Monitoring Air Pollution: Satellites' Eye View

Air pollution is a pressing issue that poses a range of adverse health effects. To effectively monitor and address this issue, satellites have become an essential tool. Satellites can provide critical observations for monitoring and forecasting air quality, helping to identify large areas of pollution caused by fires, dust or sand storms, volcanic eruptions, industrial sources, or the transport of man-made pollution.

Satellite remote sensing has been leveraged by organisations such as NASA, the European Space Agency, and the World Health Organization to track indicators of global air pollution and inform climate change research. This technology offers advantages such as high spatial resolution and consistent measurements over time and space, disrupting the traditional paradigm of relying solely on ground-based monitoring stations.

While satellite remote sensing has transformed our ability to track air pollution, there are limitations and challenges. Ground measurements are still necessary for calibration, and sustained collaboration between researchers and stakeholders is crucial. Additionally, technical expertise is required to effectively utilise satellite data for environmental and public health surveillance.

Despite these challenges, satellites remain a powerful tool for monitoring air pollution, with upcoming launches of dedicated pollution-observing satellites that will further enhance our capabilities.

The advantages of using satellites to monitor air pollution

Satellites are increasingly being used to monitor air pollution and can bring a range of advantages over traditional ground-based monitoring. Here are some of the key benefits:

• Global coverage: Satellites can provide a global view of air pollution, which is especially useful for tracking pollution in remote or inaccessible areas. This is in contrast to ground-based stations, which are often sparse or non-existent in many parts of the world.
• High spatial resolution: Satellites can provide detailed images and data with high spatial resolution, allowing for the detection of pollution sources and the monitoring of pollution levels over large areas.
• Consistency: Satellite measurements are consistent across time and space, providing a standardised way to monitor air pollution. This is in contrast to ground monitoring, which often uses different protocols and instruments that change over time and vary between countries.
• Identification of pollution sources: Satellites can help identify large areas of pollution caused by fires, dust or sand storms, volcanic eruptions, industrial sources, or the transport of pollution from other regions. This information can be critical for improving air quality and developing effective policies.
• Tracking long-term trends: Satellites can provide continuous observations over long periods, enabling the tracking of long-term trends in air pollution and climate change. This is valuable for understanding the impact of policies and interventions aimed at reducing pollution.
• Supporting air quality forecasting: Satellite data on pollutants, such as ozone, trace gases, and aerosols, are critical inputs for air quality forecasting. This helps governments and organisations make informed decisions to protect public health and implement effective environmental policies.
• Flexibility and responsiveness: Satellites can be used flexibly to respond to emerging needs and priorities. For example, they can be used to monitor the impact of specific events, such as volcanic eruptions, or to track the effects of policy changes, like transportation emission reduction policies.
• Supporting decision-making: Satellite data on air pollution can inform decision-making at various levels, from intergovernmental organisations to municipal governments. It helps identify areas in need of intervention, evaluate the effectiveness of policies, and guide the development of new strategies to mitigate air pollution and its health impacts.

The limitations of using satellites to monitor air pollution

While satellites have transformed our ability to monitor air pollution and climate change, there are some limitations to using them for this purpose.

One key limitation is the inherent difficulty in accessing, processing, and interpreting observational data from satellites. This requires a degree of technical skill that may not be available to all end-users, particularly those with limited resources. As a result, many air quality managers may not be taking full advantage of satellite data.

Another limitation is that satellites cannot always provide high-resolution images of smaller sources of air pollution, such as small industries or local roads. In addition, satellite data may not always be able to distinguish between different types of pollution, such as smoke, dust, or haze, as they often look similar in satellite images.

Furthermore, satellite data on air pollution needs to be combined with ground measurements to be truly effective. Ground measurements are necessary to "ground truth" or calibrate satellite-based estimates, and there may not be enough ground monitoring stations in some areas to provide accurate data.

Additionally, there are limitations in the algorithms used to derive surface conditions from atmospheric column measurements. These algorithms are constantly improving, but there is still room for advancement.

Finally, there is a challenge in sustaining collaboration between researchers and stakeholders. Scientists often lend their expertise on a volunteer basis, which can limit their ability to devote the necessary time and effort to transitioning scientific research into actionable knowledge for stakeholders.

Examples of satellites that monitor air pollution

Satellites are critical for monitoring and forecasting air quality. Here are some examples of satellites that monitor air pollution:

EUMETSAT Satellites

The European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT) provides data to the Copernicus Atmosphere Monitoring Service (CAMS), which is operated by the European Centre for Medium-Range Weather Forecasts (ECMWF). EUMETSAT's satellites monitor ozone, trace gases, aerosols, and ultraviolet data. They are crucial for monitoring and forecasting air quality, which is essential for the health of European citizens.

Meteosat and Metop Satellites

The geostationary Meteosat-9, -10, and 11 satellites monitor aerosols in the atmosphere, including volcanic ash, wildfires, and dust storms. They play a vital role in tracking the movement and dispersion of ash in European airspace in near real-time. Additionally, the Global Ozone Monitoring Experiment-2 (GOME-2) instrument on the Metop polar-orbiting satellites measures vertical profiles of ozone, nitrogen dioxide, and sulphur dioxide.

NASA Satellites

NASA satellites, such as Terra and Aqua, play a crucial role in tracking air pollution. Instruments like the Moderate Resolution Imaging Spectroradiometer (MODIS) provide true-color images that help identify large areas of pollution caused by fires, dust or sand storms, volcanic eruptions, industrial sources, or the transport of man-made pollution. These images help in understanding the transport of pollutants and their potential impact on air quality.

TROPOspheric Monitoring Instrument (TROPOMI)

The European Space Agency's TROPOMI, launched in 2017, collects data on nitrogen dioxide (NO2), sulfur dioxide (SO2), carbon monoxide (CO), and methane (CH4) with high spatial resolution. This data is essential for monitoring air quality and understanding the impact of these pollutants on the atmosphere.

Geosynchronous Satellites

A fleet of satellites in geosynchronous orbit, such as the National Oceanic and Atmospheric Administration GOES-R and the Japan Space Agency Himawari-8/9, provide information on aerosols and how air pollutant concentrations vary throughout the day. These satellites are crucial for monitoring air pollution in major polluted regions of the world.

Multi-Angle Imager for Aerosols (MAIA)

The upcoming NASA Multi-Angle Imager for Aerosols (MAIA) mission will collect high-resolution data on the properties of aerosols in several megacities worldwide. This data will be valuable for health researchers and air quality managers, as it can be used to infer surface-level particulate matter concentrations.

How to interpret satellite images to monitor air pollution

Satellite images can be used to identify large areas of pollution caused by fires, dust or sand storms, volcanic eruptions, large industrial sources, or the transport of man-made pollution from other regions.

To interpret a satellite image, you should:

Identify the type of pollution

To begin, you need to identify the type of pollution. Haze is usually grey-white and very uniform in texture. Dust tends to be tan, though the colour varies depending on the type of soil that is being picked up by the wind. Smoke ranges from brown to grey-white.

Identify the source of pollution

It is not always possible to identify the source of the pollution, since smoke haze and dust can look alike. However, you can look for potential sources in the satellite image. For example, you can identify the location of fires on the ground by observing unusual hotspots.

Compare with ground measurements

Satellite images do not tell you what pollution levels are on the ground. To find out if the pollution you are seeing in the satellite image is on the ground, you need to compare ground measurements to the satellite measurements. This can be done using tools such as Google Earth.

Measure aerosol optical depth

Satellites 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 measurement is called aerosol optical depth or aerosol optical thickness.

Use online tools

Online tools such as NASA's NEO (NASA Earth Observations) can be used to generate images based on data from various satellite instruments.

Compare with previous images

By comparing current satellite images with previous images, you can track changes in pollution levels over time.

Collaborate with stakeholders

Collaborating with stakeholders such as local governments, businesses, and communities can help to ensure that the data is interpreted in a way that is relevant and useful for decision-making.

Combine with other data sources

Satellite data can be combined with ground monitoring data and other data sources to validate and improve the accuracy of the interpretations.

How satellite data can be used to improve air quality

Air pollution is a pressing issue that has captured the attention of scientists, policymakers, and the general public alike. With the help of satellite technology, we can now monitor and address air quality issues more effectively. Satellite data plays a crucial role in improving air quality by providing valuable information about the Earth's atmosphere. Here are some ways in which satellite data is being used to enhance our understanding and management of air quality:

Tracking Pollutants and Emissions:

Satellites equipped with advanced sensors and instruments can detect and track various air pollutants, such as nitrogen dioxide (NO2), ozone, carbon monoxide, methane, and particulate matter (PM). This capability allows scientists and environmental agencies to identify sources of pollution, monitor their dispersion, and assess their impact on air quality.

Fire and Smoke Detection:

Satellite imagery is particularly useful for identifying large areas of pollution caused by wildfires, volcanic eruptions, and industrial sources. For example, NASA's Moderate Resolution Imaging Spectroradiometer (MODIS) instruments on the Terra and Aqua satellites can detect fires and capture the transport of smoke across long distances. This information is crucial for monitoring air quality and issuing public health advisories during wildfire seasons.

Atmospheric Composition Monitoring:

Satellites provide critical data on the composition of the Earth's atmosphere, including the presence of trace gases, aerosols, and ultraviolet radiation. This information is essential for understanding the complex interactions between different atmospheric components and their impact on air quality. For instance, the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT) provides data to the Copernicus Atmosphere Monitoring Service (CAMS), helping to monitor and forecast air quality for the health of European citizens.

Validation of Ground-Based Measurements:

Satellite data serves as a valuable tool for validating and complementing ground-based air quality measurements. By comparing satellite observations with ground measurements, scientists can assess the accuracy of their data and gain a more comprehensive understanding of air pollution levels at different altitudes. This integration of satellite and ground-based data enables a more holistic view of air quality.

Policy Formulation and Intervention:

Satellite data provides scientific evidence to support the formulation of effective air quality policies and interventions. For example, the NASA Health and Air Quality Applied Science Team (HAQAST) collaborated with civil society stakeholders to develop satellite-derived global air pollution indicators. This information is used to track wildfires, dust storms, pollen counts, urban green space, NO2 concentrations, and their impact on public health.

Climate Change and Health Impact Assessment:

Satellite data plays a crucial role in understanding the complex interplay between air pollution and climate change. By tracking indicators of global air pollution and climate change, scientists can assess their impact on human health. For instance, the Lancet Countdown project uses satellite data to monitor direct population exposure to wildfires and their trends over time, providing valuable insights for policy interventions.

Public Awareness and Advocacy:

Satellite imagery and data visualizations have the power to raise public awareness about air pollution issues, especially in regions where ground-based monitoring stations are scarce. By presenting compelling visual evidence of pollution, satellites can motivate societal and industrial behavioral changes and advocate for stronger environmental protection policies.

In conclusion, satellite data has revolutionized our ability to monitor and improve air quality. By providing a global perspective and advanced technological capabilities, satellites offer valuable insights into the complex dynamics of the Earth's atmosphere. The effective utilization of satellite data, in combination with ground-based measurements and policy interventions, holds the key to enhancing air quality and safeguarding public health on a global scale.

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