Last week, the European Space Agency (ESA) released an animation showing nitrogen dioxide (NO2) emission reductions in northern Italy. The ESA describes NO2 as "a harmful gas produced by power plants, cars and factories", one of a family of nitric oxides fueled by diesel emissions. Chemical reactions between such oxides and other elements in the air create ozone and particulate matter, which is converted into visible air pollution. Sentinel-5P satellite data from the Copernicus Atmospheric Monitoring Service (CAMS) array showed that from January 1 to March 11, shutdowns across Italy would dramatically reduce NO2 levels in the country's industrial Po Valley region. The ESA has taken the same measurements in China, showing a huge drop from December to early March last year. According to the Finnish Science Center, China's CO2 emissions alone declined by about 200 million tonnes in February, about half as much carbon dioxide than the UK per year. While China has recovered and its industry is still recovering, the latest images from the ESA show NO2 emissions recovering.
From December 20 to early March, images showed a 20% -30% decrease in particulate matter across China, starting in Wuhan, moving to the epicenter of the novel Coronavirus epicenter and moving to other parts of the country. The decline was most pronounced from mid-January to late February, falling by 40% in major cities after China took the toughest measures to spread the disease. Reduced by Chinese New Year holidays, which have reduced emissions each year, particle measurements in February were still lower compared to the last three years. By the end of February and the last days of data, based on a ten-day moving average and through March 16, clearly defined locations of particulate matter can be returned. Now that China has announced that the worst situation has begun and the desperation to get back on its supply chain may mean a quick return to compromised air quality.
Sentinel-5P is one of the seven Copernicus satellites orbiting the Earth and has a TROPOMI (Tropospheric Monitoring Instrument) to measure atmospheric gases such as aerosols, carbon dioxide, nitrogen dioxide, methane and sulfur dioxide. NO2 is considered to be the "first level indicator of industrial activity in the world". What happens after Italy is removed may boost data on measurements in China, the ESA says, and it is a detailed scientific analysis that will soon yield more visions and quantitative results in the coming weeks and months. The question will be, if any, that mitigation measures can be taken based on the lessons learned during this pandemic.