Dr. Qingxin Ma Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences. No. 18, Shuangqing Road, Haidian District, Beijing 100085, China Email:maqingxin05@gmail.com or qxma@rcees.ac.cn
maqingxin05@gmail.com
C.V. Born in 1982.
Sep. 2000-Jul. 2004: B.S. in Environmental Engineering, Department of Environmental Science and Engineering, University of Science and Technology, Beijing. Research area: Environmental Engineering
Sep. 2005-Jul. 2010: Ph.D. in Environmental Science, Graduate University of the Chinese Academy of Sciences. Research area: Atmospheric chemistry Dissertation: Heterogeneous reactions on mineral dust and the impacts on hygroscopic behavior
Jul. 2010-Now: Assistant Professor in State Key Laboratory of Environmental Aquatic Chemistry, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences. Research area: Atmospheric chemistry and Raman spectroscopy
ISI　ResearcherID: http://www.researcherid.com/rid/D-4695-2009 Google citation profile: http://scholar.google.com/citations?hl=en&user=DYPegU8AAAAJ AGU member
Abstract: Oxalic acid and oxalates represent an important fraction of atmospheric organic aerosols, however, little knowledge about the hygroscopic behavior of these particles is known. In this study, the hygroscopic behavior of oxalic acid and atmospherically relevant oxalates (H2C2O4, (NH4)2C2O4, CaC2O4, and FeC2O4) were studied by Raman spectrometry and vapor sorption analyzer. Under ambient relative humidity (RH) of 10-90%, oxalic acid and these oxalates hardly deliquesce and exhibit low hygroscopicity, however, transformation between anhydrous and hydrated particles was observed during the humidifying and dehumidifying processes. During the water adsorption process, conversion of anhydrous H2C2O4, (NH4)2C2O4, CaC2O4, and FeC2O4 to their hydrated particles (i.e., H2C2O4•2H2O, (NH4)2C2O4•H2O, CaC2O4•H2O, and FeC2O4•2H2O) occurred at about 20% RH, 55% RH, 10% RH, and 75% RH, respectively. Uptake of water on hydrated Ca-oxalate and Fe-oxalate particles can be described by a multilayer adsorption isotherm. During the dehumidifying process, dehydration of H2C2O4•2H2O and (NH4)2C2O4•H2O occurred at 5% RH while CaC2O4•H2O and FeC2O4•2H2O did not undergo dehydration. These results implied that hydrated particles represent the most stable state of oxalic acid and oxalates in the atmosphere. In addition, the assignments of Raman shift bands in the range of 1610-1650 cm−1 were discussed according to the hygroscopic behavior measurement results.
Abstract: Atmospheric aerosol is usually found to be a mixture of various inorganic and organic components in field measurements, whereas the effect of this mixing state on the hygroscopicity of aerosol particles has remained unknown. In this study, the hygroscopic behavior of mixtures of C2–C4 dicarboxylic acids and NaCl was investigated. For both externally and internally mixed malonic acid–NaCl and succinic acid–NaCl particles, correlation between water content and chemical composition was observed and the water content of these mixtures at relative humidity (RH) above 80% can be well predicted by the Zdanovskii–Stokes–Robinson (ZSR) method. In contrast, a nonlinear relation between the total water content of the mixtures and the water content of each chemical composition separately was found for oxalic acid–NaCl mixtures. Compared to the values predicted by the ZSR method, the dissolution of oxalic acid in external mixtures resulted in an increase in the total water content, whereas the formation of less hygroscopic disodium oxalate in internal mixtures led to a significant decrease in the total water content. Furthermore, we found that the hygroscopicity of the sodium dicarboxylate plays a critical role in determining the aqueous chemistry of dicarboxylic acid–NaCl mixtures during the humidifying and dehumidifying process. It was also found that the hydration of oxalic acid and the deliquescence of NaCl did not change in external oxalic acid–NaCl mixtures. The deliquescence relative humidity (DRHs) for both malonic acid and NaCl decreased in both external and internal mixtures. These results could help in understanding the conversion processes of dicarboxylic acids to dicarboxylate salts, as well as the substitution of Cl by oxalate in the atmosphere. It was demonstrated that the effect of coexisting components on the hygroscopic behavior of mixed aerosols should not be neglected.
Abstract: Mixtures of organic compounds with mineral dust are ubiquitous in the atmosphere whereas the formation pathways and hygroscopic behavior of these mixtures are not well understood. In this study, in situ DRIFTS, XRD and vapor sorption analyzer were used to investigate the heterogeneous reaction of acetic acid on α-Al2O3, MgO and CaCO3 particles under both dry and humid conditions while the effect of reactions on the hygroscopic behavior of these particles were also measured. In all cases, formation of acetate is significantly enhanced in the presence of surface water. However, the reaction extent varied with mineral phase of these particles. For α-Al2O3, the reaction is limited to surface with the formation of surface coordinated acetate under both dry and humid conditions. For MgO, the bulk of particle is involved in reaction and Mg(CH3COO)2 is formed under both dry and humid conditions, although it exhibits a saturation effect under dry condition. In the case of CaCO3, acetic acid uptake is limited to surface under dry condition while it leads to the decomposition of the bulk of CaCO3 under humid condition. While coordinated surface acetate species increased the water adsorption capacity slightly, the formation of bulk acetate promoted the water absorption capacity greatly. This study demonstrated that heterogeneous reaction between CH3COOH with mineral dust is not only an important sink for CH3COOH, but also has a significant effect on the hygroscopic behavior of mineral dust.
Abstract: Sulfate is one of the most important aerosols in the atmosphere. A new sulfate formation pathway via synergistic reactions between SO2 and NO2 on mineral oxides was proposed. The heterogeneous reactions of SO2 and NO2 on CaO, α-Fe2O3, ZnO, MgO, α-Al2O3, TiO2, and SiO2 were investigated by in situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy (in situ DRIFTS) at ambient temperature. Formation of sulfate from adsorbed SO2 was promoted by the coexisting NO2, while surface N2O4 was observed as the crucial oxidant for the oxidation of surface sulfite. This process was significantly promoted by the presence of O2. The synergistic effect between SO2 and NO2 was not observed on other mineral particles (such as CaCO3 and CaSO4) probably due to the lack of the surface reactive oxygen sites. The synergistic reaction between SO2 and NO2 on mineral oxides resulted in the formation of internal mixtures of sulfate, nitrate, and mineral oxides. The change of mixture state will affect the physicochemical properties of atmospheric particles and therefore further influence their environmental and climate effects.
Abstract: Mineral dust comprises a great fraction of the global aerosol loading, but remains the largest uncertainty in predictions of the future climate due to its complexity in composition and physico-chemical properties. In this work, a case study characterizing Asian dust storm particles was conducted by multiple analysis methods, including SEM-EDS, XPS, FT-IR, BET, TPD/mass and Knudsen cell/mass. The morphology, elemental fraction, source distribution, true uptake coefficient for SO2, and hygroscopic behavior were studied. The major components of Asian dust storm particles are aluminosilicate, SiO2 and CaCO3, with organic compounds and inorganic nitrate coated on the surface. It has a low reactivity towards SO2 with a true uptake coefficient, 5.767×10−6, which limits the conversion of SO2 to sulfate during dust storm periods. The low reactivity also means that the heterogeneous reactions of SO2 in both dry and humid air conditions have little effect on the hygroscopic behavior of the dust particles.
Abstract: Hygroscopicity is a critical property for evaluating aerosol’s environmental and climate impacts. Traditional view always considered hygroscopic behavior of aerosol as a water adsorption/absorption–desorption cycle in which the size, water content and morphology etc. are well characterized. However, the chemical reactions between coexisting components in mixed particles during humidifying-dehumidifying process are almost neglected. In this study, we found that there exists synergistic effect among Ca(NO3)2, CaCO3 and H2C2O4 mixtures during humidifying process. Substitution of strong acid (HNO3) by medium acid (H2C2O4) take place during vapor absorption on Ca(NO3)2/H2C2O4 mixture. Moreover, the presence of nitrate exhibits a promotive effect to the reaction between H2C2O4 and CaCO3 under ambient condition. These results provoke us to rethink the hygroscopic behavior of mixed aerosol in which chemical reaction can greatly change the chemical composition, mixing state and consequently environmental and climate impacts.
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Notes: Highlights
â–º Synergistic effect among mixed aerosol exists during humidifying process. â–º The coexisting Ca(NO3)2 promoted the reaction in CaCO3/H2C2O4 mixture. â–º Substitution of HNO3 by H2C2O4 occurs during the humidifying process of Ca(NO3)2/H2C2O4 mixture. â–º The physicochemical properties of mixtures were greatly changed after humidifying process.
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