NOx Emissions from California Lands
Nitrogen oxides (NOx) are air pollutants that can react with other chemicals in the air to form fine particulate matter (PM2.5) and ozone, both of which pose adverse impacts to human health and the environment. Control of NOx emissions is critical to improving air quality in California. Soils are known to emit NOx into the atmosphere, especially in agricultural areas where large amounts of nitrogen fertilizers are used to increase crop yields. The nitrogen chemicals in soil can be converted into various nitrogen gases, such as nitrous oxide (N2O) and NOx, by soil microorganisms. The contribution of soil emissions to the total NOx budget in California varies by region, depending on land uses and management activities. Researchers at CARB simulated soil NOx emissions from different land covers in California and evaluated impacts of soil NOx emissions on the formation of ambient particulate nitrate in the San Joaquin Valley (SJV), where cropland is the dominant land use. Our results indicate that soil NOx is a relatively minor fraction of the total NOx emissions in California and has a minor effect on atmospheric concentrations of particulate nitrate in the SJV. Ambient and satellite data analyses show traffic combustions being the dominate source of NOx emissions in both urban and agricultural areas of the SJV.