Limited production of sulfate and nitrate on front-associated dust storm particles moving from desert to distant populated areas in northwestern China
Feng Wu1, Daizhou Zhang2, Junji Cao1,3, Xiao Guo1,4, Yao Xia1,4, Ting Zhang1, Hui Lu5, and Yan Cheng31Key Laboratory of Aerosol Chemistry & Physics, and State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Science, Xi'an, China 2Faculty of Environmental and Symbiotic Sciences, Prefectural University of Kumamoto, Kumamoto, Japan 3Institute of Global Environmental Change, Xi'an Jiaotong University, Xi'an, China 4School of Tropical Eco-Environment Protection, Hainan Tropical Marine University, Sanya, China 5Institute of Desert Meteorology, China Meteorological Administration, Urumqi, China
Received: 04 Oct 2016 – Accepted for review: 01 Dec 2016 – Discussion started: 05 Dec 2016
Abstract. Sulfate and nitrate compounds can greatly increase the hygroscopicity of mineral particles in the atmosphere and, consequently, alter the particles' physical and chemical properties. Their uptake on long-distance transported Asian dust particles within mainland China has been reported to be substantial in previous studies, but the production was very inefficient in other studies. We compared these two salts in particles collected from a synoptic scale, mid-latitude cyclone-induced dust storm plume at the Tengger desert (38.79° N, 105.38° E) and in particles collected in a postfrontal dust plume at an urban site in Xi'an (34.22° N, 108.87° E) when a front-associated dust storm from the Tengger desert arrived there approximately 700 km downwind. Results showed that sulfate concentration was not considerably different at the two sites while nitrate concentration was slightly larger at the urban site than that at the desert site. The estimated nitrate production rate was 4–5 ng per μg mineral dust per day, which was much less than that in polluted urban air. These results indicate that the production of nitrate and sulfate on dust particles following cold fronts was limited when the particles moved from the desert to populated areas. The adiabatic process of the dust-loading air was suggested to be the reason for the absence of sulfate formation and the uptake of background HNO3 to be the reason for the small nitrate production. The significant sulfate and nitrate reported in dust-associated samples in previous studies were more likely produced on locally-emitted and urban mineral particles or from soil-derived sulfate rather than being produced via chemical conversions on desert dust particles.
Wu, F., Zhang, D., Cao, J., Guo, X., Xia, Y., Zhang, T., Lu, H., and Cheng, Y.: Limited production of sulfate and nitrate on front-associated dust storm particles moving from desert to distant populated areas in northwestern China, Atmos. Chem. Phys. Discuss., doi:10.5194/acp-2016-853, in review, 2016.