NMHCs in a heavily polluted city in Northern China: Characteristics, effects on SOA potential, and source apportionment

Abstract

Non-methane hydrocarbons (NMHCs) plays an important role in haze events. This study focused on NMHCs characteristics, effects on secondary organic aerosol (SOA) and source apportionment in Handan in heavily polluted seasons, i.e., autumn (October 2017) and winter (January 2018) and their differences in non-haze and haze days. An online instrument (AMA GC5000) was used to monitor NMHCs in Handan firstly at the campus of Hebei University of Engineering. It was found that the average NMHCs concentrations were 41.45 and 57.56 ppb in autumn and winter, respectively, which were higher than most investigated domestic and foreign megacities to the best of our knowledge. Alkanes was the largest contributor to NMHCs (45.4%), and followed by alkenes, aromatics, and acetylene. In haze days, the concentrations of NMHCs and four categories increased far more in winter than those in autumn compared to non-haze days. The total SOA potential (SOAP) in winter (3364 μg m-3) was higher than that in autumn (2804 μg m-3). The total SOAP was close in haze and non-haze days in autumn, while it was much higher in haze days in winter. Regardless of the variations of different periods, aromatics contributed most to the total SOAP, with contributions of 87 - 95%, where toluene was the most contributed species. Combined the results of diagnostic ratios with positive matrix factorization (PMF) model, NMHCs of Handan was mainly contributed by traffic emissions and combustion events. Vehicle related (from 23.2 to 30.1%) and industrial related source (from 13.7 to 26.7%) may be major contributors to the haze pollution in autumn and winter, respectively.