Extended Data Fig. 3: Sources of organic aerosol and their contribution to fine particle mass during the COVID lockdown period.
From: Substantial contribution of transported emissions to organic aerosol in Beijing

Bulk chemical composition of particulate matter from an Aerosol Chemical Speciation Monitor and Aethalometer (ToF-ACSM and AE33, left) shows that roughly one-quarter of the particulate matter mass is organic without detailed information on the sources. Additional near-molecular information based on thermal desorption chemical ionization mass spectra (FIGAERO-CIMS, right) reveals that three-quarter of the organic aerosol is secondary, with a roughly equal contributions of biogenic SOA, aromatic-dominated-SOA, and aqueous SOA. The holes in the pie charts are constituents and sources not covered, which comprise less than 20%.