Air pollution is killing 3.3 million people a year worldwide, according to a new study that includes this surprise: Farming plays a large role in smog and soot deaths in industrial nations. Scientists from Harvard and in Germany, Cyprus, and Saudi Arabia used health statistics and computer models for the study, published yesterday in the journal Nature, to calculate the most detailed estimates yet of air pollution's toll. About three quarters of the deaths are from strokes and heart attacks, says lead author Jos Lelieveld at Germany's Max Planck Institute for Chemistry, with air pollution killing more people than HIV and malaria combined. The study also projects that if trends don't change, the yearly death total will double to about 6.6 million a year by 2050.
With nearly 1.4 million deaths a year, China has the most air pollution fatalities, followed by India with 645,000 and Pakistan with 110,000. The US, with 54,905 deaths in 2010 from soot and smog, ranks seventh highest for air pollution deaths. What's unusual is that the study says agriculture caused 16,221 of those deaths, second only to 16,929 deaths blamed on power plants. The problem with farms: ammonia from fertilizer and animal waste that combines with sulfates from coal-fired power plants and nitrates from car exhaust to form the soot particles that are the big air pollution killers, Lelieveld says. It's not all bad news: A Carnegie Mellon engineering professor says there are ways to reduce that ammonia air pollution "at relatively low costs," and Lelieveld said says if the world reduces carbon dioxide—the main gas causing global warming—soot and smog levels will be cut as well. (Read more pollution stories.)