Sulfate radiative forcing

Sulfur 10-200% increase6 in surface area of sulfate particles Increased aerosol mass loading, change in radiative forcing... 

In the Charlson et al. (1992a) and Penner et al. (1994) estimates, Bsoi = 3.3 X 105 mol m-2, with uncertainties in QSOi, ysullate, and rsullatc of 1.15,1.5, and 1.5, respectively. (Note, however, that some subsequent studies have suggested that direct radiative forcing may vary nonlinearly with the sulfate concentration due to chemical interactions with other particle constituents e.g., see West et al., 1998.)... 

For example, Fig. 14.29 shows one calculation of direct radiative forcing using a global climate model, GCM (Penner et al., 1998). Due to the preponderance of anthropogenic S02 emissions in the Northern Hemisphere, the direct radiative forcing due to sulfate... 

FIGURE 14-29 Calculated direct radiative forcing due to sulfate aerosol particles (adapted from Penner et al., 1998). 

It should be noted that the magnitude of the predicted forcing is quite sensitive to treatment of relative humidity (RH) in the model because of the effects on particle size and optical properties (e.g., Haywood and Shine, 1995 Haywood and Ramaswamy, 1998 Ghan and Easter, 1998 Haywood et al., 1998a Penner et al., 1998). For example, in the calculations by Penner et al. (1998), when the particle properties were held fixed at the values for 90% RH for 90-99% RH, the predicted direct radiative forcing for sulfate particles decreased from - 1.18 W m-2 to -0.88 W m 2 for the Northern Hemisphere and from -0.81 to -0.55 W m-2 globally. 

FIGURE 14.31 Calculated direct radiative forcing by sulfate, biomass, and fossil fuel black carbon (BC) + organic carbon (OC) particles in the (a) Northern Hemisphere, (b) Southern Hemisphere, and (c) global average (adapted from Penner et at., f998). 

Ghan, S. J., and R. C. Easter, Comments on A Limited-Area-Model Case Study of the Effects of Sub-Grid Scale Variations in Relative Humidity and Cloud upon the Direct Radiative Forcing of Sulfate Aerosol, Geophys. Res. Lett., 25, 1039-1040 (1998). 

Haywood, J. M., and V. Ramaswamy, Global Sensitivity Studies of the Direct Radiative Forcing Due to Anthropogenic Sulfate and Black Carbon Aerosols, J. Geophys. Res., 103, 6043-6058 (1998b). 

Van Dorland, R.. F.J. Dentener, and J. Lelieveld, Radiative forcing due to tropospheric ozone and sulfate aerosols. J.Geophys.Res.. 102.28079-28100, 1997. 

Koch D., Jacob D., Tegen 1., Rind D., and Chin M. (1999) Tropospheric sulfur simulation and sulfate direct radiative forcing in the Goddard Institute for Space Studies general circulation model. J. Geophys. Res. 104, 23799-23822. 

Kiehl JT, Schneider TL, Rasch PJ, Barth MC, Wong J (2000) Radiative forcing due to sulfate aerosols from simulations with the National Center for Atmospheric Research Community Climate Model, Version 3. JGeophysRes 105 1441-1457... 

FIGURE 7 (a) Radiative forcing from greenhoitse gases, sulfate aerosols (direct and indirect effect),... 

Today, the anthropogenic emissions of SO, primarily from fossil fuel combustion, largely dominate the sulfur flux into in the atmosphere on the global scale. Climate models have determined the corresponding direct and indirect impacts on radiative forcing, but large uncertainties remain in these estimates. In fact, predictions of future climate need to account not only for the effects of sulfate aerosols, but also for the contributions of mineral dust, black carbon, organic carbon, and sea salt. The current view is that atmospheric particles should be treated as multicomponent, mul-... 

FIGURE 7 The radiative forcing for contemporary production of sulfate aerosols simulated by ECHAM (Roeckneretrt/., 1999). 

Aerosol Radiative Forcing Efficiency The radiative forcing of an aerosol species can be normalized by its column mass burden to produce a radiative forcing efficiency per unit mass AG. For sulfate aerosol, for example, one obtains... 

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