Air Pollution During Covid-19: A Global Snapshot

The COVID-19 pandemic caused significant disruptions to global economies and human activity, providing a unique opportunity to study the impact of reduced human mobility on air pollution. During the initial months of the pandemic, global road travel and commercial flight activity decreased by 50% and 60%, respectively, with flight activity dropping even further to 96% during lockdowns. This abrupt halt in travel led to a significant decrease in air pollution levels, particularly in ultrafine particle concentration, which are toxic pollutants linked to health issues such as inflammation in the lungs, brain, and other organs. The pandemic's effect on air quality was not uniform, with some regions experiencing improvements while others saw increases in pollution due to factors such as wildfires and dust storms. While the pandemic highlighted the potential for emissions reductions, the rebound in emissions as economies recovered, particularly in the aviation and power sectors, underscores the complex challenge of long-term emissions reduction and the need for equitable and sustainable solutions.

Air pollution fell in residential and commercial areas during lockdowns

During the COVID-19 lockdowns, air pollution decreased in both residential and commercial areas. However, the decline was more significant in commercial areas due to reduced economic activity and remote work arrangements. As many people stayed at home, emissions shifted to residential areas, with an increase in deliveries and car trips to these locations.

The pandemic provided a unique opportunity to study the impact of reduced human activity on air pollution. Air quality sensors in Park City, Utah, for instance, recorded a decrease in pollution during lockdowns, followed by an increase as restrictions eased. This intra-city variability highlighted the changing sources of pollution and the potential for lower emission levels in the future.

The lockdown period demonstrated how low pollution levels could be, setting an aspirational target for renewable and low-polluting energy sources. The reduction in emissions during the pandemic was particularly notable for ultrafine particles, which are toxic pollutants that can cause health issues for those living near major sources, such as airports.

While emissions declined across cities during lockdowns, the rebound in pollution levels varied between residential and commercial areas. Residential emissions recovered faster, with commercial emissions in Park City not returning to pre-pandemic levels by late July 2020. This discrepancy highlights the challenges and time required for a full reopening while maintaining lower emission levels.

The COVID-19 pandemic and the subsequent lockdowns had a significant impact on air pollution, particularly in commercial and residential areas. The decline in economic activity and changes in work patterns led to a decrease in emissions, with pollution sources shifting to residential neighbourhoods. The intra-city variability in pollution levels provided valuable insights into the potential for reducing emissions in the future.

Pollution rose again as areas reopened

During the COVID-19 pandemic, human-caused emissions of air pollutants decreased significantly due to reduced travel and economic activity. This led to rapid and unprecedented improvements in air quality in many parts of the world. For instance, Southeast Asia experienced a 40% reduction in harmful airborne particles from traffic and energy production. China, Europe, and North America also saw substantial emissions reductions and improved air quality.

However, as areas began to reopen and economies started to recover, pollution levels rose again. By June 2021, traffic volume had returned to pre-COVID levels, and average particle number concentration (PNC) levels followed suit, except near airports. This rebound in emissions was particularly notable in China, where emissions increased by 4% compared to 2020 and by 6% compared to 2019. The power and industrial sectors, including coal-dependent industries, saw the most significant rebounds.

The increase in coal use after the COVID-19 lockdowns contributed to the rise in global carbon emissions. While the lockdowns provided a temporary respite from pollution, they also highlighted the scale of emissions reductions required to combat climate change. The pandemic presented an opportunity to transition towards cleaner technologies and promote sustainable practices. However, without sustained efforts and equitable policies, the initial gains made during the lockdowns were short-lived.

The aviation sector is one notable exception, as it continued to be affected by COVID-19 even as other industries rebounded. As of October 2024, the number of airline passengers was still predicted to remain 50% below 2019 levels for the year. This prolonged reduction in air travel contributed to maintaining lower pollution levels in some regions, particularly those downwind from airports.

Overall, while the COVID-19 lockdowns led to a significant decrease in air pollution, this improvement was temporary. As economies reopened and emissions rebounded, pollution levels rose again, underscoring the ongoing challenges in the fight against climate change.

Changes in human activity produced measurable changes in air quality

The COVID-19 pandemic and its associated lockdowns led to rapid and unprecedented changes in human activity, which, in turn, produced measurable changes in air quality. During the first year of the pandemic, global road travel and commercial flight activity decreased by 50% and 60%, respectively, compared to pre-pandemic levels. This reduction in mobility provided researchers with a unique opportunity to study the impact of these changes on air pollution.

A study by the School of Public Health found that ultrafine particle concentration, which includes toxic pollutants that can cause inflammation in the lungs, brain, and other organs, dropped by nearly 50% due to reduced aviation and road activity during the early months of the pandemic. Ultrafine particle concentration decreased by 48% during the state-of-emergency period, coinciding with a 74% reduction in aircraft traffic and a 51% decrease in road traffic.

The World Meteorological Organization's (WMO) Air Quality and Climate Bulletin analyzed key air pollutants from over 540 observation stations in 63 cities across 25 countries. The analysis revealed a 30-40% decrease in PM2.5 concentrations during full lockdowns in 2020 compared to previous years. WMO also reported that sulphur dioxide concentrations were 25-60% lower in 2020 than in the years 2015-2019.

In addition to the WMO findings, several studies have shown that air contaminants, including PM2.5, PM10, CO, NO2, SO2, and O3, increase COVID-19 mortality rates. However, the indirect effects of the pandemic may have contributed to reducing air pollution. For example, China, Europe, and North America experienced improved air quality during the first year of the pandemic due to reduced emissions from traffic and energy production.

While the COVID-19 lockdowns led to significant improvements in air quality, the rebound effect is also notable. As economies began to reopen, carbon dioxide emissions rose again, with an increase of about 4% in 2021 compared to 2020 emissions. China's post-pandemic economic recovery, in particular, resulted in a rebound in emissions, with a substantial jump in coal use.

The COVID-19 pandemic provided a glimpse of the potential for emissions reductions and the positive impact on air quality. It demonstrated the scale of emissions reductions required for climate stabilization and the possibility of cleaner air in a fossil-free world. However, maintaining these reductions in the long term without causing economic disruption remains a challenge for policymakers.

Residential emissions rebounded faster than commercial emissions

During the first year of the COVID-19 pandemic, global road travel and commercial flight activity decreased by 50% and 60% respectively, compared to pre-pandemic levels. This led to a decrease in ultrafine particle concentration by 48%-50%.. However, by June 2021, traffic volume had returned to pre-COVID levels, while flight activity remained 44% lower.

The pandemic caused a shift in energy demand from commercial to residential buildings, as social distancing measures and remote work reduced people's use of commercial buildings and increased energy-using activities in homes. This shift is expected to increase the overall energy intensity of the buildings sector.

In the United States, commercial electricity demand was 8% below the previous year's levels between April and September 2020, as shops were closed or operated with limited hours, and offices remained partially occupied or empty. Even when commercial buildings were unoccupied, most continued to consume energy for maintenance, heating, ventilation, and air conditioning (HVAC) systems, or to power servers.

On the other hand, a day of working from home could increase daily household energy consumption by 7-23% compared to a day in the office. This increase depends on factors such as the regional differences in home sizes, heating or cooling needs, and the efficiency of IT equipment and appliances used at home.

While the pandemic initially led to a decrease in emissions due to reduced travel and commercial activities, the rebound in traffic volume and the shift towards residential energy consumption contributed to an increase in emissions and energy intensity in the subsequent months.

Intra-city variability can help us understand future emission and pollution patterns

The COVID-19 pandemic and the subsequent lockdowns and travel restrictions provided researchers with a unique opportunity to study the impact of anthropogenic emissions on air pollution. Intra-city variability in air pollution during the pandemic was observed in a case study conducted in Park City, Utah. The study found that the commercial area of the city showed a greater decrease in air pollution than residential areas during the lockdown period. This difference in the spatial distribution of pollutants was hypothesized to be a result of variations in heating needs, travel demands, and commercial activity.

The case study from Park City, Utah, provides valuable insights into the intra-city variability of air pollution during the COVID-19 lockdown. By analyzing data from both commercial and residential areas, the study traced the changing emissions patterns and human behavior's impact on air pollution. The findings indicated that the decrease in human activity during the lockdown led to a measurable improvement in air quality, with a more significant reduction in pollution levels in commercial areas compared to residential areas.

The implications of this research extend to climate policy, low-carbon energy transitions, and local policy. Understanding the changing patterns of human exposure to air pollution is crucial for public health outcomes. The study's findings highlight the importance of addressing ground-level air pollution, especially in lower-income communities that are disproportionately affected by poor air quality. By pinpointing emission sources proximal to population centers, city planners and transportation designers can make informed decisions to improve air quality and public health.

Furthermore, the COVID-19 lockdown period provided a natural experiment to study the impact of reduced transportation and industrial activities on air pollution. The decrease in global road travel and commercial flight activity during the pandemic resulted in significant reductions in harmful air pollutants, including NO2, PM2.5, and ultrafine particles. These findings underscore the predominant influence of the transportation sector on air pollution and the potential for sustainable aviation fuel technology and green transportation networks to mitigate pollution levels.

In summary, the intra-city variability in air pollution during the COVID-19 lockdown offers valuable insights into understanding future emission and pollution patterns. By analyzing the differences in pollution levels between commercial and residential areas, researchers can identify the factors driving emissions changes. This knowledge can inform policy interventions, climate adaptation strategies, and public health initiatives to create more sustainable and resilient cities.

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