Physicochemical Properties of Individual Airborne Particles in Beijing during Pollution Periods

Particulate pollution is a serious environmental problem in China and has received much attention from the public. Airborne particles were collected during haze days in Beijing from June 2013 to May 2014. The morphology and elemental composition were investigated with transmission electron microscopy coupled with energy dispersive X-ray spectrometry (TEM-EDX). Six types of individual particles were identified, including sulfate particles (35.1%), mineral particles (26.0%), metal particles (13.5%), fly ash (13.2%), organic particles (5.9%), and soot aggregates (5.7%). Non-carbonaceous particles are mainly S-rich, ranging from 37.4% in spring to 56.7% in summer, with certain amount of Sirich, Ca-rich, Fe-rich, and K-rich particles. The relative number percentage of sulfate particles shows a positive correlation with relative humidity (RH), suggesting that high RH might accelerate the sulfation of individual particles. Based on air mass backward trajectories, the high pollution in Beijing might be influenced by local emissions and air masses from adjacent areas south of Beijing. Air masses from Inner Mongolia carry higher concentrations of mineral particles and alleviate the abundance of S-rich and other particles.