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Particulate Matter

It is estimated that exposure to outdoor air pollution is responsible for about 4 million premature deaths annually with about another 3-4 million resulting from exposure to indoor air pollution; that is, air pollution is responsible for about 1 in 9 deaths worldwide (WHO, 2018;  Cohen et al., 2017). The majority of deaths are associated with fine particulate matter of less than 2.5 µm in width (PM2.5). Knowledge of both PM2.5 concentrations and the concentrations of a number of pollutants is required to devise effective mitigation strategies for PM2.5 since it is directly emitted to the atmosphere, such as in the form of smoke and dust, but can also form in the atmosphere through chemical reactions that transform gaseous pollutants (e.g., sulfur dioxide (SO2), ammonia (NH3), nitrogen dioxide (NO2)) to particles (i.e., gas to particle conversion).


U.S. Trends

Satellite data indicate that PM2.5 levels have decreased by about 30% or more over the Eastern U.S. from 2003 to 2016 because of emission control measures, but concentrations vary from year to year with meteorology and weather-sensitive sources, including wildfires.

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The animations show how the estimated surface PM2.5 (µg/m3 as an annual average) has varied from 2003 to 2016 over the eastern half of the U.S. and in Washington-Baltimore metropolitan corridor. The estimated surface PM2.5 data product is described in van Donkelaar et al. (2016). The data may be downloaded from the NASA SEDAC website or from the Dalhousie University Atmospheric Composition Analysis Group website. Figure credit: Dr. Pawan Gupta, NASA.

Satellite data show that the concentrations of several PM2.5 precursors are going down over time over the Eastern U.S. 

  • NO2 levels have decreased by about 20-60% over most major U.S. cities from 2005 to 2017 (e.g., animation). However, a recent study by Jiang et al. (2018) indicate that the downward trend in NO2 has stalled since about 2011. Please visit the Nitrogen Dioxide and News tabs for more information.
  • SO2 levels have also decreased dramatically near coal-burning power plants. Please see the animation below for the Eastern U.S., an animation for the entire U.S., and an animation of estimated changes since 1980. Please visit the Global Sulfur Dioxide Monitoring Homepage for more information.

Despite significant progress on reducing PM2.5, wildfires are an infrequent, but significant source of PM2.5 that can expose large populations to unhealthy levels of pollution. For instance, smoke from persistent wildfires in the Western U.S. during the summer of 2017 degraded air quality in a number of large cities, such as San Francisco, Portland, and Seattle. While less frequent in the Eastern U.S., fire smoke is a significant health risk.  For instance, wildfires in the Southeast U.S. impacted large regions, including heavily populated cities like Atlanta, in the fall of 2016. Please see this tutorial for an example of how an air quality agency used satellite data of wildfire smoke.

Animation showing how SO2 levels (units = Dobson Unit, DU) changed from 2005 to 2017 over the Eastern U.S. The uncertainties associated with the data are larger for smaller sources and vice versa. Therefore, some SO2 signals in remote areas may simply be data artifacts. Data courtesy of Chris McLinden, Environment Canada. Animation: NASA.


Global Trends

In addition to the U.S., several other places have seen dramatic changes in NO2 and SO2. As the animations below show, there has been a rapid increase in levels over India and a rapid decrease over China in the last decade (e.g., Li et al., 2017). Please visit the Global Sulfur Dioxide Monitoring Homepage for more information.

Animation showing how SO2 levels (units = Dobson Unit, DU) changed from 2005 to 2017 over India. The uncertainties associated with the data are larger for smaller sources and vice versa. Therefore, some SO2 signals in remote areas may simply be data artifacts. Data courtesy of Chris McLinden, Environment Canada. Animation: NASA.

Animation showing how SO2 levels (units = Dobson Unit, DU) changed from 2005 to 2017 in Asia. The uncertainties associated with the data are larger for smaller sources and vice versa. Therefore, some SO2 signals in remote areas may simply be data artifacts. Data courtesy of Chris McLinden, Environment Canada. Animation: NASA.

Animation showing how SO2 levels (units = Dobson Unit, DU) changed from 2005 to 2017 over East Asia. The uncertainties associated with the data are larger for smaller sources and vice versa. Therefore, some SO2 signals in remote areas may simply be data artifacts. Data courtesy of Chris McLinden, Environment Canada. Animation: NASA.

Visit the Nitrogen Dioxide tab for more information on trends in this pollutant.


Some Important Milestones for Observing Particulates from Space

  • May 1999: Launch of NASA’s EOS Terra Satellite with MODIS and MISR provided first state-of-art global maps of aerosol (i.e. PM) distribution. An important steps in monitoring global PM2.5
  • May 2002: Launch of NASA’s EOS Aqua satellite with MODIS and AIRS. Enabling morning and afternoon picture of aerosols from identical sensor.
  • July  2004: Launch of Aura with OMI – improved spatial resolution of absorbing aerosols measurements
  • April 2006: Launch of CALIPSO – Vertical distribution of aerosols, and important parameter in estimation of surface PM2.5 from columnar aerosol optical depth (AOD) values.
  • October 2011: VIIRS aboard Suomi-NPP, joint NOAA and NASA mission, improved spatial resolution and coverage, continuing MODIS aerosol observations
  • October 2014: AHI aboard Himawari-8, geostationary, JAXA mission, first of its kind providing very high frequency (30 sec to 10 min) aerosol measurements in Asia and Pacific. Important in monitoring real time transport of smoke from fires, volcanic plumes and dust storms at local, regional and global scales.
  • November 2016: AHI aboard Himawari-9, geostationary JAXA mission, first of its kind providing very high frequency (30 sec to 10 min) aerosol measurements in Asia and Pacific. Important in monitoring real time transport of smoke from fires, volcanic plumes and dust storms at local, regional and global scales.
  • November 2016: ABI aboard GOES-R, geostationary NOAA/NASA mission, first of its kind providing very high frequency (30 sec to 15 min) aerosol measurements over Americas. Important in monitoring real time transport of smoke from fires, volcanic plumes and dust storms at local, regional and global scales. Watching eastern side of America and Atlantic.
  • November 2017: JPSS1/NOAA 20 – Continuation of NPP-VIIRS records, a continuity mission through 2038 with JPSS2 and JPSS3 to be launched.
  • March 2018: ABI aboard GOES-S, geostationary NOAA/NASA mission, identical to GOES-R, providing very high frequency (30 sec to 15 min) aerosol measurements over Americas. Important in monitoring real time transport of smoke from fires, volcanic plumes and dust storms at local, regional and global scales. Watching western side of America and Pacific.
  • MAIA, TEMPO, GEMS, 3MI, FCI, Sentinal-4 etc. to be launched in next 5 years.

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