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Atmospheric Modeling and Analysis Research

Special Field Data

Atmospheric pollutants emitted to the atmosphere will eventually be deposited back to the surface through scavenging by precipitation (wet deposition) or by gaseous and aerosol deposition (dry deposition) to land surfaces. Once deposited, these pollutants contribute to soil acidification, surface water acidification, oxidative damage to crops and natural vegetation, and the accumulation of toxics in soils, vegetation and water. The processes governing dry deposition are not well known for most atmospheric pollutants. Collaborations between atmospheric flux measurement scientists and air quality modeling scientists have been developed to collect measurements that are not routinely measured at monitoring network sites to evaluate and improve air-quality model estimates of dry deposition. 

Collaborative field and modeling experiments were the flux (deposition and emission) of atmospheric pollutants are measured and the data necessary to drive and evaluate the uncertainty in air-quality model dry deposition parameterizations and are collected have been undertaken. The measured data is then used to evaluate and improve modeled dry deposition parameterizations. Additionally modeled results can provide estimates of processes that cannot yet be measured and provide additional understanding of the measurements and environmental variables that may be used to reduce the uncertainty in processes that cannot yet be measured.

Collaborative measurement and modeling studies have accelerated the development of bi-directional (emissions or deposition depending on the meteorology, land use and management) NH3 exchange in CMAQ resulting in improvements in modeled nutrient deposition and ambient aerosol concentrations. Detailed local assessments and the improvements in local scale models of pollutant deposition processes will help guide future regional and global scale model development and future field scale measurements. This research will improve modeled estimates of dry deposition and improve the agencies ability to connect emissions to deposition of and ecosystem exposure to atmospheric pollutants supporting secondary NAAQS standards.

Instrumented tower in Lillington NC sampling the dew off of corn leaves CMAQ model NH3 deposition estimates
Figure 1. Instrumented tower in Lillilngton, NC where NH3 and O3 concentrations

and fluxes were measured (left) and sampling the dew off of corn leaves to better understand the chemistry on the leaf surface and how that influences the deposition and emission of pollutants in a fertilized agricultural setting (center), CMAQ model NH3 deposition estimates using new parameterizations developed and evaluated using the measurements taken at Lillington, NC (right).

 

Contacts: Jesse Bash, Donna Schwede

References
Bash, J.O., Cooter, E.J., Dennis. R.W., Walker, J.T., Pleim. J.E., Evaluation of a regional air-quality model with bi-directional NH3 exchange coupled to an agro-ecosystem model, Biogeosciences Discuss. 9, 11375-11401

Walker, J.T., Jones, M.R., Bash, J.O., Myles, L., Luke, W., Meyers, T.P., Schwede, D., Herrick, J., Nemitz, E., Robarge, W., 2012, Processes of ammonia air-surface exchange in a fertilized Zea Mays canopy, Biogeosciences Discuss. 9, 7893-7941

Bash, J.O., Walker, J.T., Katul, G.G., Jones, M.R., Robarge, W., Nemitz, E. Robarge, W., 2010, Estimation of in-canopy ammonia sources and sinks in a fertilized Zea Mays field, Environ. Sci. Technol., 44, 1683-1689

Cooter, E., Bash, J.O., Walker, J.T., Jones, M.R., Robarge, W., 2010, Estimation of NH3 bi-directional flux over managed agricultural soils, Atmos. Environ. 44, 2107-2115

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