Additional size-resolved chemical information is neededbefore the physicochemical characteristics and sources of airborne particlescan be understood; however, this information remains unavailable in mostregions of China due to lacking measurement data. In this study, we reportobservations of various chemical species in size-segregated particle samplesthat were collected over 1 year in the urban area of Beijing, a megacitythat experiences severe haze episodes. In addition to fine particles, highconcentrations of coarse particles were measured during the periods of haze.The abundance and chemical compositions of the particles in this study weretemporally and spatially variable, with major contributions from organicmatter and secondary inorganic aerosols. The contributions of organic matterto the particle mass decreased from 37.9 to 31.2?%, and the totalcontribution of sulfate, nitrate and ammonium increased from 19.1to 33.9?% between non-haze and haze days, respectively. Due toheterogeneous reactions and hygroscopic growth, the peak concentrationsof the organic carbon, cadmium and sulfate, nitrate, ammonium, chloride andpotassium shifted from 0.43 to 0.65?μm on non-haze days to 0.65–1.1?μm on haze days. Although the size distributions of lead andthallium were similar during the observation period, their concentrationsincreased by a factor of more than 1.5 on haze days compared with non-hazedays. We observed that sulfate and ammonium, which have a size range of 0.43–0.65?μm, sulfate and nitrate, which have a size range of 0.65–1.1?μm,calcium, which has a size range of 5.8–9?μm, and themeteorological factors of relative humidity and wind speed were responsiblefor haze pollution when the visibility was less than 10?km. Sourceapportionment using Positive Matrix Factorization showed six PM2.1sources and seven PM2.1–9 common sources: secondary inorganic aerosol(25.1?% for fine particles vs. 9.8?% for coarse particles), coalcombustion (17.7?% vs. 7.8?%), biomass burning (11.1?% vs. 11.8?%),industrial pollution (12.1?% vs. 5.1?%), road dust (8.4?% vs.10.9?%), vehicle emissions (19.6?% for fine particles), mineral dust(22.6?% for coarse particles) and organic aerosol (23.6?% for coarseparticles). The contributions of the first four factors and vehicle emissions were higher on hazedays than non-haze days, while the reverse is true for road dust and mineral dust. The sources' contribution generally increased as the size decreased, withthe exception of mineral dust. However, two peaks were consistently found inthe fine and coarse particles. In addition, the sources' contribution variedwith the wind direction, with coal and oil combustion products increasingduring southern flows. This result suggests that future air pollutioncontrol strategies should consider wind patterns, especially during episodesof haze. Furthermore, the findings of this study indicated that thePM2.5-based data set is insufficient for determining source controlpolicies for haze in China and that detailed size-resolved information isneeded to characterize the important sources of particulate matter in urbanregions and better understand severe haze pollution.
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