Changes in atmospheric levels of certain pollutants (CH4, CO, NOx, nonmethane hydrocarbons) have the potential to affect tropospheric O3 formation and the abundance of the free radical OH on a global scale. Perturbations to stratospheric O3 and climate (temperature and moisture) also can influence tropospheric O3 and OH. We have used a tropospheric photochemical model with projections of CO, NOx, and CH4 to predict tropospheric ozone and OH changes from 1980–2030. The calculations simulate the background chemistry of various global regions and assume that increases in CH4 and CO will continue at current rates. Predicted changes in tropospheric O3 and OH are different in urban and nonurban areas, and in marine and continental regions. Generally, increasing levels of CH4 and CO at constant NOxlevels will increase O3 and suppress OH. A rough estimate of possible global changes shows tropospheric O3 increasing ˜ 10% from 1980 to 2030 and OH decreasing ˜ 10% during that period. When calculations are performed assuming that stratospheric ozone depletion and climate warming occur at anticipated rates during the same period, tropospheric O3 enhancement and OH loss in nonurban areas are both reduced relative to changes assuming that only CH4 and CO emissions change. Regional changes in surface-level O3, OH and the water-soluble oxidant H2O2 are estimated for the year 2030. Increases in CO and CH4 suppress OH and enhance 63 and H2O2 in nonpolluted (low NOx) areas. In urban environments (background NOx > 1 ppbv), increases in CO and CH4 add significantly to all three oxidants, O3, OH and H2O2. Changes in and near urban areas may be of greatest magnitude, but the high levels of OH (and H2O2) found in the tropics indicate that perturbations in that region could dominate future global oxidant changes.
All Science Journal Classification (ASJC) codes
- Environmental Engineering
- Environmental Chemistry