Scientists examined observations made from 2005 to 2014 by the Ozone Monitoring Instrument aboard NASA's Aura satellite. One of the atmospheric gases the instrument detects is nitrogen dioxide, a yellow-brown gas that is a common emission from cars, power plants and industrial activity. Nitrogen dioxide can quickly transform into ground-level ozone, a major respiratory pollutant in urban smog. Nitrogen dioxide hotspots, used as an indicator of general air quality, occur over most major cities in developed and developing nations.
The following visualizations include two types of data. The absolute concentrations show the concentration of tropospheric nitrogen dioxide, with blue and green colors denoting lower concentrations and orange and red areas indicating higher concentrations.
The second type of data is the trend data from 2005 to 2014, which shows the observed change in concentration over the ten-year period. Blue indicated an observed decrease in nitrogen dioxide, and orange indicates an observed increase. Please note that the range on the color bars (text is in white) changes from location to location in order to highlight features seen in the different geographic regions.