UNCERTAINTIES IN THE CURRENT KNOWLEDGE OF ATMOSPHERIC TRACE GASES ASSOCIATED WITH CROPPING SYSTEMS IN THE U.S.

Authors: KRUPA, SAGAR - UNIV OF MINNESOTA; Booker, Fitzgerald; BOWERSOX, VAN - ILLINOIS STATER WATER SUR; GRANTZ, DAVID - UNIV OF CALIFORNIA

Submitted to: Proceedings of the Workshop on Agricultural Air Quality: State of the Science
Publication Type: Proceedings
Publication Acceptance Date: 2/26/2006
Publication Date: 6/5/2006
Citation: Krupa, S., Booker, F.L., Bowersox, V., Grantz, D. 2006. Uncertainties in the current knowledge of atmospheric trace gases associated with cropping systems in the us. Proceedings of the Workshop on Agricultural Air Quality: State of the Science 160.

Interpretive Summary: Summary Emissions of trace gases from agriculture-related activities have a significant influence on the nation’s air quality. Although the majority of cultivated acreage in the US is planted with only about ten major crop species, uncertainties associated with trace gas emissions arise from: (1) limited data availability and consequently inaccurate estimates due to the large temporal and spatial variability in trace gas (principally carbon dioxide, methane, ammonia and nitrous oxide) composition and amounts released from agricultural activities, (2) characteristics of pollutant emissions from animal feed-lots (including emissions from dairy animals) and their geographic distribution, and (3) our limited understanding of semi-volatile organic compounds (SVOCs) associated with agriculture. SVOCs range in their composition from relatively simple acids to complex organo-chlorines and pesticides. These compounds exist in both particle (solid and liquid) and gas phases, with a highly variable rate of transition from one phase to the other, as governed by their chemical structure, receptor characteristics and by environmental factors. While emission issues are of concern, so is atmospheric wet and dry deposition of nitrogen, mineral nutrients and organic compounds to cropping systems that can, in turn, have feedback effects on trace gas emissions. There are many gaps in our understanding of these processes. The various methodologies used for quantifying emissions and deposition have limitations, and a sufficient number of monitoring sites is lacking. Other considerations include: (1) the effects of increasing concentrations of atmospheric ozone and carbon dioxide on crop production, and the potential changes in management practices of cropping systems, (2) the changing use of nitrogen fertilizers and consequent alterations in atmospheric nitrogen oxides, nitrous oxides and ammonia emissions and deposition, and (3) changing air temperature effects on crop production and also its impacts on trace gas emissions. Overall, studies are needed at various scales with better-coordinated approaches to sufficiently quantify temporal and spatial trends in trace gas emissions and deposition and their relationships to agricultural practices in the US in a changing global climate.

Technical Abstract: Emissions of C- and N-derived trace gases from agriculture-related activities have a significant influence on the nation’s air quality. Approximately 80 different crop species are grown in the US in widely differing geographic areas and climatic conditions. Other crop growth regulating factors consist of differences in soil types, moisture availability, nutrients and management practices. The crops grown include both C3 and C4 species, and a multitude of cultivars. Although the majority of cultivated acreage in the US is planted with only about ten major crop species, uncertainties associated with trace gas emissions arise from: (1) limited data availability and consequently inaccurate estimates due to the large temporal and spatial variability in trace gas (principally CO2, CH4, NH3 and N2O) composition and amounts released from agricultural activities, (2) characteristics of pollutant emissions from animal feed-lots (including emissions from dairy animals) and their geographic distribution and (3) our limited understanding of semi-volatile organic compounds (SVOCs) associated with agriculture. SVOCs range in their composition from relatively simple acids to complex organo-chlorines and pesticides. These compounds exist in both particle (solid and liquid) and gas phases, with a highly variable rate of transition from one phase to the other, as governed by their chemical structure, receptor characteristics and by environmental factors. While emission issues are of concern, so is atmospheric wet and dry deposition of N, mineral nutrients and organic compounds to cropping systems that can, in turn, have feedback effects on trace gas emissions. There are many gaps in our understanding of these processes. At present, a number of research groups are investigating agriculture-related emissions of trace gases (primarily CO2, CH4, NH3 and N2O). However, there are advantages and limitations associated with the various methodologies used for quantifying emissions and deposition (e.g., flux measurements, use of continuous monitoring versus passive sampling of the air, sample collection and chemical analyses). There is also a frequent lack of sufficient number of monitoring sites (sample size) to satisfy the requirements of spatial mapping of the measured variable with confidence. Other considerations include: (1) the effects of increasing concentrations of atmospheric O3 and CO2 on crop production, and the potential changes in management practices of cropping systems, (2) the changing use of N fertilizers in agriculture and consequent alterations in atmospheric NOx , N2O and NH3 emissions and deposition, and (3) changing air temperature effects on crop production and also its impacts on trace gas emissions, particularly molecules other than CO2. Overall, studies are needed at various scales with better-coordinated approaches to sufficiently quantify temporal and spatial trends in trace gas emissions and deposition and their relationships to agricultural practices in the US, in a changing global climate.