PERTURBATIONS TO TROPOSPHERIC OXIDANTS, 1985-2035 .2. CALCULATIONS OF HYDROGEN-PEROXIDE IN CHEMICALLY COHERENT REGIONS

Increasing global emissions of trace gases NO, CH4, and CO, along with perturbations initiated by changes in stratospheric O3 and H2O, may cause tropospheric hydrogen peroxide (H2O2) levels to change. Specific scenarios of CH4-CO-NO emissions and global climate changes are used to predict HO2 and H2O2 changes from 1985 to 2035 in a one-dimensional model that simulates different chemically coherent regions (e.g. urban, non-urban continental and marine mid-lattitudes; marine and continental low latitudes). If CH4 and CO emissions continue to increase throughout the troposphere at current rates (1% yr-1), there will be large increases in H2O2, for example, more than 100% in the urban boundary layer from 1985 to 2035. Globally, H2O2 will increase 22% with HO2 increasing 8% and O3 increasing 13%. When CH4, CO and NO emissions are specified on a regionally varying basis and are parameterized for high and low potential growth rates, globally averaged increases in surface concentrations are 12% for H2O2 and 18% for O3. A global warming (with increased H2O vapor) or stratospheric O3 depletion superimposed on CH4, CO and NO emissions changes will cut O3 increases but add to peroxide, increasing levels as much as 150% above present day in some regions. Both globally uniform and region-specific scenarios predict a 10-15% loss in global OH from 1985 to 2035. Thus, conversion of OH to HO2 and H2O2 in the atmosphere may signify a loss of gaseous oxidizing capacity in the atmosphere and an increase in aqueous-phase oxidizing capacity.