Abrupt but smaller than expected changes in surface air quality attributable to COVID-19 lockdowns

Abstract

The COVID-19 lockdowns led to major reductions in air pollutant emissions. Here, we quantitatively evaluate changes in ambient NO2, O3, and PM2.5 concentrations arising from these emission changes in 11 cities globally by applying a deweathering machine learning technique. Sudden decreases in deweathered NO2 concentrations and increases in O3 were observed in almost all cities. However, the decline in NO2 concentrations attributable to the lockdowns was not as large as expected, at reductions of 10 to 50%. Accordingly, O3 increased by 2 to 30% (except for London), the total gaseous oxidant (Ox = NO2 + O3) showed limited change, and PM2.5 concentrations decreased in most cities studied but increased in London and Paris. Our results demonstrate the need for a sophisticated analysis to quantify air quality impacts of interventions and indicate that true air quality improvements were notably more limited than some earlier reports or observational data suggested.

Changes in Air Quality Associated with Mobility Trends and Meteorological Conditions during COVID-19 Lockdown in Northern England, UK

“…Furthermore, air masses enriched with PM precursors might have increased the formation of secondary PM. Because of these conditions the UK experienced an episode of PM (also shown by [29,31]). The highest easterly wind frequencies during lockdown resulted in peak PM levels at all AQMS.…”

“…According to Jephcote et al [29], road traffic counts were down by 70% during the lockdown period as compared to the pre-lockdown period in the UK. Mobility data normalised by 13 January 2020 across the UK for the three cities were obtained from the Apple mobility website, which was grouped into three categories: walking, driving, and public transit [39].…”

“…Similarly, Ropkins and Tate [30] asserted that the changes in the values of PM across the UK cannot be directly attributed to the lockdown as the values moderately increased during the lockdown period. Shi et al [29], in a study of several cities around the world, found that the values of PM 2.5 increased during the lockdown in London. Air Quality Expert Group [31] suggested that aerosol transport from continental Europe contributed to the levels of PM observed at some sites in the UK, during the lockdown period.…”

“…To investigate the effect of meteorological conditions on the air pollutants, researchers, e.g., [29,30,[32][33][34], used different statistical and machine learning techniques such as Random Forest, Boosted Regression Tree, and Generalised Additive Models (GAM). Ropkins and Tate [30] used data from several stations across the UK to examine the effect of lockdown on air pollutants while they used the backgrounds of the stations (Rural, Urban, and Traffic) to investigate the effect of traffic.…”

COVID-19 lockdowns highlight a risk of increasing ozone pollution in European urban areas

“…The analysis conducted here was exclusively concerned with daily mean O 3 concentrations and does not explore the subtleties associated with peak and/or increases in daily minima O 3 concentrations, which are also important when considering the deleterious effects of O 3 . Efficacious management of O 3 has proven to be a challenge in Europe and in many other locations around the world (Sillman, 1999;Wang et al, 2017;Chang et al, 2017;Li et al, 2019). The struggle with O 3 control is partly due to the highly non-linear chemistry of O 3 production based on its precursors: volatile organic compounds (VOCs) and NO x .…”