Anyone who’s ever driven down Interstate 5 in central California’s Kern County knows about the smell. The one that penetrates cars despite closed vents and windows. Wafting from an adjacent cattle ranch, the largest on the West Coast, the well-known odor comes from the ammonia all those cows produce.

California’s Central Valley, which spans I-5, regularly has some of the worst air pollution in the United States because of its unfortunate combination of geography and agriculture. It is ringed by mountains that trap bad air like water in a bathtub, and it is lined with fertile soils that produce much of the country’s vegetables, fruits, nuts and meat, along with pollutants.

The region’s unique pollution profile drew the attention of NASA scientists, who recently sent two research planes on swooping arcs from Bakersfield to Fresno on a mission to improve air-quality monitoring in the United States.

Continue reading: Air Pollution Tracked By Planes Means Better Satellite Air-Quality Monitoring | LiveScience.