Did pollution decrease during the COVID-19 pandemic lockdown?
In a majority of countries, pollution decreased during the COVID-19 pandemic lockdown.
A study published in PNAS in August 2020 found that "lockdown events have reduced the population-weighted concentration of nitrogen dioxide and particulate matter levels by about 60% and 31% in 34 countries." Authors attributed the drop to "unprecedented reductions in economic activity" such as the decrease in cars on the road. The study controlled for meteorological variations.
A separate report by IQAir found that 84% of the 106 nations supplying pollutant data experienced lower levels of PM 2.5 in 2020 relative to 2019 due to lockdown measures.
NASA's computer models of 2020 pollutant levels absent the pandemic indicated that the lockdown "reduced global nitrogen dioxide concentrations by nearly 20%."
Adding nuance, a January 2021 study published in Science Advances suggested that while pollution did decline, the amount was lower than expected.