Photochemical Oxidant Episodes, Acid Deposition and Global Atmospheric Change. The Relationships with Emission Changes of Nitrogen Oxides and Volatile Organic Compounds

摘要

Ozone (O3) episodes in the atmospheric boundary layer over Europe are superimposed on slowly increasing background levels which probably is controlled by changes in the emissions of nitrogen oxides (NOx). Increase in the emission of NOx in Europe and elsewhere in the northern hemisphere will contribute to a continued rise in free tropospheric O3, while occurence of O3 episodes in the boundary layer may not change much. Nitrate due to NOx emissions contributes significantly to acid deposition in Europe and elsewhere and integrated over one year there is probably a nearly linear relationship between these changes. In clean air, decreased emissions of NOx is shown in model calculations to cause drop in the background concentration of O3 and OH, while H2O increases. The gasphase conversion of SO2 and NOx by reaction with OH to sulphate and nitrate will become less efficient. The dark reaction converting NO2 to the NO3 radical and then to nitrate by reacting with O3, would become slower, while the wet phase oxidation of SO2 to sulphate would become more efficient. The result is a more than proportional reduction in the nitrate formation could increase thus increasing the lifetime for S-compounds and decreasing the lifetime for NOx-compounds. A decrease in global NOx emissions will cause a drop in the tropospheric O3-increase and reduce it's potential warming effect and can come about by reducing the burning of fossil fuels. Reducing NO/sub x/ would also reduce tropospheric OH. With unchanged surface sources of CH/sub 4/, tropospheric CH/sub 4/ would increase in concentration more than today, contributing more to the surface warming than 0.14 K in 50 years. The combustion of fossil fuels is an important source of CO2 and it would reduce both NOx and CO2 emissions. 42 refs.