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Do cows contribute as much as cars to L.A. smog?

A study from the University of Colorado and the National Oceanic and Atmospheric Association finds automobiles and cows are equally responsible for the smog in Los Angeles. The study published in Geophysical Research Letters was conducted in May of 2010 and found a large portion of the smog was ammonium nitrate. The determined the 9.9 million automobiles in the L.A. basin generated 62 metric tons of ammonia each day. At the same time, the manure from 298,000 cattle in the basin generated between 33 and 176 metric tons of ammonia per day.

The California dairy industry says there are not that many cattle in the basin, there are something more like 100,000 mature dairy cows in the area. They also question the calculations. The National Air Emissions Monitoring Study commissioned by the National Milk Producers Federation and the EPA measured emissions from 2007 to 2009 at dairy production facilities in California, Wisconsin, Washington, Texas, Indiana and New York. That study found the average dairy cow was responsible for 60.9 grams of ammonia per day. Even if there were 298,000 cows in the basin they would put out only 18 metric tons per day. With 100,000 cows the emissions would be 6 metric tons…substantially less than the 33 to 176 metric tons claimed in the study.