BBC: NASA's Aura spacecraft has been monitoring the emission of nitrogen dioxide since 2004. Scientists who used Aura's Ozone Monitoring Instrument reveal that North America and Europe have had significant decreases in emissions while China and other developing nations have had large increases. In the 10 years covered in their report, levels fell between 20% and 50% across North America and by as much as 50% in Europe, which the researchers tie to emissions legislation. In the US, not all states had decreases—the rise in oil and natural gas extraction resulted in increased emissions in North Dakota and Texas. In China, emissions increased between 20% and 50%. However, in some areas where local and regional governments put in place emissions restrictions, such as Beijing, Shanghai, and Hong Kong, emissions were down by up to 40%. A similar mix was seen in South Africa, which had rising emissions in its inland plateau but decreasing emissions in the Johannesburg–Pretoria area.
