Impacts of Reduced NOx Emissions on Radiative Forcing Through Changes in Tropospheric O3 and CH4 - A Global 3-D Model study

摘要

This report describes the use of a three-dimensional global chemical tracer model and a radiation transfer model in a study of the role of reduced NOx emissions on radiative forcing. Through production of tropospheric O3, NOx emissions lead to positive radiative forcing and warming, but NOx also reduces the levels of CH4, which gives negative forcing and cooling. The lifetime of NOx varies from hours to days, which gives large spatial variations in the levels of NOx. Due to non-linearities in the chemistry, there are also large geographical differences in the effects of NOx on O3 as well as on OH and CH4. Six geographical regions representing different chemical and physical conditions were selected and the surface emissions of NOx in them reduced by 20% in separate model tests. The sensitivity in the chemical responses and the radiative forcing due to changes in O3 and CH4 vary widely from region to region. The ozone and methane forcing are of opposite sign and generally of similar magnitude. 24 refs., 8 figs., 2 tabs.