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Health and Air Quality Data Pathfinder

Data pathfinders are pathways to the most commonly-used datasets within NASA’s Earth science collections. Data pathfinders have been developed to aid new data users in discovering data or data visualizations. While there are numerous datasets for any air quality-related measurement, these pathfinders provide direct links to data that are most commonly used by natural resource managers, city and regional planners, air quality managers, and various federal agencies to aid in decision making.

Sources of air pollution - EPA
Sources of air pollution - EPA
Every year, around 7 million deaths occur due to exposure from air pollution and 9 out of 10 people worldwide breathe polluted air (World Health Organization, 2018). Pollution is due to both anthropogenic and natural events. It’s critical for air quality managers and public health researchers to monitor air pollutants locally, regionally, and globally to further determine the risk for health conditions or diseases that are exacerbated by poor air quality. A combination of ground- and satellite-based tools provides a unique view of the globe to better understand the impacts of air pollution events. These measurements help scientists, researchers, and decision makers in forecasting events and assessing conditions in near real-time to make timely decisions. NASA, in collaboration with other organizations, has a series of instruments that provide information for understanding a number of phenomena associated with air quality and public health. NASA’s Earth science data products are validated, meaning the accuracy has been assessed over a widely distributed set of locations and time periods via several ground-truth and validation efforts.

Applications of remotely sensed data for air quality and public health

There are three main ways to use satellite data for policy applications: for qualitative applications, for quantitative applications, and for more advanced analysis (from NASA Health and Air Quality Applied Sciences Team (HAQAST)).

  1. For qualitative understanding, satellite images allow air quality managers to see and communicate spatial patterns, atmospheric transport, and trends in air pollution. Visualizations from satellite data depict transport of wildfire smoke and dust plumes across regions, continents, and even oceans. Maps of NO2 across the U.S. show clear patterns over cities and suburbs, even major interstate highways and railroads.
  2. Satellite data can also be used to quantify change and relative abundance. The measurement units from satellite instruments typically reflect column densities (e.g., molecules/cm2) or optical properties (e.g., the unitless AOD metric, which varies from 0 to 1). These units do not compare directly with atmospheric composition unit (e.g., molecules/cm3, ug/m3, or mixing ratio). However, the percentage change or the ratio of two related species provides a metric that may be directly compared.
  3. Beyond qualitative and simple quantitative calculations, satellite data support a wide range of advanced analysis, especially when combined with complementary data sources. Satellite data are well suited to evaluate photochemical grid models and to support the derivation of ground-level pollution estimates in unmonitored areas. Particulate matter estimates derived from AOD products retrieved from multiple satellite instruments are used in public health studies. These types of advanced analysis measures usually require that users download satellite data and customize analysis to suit applications.

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Data

Monitoring air quality provides a means to visualize trends, forecast events or movement of pollutants, and respond to events. Aerosol Optical Depth/Thickness (AOD/AOT) provides a measurement of the quantity of light removed by absorption and scattering within a column. Absorption and scattering is caused by the composition (each element has a unique spectral fingerprint) and color of the particles (light reflects, dark absorbs). For more information on this process, check out the Earth Observatory article, Aerosols and Incoming Sunlight. AOD is not the equivalent of PM2.5, which is the measure of the mass of particles in a specific size range near surface, but with additional processing AOD provides a means of acquiring PM2.5, using specific conversion techniques. Many NASA data products provide information on primary (directly emitted) and secondary pollutants (formed by chemical reactions), some of which can serve as precursors to other types of air pollution. When available, NASA’s Land, Atmosphere Near real-time Capability for EOS (LANCE) provides data to the public within 3 hours of satellite overpass, which allows for almost near real-time (NRT) monitoring and decision making, specifically regarding aerosol and dust indices and pollutant transport. When coupled with public health information, the air quality data can provide a valuable resource to forecasting and monitoring exposure and risk.

Benefits and Limitations

Benefits and Limitations

The United States is fortunate to have numerous ground-based measurements for assessing atmospheric particulate matter and certain specific types of pollution, like ozone or NO2. However, this is not the case in other countries and in more rural areas of the United States. Satellite data provides a more regional to global spatial coverage; some of the information is available in near real-time allowing for more efficient response. With satellite data, assessments can be made regarding the aerosol optical depth, which can then be correlated to PM2.5, aerosol types and aerosol transport. Incorporating satellite data with in-situ data into modeling programs makes for a more robust and integrated forecasting system. While satellite data cannot alone be used to enforce air quality regulations or standards, this integrated approach can. Satellite data also provide enough information to determine exposure and risk categories.

While the data provides a more global view, it’s important to note that the satellites are measuring the vertical column of air above the surface and not at ground level (where the ground-based sensors are measuring). As such there may be some discrepancies between the two. In addition, many of the polar-orbiting satellites only pass over the same spot every 1-2 days or sometimes every 16+ days, as they are providing near-global coverage. Geostationary satellites, however, which rotate with the Earth, can monitor the fixed location as they rotate every 15-30 minutes. Finding the right instrument or understanding the modeling processes for your area of interest is key.

Aerosol Optical Depth

Aerosol Optical Depth

top of atm
top at atm
Aerosol Optical Depth (AOD) is a column-integrated value of aerosols in the atmosphere obtained by measuring the scattering and absorption of solar energy from the top of the atmosphere to the surface. The non-aerosol signal of surface reflectance needs to be separated from the aerosol signal to accurately obtain an aerosol optical depth. This is challenging because the satellite instrument cannot penetrate cloud cover and highly reflective surfaces, such as ice or snow, producing misrepresentations of the data. As such, scientists have developed algorithms for the Moderate Resolution Imaging Spectroradiometer (MODIS) data to help with these effects, dark target and deep blue. For more information on these algorithms see:https://darktarget.gsfc.nasa.gov and https://deepblue.gsfc.nasa.gov/. In the latest data set collection, these two have been merged, using the highest quality for each. While it does provide the easiest use of global coverage, there are some risks (see the websites above for more information). The Visible Infrared Imaging Radiometer Suite (VIIRS) also collects AOD data at a much finer spatial resolution. VIIRS uses the Deep Blue (DB) algorithm over land and the Satellite Ocean Aerosol Retrieval (SOAR) algorithm over water to determine atmospheric aerosol loading for daytime cloud-free, snow-free scenes. With all of the VIIRS data, downloading a file will provide the data with just the land algorithm, just the ocean algorithm, and the merged algorithm. As with all remotely sensed data, make sure you are choosing the best product for your area.

  • Science quality, or higher-level “standard” data products can be accessed via Earthdata Search. Data are in HDF (Hierarchical Data Format) or NetCDF (Network Common Data Form) format and can be opened using panoply.

  • Data products can be visualized as a time-averaged map, an animation, seasonal maps, scatter plots, and time series through an online interactive tool, Giovanni. For more information on choosing a type of plot, see the Giovanni User Manual.
    • OMI AOD in Giovanni
      The Ozone Monitoring Instrument (OMI) on Aura has a coarser spatial resolution than MODIS and VIIRS but provides data at individual wavelengths from the ultraviolet (UV) to the visible. Within Giovanni, you can plot daily data at these individual wavelengths. This is important because pollutants have different spectral signatures; for example, a wavelength range around 400 nm can be used to detect elevated layers of absorbing aerosols such as biomass burning and desert dust plumes. The two AOD products provided through Giovanni use two different algorithms—OMI Multi-wavelength (OMAERO) and OMI UV (OMAERUV). OMI Multi-wavelength (OMAERO) is based on the multi-wavelength algorithm and uses up to 20 wavelength bands between 331 nm and 500 nm. This algorithm uses reflectances for a wide variety of microphysical aerosol models representative of desert dust, biomass burning, volcanic, and weakly absorbing aerosol types. OMI UV (OMAERUV) uses the near-UV algorithm, which is capable of retrieving aerosol properties over a wider variety of land surfaces than is possible using measurements only in the visible or near-IR, because the reflectance of all terrestrial surfaces (not covered with snow) is small in the UV.
    • MODIS AOD in Giovanni
      Provides data products with both algorithms as well as the combined algorithm at daily and monthly intervals.
  • Near real-time (NRT) data can be accessed via Worldview:
    • MODIS Aqua/Terra Combined Algorithm AOD
      The merged Dark Target/Deep Blue Aerosol Optical Depth layer provides a more global, synoptic view of aerosol optical depth over land and ocean. It is available from 2000 to the present.
    • OMI AOD Multi-wavelength and UV
      The multi-wavelength layer and the UV absorbing layer displays the degree to which airborne particles (aerosols) prevent the transmission of light through the process of absorption (attenuation), and the UV extinction layer indicates the level at which particles in the air (aerosols) prevent light (extinction of light) from traveling through the atmosphere. Toggling between these three can provide more distinction on the types of aerosols present.

AOD to PM2.5

AOD to PM2.5

As mentioned above, AOD is the quantity of light removed from a beam by scattering or absorbing during its path through a medium and is a unitless measure. PM 2.5, on the other hand, is a measure of the mass of particles in a specific size range near the surface. So there are a few differences:

  • AOD is an optical measurement, PM2.5 a mass measurement.
  • AOD is an integrated column measurement from the top of the atmosphere to the surface, PM2.5 a ground measurement.
  • AOD is an area-averaged measurement, PM2.5 a point measurement.

Because the two measurements are so different, it may seem that there is no correlation. They do correlate and there are several different techniques to convert from AOD to PM2.5. It is important to note that while there is a relationship between AOD and PM2.5, there are other factors which can affect AOD, like humidity, the vertical distribution of aerosols, and the shape of the particles. For example, an increase in humidity will increase the size of particles and therefore increase the AOD even though the PM2.5 level will be the same.

The different techniques are a two-variable method, a multivariate method using neural networks, and combining satellite data, in-situ data, and models. The latter approach is the most difficult but generally preferred. For more information about the different techniques and an exercise in doing this conversion, view the course materials from the Applied Remote Sensing Training (ARSET) course, NASA Earth Observations, Data and Tools for Air Quality Applications.

aod to pm2.5Aerosol Robotic Network (AERONET). The Environmental Protection Agency’s ground-based PM and Ozone combined Air Quality Index (AQI) can be accessed at AirNow. AirNow International is an international program for AQI, with information provided from partnering organizations.

For trends in PM2.5, there are several resources that utilize both ground-based and remotely sensed data.

Trace Gases

Trace Gases

Nitrogen Dioxide

Nitrogen Dioxide (NO2) is a pollutant, the primary sources being the burning of fossil fuels, automobiles, and industry. Once in the air, it can aggravate respiratory conditions in humans, especially those with asthma, leading to an increase of symptoms, hospital admissions, and emergency visits. Long-term exposure can lead to the development of asthma and potentially increase susceptibility to respiratory infections. NO2 reacts with other chemicals in the atmosphere, forming particulate matter and ozone, producing haze and even acid rain, and contributing to nitrogen pollution in coastal waters. NASA Goddard’s Air Quality site provides more information on NO2, as well as trend maps and pre-made images of NO2 over cities and power plants.

  • Science quality, or higher-level “standard” data products can be accessed via the Earthdata Search client:
    • OMI NO2 data from Earthdata Search
      The Ozone Monitoring Instrument (OMI), aboard the Aura spacecraft, provides daily gridded and non-gridded products at 13x24 km resolution; data are in HE5 format (Hierarchical Data Format Release 5) and can be opened using Panoply. A tutorial on using OMI NO2 data is available as a PDF
    • TROPOMI NO2 data from Earthdata Search
      The TROPOspheric Monitoring Instrument (TROPOMI) aboard Sentinel 5, is a European Space Agency Mission, The ESA TROPOMI NO2 provides additional information on this level 2 data product. It is important to note that, because of the very small numbers in tropospheric vertical column of nitrogen dioxide, you will need to change the scaling factor in Panoply (see image from June 2018 to right). Data are NetCDF and can be opened using Panoply.tropomi
    • Data products can be visualized as a time-averaged map, an animation, seasonal maps, scatter plots, time series, and through an online interactive tool, Giovanni. For more information on choosing a type of plot, see the Giovanni User Manual.
    • Near real-time (NRT) data can be accessed via Worldview:
    • Trends over time

Sulfur Dioxide

Sulfur Dioxide (SO2) is a pollutant of great concern; the primary sources are the burning of fossil fuels by power plants and industry. Volcanic emissions also contribute sulfur dioxide, but in relatively smaller quantities. As with nitrogen dioxide, it can aggravate respiratory conditions in humans, especially those with asthma, leading to an increase of symptoms, hospital admissions, and emergency visits. In areas where there are high levels, sulfur oxides can react with other components creating small particles which contribute to overall particulate matter, which can be ingested by humans, affecting their health, and creates lower visibility in areas where sulfur dioxide is high. SO2 can also lead to acid rain.

SO2
Sulfur Dioxide

  • Science quality, or higher-level “standard” data products can be accessed via the Earthdata Search client:
    • OMI SO2 Data from Earthdata Search
      Ozone Monitoring Instrument (OMI), aboard the Aura spacecraft, provides daily total column data at a resolution of 13x24 km; data are in HE5 format (Hierarchical Data Format Release 5) and can be opened using Panoply.
    • OMPS SO2 Data from Earthdata Search
      SO2 Total and Tropospheric Column data from the Ozone Mapping and Profiling Suite (OMPS) Nadir-Mapper (NM) sensor is on the Suomi-NPP satellite; data are in HE5 format and can be opened using Panoply. Note that the data are at the various atmospheric levels (planetary boundary layer, stratospheric layer, and tropospheric layers).
    • TROPOMI SO2 data from Earthdata Search
      TROPOspheric Monitoring Instrument (TROPOMI) aboard Sentinel 5. TROPOMI is a European Space Agency Mission and the ESA TROPOMI SO2 provides additional information on this level 2 data product. As with the nitrogen oxide data above, you will need to adjust the scaling factor. Data are NetCDF and can be opened using Panoply.
  • Data products can be visualized as a time-averaged map, an animation, seasonal maps, scatter plots, and time series through an online interactive tool, Giovanni. For more information on choosing a type of plot, see the Giovanni User Manual.
  • Carbon Monoxide

    Carbon Monoxide (CO) is a harmful pollutant that is released when something is burned, such as in the combustion of fossil fuels, the primary source, or biomass burning. Outdoor levels are rarely high enough to cause issues; when they do reach dangerous levels, however, they can be of concern to people with certain types of heart disease.

    • Science quality, or higher-level “standard” data products can be accessed via the Earthdata Search client:
      • AIRS CO data from Earthdata Search
        Atmospheric Infrared Sounder (AIRS) measures abundances of trace components in the atmosphere including carbon monoxide. Data are available daily (AIRS3STD), over 8 days (AIRS3ST8), or monthly (AIRS3STM). The instrument measures the amount of CO in the total vertical column profile of the atmosphere (from Earth’s surface to top-of-atmosphere). Data are in HDF (Hierarchical Data Format), and can be opened using Panoply.
      • MOPITT CO data from Earthdata Search
        Measurements of Pollution in the Troposphere (MOPITT) measures the amount of carbon monoxide (CO) present in the total vertical column of the lower atmosphere (troposphere) and is measured in mole per square centimeter (mol/cm2). Data are available daily or monthly. Data are acquired using the thermal and near-infrared channels. Data are in HE5 format, and can be opened using panoply.
      • TROPOMI CO data from Earthdata Search
        TROPOspheric Monitoring Instrument (TROPOMI) aboard Sentinel 5. TROPOMI is a European Space Agency Mission and the ESA TROPOMI CO provides additional information on this level 2 data product. As with the nitrogen oxide data above, you will need to adjust the scaling factor. Data are NetCDF and can be opened using Panoply.
    • Data products can be visualized as a time-averaged map, an animation, seasonal maps, scatter plots, time series, and through an online interactive tool, Giovanni. For more information about choosing a type of plot, see the Giovanni User Manual

    Ground Level Ozone

    Ozone (O3) can be either good or bad, depending on where it is found in the atmosphere. In the stratosphere, O3 protects humans, plants, and animals from harmful UV radiation. In the troposphere or closer to the ground level, however, O3 serves as a potent greenhouse gas and can aggravate existing health problems in humans, especially those with respiratory illnesses. O3 is not emitted directly into the atmosphere but instead forms from the chemical reaction between nitrogen oxides and volatile organic compounds, emitted primarily from cars, power plants, and other industrial facilities; reactions take place in the presence of sunlight. Because of the need for sunlight, unhealthy levels are most often reached on very sunny days and in urban environments.

    • Science quality, or higher-level “standard” data products can be accessed via the Earthdata Search client:
      • OMI O3 data from Earthdata Search
        Ozone Monitoring Instrument (OMI), aboard the Aura spacecraft, provide daily total column data; data are in HE5 (Hierarchical Data Format Release 5) format and can be opened using Panoply.
      • AIRS O3 data from Earthdata Search
        Atmospheric Infrared Sounder (AIRS) measures abundances of trace components in the atmosphere including ozone. Data are available daily (AIRS3STD), over 8 days (AIRS3ST8), or monthly (AIRS3STM). The instrument measures the amount of O3 in the total vertical column profile of the atmosphere (from Earth’s surface to top-of-atmosphere). Data are in HDF ormat and can be opened using Panoply.
      • TROPOMI O3 data from Earthdata Search
        TROPOspheric Monitoring Instrument (TROPOMI) aboard Sentinel 5. TROPOMI is a European Space Agency Mission and the ESA TROPOMI O3 provides additional information on this level 2 data product. Data are in NetCDF format and can be opened using Panoply.
    • Data products can be visualized as a time-averaged map, an animation, seasonal maps, scatter plots, and time series through an online interactive tool, Giovanni. For more information on choosing a type of plot, see the Giovanni User Manual.
    • Near real-time (NRT) data can be accessed via Worldview:

    Pollutant Transport

    Pollutant Transport

    Aerosol Index

    Aerosol Index (AI) is a measurement related to Aerosol Optical Depth and indicates the presence of an increased amount of aerosols in the atmosphere. The main aerosol types that cause signals detected in this value are desert dust, significant fire events, biomass burning, and volcanic ash plumes. The lower the AI, the clearer the sky.transport of aerosols

    • Science quality, or higher-level “standard” data products, can be accessed via the Earthdata Search client.
      • OMI AI from Earthdata Search
        Ozone Monitoring Instrument (OMI), aboard the Aura spacecraft, provides an Ultraviolet Aerosol Index; data are in HE5 (Hierarchical Data Format Release 5) format, and can be opened using Panoply. Note that when opening the data in Panoply, there are a number of different data fields from which to choose. Select UVAerosolIndex.
      • TROPOMI AI data from Earthdata Search
        TROPOspheric Monitoring Instrument (TROPOMI) aboard Sentinel 5. TROPOMI is a European Space Agency Mission and the ESA TROPOMI AI provides additional information on this level 2 data product. Data are NetCDF format and can be opened using Panoply.
    • Data products can be visualized as a time-averaged map, an animation, seasonal maps, scatter plots, and time series through an online interactive tool, Giovanni. For more information on choosing a type of plot, see the Giovanni User Manual.
    • Near real-time (NRT) data can be accessed via Worldview:

    Dust Score

    A Dust Score indicates the level of atmospheric aerosols in the Earth’s atmosphere over the ocean. The numerical scale is a qualitative representation of the presence of dust in the atmosphere, an indication of where large dust storms may form and the areas that may be affected.

    • Near real-time (NRT) data can be accessed via Worldview:
      • AIRS Dust Score in Worldview
        Measurement from the Atmospheric Infrared Sounder (AIRS) Infrared quality assurance subset; the imagery resolution is 2 km.

    Surface Reflectance

    In comparison with the MODIS Corrected Reflectance product, the MODIS Land Atmospherically Corrected Surface Reflectance product (MOD09) is a more complete atmospheric correction algorithm that includes aerosol correction and is designed to derive land surface properties.

    • Near real-time (NRT) data can be accessed via Worldview:
      • MODIS Land Surface Reflectance Data in Worldview
        These images are called true-color or natural color because this combination of wavelengths is similar to what the human eye would see. The images are natural-looking images of land surface, oceanic, and atmospheric features. Some band combinations “highlight” certain types of features better than others. The information for this dataset provides more details.


    Public Health

    Public Health

    Air pollution is a serious health issue all over the world. According to the World Health Organization, there are millions of deaths every year as a result of exposure to outdoor air pollution. In addition, 91% of the world’s population lives in places where air quality exceeds WHO guideline limits. Breathing air pollution, especially particulate matter, increases the risks of numerous illnesses, specifically respiratory, including pulmonary disease, respiratory infections, and lung cancer. It can also cause heart disease, heart attacks, and strokes. There are numerous health sites that provide information regarding public health as it relates to air pollution: Air Quality Observations from Space explains how NASA is monitoring air quality and the associated health impacts from space. WHO Ambient Air Pollution Health Impacts describes the pollutants and the health risks associated with them as well as statistical information and interventions.

    For an overview of environmental parameters available from NASA Earth Science useful for monitoring and predicting health for decision support or for more information on tools available for evaluating the relationship between environmental conditions and health outcomes, view the course materials from the Applied Remote Sensing Training (ARSET) courses, Fundamentals of Satellite Remote Sensing for Health Monitoring and Methods in Using NASA Remote Sensing for Health Applications.

    Other NASA Assets of Interest

    Other NASA Assets of Interest

    Applied Remote Sensing Training program has numerous air quality webinars. For example, there are ones that include R and Python code for accessing and extracting data, deriving annual PM2.5, and applications for health monitoring.

    Multi-Angle Imager for Aerosols (MAIA) investigation will seek to understand how different types of air pollution affect human health. MAIA is set to launch in 2022.

    Tropospheric Emissions: Monitoring of Pollution (TEMPO) will be a geostationary mission and will measure lower tropospheric ozone, formaldehyde and nitrogen dioxide as the primary pollutant gases. TEMPO additionally measures sulfur dioxide, glyoxal, water vapor, halogen oxides, aerosols, clouds, ultraviolet-B radiation, and foliage properties. The goal is to launch in 2019

    Air Quality Citizen Science is a citizen science program funded by the Earth Science Data Systems Program to add value to AOD measurements obtained by NASA's Aqua and Terra satellites. Citizen scientists are helping create a network of high quality, "low-cost" sensors in Los Angeles, California; Raleigh, North Carolina; and Delhi, India.

    Citizen-Enabled Aerosol Measurements for Satellites (CEAMS) is another citizen science program funded by the Earth Science Data Systems Program to improve our understanding of how aerosols affect local air quality. Citizen scientists take backyard air quality measurements using sun photometers.

    Short-term Prediction Research and Transition Center (SPoRT) is a NASA project to transition unique observations and research capabilities to the operational weather community to improve short-term forecasts on a regional scale. SPoRT provides access to numerous near real-time datasets that provide information on dust transport. Specifically the GOES-R satellite’s Advanced Baseline Imager has a dust RGB product. The SPoRT dust guide provides information on dust imagery and the interpretation.

    Other Resources

    Other Resources

    State of the Global Air provides an interactive tool to view and compare the latest air pollution and health data, create custom maps and graphs, and download the images and data.

    Tools for Data Access and Visualization

    Tools for Data Access and Visualization

    Earthdata Search provides a means of accessing all of NASA’s Earth science data across all distributed active archive centers. It provides the only means to access all data regardless of where the data are archived. Within Earthdata Search, you can subset using temporal and geographic constraints. Some data can be customized once the data of interest are selected; to do this, add the data of interest to your project and then click download all.

    ED search

    In the project area, you can select to customize your granule. You can reformat the data and output as HDF, NetCDF, ASCII, KML or a GeoTIFF. You can also choose from a variety of projection options. Lastly you can subset the data, obtaining only the bands that are needed.

    Customize data options
    Customize data options


    bands
    Band Subsetting
    HDF and NetCDF files can be viewed in Panoply, a cross-platform application that plots geo-referenced and other arrays. Panoply offers additional functionality, such as slicing and plotting arrays, combining arrays, and exporting plots and animations.

    Giovanni is an online (Web) environment for the display and analysis of geophysical parameters.


    Page Last Updated: Jul 3, 2019 at 11:12 AM EDT