Insights into the characteristics and sources of primary and secondary organic carbon: High time resolution observation in urban Shanghai

摘要

AbstractThere is growing evidence suggesting that organic aerosols play an important role in the evolution of severe haze episodes. However, long-term investigations of the different characteristics of carbonaceous aerosols during haze and non-haze days are insufficient. In this work, hourly measurements of organic carbon (OC) and elemental carbon (EC) in PM2.5were conducted in Shanghai, a megacity in Eastern China, over the course of a year from July 2013 to June 2014. Both OC and EC exhibited a bimodal diel pattern and were highly dependent on the wind speed and direction. The concentration-weighted trajectory (CWT) analysis illustrated that primary OC (POC) and EC were largely associated with regional and long-range transport. Secondary OC (SOC) formation was the strongest during the harvest season owing to significant biomass burning emissions from the adjacent Yangtze River Delta and farther agricultural regions. Compared to OC (6.7 μg m−3) and EC (2.0 μg m−3) in the non-haze days, higher levels of both OC (15.6 μg m−3) and EC (7.7 μg m−3) were observed in the haze days as expected, but with lower OC/EC ratios in the haze days (2.4) than in non-haze days (4.6). The proportion of POC and EC in PM2.5remained relatively constant as a function of PM2.5mass loadings, while that of SOC significantly decreased on the highly polluted days. It is concluded that the haze pollution in urban Shanghai was influenced more by the primary emissions (POC and EC), while the role of SOC in triggering haze was limited.Highlights•Long-term high time resolution observation of carbonaceous aerosol was conducted in urban shanghai.•Shanghai was heavily impacted by widespread biomass burning during the harvest season.•Primary carbonaceous aerosol (POC and EC) had a larger impact in haze formation than SOC.Primary carbonaceous aerosols (POC and EC) have a larger impact than SOC on haze formation in urban Shanghai.