Perturbations to tropospheric oxidants, 1985–2035: 1. Calculations of ozone and OH in chemically coherent regions

Abstract

A one‐dimensional photochemical model has been used to calculate future changes in tropospheric O3 and OH due to CO/NOx/CH4 emissions and to possible changes in stratospheric O3 and tropospheric H2O. Perturbations are simulated for various chemically coherent regions (e.g., urban and continental mid‐latitudes, and marine and continental low latitudes) from 1985 to 2035. Estimates of global changes in O3 and OH are made by averaging over these regions. Two types of scenarios are simulated. “Global” scenarios assume that increases of CH4 and CO continue at current rates in all regions. A second set of scenarios, based on an analysis Of CH4, CO, and NO budgets in each region, assumes that emissions will be controlled in some regions and not in others. Both global and region‐specific scenarios predict a global tropospheric O3 increase of ∼10–15% from 1985 to 2035 with OH decreasing 10–15%. In the regionally varying scenarios, O3 will increase in some regions and decrease in others; for examples in regions of rapid CH4 and CO increase, growth in boundary layer O3 may be as high as 40%. Calculations that assume stratospheric O3 depletion and climate warming from 1985 to 2035 show near cancellation of the tropospheric O3 enhancement and OH loss. All scenarios of CH4/CO/NO changes considered in this study imply a 1–1.5% increase in total ozone from 1985 to 2035, assuming that tropospheric O3 is 10% of the total O3 column. This may complicate detection of stratospheric O3 change by monitoring of total O3.