Impacts of reduced NOx emissions on radiative forcing through changes in tropospheric O3 and CH4: A global 3-D model study

Abstract

A three-dimensional global chemical tracer model and a radiation transfer model have been used to study 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, thereby giving negative forcing and cooling. The lifetime of NOx varies from hours to days, giving large spatial variations in the levels of NOx, and, 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. We have selected six geographical regions representing different chemical and physical conditions, and the emissions of NOx in these regions are reduced by 20%. The sensitivity in the chemical responses and the radiative forcing due to changes in O3 and CH4 show large variations between the regions. The ozone and methane forcing are of opposite sign and generally of similar magnitude.