Efficient Heterogeneous Formation of Ammonium Nitrate on the Saline Mineral Particle Surface in the Atmosphere of East Asia during Dust Storm Periods.

To understand the chemical evolution of dust in the current East Asian atmosphere, the chemistry of PM and size-resolved aerosols in Shanghai, China, during the 2019 dust storm event was investigated. Our results showed that concentrations of SO in the city during the event highly correlated with Ca and Na due to the direct emissions of CaSO and NaSO from the upwind deserts. In contrast, during the event, NO linearly correlated with NH at a molar ratio close to 1:1, and both almost entirely stayed in coarse particles, suggesting they accumulated on the dust surface as NHNO. Based on the field observations and laboratory smog chamber simulations, we found that NO and O in Shanghai during the dust period reacted to form NO, which subsequently hydrolyzed into HNO on the surface of saline mineral dusts (e.g., CaSO and NaSO) and was further neutralized by NH as NHNO. The relative abundances of NO and NH in Shanghai during the dust event were notably higher than those a decade ago, indicating that this heterogeneous formation of NHNO on dust was enhanced by the abundantly coexisting NO, O, and NH in the current East Asian atmosphere, which should be considered in future modeling studies.