An estimate on the rainout of atmospheric CO2.

The CO2 in the atmosphere is in contact with water vapor and rain droplets forming CO2 x H2O, HCO3- and CO3(2-) . Global precipitation is about 505 x 1015 kg/a. Based on theoretical calculation for unpolluted air and measurement observations, we estimated that 100-270 x 10(12) gC/a are scavenged from the air by global precipitation. This roughly equals carbon emissions from volcanic sources or 2-6 per cent of current CO2 emissions. An inventory-based estimate on carbon removal in northwestern Europe supports the above calculation on global scale. With increasing CO2 concentration in the air, precipitation scavenging may increase.