Fig. 1: Sources of OA and their contribution to fine particle mass in winter (20 November 2019 to 25 January 2020) and summer (1 May 2020 to 2 July 2020).
From: Substantial contribution of transported emissions to organic aerosol in Beijing
The bulk chemical composition of PM2.5 from an Aerosol Chemical Speciation Monitor and Aethalometer (ToF-ACSM and AE33, left) shows that roughly one-third of the PM2.5 mass is organic, without detailed information about its sources. Additional near-molecular information based on thermal desorption chemical ionization mass spectra (FIGAERO-CIMS, right) reveals that, even in winter, well over half of the OA is secondary, with a large contribution of aqueous processing. Solid-fuel sources with primary and secondary constituents comprise almost half of wintertime OA. During summertime, half of the OA is secondary organic aerosol from aromatics, probably from mobile sources, and a quarter has biogenic origin. For the COVID lockdown period (26 January 2020 to 30 April 2020) see Extended Data Fig. 3. The holes in the pie charts represent constituents and sources not covered, which comprise less than 20% of the whole. A sensitivity assessment is presented in Extended Data Figs. 4 and 5 and shows that the FIGAERO-CIMS alone directly measures ~61% of the OA mass concentration based on MLR quantification, also including HOA and COA from the ToF-ACSM, presented in this figure.
