I link to this mostly because it has a headline you will not see every day: "Pork industry supports Purdue's efforts to improve Indiana air quality." Of course, large pork operations do contribute to the air's condition, though we might not like to think about it:
Heber said the study also will establish infrastructure that should allow researchers to test different abatement strategies to improve downwind air quality.
“For example, if we put hogs on certain diets, we can significantly reduce ammonia emissions,” Heber said. “These experiments are needed to develop real solutions in the field.”
Ammonia emissions. Downwind. Says it all.