Dust-Dominated Coarse Particles as a Medium for Rapid Secondary Organic and Inorganic Aerosol Formation in Highly Polluted Air

Abstract

Secondary aerosol (SA) frequently drives severe haze formation on the North China Plain. However, previous studies mostly focused on submicron SA formation, thus our understanding of SA formation on supermicron particles remains poor. In this study, PM2.5 chemical composition and PM10 number size distribution measurements revealed that the SA formation occurred in very distinct size ranges. In particular, SA formation on dust-dominated supermicron particles was surprisingly high and increased with relative humidity (RH). SA formed on supermicron aerosols reached comparable levels with that on submicron particles during evolutionary stages of haze episodes. These results suggested that dust particles served as a medium for rapid secondary organic and inorganic aerosol formation under favorable photochemical and RH conditions in a highly polluted environment. Further analysis indicated that SA formation pathways differed among distinct size ranges. Overall, our study highlights the importance of dust in SA formation during non-dust storm periods and the urgent need to perform size-resolved aerosol chemical and physical property measurements in future SA formation investigations that are extended to the coarse mode because the large amount of SA formed thereon might have significant impacts on ice nucleation, radiative forcing, and human health.

Measurement report: Characterization and source apportionment of coarse particulate matter in Hong Kong: Insights into the constituents of unidentified mass and source origins in a coastal city in southern China

“…The possible inter-particle interaction between fine and coarse particles on the PM10 samples is also neglected, which potentially bias the nitrate measurements in the two size modes. secondary inorganic and organic aerosols formation in highly polluted condition (Xu et al, 2020). Considering the southern China is more humid than northern China, our study region presents an atmospheric condition different from that in Xu et al's study, which is more favourable to adsorption of water on mineral dust, and consequently lead to different impacts on atmospheric chemistry and climate (Tang et al, 2016).…”

“…For example, nitrate in the coarse mode is formed by the reaction between nitric acid (HNO3) from oxidation of NOx and preexisting alkaline aerosols (e.g., sea salt and dust). A recent study showed that mineral dust can serve as a medium for rapid secondary inorganic and organic aerosol formation under high photochemical activity and relative humidity conditions, which has important implications to the life cycle of secondary aerosols (Xu et al, 2020). PMcoarse also exerts an impact on earth's climate because of its continuous loading in the atmosphere and its ability to scatter and absorb radiation or act as cloud condensation and ice nuclei (USEPA, 2019).…”

Comment on acp-2021-419

“…Secondary aerosol formation is enhanced in stagnant (low winds) and high humidity conditions (Xu et al, 2020b). NCEP (National Centers for Environmental Prediction) reanalysis horizontal wind in BCN (not shown) reveals strong winds (~18 m s -1 ) at the beginning of the episode and much more stagnant conditions (<5 m s -1 ) towards the end of the episode.…”

Aerosol radiative impact during the summer 2019 heatwave produced partly by an inter-continental Saharan dust outbreak – Part 2: Long-wave and net dust direct radiative effect

“…Secondary aerosol formation is enhanced in stagnant (low winds) and high humidity conditions (Xu et al, 2020b s -1 ) at the beginning of the episode and much more stagnant conditions (<5 m s -1 ) towards the end of the episode. All in all, such conditions might have favored the transfer of small dust particles to larger sizes and the growth of coarse-mode particles along the transport.…”

“…In particular, when the transport of mineral dust occurs over polluted regions anthropogenic inorganic acids can be absorbed by the dust surface forming hygroscopic salt compounds that coat the dust particles (Abdelkader et al, 2015;Athanasopoulou et al, 2016). Dust also favors the formation of secondary pollutants (Querol et al, 2019;Xu et al, 2020b).…”