Sulfate atmospheric burden

Kasibhatla, P., Chameides, W.L., John, J.S. A three-dimensional global model investigation of seasonal variations in the atmospheric burden of anthropogenic sulfate aerosols. J. Geophys. Res. 102, 3737-3759 (1997)... 

Here B is the world average burden of anthropogenic sulfate aerosol in a column of air, in grams per square meter. The optical depth is then used in the Beer Law (which describes the transmission of light through the entire vertical column of the atmosphere). The law yields I/Iq = where I is the intensity of transmitted radiation, Iq is the incident intensity outside the atmosphere and e is the base of natural logarithms. In the simplest case, where the optical depth is much less than 1, (5 is the fraction of light lost from the solar beam because of... 

This global average burden of anthropogenic sulfate aerosol can be estimated by considering the entire atmospheric volume as a box. Because the lifetime of sulfate aerosol is short, the sum of all sulfate sources, Q, and its lifetime in the box, f, along with the area of the earth, determine B ... 

The amount of atmospheric aerosol sulfate, expressed as the column burden Bso2-. This term can... 

Fig. 13-5 The sulfur cycle in the remote marine boundary layer. Within the 2500 m boundary layer, burden units are ng S/m and flux units are ng S/m h. Fluxes within the atmospheric layer are calculated from the burden and the residence time. Dots indicate that calculations based on independent measurements are being compared. The measured wet deposition of nss-SO " (not shown) is 13 7 //g S/m /h Inputs and outputs roughly balance, suggesting that a consistent model of the remote marine sulfur cycle within the planetary boundary layer can be constructed based on biogenic DMS inputs alone. Data (1) Andreae (1986) (2) Galloway (1985) (3) Saltzman et al. (1983) (4) sulfate aerosol lifetime calculated earlier in this chapter based on marine rainwater pH the same lifetime is applied to MSA aerosol. Modified from Crutzen et al. (1983) with the permission of Kluwer Academic Publishers.

A significant fraction of NH3 is converted into ammonium containing aerosol particles in the atmosphere. These particles are generally composed of ammonium sulfate, the formation of which will be discussed later (Subsection 3.5.3). We only note here that the concentration of NH4 in the lower troposphere is comparable to that of NH3 gas. Even, in the upper troposphere the particulate concentration may be greater than the level of gaseous NH3. For this reason Soderlund and Svensson (1976) speculate that the atmospheric NH4 burden is twice the global mass of NH3 (both expressed as nitrogen). 

We have to emphasize here that the majority of the sulfate-sulfur in the tropospheric reservoir in not sea salt. Friend (1973) estimated that the atmospheric sea-salt burden is around 0.1 x 106 t. By subtracting this value from the sulfate-sulfur loading given in Fig. 19 and considering only the strength of chemical sources (62 x 106 t yr 1), a residence time of more than 4 days is obtained for the excess sulfate. 

From the foregoing parts of this book it is clear that solar radiation in the stratosphere is primarily attenuated by ozone (see Subsection 3.4.3) and at a lesser extent by the stratospheric sulfate aerosol layer (see Subsection 4.4.3). This means that any change in the stratospheric 03 burden or aerosol concentration involves modification of radiative transfer in this atmospheric domain. We should remember that the residence time of trace constituents above the tropopause is rather long because of the thermal structure and the absence of wet removal. Furthermore at these altitudes the density of the air is low as compared to that of lower layers. For this reason even an insignificant quantity of pollutants can produce relatively long and significant effects. 

The column burden of sulfate aerosol, m Q2, can be estimated from the global source strength of SO2, 0sO i the average fractional conversion of SO2 to sulfate in the atmosphere, vso, the mean residence time of sulfate aerosol in the atmosphere, t q , and the area, A, of the geographical region over which the estimate is performed (e.g. the entire globe, the Northern Hemisphere, etc.), as... 

The State implementation plans promulgated in the U.S. in the early 1970s to meet the NAAQS for SO2 resulted in reductions in the allowable sulfur contents of fuels used, especially for smaller, distributed sources. Such limitations resulted in reductions in ambient levels of all sulfur compounds near the sources, i.e., in cities. An alternative strategy to meet the NAAQS for SO2 for sources that could not easily switch fuels involved increasing stack heights, which greatly reduces the local surface air concentrations but does not reduce the total atmospheric sulfur burden. As a result, over the past 20 years, U.S. sulfate air concentrations have not improved as much as urban SO2 concentrations and may have actually increased in some remote areas. U.S. total emissions peaked about 1970 and remain at about the levels of the late 1960s. 

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