Research and demonstration to improve air quality for the U.S. animal feeding operations in the 21st century – A critical review

•More emphasis was placed on pollutant emissions than indoor air quality.•Basic research dedicated to new pollutants, modeling, and baseline emissions.•Applied research focused on developing monitoring and mitigation technologies.•Field demonstrations combined with projects to evaluate new mitigation approaches.•Future efforts are needed in many fundamental and applied research areas.

There was an increasing interest in reducing production and emission of air pollutants to improve air quality for animal feeding operations (AFOs) in the U.S. in the 21st century. Research was focused on identification, quantification, characterization, and modeling of air pollutions; effects of emissions; and methodologies and technologies for scientific research and pollution control. Mitigation effects were on pre-excretion, pre-release, pre-emission, and post-emission. More emphasis was given on reducing pollutant emissions than improving indoor air quality. Research and demonstrations were generally continuation and improvement of previous efforts. Most demonstrated technologies were still in a limited scale of application. Future efforts are needed in many fundamental and applied research areas. Advancement in instrumentation, computer technology, and biological sciences and genetic engineering is critical to bring major changes in this area. Development in research and demonstration will depend on the actual political, economic, and environmental situations.