Regional and global trends in sulfate aerosol since the 1980s

[1] In the last two decades anthropogenic SO₂ emissions have decreased across Europe and North America but have increased across Asia. Long-term surface observations suggest that atmospheric sulfate concentrations have followed trends in sulfur emissions more closely across Asia, than across the USA and Europe. We use a global model of chemistry and aerosol to understand changes in the regional sulfur budget between 1985 and 2000. For every 1% decrease in SO₂ emissions over Europe and the USA the modelled sulfate column burden decreased by 0.65%, while over Asia a 1% increase in SO₂ resulted in a 0.88% increase in sulfate. The different responses can be explained by the availability of oxidant in cloud. We find that because emissions have moved southward to latitudes where in-cloud oxidation is less oxidant limited, the 12% reduction in global SO₂ emissions between 1985 and 2000 caused only a 3% decrease in global sulfate.