At least one-quarter of all nitrogen oxide (NOx) emissions in California's Salton Sea air basin came from soil, according to a new study from the University of California, Davis.

Using isotopic analysis, the study found that annual total soil emissions for the basin were about 9.98 tonnes per day on average, which is 10 times larger than the state's current inventory for soil NOx emissions in the region, according to the study published recently in the Nature journal Scientific Reports.

The study highlighted the need to better understand and account for emissions from agricultural soils in order to comply with state and federal air quality regulations and to improve air quality in rural Imperial Valley and Coachella Valley and other agriculturally active regions in the United States in warm climates.

The Salton Sea is among the most polluted air basins in the United States. It runs from Palm Springs, through the Coachella Valley and into the Imperial Valley before ending at the Mexican border in Calexico.

NOx is a central air pollutant serving as a precursor to the atmosphere's production of both ozone and particulate matter.

(Cover: The end sign in Salton Sea area, California, U.S. /CFP)