Sulfate atmospheric chemistry

Acid rain monitoring data in North America have been gathered by Environment Canada and stored in the National Atmospheric Chemistry (NatChem) Database, details of which can be found at www.airquality.tor.ec.gc.ca/natchem. Analysis of the deposition chemistry data has confirmed that wet sulfate deposition did indeed decline in concert with the decline in SO2 emissions in both eastern Canada and the... 

Historically, the sulfur oxides have long been known to have a deleterious effect on the atmosphere, and sulfuric acid mist and other sulfate particulate matter are well established as important sources of atmospheric contamination. However, the atmospheric chemistry is probably not as well understood as the gas-phase photoxidation reactions of the nitrogen oxides-hydrocarbon system. The pollutants form originally from the S02 emitted to the air. Just as mobile and stationary combustion sources emit some small quantities of N02 as well as NO, so do they emit some small quantities of S03 when they bum sulfur-containing fuels. Leighton [2] also discusses the oxidation of S02 in polluted atmospheres and an excellent review by Bulfalini [3] has appeared. This section draws heavily from these sources. 

Review of the literature provides ample evidence that aerosol formation is an important part of the atmospheric chemistry linked with photochemical-oxidant production. The important chemical constituents of concern include sulfate, nitrate, and secondary organic material. 

Atmospheric chemistry in the Arctic has been the subject of studies for many years, in part because of the observation of Arctic haze decades ago. This haze is composed of particles with significant amounts of sulfate, about half of which is due to long-range transport from other regions, particularly Eurasia during the winter (e.g., Barrie and Bottenheim, 1991 Polissar et al., 1998a, 1998b). 

Air pollutants, transport, 4 Air sampling—See Interstitial air sampling Aldehydes, determination in atmospheric samples, 299 Allegheny Mountain acid deposition and atmospheric chemistry, 28-36 deposition budgets for sulfate and nitrate, 33... 

Many of these naturally produced gases play important roles in atmospheric chemistry. For example, OCS may maintain the stratospheric sulfate layer 10,11). Changes in the concentration of this aerosol layer could alter the global temperature. Dimethyl sulfide is produced in the ocean and is released to the atmosphere where it probably is rapidly oxidized to SO2, which contributes substantially to the background acidity of rainwater 12). Methyl chloride, which is produced in the ocean, is the dominant... 

Natural sources of many common air contaminants make a contribution to the overall atmospheric pollutant loading. Oceans contribute large masses of saltwater spray droplets to the air as a result of wave action. As the water evaporates from these droplets very fine particles of salts are left suspended in the moving air, contributing to sea smell and atmospheric chemistry. Some 13 million tonnes of sulfate ion and similar masses of chloride are contributed to the atmosphere annually in this manner. 

Granat, L., 1978 Sulfate in precipitation as observed by the European Atmospheric Chemistry Network. Atmospheric Environment 12, 413-424. 

Atmospheric chemistry is dominated by trace species, ranging in mixing ratios (mole fractions) from a few parts per million, for methane in the troposphere and ozone in the stratosphere, to hundredths of parts per trillion, or less, for highly reactive species such as the hydroxyl radical. It is also surprising that atmospheric condensed-phase material plays very important roles in atmospheric chemistry, since there is relatively so little of it. Atmospheric condensed-phase volume to gas-phase volume ratios range from about 3 x KT7 for tropospheric clouds to 3 x ICE14 for background stratospheric sulfate aerosol. 

Another interesting example of the biological influence on atmospheric chemistry is provided by sulfur. Under natural conditions, sulfur compounds in the atmosphere are provided by the oceanic emission of dimethyl disulfide (DMS). This biogenic emission results from the breakdown of sulfoniopropionate (DMSP), which is thought to be used by marine phytoplankton to control their osmotic pre.ssure. The oxidation of DMS leads to the formation of sulfur dioxide, which is further converted to sulfate particles. As indicated above, these particles, by scattering back to space some of the incoming solar radiation, tend to cool the earth s surface. Their presence also affects the optical properties of the clouds, which introduces an indirect climatic effect. 

Seigneur, C., Saxena, P, and Roth, P. M. (1984) Computer simulations of the atmospheric chemistry of sulfate and nitrate formation, Science, 225, 1028-1029. 

Chuang, C. C., Penner, J. E., Taylor, K. E., and Walton, J. J. (1994) Climate effects of anthropogenic sulfate simulations from a coupled chemistry/climate model, in AMS Conference on Atmospheric Chemistry, Nashville, Tennessee, 23-28 Jan. 1994, pp. 170-174. 

Ambient air whieh is essentially rural in origin wiU in warm months be more elevated in SOA and secondary sulfate. The mix between SOA and sulfate will vary among localities, but these would be the two common particle types in such rural air masses. These masses would contain SOA reaction products that might not exist but for the atmospheric chemistry of SO2. If rural air masses from different parts of the eountry, with different combinations of SOA and secondary sulfate, were not assoeiated with adverse health effects, then both types of particles might be seen as relatively harmless. Alternatively, air masses heavy in one of these particulate types might be harmful, but not air masses with the reverse balance between the two emissions. Sueh information would obviously be useful in protecting the public health. 

The atmospheric chemistry of sulfur is simpler than that of nitrogen in two aspects. First, the number of stable species in air is smaller and second, the variety of interactions in the climate system is less - almost all effects come from sulfate, such as acidity and radiation scattering. In the oxidation line to sulfate, oxidants are consumed ... 

As noted before, reaction (14) does not occur in the gas phase, but it readily occurs on wetted particulate surfaces. These are always present in the lower stratosphere in the form of sulfate particles, a fact which was first discovered by Christian Junge, a pioneer in atmospheric chemistry and my predecessor as director at the Max Planck Institute for Chemistry in Mainz [59]. The sulfate particles are formed by nucleation of gas phase H2SO4, which is formed Ifom SO2, following attack by OH [60, 61] [Eqs. (31)-(33)]. 

According to a review by J. Heintzenberg [Tellus, 41B 149 (1989)], in North / taica and Europe, uiban fine aerosols typieally contain 28 % sulfate, 31 % oiganics, 9 % BC, 8 % ammonium, 6 % nitrate, and 18 % other material (mean mass = 32 tg/m ) suburban aerosols contain 37 % sulfate, 24 % tn-ganies, 5 % BC, 11 % ammonium, 4 % nitrate, and 19 % other material (mean mass = 15 pg/m ) and remote continental aerosols contain 22 % sulfate, 11 % organics, 3 % BC, 7 % ammonium, 3 % nitrate, and 56 % other material (mean mass = 4.8 pg/m ). Additional data on different aero-sol types, consistent with this review, are presented by J.H. Seiirfeld and S.N. Pandis [Atmospheric Chemistry and Physics (Wiley New York, 1998)]. 

Atmospheric aerosols have a direct impact on earth s radiation balance, fog formation and cloud physics, and visibility degradation as well as human health effect[l]. Both natural and anthropogenic sources contribute to the formation of ambient aerosol, which are composed mostly of sulfates, nitrates and ammoniums in either pure or mixed forms[2]. These inorganic salt aerosols are hygroscopic by nature and exhibit the properties of deliquescence and efflorescence in humid air. That is, relative humidity(RH) history and chemical composition determine whether atmospheric aerosols are liquid or solid. Aerosol physical state affects climate and environmental phenomena such as radiative transfer, visibility, and heterogeneous chemistry. Here we present a mathematical model that considers the relative humidity history and chemical composition dependence of deliquescence and efflorescence for describing the dynamic and transport behavior of ambient aerosols[3]. 

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