Glyoxal (CHOCHO) is produced in the atmosphere by oxidation of isoprene. It has been proposed as an important source of organic aerosol. We examine here its potential importance in the United States.
4.1 Glyoxal has mean atmospheric lifetimes of 2 hours against photolysis, 8 hours against oxidation by OH, and 8 hours against uptake by aqueous particles to form aerosol. What fraction of atmospheric glyoxal will form aerosol?
4.2 Isoprene emission in the U.S. in summer is estimated to be 5x1011 molecules cm-2 s-1. The glyoxal molar yield from isoprene oxidation is 10%. Assume a mixing depth of 1 km and an aerosol lifetime of 3 days, and further assume that glyoxal is in steady state. Calculate the resulting mean concentration of organic aerosol (in units of µg carbon m-3) from the glyoxal formation pathway. Compare to typical U.S. observations of 2 µg C m-3 for the concentration of organic aerosol.