Progress Report

Air Quality

The Acid Rain Program (ARP), Cross-State Air Pollution Rule (CSAPR), and CSAPR Update 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 temporal trends in regional air quality.

Sulfur Dioxide and Nitrogen Oxides Trends Figures

National SO₂ Air Quality
National SO₂ Air Quality Trend, 1980–2019
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 2017–2019
Trend in Rural Ozone
Shifts in 8-Hour Seasonal Rural Ozone Concentrations in CSAPR NOₓ Ozone Season and CSAPR Update Regions, 1990–2019
Changes in 8-Hour Ozone Concentrations
Seasonal Average of 8-Hour Ozone Concentrations in CSAPR and CSAPR Update States, Unadjusted and Adjusted for Weather
Changes in 1997 Ozone Nonattainment Areas
Changes in 1997 Ozone NAAQS Nonattainment Areas in CSAPR Region, 2001–2003 (Original Designations) versus 2017–2019
Changes in 2008 Ozone Nonattainment Areas
Changes in 2008 Ozone NAAQS Nonattainment Areas, 2008–2010 (Original Designations) versus 2017–2019

Particulate Matter Figures

PM₂.₅ Seasonal Trends
PM₂.₅ Seasonal Trends, 2000–2019
Changes in 1997 PM₂.₅ Nonattainment Areas
Changes in the 1997 Annual PM₂.₅ NAAQS Nonattainment Areas in CSAPR States, 2001–2003 (Original Designations) versus 2017–2019