Compositional variations of primary organic aerosol tracers of PM2.5 in Shanghai during the 2019 China International Import Expo

Abstract

To reflect the changes in pollution sources and evaluate the control efficiency more reasonably, seven groups of PM2.5-bound primary organic aerosol (POA) tracers indicative of pollution sources in urban Shanghai were analyzed before (BP), during (CIIE) and after (AP) the second China International Import Expo (CIIE, October 28–November 17, 2019). Combined with meteorological conditions, correlation analysis among the tracers and diagnostic ratios, the sources and influencing factors of POA tracers were investigated. During CIIE, the concentrations of POA tracers showed a downward trend from 287 ng/m3 in the BP period to 219 ng/m3, while the proportion of POA tracers in PM2.5 increased from 0.58% to 1.0%. The sandstorm during BP caused the high concentrations of PM10 and PM2.5, the temporal variation of the concentrations of monosaccharides and sugar compounds and plant wax n-alkanes (WAX Cn) well reflected the impact of dust. The obvious increase of the relative concentrations of hopanes and steranes to EC during CIIE reflected that the decrease of EC concentration was due to the decrease of emission from sources other than traffic sources. The control of illegal emissions of factories and the decreased biomass burning might contribute to the decrease of EC during the CIIE. The results showed that the variations in POA tracers revealed the changes in pollution sources. Hence, it is necessary to pay attention to the compositional changes in organic aerosols when evaluating the causes of variation in concentration of PM2.5.