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Distinguishing between greenhouse gas emissions from cropland, animal operations, and urban land cover with isotopic tracers
Atmospheric monitoring of pollutants and greenhouse gases in agricultural fields and facilities can provide a means of constraining and validating emissions inventories. However, atmospheric trace gases may originate from many different sources. In particular, when agricultural areas are located near or downwind of urban areas as is increasingly common, it is difficult to distinguish between pollution sources by measuring atmospheric concentrations alone. Measurements of the isotopic composition of trace gases have a great deal of potential for distinguishing between pollutant sources and quantifying the proportional contribution of agricultural activities to the total atmospheric concentration. We are measuring the isotopic composition of greenhouse gases (primarily N2O, and CH4) emitted from cropland, animal feeding operations, and urban activities in the South Coast Air Basin in southern California. This highly polluted area is characterized by a gradient of marine air offshore, large emissions from Los Angeles and surrounding urban areas near the coast, as well as agricultural emissions in inland areas of San Bernardino and Riverside counties. The goal of this measurement program is to utilize atmospheric measurements of the isotopic composition of CO2, N2O, and CH4 combined with studies of source signatures to determine the proportional contributions of cropland, animal operations, and urban sources of greenhouse gases to the atmosphere. Such source apportionment is critical to developing effective methods of quantifying and reducing emissions.
