Negligible contribution from conventionally-recognized ambient secondary conversion to severe PM2.5 pollution in today’s China

Abstract:

The concept, formation of secondary particulate matter (FSPM) in ambient air referred as conventionally-recognized FSPM in this study, overwhelmingly navigates studies of severe air pollution events characterized by high mass concentrations of particles with diameter <2.5 µm (PM_2.5) in China. Here, we provide solid evidences to confirm conventionally-recognized FSPM too weak to yield a detectable contribution to largely increased PM_2.5 during an extremely severe PM_2.5 pollution event sweeping northern China on 11-14 January 2019. After excluding the contributor, the truth on the mechanism of the severe pollution event rises to the surface. A novel hypothesis is proposed, i.e., in-fresh-plume non-precipitation-cloud processing of aerosols, following by evaporation of semi-volatile components from the aerosols. What supports the processed aerosols as the dominant contributor to largely increased PM_2.5 during severe PM_2.5 pollution events in today’s China and how the processing of aerosols gains enhanced largely by favorable ambient conditions are delivered.