Size-resolved source apportionment of particulate matter in urban Beijing during haze and non-haze episodes

摘要

pstrongAbstract./strong Additional size-resolved chemical information is needed before the physicochemical characteristics and sources of airborne particles can be understood; however, this information remains unavailable in most regions of China due to lacking measurement data. In this study, we report observations of various chemical species in size-segregated particle samples that were collected over 1 year in the urban area of Beijing, a megacity that experiences severe haze episodes. In addition to fine particles, high concentrations of coarse particles were measured during the periods of haze. The abundance and chemical compositions of the particles in this study were temporally and spatially variable, with major contributions from organic matter and secondary inorganic aerosols. The contributions of organic matter to the particle mass decreased from 37.9 to 31.2span class="thinspace"/span%, and the total contribution of sulfate, nitrate and ammonium increased from 19.1 to 33.9span class="thinspace"/span% between non-haze and haze days, respectively. Due to heterogeneous reactions and hygroscopic growth, the peak concentrations of the organic carbon, cadmium and sulfate, nitrate, ammonium, chloride and potassium shifted from 0.43 to 0.65span class="thinspace"/span?μm on non-haze days to 0.65–1.1span class="thinspace"/span?μm on haze days. Although the size distributions of lead and thallium were similar during the observation period, their concentrations increased by a factor of more than 1.5 on haze days compared with non-haze days. We observed that sulfate and ammonium, which have a size range of 0.43–0.65span class="thinspace"/span?μm, sulfate and nitrate, which have a size range of 0.65–1.1span class="thinspace"/span?μm, calcium, which has a size range of 5.8–9span class="thinspace"/span?μm, and the meteorological factors of relative humidity and wind speed were responsible for haze pollution when the visibility was less than 10span class="thinspace"/spankm. Source apportionment using Positive Matrix Factorization showed six PMsub2.1/sub sources and seven PMsub2.1–9/sub common sources secondary inorganic aerosol (25.1span class="thinspace"/span% for fine particles vs. 9.8span class="thinspace"/span% for coarse particles), coal combustion (17.7span class="thinspace"/span% vs. 7.8span class="thinspace"/span%), biomass burning (11.1span class="thinspace"/span% vs. 11.8span class="thinspace"/span%), industrial pollution (12.1span class="thinspace"/span% vs. 5.1span class="thinspace"/span%), road dust (8.4span class="thinspace"/span% vs. 10.9span class="thinspace"/span%), vehicle emissions (19.6span class="thinspace"/span% for fine particles), mineral dust (22.6span class="thinspace"/span% for coarse particles) and organic aerosol (23.6span class="thinspace"/span% for coarse particles). The contributions of the first four factors and vehicle emissions were higher on haze days than non-haze days, while the reverse is true for road dust and mineral dust. The sources' contribution generally increased as the size decreased, with the exception of mineral dust. However, two peaks were consistently found in the fine and coarse particles. In addition, the sources' contribution varied with the wind direction, with coal and oil combustion products increasing during southern flows. This result