The biggest source of the world's fine particulate air pollution is not cars, or factories, or power plants. It's farms.
A new study explains that when ammonia from fertilizers and animal waste combines with nitrogen oxides and sulfates from exhaust pollution, microscopic solid particles, so-called aerosols, are created.
Aerosols can reach deep into the lungs, causing heart or pulmonary disease. It's estimated fine particulate air pollution is responsible for more than 3 million death each year around the world.
The authors of the study in Geophysical Research Letters stress that their work is not meant to discourage the use of fertilizer. Atmospheric scientist Susanne Bauer, the lead author, said, "We expect population to go up, and to produce more food, we will need more fertilizer."
Bauer points out, however, that since agricultural emissions must combine with other pollutants to create aerosols, having cleaner sources of energy and more efficient cars in the future will greatly reduce those other ingredients. So, even if ammonia emissions hold steady or increase, air quality would not decline.
Johannes Lelieveld, lead author of a 2015 report on aerosols, warns that assessment will hold true only if societies successfully curb industrial emissions.