...[O]dor is only part of the concern. [Ammonia and hydrogen sulfide] are also airway irritants that can cause respiratory problems. If you’re in a situation where you’re exposed to a high level of ammonia in the air, your eyes are going to water. Your throat is going to hurt. These are the biological and physiological signs that something is wrong — that these compounds are not good for you.
Particulate matter is also an issue with livestock confinements. This includes things such as dust, feathers, fecal matter, and fur. There is extensive research on associations between airborne particulate matter and respiratory problems or cardiovascular problems.
But as far as the irritation from ammonia and hydrogen sulfide — that’s essentially what you see in areas that are downwind or surrounding these facilities. There have also been documented respiratory problems in the people who work in these facilities — in livestock confinements — that are likely due to those exposures [Dr. Donna Wong Gibbons, interview with Julia Wasson, "Plains Justice -- CAFOs and Threats to Human Health," Blue Planet, Green Living, 2010.01.06.
Kelly Fuller pointed me toward this report, which Dr. Wong-Gibbons produced for Plains Justice, the group for which Fuller works, to document the range of public health threats caused by CAFOs. The report also documents higher instances of asthma, water pollution, arsenic in chicken, antibiotic resistance, and bird and swine flu, all related to big animal feedlots.
Read the full (PDF) report here. Then be prepared for the likely impolite and aggressive responses from the defenders of unhealthy factory farms.