Mechanism Of Sulfate Formation Research Articles

Evolution of particulate sulfate and nitrate along the Asian dust pathway: Secondary transformation and primary pollutants via long-range transport

Both PM2.5 and TSP over Yulin, a rural site near the Asian dust source region, were collected from 2007 to 2009. Characteristics, sources, and formation mechanisms of sulfate and nitrate were investigated. SO42− displayed a distinct seasonal variation with the highest average concentration observed in summer when SO42− accounted for an average of 14.1% and 13.7% of the PM2.5 and PMcoarse mass concentrations, respectively. Ambient temperature and relative humidity were two important factors influencing the formation processes of SO42− and NO3−. In summer, the high concentrations of SO42− in PM2.5 were probably from the gas phase oxidation of SO2, while the low concentrations of NO3− in PM2.5 were attributed to the high temperature that was not favorable for the formation of NH4NO3. In spring, autumn, and winter, SO42− and NO3− were significantly enhanced in those days with high relative humidity, implying that in-cloud/aqueous processing dominated the formations of SO42− and NO3−. Different from PM2.5 in which NH4+ acted as the dominant neutralizer for acids, alkaline species such as Ca2+ and Mg2+ played an important role in the formation of sulfate and nitrate salts in coarse particles throughout the whole year. During the dust event days, SO42− in coarse particles significantly increased, while black carbon and NO3− largely decreased, suggesting that the primary mineral dust could be one of the major sources of SO42−. By comparing the mass ratio of SO42−/3/S in the dust aerosols of Yulin with different dust source regions (i.e., Taklimakan Desert and Gobi Desert) and the application of air mass backward trajectory analysis, it was found the long-range transported dust from the Taklimakan Desert, which was rich in primary sulfate due to its paleo-ocean characteristics, was a non-negligible source of SO42− over Yulin. In spring and winter, the prevailing northerlies and northwesterlies promoted chemical interaction between alkaline mineral dust and acid gaseous precursors from local and/or regional emissions. While in summer, regional transport facilitated by the southerlies and southeasterlies may contribute to the high secondary aerosol concentrations over Yulin. This study demonstrated that a considerable portion of aerosol over a Chinese rural area could be derived from complex chemical reactions via long-range/regional transport.

Observations of linear dependence between sulfate and nitrate in atmospheric particles

AbstractHourly measurements of water‐soluble inorganic ionic species in ambient atmospheric particles were conducted at Shanghai, Hangzhou, and Guangzhou sampling sites in China during the period of 2009–2011. The relation between sulfate and nitrate in particulate matter (PM10 and PM2.5) was examined based on these measurements. Results showed that the mass fraction of sulfate was strongly negatively correlated with that of nitrate in atmospheric particles on most of the sampling days, especially when sulfate and nitrate made up the vast majority of the total soluble anions and cations (Na+, K+, Ca2+, and Mg2+) made a small contribution to the total water‐soluble ions, revealing that the formation mechanisms of sulfate and nitrate in the atmosphere are highly correlated, and there exists a significant negative correlation trend between sulfate and nitrate mass fractions in the atmospheric particles. We found that local meteorological conditions presented opposite influences on the mass fractions of sulfate and nitrate. Further analysis indicated that the two mass fractions were modulated by the neutralizing level of atmospheric aerosols, and the negative correlation could be found in acidic atmospheric particles. Strong negative correlation was usually observed on clear days, hazy days, foggy days, and respirable particulate air pollution days, whereas poor negative correlation was often observed during cloud, rain, snow, dust storm, and suspended dust events. The results can help to better understand the formation mechanisms of atmospheric sulfate and nitrate during air pollution episodes and to better explain field results of atmospheric chemistry concerning sulfate and nitrate.

The evolution of chemical components of aerosols at five monitoring sites of China during dust storms

Daily PM 2.5 and TSP and their chemical composition with two dust events (DS1: 9–10 March and DS2: 27–30 March) were simultaneously observed for the period of 9 March–23 April 2004 from a monitoring network over China. Five monitoring sites were performed along the transport pathway of Asian dust storm, located in Northwest, North, East, and Southeast regions of China. The dust and non-dust days exhibited different characteristics with respect to the composition and the meteorological conditions. In non-dust days, particulate pollution was found to be associated with the city economy, and it primarily consisted of the crustal, the secondary, and the carbonaceous material. In the dust episodes, significant increase in the particle concentration with a large part of the secondary components diluted by the crustal components was observed at all the sites. Particles were getting more and more acidic as the episodic dust progressed eastward. Dust particles were suggested to react with SO 2/NO X /sulfate/nitrate based on the variations of SO 4 2−/Ca 2+ and NO 3 −/Ca 2+ along the transport pathway, and the formation mechanism of sulfate and nitrate was proved to be different. Positive matrix factorization analysis showed that the sources from the upstream and the transport pathways could account for 49%, 82%, and 28% of PM mass, crust, and secondary aerosol, respectively, and the contribution decreased, as the dust made its way from source area to the coastal regions. Enrichment factors of the species presented significant correlations among different sites in the dust episodes, suggesting the significant impact of those dust emissions on the local environment.

Oxygen-18 study of high-temperature air oxidation of SO 2

The oxygen-18 enrichment in sulfates formed at high temperatures (475–500°C) by platinum-catalyzed air oxidation of SO 2 to SO 3 in humidified air, was found to be several parts per thousand higher than in the air oxygen, SO 2, or water vapor from which the sulfates were formed. Variation of the δ 18O in the sulfates showed little dependence on variation of the δ 18O in the water vapor. The mechanism of sulfate formation involved isotopic exchange between the air oxygen and water vapor, isotopic exchange between the water vapor and SO 2, and formation of the hydrate, H 2SO 4· 3H 2O. When Fe 2O 3 or V 2O 5 was heated in mixtures of air, water vapor, and SO 2, some of the SO 2 was analytically oxidized (via SO 3 formation) to sulfate of relatively high δ 18O and the remainder to chemisorbed sulfate of relatively low δ 18O. Charcoal and fly ash (containing unburned carbon and basic oxides) reacted with the SO 2 to yield chemisorbed sulfates of relatively low δ 18O.

SULFATE AND NITRATE CONCENTRATION IN AEROSOL ABOVE KANTO AREA

Abstract The concentration of sulfate and nitrate in aerosol above Kanto area was measured by aircraft on 6 th and 7 th August 1980 as a survey of photochemical smog. The concentration variation of both ions coincided with that of ozone throughout the field observation. This phenomenon is explained that the formation mechanism of sulfate and nitrate is closely concerned with that of ozone formation. The transport of ozone, sulfate and nitrate is governed mainly by Sagami Bay sea breeze and Kashima Nada sea breeze.

Contribution to the atmospheric sulfur budget

The paper presents preliminary results on tropospheric measurements of SO/sub 2/ and sulfate aerosols by means of aircraft ascents. The results show an increase of the SO/sub 4//sup 2 -//SO/sub 2/ ration with altitude. A hypothesis on the mechanism of sulfate formation in the troposphere in the presence of clouds is offered, along with new data on the background concentration of SO/sub 2/ and sulfate aerosols in pure air. The SO/sub 2/ concentration over the Atlantic Ocean varies between 0 and 3 micrograms SO/sub 2//m/sup 3/, and the sulfate concentration was found to be around 2 to 5 micrograms/m/sup 3/.

The Mechanism of Sulfate Formation by Sulfamic Acid in the Presence of Pyridine

The Mechanism of Sulfate Formation by Sulfamic Acid in the Presence of Pyridine

O18 Studies on the Mechanism of Sulfate Formation and Phosphorylation in Extracts of Thiobacillus thioparus

O18 Studies on the Mechanism of Sulfate Formation and Phosphorylation in Extracts of Thiobacillus thioparus

Mechanism of Sulfate Formation During the Roasting of Cuprous Sulfide

Mechanism of Sulfate Formation During the Roasting of Cuprous Sulfide

FUNDAMENTAL FACTORS INFLUENCING EFFLORESCENCE OF CLAY PRODUCTS*

AbstractSamples of shale from the Sew York State Clay and Shale Survey were selected for the study of efflorescence. Some of the shales had no tendency to effloresce after firing whereas others produced slight to heavy efflorescence. A satisfactory means of qualitative and quantitative measurement of soluble salt content was applied to the raw and fired shale specimens. These analyses provided an indication of the liability to effloresce. The causes of the development of soluble salts in these materials were traced. It was found that soluble salts were formed in the ceramic body during firing by reaction with SO2 gas and by solid‐state reactions involving SO4 ions. The presence of insoluble mineral sulfides and sulfur‐bearing organic compounds in the raw materials were important causes of sulfate formation. The mechanism of sulfate formation was studied. Procedures for the prevention of efflorescence are discussed.