Chemical Compositions and Sources Contribution of Atmospheric Particles at a Typical Steel Industrial Urban Site

Online monitoring concentrations of PM at five sites were obtained from 01/01/2016 to 31/12/2016 in Laiwu, China, and PM2.5 filters were manually sampled for total 34 days at the same sites in four seasons in 2016. PM pollution sources, including soil dust, urban dust, construction dust, coal-fired power plants dust, steel plant dust and motor vehicle exhaust dust were sampled, respectively. The overall mean PM2.5/PM10 ratio (0.57) in Laiwu was at a relatively lower level compared with that in other Chinese cities, which was higher in winter, indicating fine particulate was the main contributor of atmospheric pollution in this period. NH4+ mainly existed in the form of NH4NO3 and (NH4)(2)SO4 during the sampling periods. Higher sulfate and NH4+ concentrations were in summer while higher nitrate concentrations prevailed in winter. The annual value of OC/EC was (5.38 +/- 1.70), higher in summer and lower in winter, and the calculated SOC/OC value (%) was (43.68 +/- 12.98)%. The characteristic components were Si, Fe and Ca in urban dust and soil dust; Ca, Mg, and NH4+ in construction dust; Fe, Ca and SO42- in steel dust; OC, EC and Si in motor vehicle exhaust dust; SO42-, Al and NH4+ in power plant dust. Compared with other cities at home and abroad, it was found that the concentrations of metal elements in Laiwu were significantly higher than those in foreign cities, and at a medium level in China. With the improved CRAESCMB model, the urban dust was regarded as the receptor and the source of PM2.5 and apportioned its secondary sources contributions to PM2.5. The CMB results showed the contributions of secondary sources including sulfate (17%), nitrate (17%) and SOC (13%) to PM2.5 accounted for nearly half of all sources. Therefore, more attentions should be paid on secondary sources from the primary emission sources of the motor vehicle exhaust, coal combustion sources especially.