Typical atmospheric haze during crop harvest season in northeastern China: A case in the Changchun region.

This study presents the mass concentrations of PM2.5, O3, SO2 and NOx at one urban, one suburban and two rural locations in the Changchun region from September 25 to October 27 2013. Major chemical components of PM2.5 at the four sites were daily sampled and analyzed. Most of daily concentrations of SO2 (7-82μg/m3), O3 (27-171μg/m3) and NOx (14-213μg/m3) were below the limits of the National Ambient Air Quality Standard (NAAQS) in China. However, PM2.5 concentrations (143-168μg/m3) were 2-fold higher than NAAQS. Higher PM2.5 concentrations (~150μg/m3) were measured during the pre-harvest and harvest at the urban site, while PM2.5 concentrations significantly increased from 250 to 400μgm-3 at suburban and rural sites with widespread biomass burning. At all sites, PM2.5 components were dominated by organic carbon (OC) and followed by soluble component sulfate (SO42-), ammonium (NH4+) and nitrate (NO3-). Compared with rural sites, urban site had a higher mineral contribution and lower potassium (K+ and K) contribution to PM2.5. Severe atmospheric haze events that occurred from October 21 to 23 were attributed to strong source emissions (e.g., biomass burning) and unfavorable air diffusion conditions. Furthermore, coal burning originating from winter heating supply beginning on October 18 increased the atmospheric pollutant emissions. For entire crop harvest period, the Positive Matrix Factorization (PMF) analysis indicated five important emission contributors in the Changchun region, as follows: secondary aerosol (39%), biomass burning (20%), supply heating (18%), soil/road dust (14%) and traffic (9%).