Chemical composition and source apportionment of PM2.5 during heavy pollution episodes in 2013-2015 in Handan, China

To investigate the formation mechanism of heavy air pollution in Handan, China, a comprehensive dataset including continuous online hourly observations of the meteorological parameters and air pollutants, i.e., SO2 NO, NO2, NOx, CO, O3, in January, 2013-2015, as well as water-soluble inorganic ions (WSII) (NO3-, SO42-, NH4+, Cl-, Na+, Mg2+, K+, Ca2+), carbon components (OC, EC) and inorganic elements in PM2.5 are analyzed in this study. The HYSPLIT Trajectory Model is applied to analyze the transport pathway of air mass. NO, SO2 and PM2.5 showed an obvious decreasing trend. Compared with 2013, NO, SO2 and PM2.5 decreased by 12.1%, 25.5%, 7.6% and 12.5%, 33.5%, 30.9% in 2014 and 2015, respectively. Heavy pollution episodes were often observed in winter during this period. A severe pollution episode was occurred from 2 to 20 January 2013. The peak concentrations of PM2.5 and PM10 were 1144.3 μg/m3 and 780.2 μg/m3 on 11 January 2013, respectively. The polluted level of heavy pollution episodes in 2014 and 2015 were slighter than 2013, but still can't be ignored. Their durations were short and generally lasted about 4-7 days, however, the frequency of occurrence was increased. Low temperature and wind speed and high humidity were always observed during these pollution episodes. The concentrations of chemical compositions of PM2.5 during heavy pollution episodes were significantly higher than those in clean day. The concentrations of SNA (SO42-, NO3- and NH4+) and OC peaked at 12 January 2013, 16 January 2014 and 15 January 2015, respectively, which is consistent with the previous analysis. The average monthly concentrations of SO42- and NH4+ were in the order of: 2013>2014>2015, indicating that this was related to the decrease of SO2 concentration. Cu, Zn, Pb were highly enriched elements, indicating the industrial pollution, especially from iron and steel smelting had a significant contribution to PM2.5 in Handan. Additionally, Cr in 2015, Mn, Co in 2014 and 2015 were highly enriched elements, respectively. Finally, the major spatial sources of pollutants in Handan are local emissions and from Hebei Province. The short-distance trajectories in January accounted for 63%, 64%, 50%, respectively.