Geneva, 3 September 2021 (dpa/MIA) - Many cities in the world enjoyed significantly better air quality during the past year because there was less traffic due to coronavirus-related restrictions, the World Meteorological Organization (WMO) reported on Friday. But, when the health measures were relaxed, air quality fell back to pre-pandemic levels, the WMO's first air quality and climate bulletin said. While man-made emissions fell, weather extremes caused by climate change resulted in sand and dust storms and forest fires that affected air quality. In its bulletin, the WMO cites earlier reports that the number of deaths from air pollution rose from 2.3 million people in 1990 to 4.5 million in 2019. In places where curfews have been imposed, nitrogen dioxide has decreased by up to 70 per cent compared to previous years, and particulate matter by 30 to 40 per cent, depending on the region. In some cities in Spain, however, fine dust pollution has increased despite curfews. Experts put this down to dust pollution from Africa and the burning of biomass. The amount of sulfur dioxide fell between 25 and 60 per cent. The WMO included measurements from 63 cities in 25 countries on all continents.