Chemical characteristics of airborne particles in Xi'an, inland China during dust storm episodes: Implications for heterogeneous formation of ammonium nitrate and enhancement of N-deposition

To identify the sources and heterogeneous reactions of sulfate and nitrate with dust in the atmosphere, airborne particles in Xi'an, inland China during the spring of 2017 were collected and measured for chemical compositions, along with a laboratory simulation of the heterogeneous formation of ammonium nitrate on the dust surface. Our results showed that concentrations of Ca2+, Na+ and Cl- in the TSP samples were enhanced in the dust events, with the values of 41.8, 5.4 and 4.0 mu g m(-3), respectively, while NO3- (7.1 mu g m(-3)) and NH4+ (2.4 mu g m(-3)) remarkably decreased, compared to those in the non-dust periods. During the dust events, NH4+ correlated only with NO3- (R-2 = 0.52) and abundantly occurred in the coarse mode (>2.1 mu m), in contrast to that in the non-dust periods, which well correlated with sulfate and nitrate and enriched in the fine mode (