Heterogeneous Sulfate Formation on Dust Surface and Its Dependence on Mineralogy: Balloon-Borne Observations from Balloon-Borne Measurements in The Surface Atmosphere of Beijing, China

Abstract

This study focuses on providing a direct insight into the process by which sulfate is formed on mineral dust surface in the actual atmosphere. Six sets of aerosol measurements were conducted in the outskirts of Beijing, China, in 2002-2003 using a tethered balloon. The mineralogy of individual dust particles, as well as its influence on the S (sulfur) loadings was investigated by SEM-EDX analysis of the directly collected particles.The mixed layer in the urban atmosphere was found to be quite low (500-600 m), often appearing as a particle dense stagnant layer above the surface. It is suggested that mineral dust is a common and important fraction of the coarse particles in Beijing (35-68%), and that it is relatively enriched with Calcite (>28%).An exceptional amount of S was detected in the mineral particles, which can be explained neither by their original composition, nor by coagulation processes between the submicron sulfates and the dust. Heterogeneous uptake of gaseous SO 2 , and its subsequent oxidation on dust was suggested as the main pathway that has actually taken place in the ambient environment. The mineral class found with the largest number of particles containing S was Calcite, followed by Dolomite, Clay, Amphibole etc., Feldspar, and Quartz. Among them, Calcite and Dolomite showed distinctly higher efficiency in collecting sulfate than the other types.A positive correlation was found with the number of S containing particles and the relative humidity. Calcite in particular, since almost all of its particles was found to contain S above 60% r.h. On the other hand, the active uptake of SO 2 by the carbonates was not suggested in the free troposphere downwind, and all the mineral classes exhibited similar S content. Relative humidity in the free troposphere was suggested as the key factor controlling the SO 2 uptake among the mineral types. In terms of sulfate loadings, the relationship was not linear, but rather increased exponentially as a function of relative humidity. The humidity-dependent uptake capacity of mineral types altogether showed an intermediate value of 0.07 gSO 2− 4 g −1 mineral at 30% r.h. and 0.40 gSO 2− 4 g −1 mineral at 80%, which is fairly consistent with laboratory experiments.

Morphological and chemical modification of mineral dust: Observational insight into the heterogeneous uptake of acidic gases

“…[8] The sampling and analytical procedures are basically identical to those described in detail by Matsuki et al [2005] for the previous measurements. However, instead of using Carbon-coated nitrocellulose (collodion) film supported by Ni-grids, we applied an additional nitron (C 20 H 16 N 4 ) coating on the sampling substrate, which enables the detection of particulate nitrate [Isawa and Ono, 1979].…”

“…Those having elemental ratios of Ca > 50% (or (Mg + Ca) > 50%) are termed ''carbonate'' (mostly calcite including dolomite), and the rest, ''silicate'' (mostly clay and mica, including quartz, feldspars, etc.) because these are generally the two dominant atmospheric mineral species found in the region [Matsuki et al, 2005]. Silicate is enriched in Al and Si and often includes minor fractions of other metals (Na, Mg, K, Ca, Ti, Mn, Fe).…”

“…[5] Based upon tethered balloon measurements in Beijing, China and successive individual particle analyses, our previous report provided field evidence of the mineralogy and the humidity-dependent formation of sulfate on dust particles [Matsuki et al, 2005]. However, the actual atmosphere is a melting pot where the simultaneous uptake of various gases takes place on different aerosol types.…”

Cloud processing of mineral dust: direct comparison of cloud residual and clear sky particles during AMMA aircraft campaign in summer 2006

“…The impactor used in this study is basically identical to that described in Matsuki et al (2005a, b). The aerodynamic diameter at which particles are collected with 50% collection efficiency was at 1.6 µm and 0.2µm, respectively, at the first and second stage of the impactor with a volume flow rate of approximately 1.0 L min −1 (1013 hPa, 293 K).…”

Enhanced ice nucleation efficiency of microcline immersed in dilute NH<sub>3</sub> and NH<sub>4</sub><sup>+</sup>-containing solutions

“…The chemical composition and thickness of the coating depend on the particle mineralogy and on the transport pathway (Matsuki et al, 2005a;Sullivan et al, 2007;Fitzgerald et al, 2015). Calcium-rich particles, originating from calcite, have been shown to be more susceptible to processing by SO2 and NOy than silicates and aluminosilicates (Matsuki et al, 2005b).…”