Emissions of nitrogen and gaseous sulfur compounds from animal and crop agriculture have become a serious political and environmental problem. Compliance with increasingly stringent federal and state air pollution regulations pose both economic and technical challenges to agricultural operations. The U.S. Department of Agriculture has taken several steps to respond to the growing need to increase understanding of the current state of knowledge in this area and to develop socioeconomically beneficial policies. One of these responses was a USDA – Air Quality call for proposals which led to the Workshop on Agricultural Air Quality: State of the Science.

Recent studies, including the US National Research Council report (http://books.nap.edu/catalog/10586.html) provide convincing evidence that changes in agricultural crop production and animal activities are increasing the emissions of trace gases (e.g., carbon dioxide, sulfur, nitrogen, hydrocarbon species, etc.) to the atmosphere. All of these emissions can perturb the environment with a host of beneficial and detrimental effects such as increased crop yields from nitrogen loading or decreased visibility from increased aerosol production.

Emissions of nitrogen (e.g., ammonia, NH₃) and gaseous sulfur compounds (e.g., hydrogen sulfide, H₂S) from animal and crop agriculture have become a serious political and environmental problem of unknown extent as animal production operations have grown in recent years. Globally, domestic animals are estimated to be the largest source (32 x 10¹²g N yr^-1 ) of atmospheric NH₃, comprising approximately 40% of total natural and anthropogenic emissions, while synthetic fertilizers and agricultural crops together contribute an additional 12.6 x 10¹² g NH₃ -N yr^-1 (23% of total emissions) (Aneja et al. 2001). However, emissions of sulfur compounds and particulate matter from agricultural sources are less well quantified.

There are immediate societal and economical issues associated with odors and potential health impacts of agricultural and animal operations that affect local, regional, and national policies and livelihoods. The increased size and geographical concentration of animal feeding operations and growing concerns with emissions from them have led regulators and policy makers to begin considering mitigation of the harmful effects of animal-feeding operations (AFO) and emissions from crop agriculture.

Compliance Issues

Compliance with increasingly stringent federal and state air pollution regulations pose both economic and technical challenges to agricultural operations. Technical challenges include limitations in monitoring and measurement techniques, unresolved standards for dispersion and transport models, the lack of accurate emission factors, and a need for process-based emissions and transport/ transformation models. These challenges cause substantial uncertainty in estimating pollutant emission rates and inventories required for Federal Operating Permits for animal- feeding operations.

These issues are further complicated by the need to consider abatement strategies, the cost of compliance, and determination of reductions associated with Best Management and Best Available Control Technologies (BMPs, BACTs).

Compliance with air pollution regulations may often be perceived as inappropriate and unfair regulation of agricultural operations, resulting in financial stress that threatens the economic viability of rural and agricultural communities and regional economies. Thus, there is a clear need for science-based research to address agricultural air quality problems and to provide appropriate BMP's which can be used to manage the problem without destroying the industry.

Response

The U.S. Department of Agriculture has taken several steps to respond to the growing need to increase understanding of the current state of knowledge in this area and to develop socioeconomically beneficial policies. Examples including forming the Agricultural Air Quality Task Force (AAQTF, http://aaqtf.tamu.edu/) and requesting the National Academy of Sciences (NAS) to evaluate the state of the science related to emissions from AFOs.

This Workshop on Agricultural Air Quality: State of the Science resulted from a USDA – Air Quality call for proposals to address agricultural air quality, with a focus on improving air quality inventories and recommendations for technological and methodological changes in current modeling and measurement practices. The Workshop on Agricultural Air Quality: State of the Science, has taken on these challenges. It was the first such venue where truly multidisciplinary teams of experts shared their knowledge, presented new research, and helped shape the future of the agricultural practices and agricultural air quality analysis framework for the United States.

Aneja, V.P., P.A. Roelle, G.C. Murray, J. Sutherland, J.W. Erisman, D. Fowler, W.A.H. Asman, N. Patni. 2001. Atmospheric nitrogen compounds II: emissions, transport, transformation, deposition and assessment. Atmospheric Environment. 35(2001) 1903-1911. http://www.meas.ncsu.edu/airquality/papers/atScience4.pdf

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