Calculation of trends in the tropospheric concentration of O₃, OH, CO, CH₄ and NO_x

Abstract

A 2-dimensional transport-photochemistry model of the global troposphere was applied to carry out long-term calculations of the effect of emission changes in nitrogen oxides, carbon monoxide, methane and nonmethane hydrocarbon, on ozone, hydroxyl and on the concentration of the precursors. For a model calculation for the 60-year period 1950-2010, where the tropospheric methane concentration was fixed to increase 1.5% per year, an average emission increase of only 1.05% per year was required to support the concentration increase. The 1.5% per year increase in methane, reduced hydroxyl by approximately 25%, over the period 1950-2010, while ozone increased by 0.45% per year. Increasing the emissions of carbon monoxide caused a slight reduction in hydroxyl. Increasing the NO,-emission by 3% per year in the 30-year period 1965-1995, gave rise to a significant increase in both ozone and hydroxyl. If the emissions of carbon monoxide, nitrogen oxides and nonmethane hydrocarbons were increased by 3% per year and methane by 0.5% per year, the concentration of hydroxyl hardly changed over a 30-year period, while ozone increased by about 1% per year. If the emissions of carbon monoxide, nonmethane hydrocarbons and methane went up 3-3-by and 0.5% per year, respectively, and the emissions of nitrogen oxides dropped by 3% per year, the concentration of hydroxyl declined markedly (- 0.7% per year). As a consequence of the drop in the concentration of the hydroxyl radical, there was an increase in the concentration of methane which was more than twice the emission increase over the 1965-1995 time period.