Valley Soil A Major Air Pollution Source, Says New Study

Jan 31, 2018


When you hear about air pollution, you may think of vehicle emissions, industrial smokestacks and wood burning. But a new study reveals another major source right below your feet in the Central Valley.

The pollutants in question are nitrogen oxides, a family of harmful gases known collectively as NOx. They’re precursors to ozone and particulate matter, which can lead to a litany of short and long-term health problems.

The study, published today in the journal Science Advances, asserts that one major source of NOx has been overlooked: The soil.

Using a combination of computer models and airborne surveys, lead author Maya Almaraz of UC Davis found soils could be a huge NOx contributor. "We show that soils account for 25-41% of the total NOx budget in the state," she says.

That puts soils in the same ballpark as vehicle emissions as NOx sources.

Almaraz says most soils contain microbes that process nitrogen and expel NOx. But those microbes pump out even more NOx where there’s heat and nitrogen-rich fertilizer—like in the Central Valley. "We sort of have this perfect storm," she says: "We have high nitrogen inputs on soils that are hot and dry, so we get these emissions and they stay in that valley."

Almaraz says it’s important to not blame agriculture, but to develop tools for applying fertilizer more efficiently.