Effects of nonmethane hydrocarbons on lower stratospheric and upper tropospheric chemical climatology in a two-dimensional zonal average model

The effect on the modeled chemical climatology of the upper troposphere and lower stratosphere of including a limited set of nonmethane hydrocarbons i n a two-dimensional (2-D) zonal average model is presented. Recent measurem ents of nitrogenated and oxygenated hydrocarbons in the upper troposphere a nd lower stratosphere have revealed the possibility of significant perturba tion of this region. A zonally averaged 2-D chemical transport model enhanc ed to represent tropospheric processes was used to explore the extent of th is perturbation on global and regional spatial scales and on seasonal and a nnual average timescales. Acetone was shown to cause a significant increase in the HOx budgets of the upper troposphere in the midlatitude Northern He misphere during the winter and early spring months, with acetone photolysis providing the most significant source of HOx radicals. The tropical upper troposphere has a uniform increase in HOx of up to 20% throughout the year because of acetone photolysis. Including the hydrocarbons caused a net incr ease in ozone of 5 ppbv in the lower and middle troposphere and 5-10 ppbv i n the upper troposphere for global and annual averages. The effect of inclu ding the hydrocarbons on the calculated model ozone response for the case o f doubled surface mixing ratios of atmospheric CH4 is also discussed. It is shown that including hydrocarbons in the model has a significant effect on the modeled ozone response to the methane increase.