Progress Report

Air Quality

The Acid Rain Program (ARP) and Cross-State Air Pollution Rule (CSAPR) were designed to reduce sulfur dioxide (SO₂) and nitrogen oxides (NOₓ) emissions from power plants. These pollutants contribute to the formation of ground-level ozone and particulate matter, which cause a range of serious health effects and degrade visibility in many American cities and scenic areas, including National Parks. The dramatic emission reductions achieved under these programs have improved air quality and delivered significant human health and ecological benefits across the United States.

To evaluate the impact of emission reductions on air quality, scientists and policymakers use data collected from long-term national air quality monitoring networks. These networks provide information on a variety of indicators useful for tracking and understanding trends in regional air quality over time and in different areas.

Sulfur Dioxide and Nitrogen Oxides Trends Figures

National SO₂ Air Quality
National SO₂ Air Quality Trend, 1980-2016
Regional Changes in Air Quality
Regional Changes in Air Quality

Ozone Figures

Percent Change Ozone Season Map
Percent Change in the Highest Values (99ᵗʰ percentile) of 1-hour Ozone Concentrations during the Ozone Season, 2000–2002 versus 2014-2016
Trend in Rural Ozone
Shifts in 8-hour Seasonal Rural Ozone Concentrations in the CSAPR NOₓ Ozone Season Region, 1990–2016
Changes in 8-Hour Ozone Concentrations
Seasonal Average of 8-Hour Ozone Concentrations in CSAPR States, Unadjusted and Adjusted for Weather
Changes in 1997 Ozone Nonattainment Areas
Changes in 1997 Ozone NAAQS Nonattainment Areas in the CSAPR Region, 2001–2003 (Original Designations) versus 2014-2016
Changes in 2008 Ozone Nonattainment Areas
Changes in 2008 Ozone NAAQS Nonattainment Areas, 2008–2010 (Original Designations) versus 2014-2016

Particulate Matter Figures

PM₂.₅ Seasonal Trends
PM₂.₅ Seasonal Trends, 2000-2016
Changes in PM₂.₅ Nonattainment Areas
Changes in PM₂.₅ NAAQS Nonattainment Areas in the CSAPR Region, 2001–2003 (Original Designations) versus 2014–2016