NOX EMISSIONS FROM SOIL - IMPLICATIONS FOR AIR-QUALITY MODELING IN AGRICULTURAL REGIONS

Attaining the ambient standard for tropospheric ozone has been difficu lt in many metropolitan areas, despite efforts to reduce anthropogenic sources of the ozone precursors, including the nitrogen oxides (NOx). Until recently, NOx emissions from biogenic sources in soils were not considered in simulations of air quality and emissions reductions sce narios, yet they may be significant, especially in agricultural region s where nitrogen fertilizers are applied. Soil NOx is produced primari ly by microbial processes; production and emissions from soils are con trolled by a suite of environmental variables, including inorganic nit rogen availability, water-filled pore space, and soil temperature. Agr icultural management practices such as fertilization and irrigation af fect these environmental variables and thus have the potential to dram atically alter soil NOx emissions. Although current models incorporate some of these variables, accurate regional estimation of soil NOx emi ssions requires modeling approaches that explicitly incorporate the sp atial and temporal patterns of management practices, especially fertil ization, as well as other environmental controlling variables such as water-filled pore space and soil temperature.