Mixing state and hygroscopicity of dust and haze particles before leaving Asian continent

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, cycloneinduced 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. The results showed that the sulfate concentration was not considerably different at the two sites, while the nitrate concentration was slightly larger at the urban site than that at the desert site. The estimated nitrate production rate was 4-5 ng µg −1 of mineral dust per day, which was much less than that in polluted urban air. 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 HNO 3 was suggested to be the reason for the small nitrate production. According to our investigation of the published literature, the significant sulfate and nitrate in dust-storm-associated samples within the continental atmosphere reported in previous studies cannot be confirmed as actually produced on desert dust particles; the contribution from locally emitted and urban mineral particles or from soil-derived sulfate was likely substantial because the weather conditions in those studies indicated that the collection of the samples was started before dust arrival, or the air from which the samples were collected was a mixture of desert dust and locally emitted mineral particles. These results suggest that the production of nitrate and sulfate on dust particles following cold fronts is likely limited when the particles move from the desert to populated areas within the continent. For an accurate quantification of sulfate and nitrate formed on long-distance-transported desert dust particles at downwind populated areas in eastern China, dust collection efforts are indispensable to minimize any possible influence by locally emitted particles or at least to ensure that the samples are collected after dust arrival.

Section: Intercomparisons and Implicationscontrasting

confidence: 89%

Limited production of sulfate and nitrate on front-associated dust storm particles moving from desert to distant populated areas in northwestern China

Zhang

Cao

et al. 2017

“…Z. . The phenomenon was also observed in Shanghai, a megacity a few thousands of kilometers from dust source zones in China, and more downwind sites (Kang et al, 2013;Li et al, 2014;Wang et al, 2013).…”

Section: Introductionmentioning

confidence: 69%

“…In an extreme case, Asian dust was found to be transported more than one full circuit around the globe in approximately 13 days (Uno et al, 2009). During long-range transport, dust particles may mix with anthropogenic air pollutants and consequently undergo complicated chemical reactions Li et al, 2014;Ma et al, 2012;Q. Z. Wang et al, 2011Q.…”

Section: Introductionmentioning

confidence: 99%

The concentration, source and deposition flux of ammonium and nitrate in atmospheric particles during dust events at a coastal site in northern China

Liu

Yao

et al. 2018

Abstract. Asian dust has been reported to carry anthropogenic reactive nitrogen during transport from source areas to the oceans. In this study, we attempted to characterize NH 4 and NO − 3 in each total suspended particle (TSP) sample, the samples can be classified into increasing or decreasing types. In Category 1, the concentrations of NH + 4 and NO − 3 were 20-440 % higher in dust day samples relative to samples collected immediately before or after a dust event. These concentrations decreased by 10-75 % in the dust day samples in Categories 2 and 3. Back trajectory analysis suggested that multiple factors, such as the transport distance prior to the reception site, the mixing layer depth on the transport route and the residence time across highly polluted regions, might affect the concentrations of NH .

“…For example, mineral dust particles normally display irregular shapes and fly ash particles are spherical, although they both have similar elemental composition, such as Si and Al. A detailed particle classification scheme is described in our previous studies (Li et al, 2014b. The nanometer-sized metal particles which have been frequently detected in ambient aerosols in East China (W. Li et al, 2013a, b) were absent in the Qinghai-Tibet plateau.…”

Section: Major Fine Aerosol Particles and Mixing Statesmentioning

confidence: 99%

Mixing state and sources of submicron regional background aerosols in the northern Qinghai–Tibet Plateau and the influence of biomass burning

Chen

et al. 2015

Abstract. Transmission electron microscopy (TEM) was employed to obtain morphology, size, composition, and mixing state of background aerosols with diameter less than 1 µm in the northern Qinghai-Tibet Plateau (QTP) during 15 September to 15 October 2013. Individual aerosol particles mainly contained secondary inorganic aerosols (SIA -sulfate and nitrate) and organics during clean periods (PM 2.5 mass concentration less than 2.5 µg m −3 ). The presence of K-Na-Cl associated with organics and an increase in soot particles suggest that an intense biomass burning event caused the highest PM 2.5 concentrations (> 30 µg m −3 ) during the study. A large number fraction of the fly-ashcontaining particles (21.73 %) suggests that coal combustion emissions in the QTP significantly contributed to air pollutants at the medium pollution level (PM 2.5 : 10-30 µg m −3 ). We concluded that emissions from biomass burning and from coal combustion both constantly contribute to anthropogenic particles in the QTP atmosphere. Based on size distributions of individual particles at different pollution levels, we found that gas condensation on existing particles is an important chemical process for the formation of SIA with organic coating. TEM observations show that refractory aerosols (e.g., soot, fly ash, and visible organic particles) likely adhere to the surface of SIA particles larger than 200 nm due to coagulation. Organic coating and soot on surface of the aged particles likely influence their hygroscopic and optical properties, respectively, in the QTP. To our knowledge, this study reports the first microscopic analysis of fine particles in the background QTP air.