Description:
<jats:p>The sensitivities of tropospheric HO<jats:sub>2</jats:sub> and hydrogen peroxide (H<jats:sub>2</jats:sub>O<jats:sub>2</jats:sub>) levels to increases in CH<jats:sub>4</jats:sub>, CO and NO emissions and to changes in stratospheric O<jats:sub>3</jats:sub> and tropospheric O<jats:sub>3</jats:sub> and H<jats:sub>2</jats:sub>O have been evaluated with a one‐dimensional photochemical model. Specific scenarios of CH<jats:sub>4</jats:sub>‐CO‐NO<jats:sub>x</jats:sub> emissions and global climate changes are used to predict HO<jats:sub>2</jats:sub> and H<jats:sub>2</jats:sub>O<jats:sub>2</jats:sub> changes between 1980 and 2030. Calculations are made for urban and nonurban continental conditions and for low latitudes. Generally, CO and CH<jats:sub>4</jats:sub> emissions will enhance H<jats:sub>2</jats:sub>O<jats:sub>2</jats:sub> (as OH is converted to HO<jats:sub>2</jats:sub>); NO emissions will suppress H<jats:sub>2</jats:sub>O<jats:sub>2</jats:sub> except in very low NO<jats:sub>x</jats:sub> regions. A global warming (with increased H<jats:sub>2</jats:sub>O vapor) or stratospheric O<jats:sub>3</jats:sub> depletion will add to H<jats:sub>2</jats:sub>O<jats:sub>2</jats:sub>. Hydrogen peroxide increases from 1980 to 2030 could be 100% or more in the urban boundary layer.</jats:p><jats:p>Increases in CH<jats:sub>4</jats:sub>, CO and O<jats:sub>3</jats:sub> that have occurred in the industrial era (since 1800) have probably produced temporal increases in background HO<jats:sub>2</jats:sub> and H<jats:sub>2</jats:sub>O<jats:sub>2</jats:sub>. It might be possible to use H<jats:sub>2</jats:sub>O<jats:sub>2</jats:sub> in ice cores to track these changes. Where formation of sulfuric acid in cloudwater and precipitation is oxidant limited, H<jats:sub>2</jats:sub>O<jats:sub>2</jats:sub> and HO<jats:sub>2</jats:sub> increases could be contributing to increases in acid precipitation.</jats:p>