Primary emissions versus secondary formation of fine particulate matter in the most polluted city (Shijiazhuang) in North China

Abstract

Abstract. Particulate matter (PM) pollution is a severe environmental problem in the Beijing–Tianjin–Hebei (BTH) region in North\nChina. PM studies have been conducted extensively in Beijing, but the\nchemical composition, sources, and atmospheric processes of PM are still\nrelatively less known in nearby Tianjin and Hebei. In this study, fine PM\nin urban Shijiazhuang (the capital of Hebei Province) was characterized using\nan Aerodyne quadrupole aerosol chemical speciation monitor (Q-ACSM) from\n11\xa0January to 18\xa0February in 2014. The average mass concentration of\nnon-refractory submicron PM (diameter\u2009 µm , NR-PM 1 ) was\n 178±101 µg\u2009m−3 , and it was composed of 50\u2009% organic aerosol\n(OA), 21\u2009% sulfate, 12\u2009% nitrate, 11\u2009% ammonium, and 6\u2009% chloride.\nUsing the multilinear engine (ME-2) receptor model, five OA sources were\nidentified and quantified, including hydrocarbon-like OA from vehicle\nemissions (HOA, 13\u2009%), cooking OA (COA, 16\u2009%), biomass burning OA (BBOA,\n17\u2009%), coal combustion OA (CCOA, 27\u2009%), and oxygenated OA (OOA, 27\u2009%).\nWe found that secondary formation contributed substantially to PM in episodic\nevents, whereas primary emissions were dominant (most significant) on average.\nThe episodic events with the highest NR-PM 1 mass range of\n300–360\u2009 µg\u2009m−3 were comprised of 55\u2009% of secondary species. On the\ncontrary, a campaign-average low OOA fraction (27\u2009%) in OA indicated the\nimportance of primary emissions, and a low sulfur oxidation degree\n( F SO 4 ) of 0.18 even at RH\u2009 >90 \u2009% hinted at insufficient\noxidation. These results suggested that in Shijiazhuang in wintertime fine PM\nwas mostly from primary emissions without sufficient atmospheric aging,\nindicating opportunities for air quality improvement by mitigating direct\nemissions. In addition, secondary inorganic and organic (OOA) species\ndominated in pollution events with high-RH conditions, most likely due to\nenhanced aqueous-phase chemistry, whereas primary organic aerosol (POA)\ndominated in pollution events with low-RH and stagnant conditions. These\nresults also highlighted the importance of meteorological conditions for PM\npollution in this highly polluted city in North China.