Mean nitrogen dioxide (NO2) pollution map for 2006, measured by Envisat's Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) instrument, which records the spectrum of sunlight shining through the atmosphere. NO2, a mainly man-made gas, can cause lung damage and respiratory problems in the case of excess exposure. It also plays an important role in atmospheric chemistry, because it leads to the production of ozone in the lowest part of the atmosphere – the troposphere.