Pollution attribution

Mooove along. Nothing to see here.

In the part of the United States with the worst air pollution, guess what the biggest source of smog is. Do you think it's cars? Or maybe trucks? How about oil refineries? Or coal-burning power plants?

Those would be good guesses, but the answer is cows. Over the last six years, California's San Joaquin Valley has been worse than either Los Angeles or Houston, especially for ozone. L.A.'s air has cleaned up dramatically over the past several decades, thanks to the Clean Air Act. Meanwhile the San Joaquin Valley has seen dramatic increases in both urbanization and factory dairy farming.

The San Joaquin Valley has about 2.5 million cows, and each one produces almost 20 pounds of "volatile organic compounds" per year. I was disappointed to find out that methane and other VOCs mostly come from "the front end of the cow" — they are mostly not from cow farts. Darn, there goes my joke about tailpipe emissions.