AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
Observation on Chemical Characteristics of Airborne Particles in Xi'an, Inland China during Dust Storm Events with Implications for Heterogeneous Formation of Ammonium Nitrate and Enhancement of N-deposition
GEHUI WANG, Wu Can, Jianjun Li, Cong Cao, Jin Li, East China Normal University
Abstract Number: 821 Working Group: Aerosol Chemistry
Abstract 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 µg/m3, respectively, while NO3- (7.1 µg/m3) and NH4+ (2.4 µg/m3) remarkably decreased, compared to those in the non-dust periods. During the dust events NH4+ correlated only with NO3- (R2=0.52) and abundantly occurred in the coarse mode (>2.1 µm), in contrast to that in the non-dust periods, which well correlated with sulfate and nitrate and enriched in the fine mode (2.1 µm), suggesting that they were directly transported from the upwind Gobi Desert region. Our laboratory simulation results showed that during the long range transport hygroscopic salts in the Gobi dust such as mirabilite can absorb water vapor and form a liquid phase on the particle sur-face, then gaseous NH3 and HNO3 partition into the aqueous phase and form NH4NO3, resulting in the strong correlation of NH4+ with NO3- and their accumulation on dust particles. The dry de-position flux of total inorganic nitrogen (NH4+ + NO3-) in Xi’an during the dust events was 1.28 mgï€N/(m2 d) and 80% higher than that in the non-dust periods. Such a significant enhanced N-deposition is ascribed to the heterogeneous formation of NH4NO3 on the dust particle surface, which has been ignored and should be included in future model simulations.