The Sentinel-5 Precursor (or Sentinel-5p) is a satellite system that was finally launched in October 2017 after a three-year delay. The satellite is focused on collecting pollution data and is part of the European Union’s Copernicus Program, which has already launched Sentinels 1-3. One of its key instruments is the TROPOspheric Monitoring Instrument (Tropomi), which monitors the visible, ultraviolet, near and shortwave infrared spectrums to quantify ozone, methane, carbon monoxide, sulfur dioxide and other pollutants in the atmosphere. This will be one of the first satellites that provides high resolution pollution monitoring and will provide a large data capture that enables daily and even hourly monitoring.
Mapping Air Pollution
With air quality, and not just greenhouse gases, being of major concern for states and cities, the satellite system is very timely. In fact, it is likely that we wil see more accurate daily pollution reporting as part of our weather forecasts over areas such as Europe, or even other regions as different countries and organizations begin to use the system, as part of this program. The data will be made free and open, allowing not only scientists to utilize the data but it is also intended that applications that make use of the data will be developed so that governments, NGOs, and businesses can observe pollution levels and devise pollution reduction measures using the monitoring capabilities. The Copernicus Atmosphere Monitoring Service (CAMS) will provide ways to interpret the complex data in machine readable and human understandable form, making its utility more useful to a wider audience.
Earlier Sentinel missions focused on weather, land and the oceans. This mission focuses on the atmosphere. The satellite follows a relatively low orbit and methods being developed include new and better monitoring techniques using the data from the satellite system to monitor and estimate pollution levels. This includes carbon monoxide, where current wide area coverage data have not been sufficient and often depend on having many sensors scattered over a wide area such as a city region. Critically, the data will have temporal and spatial resolution divisible by hourly data. This allows pollution monitoring to be far more precise on changing air quality in regions that are particularly sensitive to environmental changes such as humidity and temperature fluctuations that can affect the degree to which pollution concentration changes. Large- and small-scale events, including forest fires and local weather fluctuation, are qualities that could be captured by the data and applied in forecast models.
Other sets of data retrieved include ozone profile and tropospheric ozone column data that can monitor. This will include daily monitoring of global ozone levels, providing a much greater temporal resolution of fluctuations to atmospheric ozone than previous monitoring. Related to ozone levels, surface ultraviolet light will also be monitoring to allow a day-to-day global and local perspective on ultraviolet damage caused by the sun.
In late October 2017, the satellite was undergoing preliminary testing on its various instruments. These are being prepared and tested before scientifically useful data are collected and released. While Sentinel 5-p will soon be providing new data, the larger Copernicus Program will offer many more Sentinel satellites to provide the most comprehensive earth observation program than what has been done previously. There are threats to the wider program, including budgetary constraints, but the need for earth observation relatively to a rapidly changing planet has meant that so far governments in the European Union have seen this as a wider benefit than cost.
 For more on the background to the satellite system, see: https://earth.esa.int/web/guest/missions/esa-eo-missions/sentinel-5p
 For a recent article discussing the benefits of the system, see: http://www.esa.int/Our_Activities/Observing_the_Earth/Copernicus/Sentinel-5P/Ready_to_reap_the_benefits_from_Copernicus_Sentinel-5P.
 For more on monitoring carbon monoxide using the Sentinel-5 mission, see: Dekker, I., S. Houweling, I. Aben, T. Roeckmann, and M. Krol (2017), Quantification of point sources of carbon monoxide using satellite measurements, vol. 19, p. 13167. [online] Available from: http://adsabs.harvard.edu/abs/2017EGUGA..1913167D.
 For more on the temporal quality of the data and its applicability, see: Zoogman, P., Liu, X., Suleiman, R.M., Pennington, W.F., et al. (2017) Tropospheric emissions: Monitoring of pollution (TEMPO). Journal of Quantitative Spectroscopy and Radiative Transfer. [Online] 186, 17–39. Available from: doi:10.1016/j.jqsrt.2016.05.008.
 For more on events that could be captured by Sentinel-5p, see: Abida, R., Attié, J.-L., El Amraoui, L., Ricaud, P., et al. (2017) Impact of spaceborne carbon monoxide observations from the S-5P platform on tropospheric composition analyses and forecasts. Atmospheric Chemistry and Physics. [Online] 17 (2), 1081–1103. Available from: doi:10.5194/acp-17-1081-2017.
 For more on ozone monitoring, see: https://sentinel.esa.int/documents/247904/2474724/Sentinel-5P-Science-Validation-Implementation-Plan