Scientists are searching for ways to reduce air pollution that is harmful to humans. An area that you might not be familiar with is pollution from agricultural operations. reddit science recently linked to “Farms a Major Source of Air Pollution, Study Finds”.
The study notes that gases from fertilizers and animal wastes mixed in the air with combustion products produces small (less than 25 micrometers) solid particles. Particles of this size penetrate deep into the lungs and cause cardiac and pulmonary disease. Another 2015 study estimates that each year 3.3 million people (worldwide) are killed by this pollution. A very detailed article about the effects of air-borne particles can be found at wiki Particulates.
Because food production is very important, the “Farms…” article suggests that the best way to reduce the particulate pollution is to reduce the combustion products in the atmosphere since both forms of pollution combine to produce the particles in question. Reducing combustion products air pollution is, of itself, a major goal in the reduction of greenhouse gases. Reducing agricultural emissions may be very difficult, while at the same time, increasing production. The major agricultural emission is generally ammonia gas, which, in small concentrations typical of its level in the atmosphere, is not much of a problem.