Characterization of criteria air pollutants in Beijing during 2014-2015

One year-long criteria air pollutants data collected in Beijing were analyzed in this paper, which can support the research on formation, transport and human health effects of air pollutants. This is the first time to study the spatial and temporal variations of criteria pollutants in Beijing using hourly observational data from 12 sites between June 2014 and May 2015 released by the Ministry of Environmental Protection (MEP) of China. Beijing is facing tremendous air pollution as the daily averaged PM2.5 (particulate matter with aerodynamic diameter less than 2.5 µm) concentrations in all sites exceeding the Chinese Ambient Air Quality Standards (CAAQS) Grade I & II standards (15 and 35 µg/m3). Slightly differences in PM2.5 and ozone (O3) were observed between sites at the urban and rural areas. Pearson correlation coefficients show that most pollutants are temporally correlated in Beijing except for O3. The coefficients of divergence (COD) indicate that PM2.5 is associated at most sites with only one rural site (Dingling) having observable difference and one site may be insufficient for monitoring surrounding area. The 8 h peak O3 (O3-8 h) also correlates at different sites but with one urban site (Haidianquwanliu) different from others. In addition, an extreme PM2.5 event (hourly average concentration exceeding 300 μg/m3 for ~40 h) was examined with the consideration of meteorological conditions. Southerly wind with low speed and high relative humidity allow the accumulation of pollutants while northerly wind with high speed and low relative humidity result in good air quality.