A new study published in Geophysical Research Letters concludes that ammonia emissions from Southern California dairy cattle are a significant source of smog in Los Angeles. The National Oceanic and Atmospheric Administration gathered data on fly-overs in the Southern California air basin in May and June 2010, resulting in estimates ranging from 33 tons to 176 tons of cow ammonia per day, compared to 62 tons from car emissions. The calculations are based on the 298,000 head of cattle in the region during the study, though the Dairy Herd Network says that only 100,000 cows remain. Ammonia creates smog only when mixed with nitrogen oxides not originating from farms.
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