If we look at the concentrations of several biogenic and human pollunant gases, like CH4, CO, SO2, NO2, DMS we would expect that the speed of chemical reaction with OH alone would make the concentration of these gases infitessimally small. Instead we see that most of these gases exist in far greater amounts than expected. Another way of saying this is that if we were to shut off all natural and human supply of these gases to the atmosphere, in the blink of an eye, these gases would be gone because OH reacts very quickly with them. MRT of trace gases is short, many on the order of days, so they are not well mixed in the atmosphere. One of the more intriguing aspects of global change research is the role of sulfur aerosols on the earth s heat balance .
Aerosols are excellent at increasing the reflectivity, or albedo, of the earth s atmosphere.
So by increasing aerosols in the atmosphere, more sunlight is reflected back to space and the earth cools.