In February 2020, the Geostationary Environment Monitoring Spectrometer (GEMS) was launched by the Republic of Korea. It is the first of the three-satellite constellation which enables the hourly monitoring of air pollution levels for almost 20 countries in Asia. This marks a significant leap forward in the ability of scientists to monitor air pollution from space.
Previously, air quality monitoring has been mainly based upon in-situ measurements by Governments using ground-based air quality monitoring networks within their territories. However, ground-based monitoring has limitations since monitoring stations are mostly concentrated in densely populated cities with rigid installation requirements and very narrow spatial coverage. Furthermore, air pollution monitoring stations are often based in urban areas, and yet pollutants can be generated or travel great distances and affect not only rural areas but also on a transboundary basis. Satellite observations complement the ground-based networks by providing data over wider areas, which is particularly useful for regions where no surface monitors are installed, such as rural areas or countries with limited air pollution monitoring equipment or capacity. For example, the regular measurement of O3 and its precursors NOx and volatile organic compounds, along with particulate matter, SO2 and other pollutants, will improve the accuracy of air quality forecasts, top-down emission rates and understanding on long-range transport of air pollutants. This satellite-derived data will help evaluate and improve air quality and chemical transportation models, emissions inventories and allow the better production of hourly air pollution forecasts which are accessible to the public through a broad range of platforms and applications. It can fill in information gaps left by ground-data collected through monitoring stations to help evidence-based policy making to address not only national and local air quality, but transboundary pollution issues.