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Air quality trends in the Persian Gulf. Map of the Persian Gulf, including Saudi Arabia, Iraq and Iran, showing changes in atmospheric nitrogen dioxide concentrations from 2005 to 2014. Blue indicates a decrease in nitrogen dioxide, and red indicates an increase. Nitrogen dioxide gas is a common emission from vehicles, power plants and industry, and is used as an indicator of general air quality. It can cause respiratory problems, and can transform into ozone, another major respiratory pollutant. Observations indicate an increase in air pollution in many parts of the region. Data obtained by the Ozone Monitoring Instrument aboard NASA's Aura satellite.