Evaluation of bi-directional ammonia exchange with the GEOS-Chem model

Author: L. Zhu and Karen Cady-Pereira
December 4, 2012
AGU Fall Meeting 2012

Liye Zhu; Daven K. Henze; Jesse O. Bash; Karen E. Cady-Pereira; Mark W. Shephard; Gill-Ran Jeong; Robert W. Pinder; Mingzhao Luo (2012) Evaluation of bi-directional ammonia exchange with the GEOS-Chem model. AGU Fall Meeting, San Francisco, CA.

Ammonia is an important contributor to air pollution, climate change and environmental health. Ammonia emissions are known to be primarily from agricultural sources, however there is persistent uncertainty in the magnitude and seasonal trends of these sources. Inventories currently used in most air quality models are based on the assumption of unidirectional ammonia emissions from soil and vegetation canopies. However, the air-surface exchange of ammonia is known to be bi-directional. Explicit consideration of process-based ammonia fluxes can impact estimated distributions of ammonia and associated particulate matter. Here, we investigate the impact of implementing bi-directional ammonia fluxes in the global GEOS-Chem chemical transport model. We consider the impacts of bidirectional exchange on the model representation of ammonia and ammonium nitrate aerosol. This coupled bi-directional ammonia exchange modeling system is evaluated by comparing estimates of surface ammonia, aerosol ammonium and nitrate, and nitrogen wet deposition to independent surface measurements (AMoN, NTN, IMPROVE). We also compare the impacts of ammonia bi-directional fluxes to constraints on ammonia sources from remote sensing observations (TES).