Acidic sulfate aerosols

Larson, T. V., Covert, D.S., Frank, R., and Charlson, R.J. (1977). Ammonia in the human airways neutralization of inspired acid sulfate aerosols. Science 197, 161-163. 

Delumyea, R.G. Macias, E.S. Cobourn, W.G. Detection of the Presence of Ambient Acid Sulfate Aerosols from the Sulfur/Nitrogen Ratio. Atmos. Environ. 1979, 33, 1337,... 

Anastasio, C., B. C. Faust, and C. J. Rao, Aromatic Carbonyl Compounds as Aqueous-Phase Photochemical Sources of Hydrogen Peroxide in Acidic Sulfate Aerosols, Fogs, and Clouds. 1. Non-Phenolic Methoxybenzaldehydes and Methoxyacetophe-nones with Reductants (Phenols), Environ. Sci. Techno ., 31, 218-232 (1997). 

The respiratory health effects of vog and volcanic gases such as sulfur dioxide are tied to the generation of locally acidic environments in the lung and respiratory tract fluids by condensation of SO2 and other acid gases, uptake of acid-sulfate aerosol droplets, and the dissolution of acid-bearing, sulfate- or chloride-rich salts from the vog particulates by the fluids lining the respiratory tract. 

Note that non-acidic sulfate aerosols are produced from sea spray and crustal materials these compounds tend to have larger particle sizes than the typically acidic particles. With the exception of primary emissions of acids, the transformation processes are just as important as the source terms both are needed to produce acid aerosols. Reactions in the aqueous phase (fog) are much faster than in the gas phase and can produce acids on a local scale. The slower gas-phase reactions tend to produce acids on a larger scale, often regional in extent. Organic acids are usually the products of photochemical smog reactions. 

Johnson, S.A., R. Kumar, and P.T. Cunningham (1983), Airborne detection of acidic sulfate aerosol using an ATR impactor. Aerosol Sci. Technol. 2 401-405. 

Lioy, P.J. and J.M. Waldman (1989), Acidic sulfate aerosols Characterization and exposure. Environ. Health Persp., 79 15-34. 

Other aerosol work with PTR-MS has been undertaken by Liggio et al. to investigate the direct polymerization of isoprene and a-pinene on acidic sulfate aerosols [199]. For this study they utilized an aerosol mass spectrometer together with a Teflon reaction chamber of volume 2 m, while PTR-MS was employed to monitor the gas-phase concentrations of isoprene and a-pinene. It was found that isoprene and a-pinene were taken up directly by acidic aerosols, with polymers being formed that contain at least four isoprene and two a-pinene repeating units. 

Similar heterogeneous reactions also can occur, but somewhat less efticientiy, in the lower stratosphere on global sulfate clouds (ie, aerosols of sulfuric acid), which are formed by oxidation of SO2 and COS from volcanic and biological activity, respectively (80). The effect is most pronounced in the colder regions of the stratosphere at high latitudes. Indeed, the sulfate aerosols resulting from emptions of El Chicon in 1982 and Mt. Pinatubo in 1991 have been impHcated in subsequent reduced ozone concentrations (85). 

Sulfur oxides (SO,) are compounds of sulfur and oxygen molecules. Sulfur dioxide (SO2) is the predominant form found in the lower atmosphere. It is a colorless gas that can be detected by taste and smell in the range of 1, (X)0 to 3,000 uglm. At concentrations of 10,000 uglm , it has a pungent, unpleasant odor. Sulfur dioxide dissolves readily in water present in the atmosphere to form sulfurous acid (H SOj). About 30% of the sulfur dioxide in the atmosphere is converted to sulfate aerosol (acid aerosol), which is removed through wet or dry deposition processes. Sulfur trioxide (SO3), another oxide of sulfur, is either emitted directly into the atmosphere or produced from sulfur dioxide and is readily converted to sulfuric acid (H2SO4). 

Health effects attributed to sulfur oxides are likely due to exposure to sulfur dioxide, sulfate aerosols, and sulfur dioxide adsorbed onto particulate matter. Alone, sulfur dioxide will dissolve in the watery fluids of the upper respiratory system and be absorbed into the bloodstream. Sulfur dioxide reacts with other substances in the atmosphere to form sulfate aerosols. Since most sulfate aerosols are part of PMj 5, they may have an important role in the health impacts associated with fine particulates. However, sulfate aerosols can be transported long distances through the atmosphere before deposition actually occurs. Average sulfate aerosol concentrations are about 40% of average fine particulate levels in regions where fuels with high sulfur content are commonly used. Sulfur dioxide adsorbed on particles can be carried deep into the pulmonary system. Therefore, reducing concentrations of particulate matter may also reduce the health impacts of sulfur dioxide. Acid aerosols affect respiratory and sensory functions. 

There is a large variety of atmospheric sulfur compounds, in the gas, solid, and liquid phases. Table 7-3 lists a number of gaseous compounds, range of concentration, source, and sink (where known). As this list illustrates, a significant number of these gases contribute to the existence of oxidized sulfur in the forms of SO2 and sulfate aerosol particles. Table 7-4 lists the oxy-acids of sulfur and their ionized forms that could exist in the atmosphere. Of these the sulfates certainly are dominant, with H2SO4 and its products of neutralization with NH3 as the most frequently reported forms. 

About half the manmade emissions of sulfur dioxide become sulfate aerosol. That implies that currently 35 Tg per year of sulfur in sulfur dioxide is converted chemically to sulfate. Because the molecular weight of sulfate is three times that of elemental sulfur, Q is about 105 Tg per year. Studies of sulfate in acid rain have shown that sulfates persist in the air for about five days, or 0.014 year. The area of the Earth is 5.1 x lO m. Substituting these values into the equation for B yields about 2.8 X 10 g/m for the burden. 

Although no conclusive evidence has been reported so far, the possible importance of organic sulfur species as sulfate aerosol precursors is supported by several observations. Sulfuric acids, sulfonic acids, and other organic sulfur compounds are formed in sulfur dioxide-hydrocarbon reactions at high concentrations. Organosulfiir radical species, such as RSO2 and RO2SO2 have been postulated as intermediates for these reactions. Suzuki (see Penzhom et o/. ) observed polymer formation from... 

CASRN 75-18-3 molecular formula C2H0S FW 62.14 Photolytic. Sunlight irradiation of a mixture of methyl sulfide (initial concentrations 0.2-2.5 ppm) and oxides of nitrogen (86-580 ppb) in an outdoor chamber at various time intervals (2-7 h) yielded nitrogen dioxide, ozone, sulfur dioxide, nitric acid, formaldehyde, and methyl nitrate, a sulfate aerosol, and methane sulfonic acid (Grosjean, 1984a). 

There have been many studies of reaction (47) using sulfuric acid or sulfate aerosols (e.g., ammonium sulfate) of various compositions and over a range of... 

Hu, J. H and J. P. D. Abbatt, Reaction Probabilities for N2Os Hydrolysis on Sulfuric Acid and Ammonium Sulfate Aerosols at Room Temperature, . /. Phys. Chem. A, 101, 871-878 (1997). 

Zhang, R., M.-T. Leu, and L. F. Keyser, Heterogeneous Chemistry of HONO on Liquid Sulfuric Acid A New Mechanism of Chlorine Activation on Stratospheric Sulfate Aerosols, . /. Phys. Chem., 100, 339-345 (1996). 

Charlson, R. J., A. H. Vanderpol, D. S. Covert, A. P. Waggoner, and N. C. Ahlquist, Sulfuric Acid-Ammonium Sulfate Aerosol Opti-... 

Descriptions of analytical methods for strong acid and acidic sulfate content of atmospheric aerosols have been reviewed (6-10). Methods for acidic aerosol determination are reviewed in this chapter according to the measurement principle either filter collection and post-collection extraction, deriv-atization or thermal treatment, and analysis or in situ collection (real-time or stepwise) and analysis. 

Thermal Volatilization. Thermal volatilization schemes have been popular for speciation of acidic sulfate compounds in aerosols. Both filter-... 

Particle-Particle Interactions. Loss of strong acid content of aerosol particles can also occur because of reactions between co-collected acidic and basic particles impacted together on the collection surface. This phenomenon most frequently occurs as the result of interaction of coarse (>2.5 xm diameter), alkaline, soil-derived particles with fine (<2.5 xm diameter) acidic sulfate particles (66). Particle-particle interactions with net neutralization can be reduced in many cases by sampling with a virtual impactor or a cyclone to remove coarse particles, although this procedure does not prevent the effect if external mixtures of fine particles of different acid contents are sampled. In situ methods with shorter sampling times can be used such that these topochemical reactions are less likely to occur. 

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