Grass-fed beef is environmentally friendlier.

RODALE NEWS, EMMAUS, PA—One more reason to try grass-fed beef: The food that farmers feed their cows doesn’t just affect the bovines. California's San Joaquin Valley produces an estimated 10 percent of this country's food supply, including much of the food that livestock eat, and a new study published in the journal Environmental Science & Technology has found that all that livestock food is contributing to the area's dangerously high ozone levels.

THE DETAILS: Ozone is formed when nitrogen oxides react with different gases in the air, and the researchers suspected that crops could be contributing some of the gases in the San Joaquin Valley, which ranks among the top 10 geographical areas for ozone levels but has a fraction of the population of other equally polluted areas (the most common culprit in ozone formation is cars). For their study, the researchers measured the gases being emitted in fields growing traditional livestock feed, such as corn, wheat, and oats, and found that those crops emitted ozone-forming gases at levels just slightly below that of gasoline. They then plugged those figures into computer models to predict the levels of ozone emitted by these crops on a daily basis, and found that livestock feed emits nearly twice as much ozone as the area's gasoline-powered cars.

WHAT IT MEANS: Cows, pigs, and chickens aren't exactly innocent bystanders when it comes to air pollution. They pass gas and produce waste that's heavy on methane, a potent greenhouse gas, in part because of what they eat. A grass-based diet is easier on a cow's system, so grass-fed cows produce less methane than their corn-fed peers. But this study shows that livestock feed can pollute before it even passes through an animal. It seems that animal feed contains certain compounds called alkanes, alkenes, ketones, aldehydes, and alcohols, which react with nitrogen oxides and with sunlight to increase ozone levels. The same chemicals exist in paints, which is why that "new paint smell" can be so irritating to sensitive individuals.