Global direct radiative forcing due to multicomponent anthropogenic and natural aerosols

Global simulations of the composition of and direct forcing due to aerosols containing natural and/or anthropogenic sulfate, nitrate, chloride, carbon ate, ammonium, sodium, calcium, magnesium, potassium, black carbon, organic matter, silica, ferrous oxide, and aluminum oxide were carried out. Chlori de and natural sulfate were found to be the most important natural aerosol constituents in the atmosphere in terms of solar plus thermal-infrared forc ing. Sea spray was the most important natural aerosol type, indicating that it should be accounted for in weather and climate calculations. Ammonium w as found to have a positive direct forcing, since it reduces water uptake i n sulfate-containing solutions; thus, anthropogenic ammonium contributes to global warming. The magnitudes of ammonium and nitrate forcing were smalle r than those of chloride or sulfate forcing. When organics were divided int o three groups with different assumed UV absorption characteristics, total aerosol direct forcing at the tropopause increased by about +0.03 to +0.05 W m(-2) (direct forcing by organics remained negative), suggesting that W a bsorption by organics is a nontrivial component of the global energy balanc e. Gypsum [CaSO4-2H(2)O], sal ammoniac [NH4Cl], halite [NaCl], halite, and nitrum [KNO3] were estimated to be the most common sulfate-, ammonium-, sod ium-, chloride-, and nitrate-containing solid-phase aerosol constituents, r espectively, in the global atmosphere. Solid formation in aerosols was foun d to increase total-aerosol direct forcing by +0.03 to +0.05 W m(-2). Spati al and vertical forcing estimates, sensitivities of forcing to relative hum idity and concentration, and estimates of global aerosol liquid water conte nt are given. Modeled aerosol optical properties are compared with satellit e and field measurements.