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U.S. Air Quality Trends

Efficacy of Environmental Regulations to Improve Air Quality in the U.S.

Between 1990 and 2015, the U.S. average concentration of PM2.5 decreased by 37% and O3 decreased by 22% (EPA, 2016).  These decreased concentrations are expected to have brought substantial benefits for public health in the U.S., but assessing the health benefit requires an understanding of where air quality has improved, relative to where people live. We demonstrate the efficacy of environmental regulations by analyzing time trends of pollutants in the eastern US.  We then apply these trends in exposure to pollutants for estimates of health benefits. Specifically, we analyze satellite, ground-based networks, and model concentration trends for ozone (O3), nitrogen dioxide (NO2 – an O3 precursor), particulate matter (PM), and PM precursors, including ammonia (NH3), NO2 and sulfur dioxide (SO2). This work is a product of the NASA HAQAST Year 1 (2017-2018) Tiger Team “Efficacy of Environmental Regulations to Improve Air Quality in the Eastern U.S.”

Our team has developed a collection of free, publicly-available and downloadable resources (e.g., informational fact sheet, visualizations, summaries, etc.) to aid health and air quality managers to demonstrate the successes of environmental regulations on improving air quality.

Click on the icon to download or view a fact sheet demonstrating that efforts to improve air quality have worked and have had significant benefits for human health.



Air Quality Trends as Viewed from Space


  • Images of NO2 over the U.S. for 2005 and 2018.
  • Download ready-made plots of satellite NO2 trends (2005-2016) for various U.S. cities.
  • Trends (2005-2013) in satellite NO2 over major U.S. power plants.
  • A recent study using satellite data of NO2 by Jiang et al. (2018) indicates that the downward trend in NO2 has stalled since about 2011: Jiang et al. (2018), Unexpected slowdown of US pollutant emission reduction in the past decade, Proceedings of the National Academy of Sciences, 201801191; DOI: 10.1073/pnas.1801191115.
  • A recent study by Silvern et al. (2019) using satellite data of NO2 suggests that the flattening of the OMI NO2 trend may reflect the increasing relative importance of the non-anthropogenic NO2 background to the tropospheric column, rather than a flattening of US NOx emissions: Silvern et al. (2019), Using satellite observations of tropospheric NO2 columns to infer long-term trends in US NOx emissions:the importance of accounting for the free tropospheric NO2 background,
  • Animation of annual mean NO2 (satellite data) over the U.S. from 2005 to 2016.
  • Still of annual mean NO2 (satellite data) over the Mid-Atlantic/Ohio River Valley and U.S. in 2005 and 2016.

O3 & Precursors

PM & Precursors

  • Satellite data are used to infer surface trends of PM and its chemical precursors, which have decreased in the eastern U.S. from 2005 to present.
  • Animation of annual mean SO2 (satellite data) over the eastern U.S. from 2005 to 2017.
  • Animation of annual mean PM2.5 (µg/m3; estimated from satellite data) over the eastern U.S. from 2003 to 2016.
  • Satellite data of trends and variations in NH3 show a generally increasing trend in eastern Pennsylvania from 2008 to 2016.

Estimated Benefits of Air Quality Improvements*

*No satellite data were used to estimate these benefits.

Surface PM, O3, & Human Health (1990-2010)

  • Jason West (HAQAST) led a recent model (i.e., no satellite data) study (Zhang et al., 2018) that estimates the concomitant health benefits (i.e., avoided deaths) of improvements in U.S. air pollution levels of PM2.5 and O3 from 1990 to 2010. Their analyses show that deaths related to air pollution exposure in the U.S. decreased by about 47 percent, dropping from about 135,000 deaths in 1990 to 71,000 in 2010. [press release] [NASA news story] [New York Times article]

Surface O3 & Human Health

  • A model study by Loughner et al. (2014) estimated that the anthropogenic emissions reductions that occurred between 2002 and 2011 led to potentially 9-13 fewer O3 exceedances (using the 2011 maximum eight hour average O3 standard of 75 ppbv) throughout much of the Ohio River Valley and 3-9 O3 fewer exceedances throughout much of the Washington, DC – Baltimore, MD metropolitan area in July 2011. In unpublished work, we estimate, over the study region (most of the Eastern US), that these emission reductions prevented 569-801 deaths (95% CI: 319-1011), 950 hospital admissions due to respiratory symptoms (95% CI: 91-2346), 573 Emergency Room visits for Asthma (95% CI: 0-1645), and asthma exacerbation symptoms for more than 430,000 people (95% CI: 0-960,000+).  Visit the Surface-Level Ozone page for details and graphics.


  • The benefits of air pollution mitigation more than 30 times exceed the associated costs; although the U.S. dedicates roughly $65 billion annually to improve air quality, there is a resulting $2 trillion in benefits from economic production due to reduced premature mortality (US EPA, 2011). The EPA has quantified the benefits of the U.S. Clean Air Act in a report, entitled "Benefits and Costs of the Clean Air Act 1990-2020, the Second Prospective Study."

to References

HAQAST Co-Leads: Dr. Bryan N. Duncan (, Dr. Jason West

HAQAST Participants: Dr. Arlene Fiore, Dr. Susan Anenberg, Dr. Daven Henze, Dr. Daniel Tong, Dr. Lok Lamsal, Dr. Yang Liu, Dr. Mark Zondlo

Stakeholder Partners: Susan Wierman (retired from MARAMA), Tad Aburn (MDE), John Walker (EPA), Fuyuen Yip (CDC/NCEH), Paul Miller (NESCAUM), Neal Fann (EPA), Julie McDill (MARAMA), Rish Vaidyanathan (CDC)