Intensified wintertime secondary inorganic aerosol formation during heavy haze pollution episodes(HPEs) in Beijing,China

Air pollution in China is complex,and the formation mechanism of chemical components in particulate matter is still unclear.This study selected three consecutive heavy haze pollution episodes(HPEs)during winter in Beijing for continuous field observation,including an episode with heavy air pollution under red alert.Clean days during the observation period were selected for comparison.The HPE characteristics of Beijing in winter were:under the influence of adverse meteorological conditions such as high relative humidity,temperature inversion and low wind speed;and strengthening of secondary transformation reactions,which further intensified the accumulation of secondary aerosols and other pollutants,promoting the explosive growth of PM_(2.5).PM_(2.5)/CO values,as indicators of the contribution of secondary transformation in PM_(2.5),were approximately 2 times higher in the HPEs than the average PM_(2.5)/CO during the clean period.The secondary inorganic aerosols(sulfate nitrate and ammonium salt)were significantly enhanced during the HPEs,and the conversion coefficients were remarkably improved.In addition,it is interesting to observe that the production of sulfate tended to exceed that of nitrate in the late stage of all three HPEs.The existence of aqueous phase reactions led to the explosive growth sulfur oxidation ratio(SOR)and rapid generation of sulfate under high relative humidity(RH>70%).

Heavy haze pollution during the COVID-19 lockdown in the Beijing-Tianjin-Hebei region,China

To investigate the characteristics of particulate matter with an aerodynamic diameter less than 2.5μm(PM_(2.5))and its chemical compositions in the Beijing-Tianjin-Hebei(BTH)region of China during the novel coronavirus disease(COVID-19)lockdown,the ground-based data of PM_(2.5),trace gases,water-soluble inorganic ions,and organic and elemental carbon were analyzed in three typical cities(Beijing,Tianjin,and Baoding)in the BTH region of China from 5-15 February 2020.The PM_(2.5)source apportionment was established by combining the weather research and forecasting model and comprehensive air quality model with extensions(WRF-CAMx).The results showed that the maximum daily PM_(2.5)concentration reached the heavy pollution level(>150μg/m^(3))in the above three cities.The sum concentration of SO_(4)^(2-),NO_(3)^(-)and NH_(4)^(+)played a dominant position in PM_(2.5)chemical compositions of Beijing,Tianjin,and Baoding;secondary transformation of gaseous pollutants contributed significantly to PM_(2.5)generation,and the secondary transformation was enhanced as the increased PM_(2.5)concentrations.The results of WRF-CAMx showed obviously inter-transport of PM_(2.5)in the BTH region;the contribution of transportation source decreased significantly than previous reports in Beijing,Tianjin,and Baoding during the COVID-19 lockdown;but the contribution of industrial and residential emission sources increased significantly with the increase of PM_(2.5)concentration,and industry emission sources contributed the most to PM_(2.5)concentrations.Therefore,control policies should be devoted to reducing industrial emissions and regional joint control strategies to mitigate haze pollution.