Anthropogenic sulphate aerosol from India: estimates of burden and direct radiative forcing

A one-box chemical-meteorological model had been formulated to make preliminary estimates of sulphate aerosol formation and direct radiative forcing over India. Anthropogenic SO₂ emissions from India, from industrial fuel use and biomass burning, were estimated at 2.0 Tg S yr^-1 for 1990 in the range of previous estimates of 1.54 and 2.55 Tg S yr ^-1 for 1987. Meteorological parameters for 1990 from 18 Indian Meteorological Department stations were used to estimate spatial average sulphate burdens through formation from SO₂ reactions in gas and aqueous phase and removal by dry and wet deposition. The hydrogen peroxide reaction was found dominating for undepleted oxidant-rich conditions. Monthly mean sulphate burdens ranged from 2–10 mg m^-2 with a seasonal variation of winter–spring highs and summer lows in agreement with previous GCM studies. The sulphate burdens are dominated by sulphate removal rates by wet deposition, which are high in the monsoon period from June–November. Monthly mean direct radiative forcing from sulphate aerosols is high (−3.5 and −2.3 W m^-2) in December and January, is moderate (−1.3 to −1.5 W m^-2) during February to April and November and low (−0.4 to −0.6 W m^-2) during May to October also in general agreement with previous GCM estimates. This model, in reasonable agreement with detailed GCM results, gives us a simple tool to make preliminary estimates of sulphate burdens and direct radiative forcing.