Publication Date:
2014-08-17
Description:
This paper interprets tropical tropospheric nitric acid columns from the IASI satellite instrument with a global chemical transport model (GEOS-Chem). GEOS-Chem columns generally agree with IASI over the tropical ocean to within 10%. However the GEOS-Chem simulation underestimates IASI nitric acid over Southeast Asia by a factor of two. The regional nitric acid bias is confirmed by comparing the GEOS-Chem simulation with additional satellite (HIRDLS, ACE-FTS) and aircraft (PEM-Tropics A and PEM-West B) observations of the middle and upper troposphere. This bias is likely driven by the lightning NO x parameterization, both in terms of the magnitude of the NO x source and the ozone production efficiency of concentrated lightning NO x plumes. We tested a subgrid lightning plume parameterization and found that an ozone production efficiency of 15 mol/mol in lightning plumes over Southeast Asia in conjunction with an additional 0.5 Tg N would reduce the regional nitric acid bias from 92% to 6% without perturbing the rest of the tropics. Other sensitivity studies such as modified NO x yield per flash, increased altitude of lightning NO x emissions, decreased convective mass flux, or increased scavenging of nitric acid required unrealistic changes to reduce the bias.
Print ISSN:
0148-0227
Topics:
Geosciences
,
Physics
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