Measurement Report: Year-to-year Variability and Influence of Winter Olympics and other Special Events on Air Quality in Urban Beijing during Wintertime

Abstract. Comprehensive measurements are vital to obtain big enough datasets for better understanding the complex atmosphere and further improving the air quality. To investigate the year-to-year variabilities of air quality and influences of special events (Beijing Winter Olympics, COVID lockdown and Chinese New Year) on it during the wintertime in a polluted urban air, we conducted comprehensive observations in Beijing, China, during January 1^st – February 20^th, in the years from 2019 to 2022. The mass concentration of PM_2.5 and its composition (organics, nitrate, sulfate, ammonium, chloride and black carbon), number size distributions of particles (down to ~1 nm) and ions, gaseous pollutants (CO, NO_x, SO₂, O₃), condensable vapors (sulfuric acid and oxygenated organic molecules), as well as meteorological parameters were simultaneously measured. We selected the period before January 22^nd without any special events in each year to show the year-to-year variabilities of the air quality. We found that the concentrations of PM_2.5, black carbon, chloride, organics, CO, NO_x, total oxygenated organic molecules and number concentration of sub 3 nm particles showed similar year-to-year variabilities, decreasing from 2019 to 2021 and then increasing in 2022. On the contrary, SO₂ concentrations decreased year by year due to the significant emission reduction, leading to decreasing mass concentrations of sulfate and number concentration of sulfuric acid monomer and dimer from 2019 to 2022. As for the influence of special events, due to the favorable meteorological conditions together with reductions in anthropogenic emissions, there were basically no haze events during Beijing Winter Olympics. Although there was emission reduction also during the COVID lockdown period, especially for NO_x, the enhancement of secondary inorganic aerosol formation, together with unfavorable meteorological conditions, caused severe haze events during this period. Additionally, these special events had only little impacts on the new particle formation processes. These results provide useful information to the development of more targeted pollution control plans.