ABSTRACT

Scientific Colloquium
Thursday, May 1, 2003

SPECIAL COLLOQUIUM

PLEASE NOTE DAY CHANGE

PAUL CRUTZEN

MAX PLANCK INSTITUTE FOR CHEMISTRY

"The Importance of the Tropics in Atmospheric Chemistry"

Although the atmosphere consists of almost 21% oxygen,

its most important oxidizing agent is the hydroxyl (OH) radical,

'the detergent of the atmosphere', which is present at an average

volume mixing ratio of only 0.04 pmol/mol (pptv) in the

troposphere. Because the production of OH radicals depends on the

levels of solar UV radiation and water vapor, OH concentrations,

and thus the cleaning of the atmosphere from natural and

anthropogenic emissions, on average maximizes in the tropics.

One might thus expect the tropics to be the cleanest parts of

Earth atmosphere. This is by far not the case. Over extended

regions, also in parts of the southern hemisphere, the tropics and

the subtropics are highly polluted, especially as a result of

primitive biomass burning, conducted by poor people during the dry

season. Of particular interest for Earth's climate are the high rates of

production of sunlight absorbing smoke particles.