Williamson, E. J., A. J. Walker, K. Bhaskaran, et al. 2020. “Factors associated with COVID-19-related death using OpenSAFELY.” Nature 584(7821) (Aug): 430-436. https://doi.org/10.1038/s41586-020-2521-4.
15. Payne, R. 2020. “Will the COVID-19 outbreak propel the demand for active spaces or scare the public away?” Cities & Health. https://doi.org/10.1080/23748834.2020.1790259.
16. Higham, J., C. A. Ramirez, and M. Green. 2020. “UK COVID-19 lockdown: 100 days of air pollution reduction?” Air Quality, Atmosphere & Health. https://doi.org/10.1007/s11869-020-00937-0.
17. Troko, J., P. Myles, J. Gibson, A. Hashim, J. Enstone, S. Kingdon, C. Packham, S. Amin, A. Hayward, and J. N. Van-Tam. 2011. “Is public transport a risk factor for acute respiratory infection?” BMC Infectious Diseases 11:16. https://doi.org/10.1186/1471-2334-11-16
18. De Vos, J. 2020. “The effect of COVID-19 and subsequent social distancing on travel behavior.” Transportation Research Interdisciplinary Perspectives 5:100121. https://doi.org/10.1016/j.trip.2020.100121.
19. Ettema, D., T. Gärling, L. E. Olsson, and M. Friman. 2010. “Out-of-home activities, daily travel, and subjective well-being.” Transportation Research Part A 44 (9): 723-732. https://doi.org/10.1016/j.tra.2010.07.005.
20. Department for the Environment, Food & Rural Affairs. 2004a. “Nitrogen Dioxide in the UK (PB 9144).” gov.uk/defra. https://uk-air.defra.gov.uk/assets/documents/reports/aqeg/nd-summary.pdf.
21. Chen, B., and H. Kan. 2008. “Air pollution and population health: a global challenge.” Environ Health & Preventive Medicine, no. 13, 94-101. https://doi.org/10.1007/s12199-007-0018-5.
22. Shima, M., and M. Adachi. 2000. “Effect of outdoor and indoor nitrogen dioxide on respiratory symptoms in schoolchildren.” International Journal of Epidemiology 29 (5): 862-870. https://doi.org/10.1093/ije/29.5.862.
23. Gautam, S. 2020. “COVID-19: air pollution remains low as people stay at home.” Air Quality, Atmosphere & Health 13:853–857. https://doi.org/10.1007/s11869-020-00842-6.
24. United Nations Framework Convention on Climate Change. 2015. “The Paris Agreement.” unfccc. https://unfccc.int/sites/default/files/english_paris_agreement.pdf.
25. Doukas, H., A. Nikas, M. González-Eguino, I. Arto, and A. Anger-Kraavi. 2018. “From Integrated to Integrative: Delivering on the Paris Agreement.” Sustainability 10 (7): 2299. https://doi.org/10.3390/su10072299.
26. European Commission. 2013. “GREEN PAPER. A 2030 framework for climate and energy policies.” eur-lex.europa. https://eur-lex.europa.eu/legal-content/EN/TXT/PDF/?uri=CELEX:52013DC0169&from=EN.
27. Liu, Z., P. Ciais, Z. Deng, et al. 2020. “Near-real-time monitoring of global CO2 emissions reveals the effects of the COVID-19 pandemic.” Nature Communications 11:5172. https://doi.org/10.1038/s41467-020-18922-7.
28. Peters, G. P., R. M. Andrew, and J. G. Canadell. 2020. “Carbon dioxide emissions continue to grow amidst slowly emerging climate policies.” Nature Climate Change 10:3-6. https://doi.org/10.1038/s41558-019-0659-6.
29. Figueres, C., C. Le Quéré, A. Mahindra, O. Bäte, G. Whiteman, G. Peters, and D. Guan. 2018. “Emissions are still rising: ramp up the cuts.” Nature, no. 564, 27-30. https://doi.org/10.1038/d41586-018-07585-6.
30. Forster, P. M., H. I. Forster, and M. J. Evans. 2020. “Current and future global climate impacts resulting from COVID-19.” Nature Climate Change, no. 10, 913-919. https://doi.org/10.1038/s41558-020-0883-0.
31. Holgate, S. T. 2017. “\’Every breath we take: the lifelong impact of air pollution\’ – a call for action.” Clin Med (Lond) 17 (1): 8-12. https://pubmed.ncbi.nlm.nih.gov/28148571/.
32. Bignal, K. L., M. R. Ashmore, A. D. Headley, K. Stewart, and K. Weigert. 2007. “Ecological impacts of air pollution from road transport on local vegetation.” Applied Geochemistry 22 (6): 1265-1271. https://doi.org/10.1016/j.apgeochem.2007.03.017.
33. Budd, L., and S. Ison. 2020. “Responsible Transport: A post-COVID agenda for transport policy and practice.” Transportation Research Interdisciplinary Perspectives 6:100151. https:/doi.org/10.1016/j.trip.2020.100151
34. Taylor, M. A., and E. S. Ampt. 2003. “Travelling smarter down under: policies for voluntary travel behaviour change in Australia.” Transport Policy 10 (3): 167-177. https://doi.org/10.1016/S0967-070X(03)00018-0.
35. Deng, Y., W. Qi, B. Fu, and K. Wang. 2020. “Geographical transformations of urban sprawl: Exploring the spatial heterogeneity across cities in China 1992–2015.” Cities 105 (102415). https://doi.org/10.1016/j.cities.2019.102415.
36. Mi, Z., J. Zheng, J. Meng, H. Zhanh, X. Li, D. Coffman, J. Woltjer, S. Wang, and D. Guon. 2019. “Carbon Emissions of cities from a consumption based perspective.” Applied Energy 235:509-518. https://doi.org/10.1016/j.apenergy.2018.10.137.
37. Dantas, G., B. Siciliano, B. B. França, C. M. da Silva, and G. Arbilla. 2020. “The impact of COVID-19 partial lockdown on the air quality of the city of Rio de Janeiro, Brazil.” Science of The Total Environment 729:139085. https://doi.org/10.1016/j.scitotenv.2020.139085.
38. Collivignarelli, M. C., A. Abbà, G. Bertanza, R. Pedrazzani, P. Ricciardi, and M. C. Miino. 2020. “Lockdown for CoViD-2019 in Milan: What are the effects on air quality?” Science of The Total Environment 732 (139280). https://doi.org/10.1016/j.scitotenv.2020.139280.
39. Bao, R., and A. Zhang. 2020. “Does lockdown reduce air pollution? Evidence from 44 cities in northern China.” Science of The Total Environment 731 (139052). https://doi.org/10.1016/j.scitotenv.2020.139052.
40. Menut, L., B. Bessagnet, G. Siour, S. Mailler, R. Pennel, and A. Cholakian. 2020. “Impact of lockdown measures to combat Covid-19 on air quality over western Europe.” Science of The Total Environment 741 (140426). https://doi.org/10.1016/j.scitotenv.2020.140426.
41. Tobias, A., C. Carnerero, C. Reche, J. Massagué, M. Via, M. C. Minguillón, A. Alastuey, and X. Querol. 2020. “Changes in air quality during the lockdown in Barcelona (Spain) one month into the SARS-CoV-2 epidemic.” Science of The Total Environment 726 (138540). https://doi.org/10.1016/j.scitotenv.2020.138540.
42. Department for the Environment, Food & Rural Affairs. 2004b. “Nitrogen Dioxide in the United Kingdom. Chapter 4: Measurement methods and UK monitoring networks for NO2, Chapter 4.2 page 114-116.” gov.uk/defra. https://uk-air.defra.gov.uk/library/assets/documents/reports/aqeg/chapter4.pdf.
43-52 are Data References. They are cited at the end of this list.
53. Le Quéré, C., R. B. Jackson, and M. W. Jones. 2020. “Temporary reduction in daily global CO2 emissions during the COVID-19 forced confinement.” Nature Climate Change 10:647-653. https://doi.org/10.1038/s41558-020-0797-x.
54. Carbon Brief. 2020. “Coronavirus set to cause largest ever annual fall in CO2 emissions.” carbonbrief.org. https://www.carbonbrief.org/analysis-coronavirus-set-to-cause-largest-ever-annual-fall-in-co2-emissions
55. Carrero, J. A., I. Arrizabalaga, J. Bustamante, N. Goienaga, G. Arana, and J. M. Madariaga. 2013. “Diagnosing the traffic impact on roadside soils through a multianalytical data analysis of the concentration profiles of traffic-related elements.” Science of The Total Environment 458-460:427-434. https://doi.org/10.1016/j.scitotenv.2013.04.047.
56. Muhammad, S., X. Long, and M. Salman. 2020. “COVID-19 pandemic and environmental pollution: A blessing in disguise?” Science of The Total Environment 728 (138820). https://doi.org/10.1016/j.scitotenv.2020.138820.
57. Statistica. 2020. “Respondents who fear being infected by the COVID-19 virus in Great Britain 2020.” statistica.com. https://www.statista.com/statistics/1101620/fear-of-contracting-coronavirus-in-great-britain/.
58. Peters, G., G. Marland, and C. Le Quéré. 2012. “Rapid growth in CO2 emissions after the 2008–2009 global financial crisis.” Nature Climate Change 2:2-4. https://doi.org/10.1038/nclimate1332.
43. Civil Aviation Authority. 2020. “Table_09_Terminal_and_Transit_Passengers.” caa.co.uk. https://www.caa.co.uk/Data-and-analysis/UK-aviation-market/Airports/Datasets/UK-airport-data/.
44. Europa. 2021. “Inverness City Centre Air Quality Management Area.” highland.gov.uk/ europa.co.uk. Map produced by The Highland Council Environmental Health team for the purpose of this study. Copyright Via Europa @ 2020 Europa Technologies Ltd. All rights reserved. https://www.europa.uk.com/services/viaeuropa/
45. Department for the Environment, Food & Rural Affairs. 2020. “Air Information Resource. AQMA boundaries.” uk-air.defra. https://uk-air.defra.gov.uk/aqma/maps/.
46. Air Quality England. 2020. “Download data for Camden – Euston Road.” airqualityengland.co.uk. https://www.airqualityengland.co.uk/site/data.php?site_id=CD009¶meter_id%5B%5D=NO2&f_query_id=2970893&f_date_started=2020-01-01&f_date_ended=2020-07-29&la_id=189&action=download&data=&submit=Download+Data.
47. Air Quality in Scotland. 2020. “Measurement and Annual Statistics – Inverness Academy Street.” scottishairquality.scot. http://www.scottishairquality.scot/data/data-selector?f_site_id%5B%5D=INV03&go=Step+5&f_query_id=9425416&f_group_id=4&action=step5.
48. Air Quality England. 2020. “Download data for London Eltham.” airqualityengland.co.uk. https://www.airqualityengland.co.uk/site/data.php?site_id=LON6¶meter_id%5B%5D=NO2&f_query_id=1731956&f_date_started=2020-01-01&f_date_ended=2020-07-29&la_id=193&action=download&data=&submit=Download+Data.
49. Air Quality in Scotland. 2020. “Measurement And Annual Statistics for Fort William.” scottishairquality.scot. http://www.scottishairquality.scot/data/data-selector?f_site_id%5B%5D=FW&go=Step+5&f_query_id=9425416&f_group_id=4&action=step5.
50a. Air Quality England. 2020. “Download data for RBKC Cromwell Road.” airqualityengland.co.uk. https://www.airqualityengland.co.uk/site/data.php?site_id=KC2¶meter_id%5B%5D=NO2&f_query_id=3361018&f_date_started=2020-01-01&f_date_ended=2020-07-31&la_id=291&action=download&data=&submit=Download+Data.
50b. Air Quality England. 2019. “Download data for RBKC Cromwell Road.” airqualityengland.co.uk. https://www.airqualityengland.co.uk/local-authority/data.php?site_id=KC2¶meter_id%5B%5D=NO2&f_query_id=3380825&f_date_started=2019-01-01&f_date_ended=2019-12-31&la_id=291&action=download&data=&submit=Download+Data.
50c. Air Quality England. 2018. “Download data for RBKC Cromwell Road.” airqualityengland.co.uk. https://www.airqualityengland.co.uk/local-authority/data.php?site_id=KC2¶meter_id%5B%5D=NO2&f_query_id=3380825&f_date_started=2018-01-01&f_date_ended=2018-12-31&la_id=291&action=download&data=&submit=Download+Data.
50d. Air Quality England. 2017. “Download data for RBKC Cromwell Road.” airqualityengland.co.uk. https://www.airqualityengland.co.uk/local-authority/data.php?site_id=KC2¶meter_id%5B%5D=NO2&f_query_id=3380816&f_date_started=2017-01-01&f_date_ended=2017-12-31&la_id=291&action=download&data=&submit=Download+Data.
51. Air Quality in Scotland. 2020, 2019, 2018, 2017. “Statistics for Inverness Academy Street.” scottishairquality.scot. http://www.scottishairquality.scot/latest/site-info?site_id=INV03&view=statistics.
52a. Department for Business, Energy & Industrial Strategy. 2020. “UK Greenhouse Gas Emissions.” gov.uk/beis. https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/875485/2019_UK_greenhouse_gas_emissions_provisional_figures_statistical_release.pdf.
52b. Department for Business, Energy & Industrial Strategy. 2020. “UK Greenhouse Gas Emissions.” gov.uk/beis. https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/862887/2018_Final_greenhouse_gas_emissions_statistical_release.pdf.
52c. Department for Business, Energy & Industrial Strategy. 2019. “UK Greenhouse Gas Emissions.” gov.uk/beis. https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/776085/2017_Final_emissions_statistics_-_report.pdf.
52d. Department for Business, Energy & Industrial Strategy. 2018. “UK Greenhouse Gas Emissions.” gov.uk/beis. https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/680473/2016_Final_Emissions_statistics.pdf.