Bronte Wells
Satellite data has become an invaluable tool for measuring and tracking atmospheric pollutants, filling in spatial gaps where ground monitoring is lacking. Satellites can observe the entire atmosphere, and by measuring the amount of light that reaches the surface of the Earth and how much is reflected off aerosols, they can determine the concentration of particles (aerosols) in the atmosphere. This data can be used to estimate emissions, track pollutant plumes, support air quality forecasting, and identify air pollution hotspots. Remote sensing instruments can be deployed not only on satellites but also on the ground and in aircraft, and these measurements are consistent across time and space. NASA, for example, has developed methods to track nitrogen dioxide concentrations, tropospheric ozone concentrations, and urban particulate matter mortality. However, a degree of technical skill is required to access, process, and interpret observational data, and ground measurements are still needed for ground-truthing.
| Characteristics | Values |
|---|---|
| How it works | Satellites measure the concentration of particles (aerosols) in the atmosphere by observing how much light reaches the Earth's surface and how much is reflected off the aerosols. |
| Use cases | Estimating emissions, tracking pollutant plumes, supporting air quality forecasting, providing evidence for "exceptional event" declarations, monitoring long-term trends, evaluating air quality model output, tracking wildfires, tracking dust storms, tracking pollen counts, tracking urban green space, tracking nitrogen dioxide concentrations, tracking asthma burdens, tracking tropospheric ozone concentrations, tracking urban particulate matter mortality, tracking climate change indicators, tracking air quality indicators |
| Advantages | Fills in spatial gaps of ground monitoring resources, provides consistent measurements across time and space, provides high spatial resolution everywhere on Earth |
| Disadvantages | Requires a degree of technical skill to access, process, and interpret data, ground measurements are still needed for ground truthing |
| Tools | ArcGIS Pro, Google Earth, NASA's Air Quality site, NASA's Giovanni tool, Terra Satellite Earth Observing System, MODIS Rapid Response System |
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What You'll Learn
Utilise NASA's Moderate Resolution Imaging Spectroradiometer (MODIS) Aerosol Optical Depth (AOD) data
NASA's Moderate Resolution Imaging Spectroradiometer (MODIS) is a satellite-based instrument that has been extensively used in climate change and air quality research. It provides valuable data on Aerosol Optical Depth (AOD), which is a measure of light extinction (scattering and absorption) by atmospheric aerosols. By observing how much light reaches the Earth's surface and how much is reflected off the aerosols, satellites can measure the concentration of particles (aerosols) in the atmosphere.
MODIS offers AOD data at varying spatial resolutions (1, 3, and 10 km) and Level 3 data at 1 degree. The 10 km resolution data is considered more accurate than the 3 km data due to the increased opportunity to discard marginal pixels. The 3 km data, however, is still valuable for air pollution studies at small to medium scales.
To utilise MODIS AOD data, you can follow these steps:
- Access the MODIS Rapid Response System and select your area of interest. This system provides near real-time images, typically within 4-6 hours of acquisition.
- Compare the satellite images with ground measurements using Google Earth. EPA ground measurements are overlaid on MODIS satellite images, allowing you to observe how areas with poor air quality correspond with haze in the satellite image.
- Note any pollution entering your region from elsewhere, as satellite images can help identify long-range transport of pollutants.
- For more detailed analysis, you can utilise the MODIS Collection 6.1 3 km resolution AOD product, which offers higher spatial resolution but may require more advanced computing resources and skills to process and analyse the larger data volumes.
By utilising NASA's MODIS AOD data, researchers and organisations can gain valuable insights into air quality and pollution levels, supporting decision-making and environmental management activities.
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Compare ground measurements to satellite measurements
Satellite data is becoming more widely used for estimating emissions, tracking pollutant plumes, supporting air quality forecasting, and monitoring regional long-term trends. However, to understand the pollution levels on the ground, it is necessary to compare ground measurements to satellite measurements.
Satellite images are useful for observing the long-range transport of pollutants from other regions, but they do not provide information about ground-level pollution. The pollutants visible in a satellite image could be kilometres above the Earth's surface. To determine if the pollution in the satellite image is on the ground, you need to compare ground measurements to the satellite measurements. This can be done using Google Earth, which overlays EPA ground measurements on a MODIS satellite image.
To make this comparison, first, locate the most recent MODIS image of your area of interest. Then, note the time and date the data was updated and whether it corresponds to the date the satellite image was taken. Next, observe whether areas with poor air quality (indicated by yellow, orange, or red dots) correspond with haze in the satellite image. If there is a match, you can attribute the pollution to the source identified in the satellite image.
In addition to visual observations, quantitative comparisons can be made between ground and satellite measurements. For example, NASA's Moderate Resolution Imaging Spectroradiometer (MODIS) Aerosol Optical Depth (AOD) data can be used to estimate ambient PM2.5 concentrations. This AOD measurement can be compared to ground measurements from a sun photometer. Furthermore, remote sensing instruments can be deployed on the ground to scan for pollutants, providing another means of comparison to satellite measurements.
Comparing ground and satellite measurements is a valuable approach for validating and interpreting the data. For instance, a study in Dwarka, Knowledge Park III, Sector 125, and Vivek Vihar found that the ground-based instrumental concentration of PM2.5 was greater than that of satellite observations, while the mean concentration of satellite-based monitoring was higher for SO2 and NO2. Such comparisons can provide insights into the observable behaviour of pollutants, their variation with meteorological parameters, and the health hazards associated with exposure.
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Observe how much light reaches the Earth's surface
To observe how much light reaches the Earth's surface, it is important to understand the different types of light that interact with Earth. Sunlight is scattered and filtered through the Earth's atmosphere as daylight when the Sun is above the horizon. When direct solar radiation is unobstructed by clouds, it is experienced as sunshine, a combination of bright light and radiant heat. The Sun provides the Earth with most of its energy, and about 71% of the sunlight that reaches the Earth is absorbed by its surface and atmosphere. The remaining 29% of the incoming solar radiation is reflected by the Earth, and this is known as its albedo. Snow and ice, airborne particles, and certain gases have high albedos and reflect different amounts of sunlight back into space. Clouds can also influence the amount of sunlight that reaches the Earth's surface, with low, thick clouds blocking sunlight and high, thin clouds contributing to the greenhouse effect.
The light that reaches the Earth's surface is composed of various wavelengths, including visible light, near-infrared rays, and ultraviolet rays. The Earth's atmosphere plays a crucial role in filtering out certain types of light. For example, high-energy X-rays and gamma rays are blocked by the atmosphere, preventing them from reaching the Earth's surface and causing harm to organisms and cells. Similarly, long-wavelength radio waves and most ultraviolet rays are also unable to penetrate the atmosphere.
The composition of the Earth's surface and atmosphere affects how much light is absorbed or reflected. Earth's surfaces are generally better at absorbing solar radiation than air, particularly darker surfaces. This can be observed when wearing a black jacket on a cold, sunny day—the black jacket absorbs more radiation and makes you feel warmer compared to a white or light-colored jacket. The development and spread of urban areas, especially with the use of dark-coloured materials like asphalt, can significantly increase the absorptivity of the surface, leading to the creation of urban heat islands.
To quantify the amount of light reaching the Earth's surface, researchers employ various instruments and calculations. The intensity of sunlight can be measured using tools such as a sunshine recorder, pyranometer, or pyrheliometer. To calculate the precise amount of sunlight reaching the ground, factors such as the eccentricity of Earth's elliptic orbit and the attenuation by the Earth's atmosphere must be taken into account.
By studying satellite data, scientists can gain insights into the concentration of pollutants in the atmosphere by observing how much light reaches the Earth's surface and how much is reflected or scattered by particles in the atmosphere. This technique, known as satellite remote sensing, provides valuable information about air quality and helps address challenges in environmental management.
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Use satellite data to identify air pollution hotspots
Satellite data has become an increasingly valuable tool for identifying air pollution hotspots. Satellites can measure the concentration of particles (aerosols) in the atmosphere by observing how much light reaches the Earth's surface and how much is reflected off these particles. This is known as Aerosol Optical Depth (AOD), which is a measure of light extinction (scattering and absorption) by atmospheric aerosols. AOD can be used to predict ambient PM2.5 levels, which are tiny airborne particles that have been linked to adverse health effects due to their ability to penetrate deep into the lungs.
Satellite remote sensing provides data on air quality, filling in spatial gaps where ground monitoring resources are unavailable. It can indicate criteria air pollutants such as PM2.5 and NO2, as well as greenhouse gases like CH4 and CO2. These data can be particularly useful for identifying air pollution hotspots, tracking pollutant plumes, and supporting air quality forecasting. For example, researchers at Duke University have developed a method using machine learning, satellite imagery, and weather data to autonomously identify hotspots of heavy air pollution at a city block level.
To identify air pollution hotspots using satellite data, one can utilise tools such as NASA's Moderate Resolution Imaging Spectroradiometer (MODIS) and Google Earth. MODIS provides near real-time images of your area of interest, allowing you to observe pollution in the satellite image, such as haze, dust, or smoke. By comparing these observations with ground measurements, you can determine if the pollution is near the surface. Google Earth overlays EPA ground measurements on MODIS satellite images, enabling you to attribute pollution to specific sources.
Additionally, the Multi-angle Imaging SpectroRadiometer (MISR) provides high-resolution AOD data, enhancing the understanding of PM2.5 spatial distribution. This data can be used to estimate PM2.5 species concentrations, including sulfate, nitrate, organic carbon, and elemental carbon. By combining these estimates with weather data and satellite images, algorithms can be trained to automatically identify air pollution hotspots with increased accuracy.
Overall, satellite data offers a powerful means to identify air pollution hotspots, providing valuable insights for environmental management, policy decisions, and addressing health disparities related to air quality.
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Track indicators of global air pollution
Tracking indicators of global air pollution is crucial for understanding the impact of air pollution on human health and the environment. Satellite data plays a vital role in monitoring and addressing air quality issues by providing valuable information on pollutant concentrations. Here are some ways to track indicators of global air pollution using satellite data:
Utilize Satellite Remote Sensing
Satellite remote sensing offers a comprehensive view of air quality by filling in data gaps from ground monitoring resources. It provides information on criteria air pollutants, such as PM2.5 and NO2, and greenhouse gases like CH4 and CO2. By analyzing these data, scientists can identify air pollution hotspots, study health effects, and track air pollution trends over time.
Analyze Aerosol Optical Depth (AOD)
AOD measures the scattering and absorption of light by atmospheric aerosols, which are tiny particles or droplets suspended in the air. AOD data, combined with land use regression, helps estimate PM2.5 concentrations. This information strengthens our understanding of the spatial distribution of pollutants and their sources, enabling the development of effective mitigation strategies.
Leverage MODIS Satellite Imagery
The MODIS Rapid Response System provides timely satellite images, often within 4-6 hours of acquisition. By accessing these images through platforms like Google Earth, observers can identify areas of haze or pollution. Comparing ground measurements with satellite observations helps determine if the pollution is near the surface and identify potential pollution sources.
Monitor Real-time Air Quality Index (AQI)
The World Air Quality Index project offers real-time air pollution data from stations worldwide. These stations primarily monitor PM2.5 and PM10 levels, providing hourly readings that contribute to the AQI. By tracking this data, organizations can identify regions exceeding air quality guidelines and implement necessary measures to improve air quality.
Assess Health and Environmental Impacts
Organizations like the World Health Organization (WHO) monitor the exposure levels and health impacts of air pollution at global, regional, and national levels. They assess the burden of diseases associated with air pollution, including respiratory illnesses, heart disease, stroke, and cancer. These estimates are crucial for official reporting, policy formulation, and achieving sustainable development goals.
By combining satellite data with ground measurements and health impact assessments, we can more effectively track indicators of global air pollution, identify areas of concern, and develop strategies to mitigate the adverse effects of air pollution on human health and the environment.
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Frequently asked questions
Satellite remote sensing is a method of observing the Earth from space to gather information that can be used to analyse and monitor changes on the planet's surface, such as air pollution.
Satellites can measure the concentration of particles (aerosols) in the atmosphere by observing how much light reaches the surface of the Earth and how much is reflected off the aerosols. This is known as Aerosol Optical Depth (AOD). AOD is a measure of light extinction (scattering + absorption) by atmospheric aerosols, thus enabling AOD to be a predictor of ambient PM2.5.
Satellite data can be used to track criteria air pollutants such as PM2.5 and NO2, and greenhouse gases such as CH4 and CO2. Other examples include nitrogen dioxide concentrations, tropospheric ozone concentrations, and urban particulate matter.
Satellite remote sensing provides consistent measurements across time and space, whereas ground monitoring protocols and instruments change over time and are not harmonised across countries. Satellites can also provide data for areas without ground monitors.
Satellite data on pollutant concentration can be visualised using tools such as Google Earth, ArcGIS Pro, and NASA's Giovanni. These tools allow users to explore and analyse pollution data in the form of maps, animations, seasonal maps, scatter plots, or time series.
