If you’re looking for one more way in which industrial agribusiness is poisoning rural communities, look up—as in, up in the air.

A new study published in the journal Science Advances attributes a large share (41 percent) of California’s unhealthy smog to nitrogen oxide (NOx) emissions directly related to the use of chemical fertilizers on croplands.

According to Mother Jones, which reported on the study, California’s economically disadvantaged Central Valley region has suffered disproportionately from agriculture-related smog:

Many poor communities surround the Valley and bear the brunt of smog-related health effects, including an increased rate of asthma attacks, acute bronchitis, and missed days of school and work. Fresno, for example, is home to about 970,000 residents; 240,000 of them live in poverty and 70,000 have asthma and are at risk to ozone pollution (which is formed from nitrogen oxides), according to the American Lung Association. Between 2013 and 2015, Fresno residents saw, on average, about 93 high ozone days in unhealthy ranges per year.

As OCA’s Ronnie Cummins wrote, at $175 billion, the global fertilizer industry is the largest sector of global agribusiness. And the biggest player? None other than Koch Industries.

But farmers can’t grow crops without chemical fertilizers, right? The Koch brothers would love for us to think so—but that’s because they make big profits, not because they’re right.

There’s a better way. Organic regenerative farming which uses techniques that build healthy, organic soil matter without the use of chemicals.

Read ‘Researchers Just Found a Hidden Cause of California’s Smog Problem’ 

Read the full study in the journal Science Advances