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Atmospheric Composition, Climate Variability & Change

We propose a four-year project to investigate tropospheric nitrate and ammonium aerosols and their influence on atmospheric radiative fields, chemistry fields, and various ecosystems at present day and the year 2050 using NASA Global Modeling Initiative (GMI). Nitrate and ammonium can influence air quality and ecosystems substantially, and their importance will be increasing in the future due to the predicted increase of nitrogen emissions. However, there have been relatively few studies of nitrate and ammonium and the uncertainty of their representations in models is necessarily large. We propose the study of nitrate and ammonium aerosols through the following tasks: 1. We will add seasonal information to the GEIA annual ammonia inventory. This is important since nitrate aerosol mostly forms in winter when it is cold. We will implement a thermodynamic equilibrium model to partition semi-volatile species such as HNO3 between gas and aerosol phases. The simulated nitrate and ammonium aerosol will be evaluated using ground network measurements (CASTNET, EMEP, etc). 2. We will investigate the impact of nitrate particles on atmospheric radiative forcing using a NASA GSFC radiative transfer model (CLDRAD) and compare the results with estimates from other models. 3. We will investigate the changes of atmospheric chemistry fields due to inclusion of nitrate and ammonium, which operate by altering the lifetime of nitric acid gas, providing additional particle surfaces for heterogeneous reactions, and changing photolysis rates. The simulated chemical fields of O3, NO2, and HNO3 will be evaluated using aircraft and satellite measurements including OMI and TES. 4. We will use MODIS global characterization of landscapes and vegetation types together with our model results to estimate the nitrogen (including NOx, N2O5, NH3, HNO3, HO2NO2, NH4+, NO3-, PAN, and other organic nitrates) deposition to different ecosystems. A map of nitrogen "critical load", which is a deposition threshold above which detrimental impact may occur, will be summarized for ecosystems based on the available measurements. This provides a first order usage of our nitrogen deposition estimation. 5. We will examine future impact on global nitrate and ammonium distributions by comparing the present day and the year 2050 model simulations. Overall, the work proposed here will lead to a more complete treatment of the nitrate and ammonium aerosol lifecycle--from sources to chemical evolution and atmospheric impacts during transport to their ultimate fate and the subsequent potential effect on land and ocean ecosystems.

Project PI: Huisheng Bian/University of Maryland at Baltimore County and NASA GSFC

Email: Hongbin.Yu@nasa.gov

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Started: Aug 10, 2010

Last Activity: Dec 15, 2010

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