The Air Quality: NO₂ Satellite Measurements dataset provides global monthly averages of nitrogen dioxide (NO₂) density in the troposphere. Each value shown in the dataset represents the density of NO₂ between Earth’s surface and the top of the troposphere. The NO₂ density is reported with units of moles of NO₂ per square meter of air (mol/m²).
Nitrogen dioxide (NO₂) is one of the most common compounds in the nitrogen oxides (NOx) group. Other nitrogen oxides include nitric acid (HNO₃) and nitric oxide (NO). NO₂ is used as the indicator for the larger group of nitrogen oxides, meaning if NO₂ is present it is likely other nitrogen oxides are as well. NO₂ is primarily created by the burning of fuel, which can be from cars, trucks and buses, power plants, and off-road equipment. Breathing air with a high concentration of NO₂ can irritate airways in the human respiratory system. Acute exposures can aggravate respiratory diseases, particularly asthma, leading to respiratory symptoms, like coughing, wheezing or difficulty breathing. Longer chronic exposures to elevated concentrations of NO₂ may contribute to the development of asthma and potentially increase susceptibility to respiratory infections. People with asthma, as well as children and the elderly are generally at greater risk for the health effects of NO₂.
The dataset is made up of data collected from the Sentinel-5 Precursor (S5p) mission, a low Earth orbit polar satellite system. The S5p mission is part of the Global Monitoring of the Environment and Security (GMES/COPERNICUS) space component program headed by the European Commission (EC) in partnership with the European Space Agency (ESA). Its goal is to provide information and services on air quality, climate, and the ozone layer. The S5p mission includes the TROPOspheric Monitoring Instrument (TROPOMI), which takes daily global observations of key atmospheric components, such as NO₂, at a 5.5 x 3.5 kilometer (km) resolution.
The TROPOMI NO₂ dataset was created with data collected by the S5P satellite mission. The data was retrieved and analyzed using a 3 step process.
Total NO₂ slant column density was determined from radiance and irradiance spectra measured by TROPOMI. It was analyzed using a Differential Optical Absorption Spectroscopy (DOAS) method. NO₂ slant column density is the amount of NO₂ found along an average path taken by photons traveling from the sun to the satellite sensor.
Slant column density data was then separated into stratospheric and tropospheric categories based on information coming from the satellite’s data assimilation system. Stratospheric data was then removed from the dataset.
Tropospheric slant column density was converted into tropospheric vertical column density and the average NO₂ density for the entire vertical column was calculated. This was determined by applying an appropriate air mass factor (AMF) and actual, daily information on the vertical distribution of NO₂ calculated by the TM5-MP global chemistry transport model. The altitude-dependent AMF used depended on the satellite geometry, terrain height, cloud fraction and height, and surface albedo.
The dataset shown on Resource Watch was mapped by the Google Earth Engine team using the harpconvert tool. For more information on this conversion please see the Google Earth Engine documentation. The offline version of this data is displayed on Resource Watch, which is more complete than its near real-time counterpart, but is released on a greater delay due to the additional processing time needed. For the full documentation, please see the source methodology associated with the “Nitrogen Dioxide (NO₂) Total Column”.
Excerpts of this description page were taken from the source metadata. Resource Watch shows only a subset of the dataset. For access to the full dataset and additional information, click on the “Learn more” button.
Sentinel 5 Precursor Tropospheric Monitoring Instrument (S5P/TROPOMI) Offline (OFFL) Level 3 (L3) Nitrogen Dioxide (NO₂)
The current surface albedo climatology used has a spatial resolution of 0.5° x 0.5° (approximately 55 x 55 km), which is coarse compared to the much higher spatial resolution used by S5p TROPOMI of 3.5 x 5.5 km. As a consequence, the albedo grid affects the NO₂ column products quality, especially in coastal areas.
In general, TROPOMI underestimates the tropospheric NO₂ densities at polluted sites. The median negative biases of the daily comparisons are generally less than 50% (the product requirement for tropospheric NO₂), but can be quite variable depending on station and NO₂ level.
Good coherence is found between TROPOMI and Multi Axis Differential Absorption Spectroscopy (MAX-DOAS) NO₂ datasets with a correlation coefficient of 0.84.
For more information on the data quality, please see the product readme file.
European Space Agency. 2018. ESA Sentinel-5P TROPOMI L3 products. Accessed through Resource Watch, (date). www.resourcewatch.org.
3.5 x 5.5 km