Abstract:
This study presents a CO source contribution analysis for the atmosphere of South
Asia during January–February 2008. The approach includes into the Weather Research
and Forecasting Model with Chemistry 11 CO tracers, which track CO from different
source types and regions. The comparison of model results with Measurement of Pollution
in the Troposphere CO retrievals shows that the model reproduces the spatial, vertical, and
temporal distributions of Measurement of Pollution in the Troposphere retrievals fairly
well, but generally overestimates CO retrievals in the lower troposphere. CO mixing ratios
averaged over the model domain at the surface, in the planetary boundary layer, and the
free troposphere are estimated as 321 Æ 291, 280 Æ 208, and 125 Æ 27 ppbv, respectively.
Model results show that wintertime CO in the boundary layer and free troposphere over
India is mostly due to anthropogenic emissions and to CO inflow. In the boundary layer,
the contribution from anthropogenic sources dominates (40–90%), while in the free
troposphere the main contribution is due to CO inflow from the lateral boundaries (50–90%).
Over the Arabian Sea and the Bay of Bengal, 43–51% of surface CO mixing ratios come from
the Indian subcontinent and 49–57% from regions outside of South Asia. The anthropogenic
sources in the Indo-Gangetic Plain region are found to contribute, on average, 42% and 76%
to anthropogenic surface CO over the Arabian Sea and the Bay of Bengal, respectively. The
anthropogenic emissions from western and southern India contribute 49% to anthropogenic
surface CO over the Arabian Sea. Anthropogenic emissions contribute only up to 40% over
Burma where biomass burning plays a more important role. Regional transport contributes
significantly to total anthropogenic CO over southern India (41%), Burma (49%), and even
exceeds the contribution from local sources in western India (58%).
