Lockdowns only slightly ease air pollution, study finds
The University of Birmingham recently published a study on the air pollution levels during the spring 2020 lockdowns (the “first lockdown”). The study covered 11 cities, including Milan, Rome, Madrid, London, Paris, Berlin, New York, Los Angeles, Beijing, Wuhan and Delhi. It reports that the first lockdown’s impact on air pollution was overstated.
The researchers studied the levels of nitrogen dioxide (NO2), ozone (O3) and fine particles smaller than 2.5 micrometers (PM2.5). They found that levels of NO2 and PM2.5 decreased but in a much smaller scale than proposed by some previous studies. For example, one study claimed that NO₂ emissions fell by up to 90% in Wuhan at the peak of the outbreak. The 90% figure might be true in a particular timeframe. However, the current study suggests that NO2 concentrations fell by 47% during the second and fifth week of lockdown in Wuhan.
PM2.5 levels fell in most of the 11 cities during the first lockdown due to the reduced road traffic. However, levels in major cities like London and Paris were still high.
The study may imply that even reduction in physical economic activities helps alleviate air pollution, the problem and global warming cannot be solved solely by having more people working remotely. More proactive actions at the global level are needed.
To see how much mobility was reduced in individual cities because of Covid-19, you may go to Google’s COVID-19 Community Mobility Reports with the link in Further Reading below. The figures there would give you a sense of how much remote working and traffic is needed to reduce air pollution to acceptable levels. This is why the study suggests that “if similar levels of restriction were to have remained in place, the annual average NO2 concentration would comply with the air quality guidelines from the World Health Organization (WHO) (i.e., 40 μg m−3 for annual NO2) for the cities considered under average meteorological conditions.”
However, the reduction of NO2 alone is insufficient for tackling air pollution. To the contrary, the research points out that O3 concentrations even increased in most cities during the same period. The scientists explain that since NO2 would remove some O3 by chemical reaction, the reduced road traffic made less NO2 and in return more O3 remained in the atmosphere. The increase in O3 counteracted the public health benefits brought by the decrease in NO2. Thus, the research summarises that a systematic approach is needed for future air pollution control.
Abrupt but smaller than expected changes in surface air quality attributable to COVID-19 lockdowns
First lockdown’s effect on air pollution was overstated, our study reveals
Early COVID-19 lockdowns had less impact on urban air quality than first believed
Google COVID-19 Community Mobility Reports