Integrated Science Assessment (ISA) Ecological Criteria Assessment for Oxides of Nitrogen, Oxides of Sulfur, and Particulate Matter

The Integrated Science Assessment for Oxides of Nitrogen, Oxides of Sulfur and Particulate Matter  - Ecological Criteria (Final) provides the U.S. EPA’s evaluation and synthesis of the most policy-relevant science related to the ecological effects of nitrogen oxides, sulfur oxides and particulate matter (PM). This ISA is an update to the 2008 Integrated Science Assessment for Oxides of Nitrogen and Sulfur - Ecological Criteria (Final). Due to the overlap of effects of air pollutants on ecosystems, particulate matter was included in the updated report. In addition, in late 2019 EPA released the Integrated Science Assessment for Particulate Matter (Final Report), which includes the EPA’s evaluation of the policy-relevant science related to human health and other non-ecological aspects of PM effects on welfare (e.g.; visibility and climate). The ISAs provide a comprehensive evaluation and synthesis of the policy-relevant scientific literature, including that published since the last assessment, and serve as the scientific foundation for establishing and reviewing the primary (health-based) and secondary (welfare-based) national ambient air quality standards (NAAQS). 

Oxides of nitrogen or "nitrogen oxides" is a group of highly reactive gases, that also includes nitrogen dioxide (NO₂). Oxides of sulfur or “sulfur oxides is a group of highly reactive gases that includes sulfur dioxide (SO₂). Particulate matter (PM) is a complex mixture of extremely small particles and liquid droplets suspended in the air. Particulate matter is composed of some or all of the following components: nitrate (NO₃₋), SO₄²⁻, ammonium (NH₄₊), metals, minerals (dust), and organic and elemental carbon (C). Effects of gaseous oxides of sulfur and nitrogen in the ambient air include injury to leaves and plant physiology. Additionally, both pollutants and PM, contribute to nitrogen and sulfur deposition in ecosystems, which can alter the aquatic and terrestrial biogeochemistry and the physiology of organisms from multiple taxonomic groups. In 2020, the EPA released Integrated Science Assessment (ISA) for Oxides of Nitrogen, Oxides of Sulfur and Particulate Matter Ecological Criteria (Final Report).