Chemical composition and sources of fine particles in Beijing around the Winter Olympics
To quantify the impact of air quality control measures on the chemical composition of PM25 in Beijing,simultaneous observations were carried out at an urban site and a montane background site located northwest of the city around the 2022 Winter Olympics.PM2.5 samples were analyzed for water-soluble inorganic ions and carbonaceous components.Results demonstrated a significant difference in carbonaceous contents between the urban and montane sites.At the montane site,the mean mass ratio of organic carbon(OC)to elemental carbon(EC)was 28.99,and the mean proportion of water-soluble OC(WSOC)in OC was 77％,both of which were significantly higher than at the urban site(12.93 and 48％,respectively).During the observation period,the Beijing-Tianjin-Hebei region and the Liaodong Peninsula were the dominant potential source regions of all the chemical components at the urban site,except for Ca2+.Apart from emissions from the Beijing-Tianjin-Hebei region,particles transported from the Hetao Plain also affected the montane site.The proportion of organic matter(OM)in PM2.5 increased from 22.7％to 31.7％at the urban site,and from 27.7％to 34.9％at the montane site,which might indicate that elevated temperatures and solar radiation favored secondary organic aerosol formation,or that emission sources changed during the latter part of the observation period.During the Winter Olympics,the mass concentration and proportion of nitrates in PM2.5 declined,while the proportion of sulfates increased at the urban site,highlighting the effect of traffic control.The equivalence ratio of anions to cations in PM2.5 at the urban site gradually rose from 0.96 to 1.20,exhibiting elevated acidity.This result may be closely linked to the formation of nitric acid,suggesting a fast rebound in NOx emissions after partial lifting of control measures.Throughout the observation period,the contribution of combustion and secondary sources to PM2.5 exceeded 70％at both sites,reflecting the dominant contribution of anthropogenic particles to PM2.5 in Beijing.However,their contribution dropped by 8.7％during the Winter Olympics at the urban site,indicating that the control of anthropogenic emissions was effective.All the major components in urban PM2.5 declined significantly during the Winter Olympics compared to similar periods in past years.The control measures led to the best air quality during the Winter Olympics compared to similar periods in recent years,despite unfavorable meteorological conditions for pollutant dispersion.
万方数据
维普
