Analysis of the meteorological factors affecting the short-term increase in O concentrations in nine global cities during COVID-19.

Surface ozone (O) is a major air pollutant around the world. This study investigated O concentrations in nine cities during the Coronavirus disease 2019 (COVID-19) lockdown phases. A statistical model, named Generalized Additive Model (GAM), was also developed to assess different meteorological factors, estimate daily O release during COVID-19 lockdown and determine the relationship between the two. We found that: (1) Daily O significantly increased in all selected cities during the COVID-19 lockdown, presenting relative increases from -5.7% (in São Paulo) to 58.9% (in Guangzhou), with respect to the average value for the same period in the previous five years. (2) In the GAM model, the adjusted coefficient of determination (R) ranged from 0.48 (Sao Paulo) to 0.84 (Rome), and it captured 51-85% of daily O variations. (3) Analyzing the expected O concentrations during the lockdown, using GAM fed by meteorological data, showed that O anomalies were dominantly controlled by meteorology. (4) The relevance of different meteorological variables depended on the cities. The positive O anomalies in Beijing, Wuhan, Guangzhou, and Delhi were mostly associated with low relative humidity and elevated maximum temperature. Low wind speed, elevated maximum temperature, and low relative humidity were the leading meteorological factors for O anomalies in London, Paris, and Rome. The two other cities had different leading factor combinations.