Analysis of tropospheric NOx over Asia using the model of atmospheric transport and chemistry (MATCH-MPIC) and GOME-satellite observations

Abstract

Abstract The distribution and budget of tropospheric NOx over Asia, especially India, are examined using the global 3D chemistry–meteorology model MATCH-MPIC and GOME NO2 columns. Enhanced abundances of NO2 over China and northeast India are reproduced by the model, as are the pronounced maxima during biomass burning periods, though somewhat underestimated. The mean NO2 column over India is also reproduced, though the model has trouble with the seasonal cycle for unknown reasons. Model sensitivity tests for the Indian region indicate that the scaled sensitivity to changes in the local NOx source is 60–70% for lower tropospheric NOx and is only 10–25% for tropospheric O3, indicating that moderate reductions or increases in current NOx emissions are not expected to lead to large changes in regional O3 levels. In the upper troposphere, during winter nearly all of the NOx comes from remote sources, while in summer deep convection causes the upper troposphere to become sensitive to local surface emissions (∼40–50% scaled sensitivity) and lightning NOx production (∼10–20%). The regional lifetime of NOx estimated for India, based on MATCH output is about 15–23 h, comparable to the lifetime of NOx over China (14–21 h), while over Indonesia (23–43 h) and North Asia (21–47 h), it is longer and highly seasonal. Implications of these results are discussed.