Haze problems lead great public concern in megacities because of its impacts on visibility, radiation, and human health. In recent years, on-line instruments like Aerodyne aerosol mass spectrometer and aerosol chemical speciation monitor are commonly used to characterize the aerosol composition and the sources of organic aerosol (OA) in China. Most of these instruments can only detect the submicron domain. In this study, we deployed a time-of-flight aerosol chemical speciation monitor (TOF-ACSM) equipped with 2.5-µm aerodynamic lens, a capture vaporizer, and a novel size-switching system in urban Beijing for the summer and the winter. Non-refractory submicron and fine particles were alternatively detected for every half an hour by the same mass spectrometer under a time resolution of 2.5 min, which allows source apportionments of particles in the two size domains without complications from instrument differences and uncertain collection efficiency. In Beijing, submicron particles contribute to the majority (80~90%) of fine-particle mass. The chemical compositions are similar for the two size domains. The mass ratios of submicron- to fine-mode non-refractory particles and their major chemical components however decrease significantly during severe haze events when the relative humidity was high. In winter, six OA factors such as hydrocarbon-like OA, cooking OA, biomass-burning OA, coal-combustion OA and two types of oxidized OA are identified by positive matrix factorization, which is consistent with the findings of previous studies. In summer, four factors including hydrocarbon-like OA, cooking OA, two oxidized OA are identified. One type of the oxygenated OA factor is mainly associated with the haze events and is correlated with aerosol water content. Our data suggest significant aqueous-phase oxidation or heterogeneous production of SOA and other components during the severe haze events.

Sources of secondary aerosol species in a highly polluted urban environment: Insights from online composition measurements for PM<sub>1 </sub>and PM<sub>2.5</sub>

2019 Fall National Meeting

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Sources of secondary aerosol species in a highly polluted urban environment: Insights from online composition measurements for PM1 and PM2.5

Sources of secondary aerosol species in a highly polluted urban environment: Insights from online composition measurements for PM₁and PM_2.5