摘要：

Although secondary participate matter is reported to be the main contributor of PM[sub 2.5] during haze in Chinese megacities, primary particle emissions also affect particle concentrations. In order to improve estimates of the contribution of primary sources to the particle number and mass concentrations, we performed source apportionment analyses using both chemical fingerprints and particle size distributions measured at the same site in urban Beijing from April to July 2018. Both methods resolved factors related to primary emissions, including vehicular emissions and cooking emissions, which together make up 76% and 24% of total particle number and organic aerosol (OA) mass, respectively. Similar source-types, including particles related to vehicular emissions (1.6 ± 1.1 (g m-3; 2.4 ± 1.8 x 10 cm-3 and 5.5 ± 2.8 x 10 cm-3 for two traffic-related components), cooking emissions (2.6 ± 1.9 g m-3 and 5.5 ± 3.3 x 10cm-3) and secondary aerosols (51 ± 41 g m-3 and 4.2 ± 3.0 x 10 cm-3) were resolved by both methods. Converted mass concentrations from particle size distributions components were comparable with those from chemical fingerprints. Size distribution source apportionment separated vehicular emissions into a component with a mode diameter of 20 nm ("Traffic-ultrafine") and a component with a mode diameter of 100 nm ("Traffic-fine"). Consistent with similar day and night-time diesel vehicle PM2.5 emissions estimated for the Beijing area, Traffic-fine, hydrocarbon-like OA (HOA, traffic-related factor resulting from source apportionment using chemical fingerprints), and black carbon (BC) showed similar diurnal patterns, with higher concentrations during the night and morning than during the afternoon when the boundary layer is higher. Traffic-ultrafine particles showed the highest concentrations during the rush-hour period, suggesting a prominent role of local gasoline vehicle emissions. In the absence of new-particle formation, our results show that vehicular related emissions (14% and 30% for ultrafine and fine particles, respectively) and cooking activity related emissions (32%) dominate the particle number concentration while secondary particulate matter (over 80%) governs PM[sub 2.5] mass during the nonheating season in Beijing.

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