Scientists at Tel Aviv University tracked pollution trends for 189 megacities, including Mumbai, New York City and Tokyo, by analysing eight years' worth of data from three of NASA's high-tech aerosol monitoring satellites.

Northeast China, India, the Middle East, and Central Africa are currently leading in pollution increase, including Bangalore, with a 34 per cent average increase in aerosol concentration between 2002 and 2010, website Tel Aviv University's American Friends (AFTAU) reported.

Europe and Northeast and Central North America are seeing the largest decreases in aerosol concentrations overall, the website said.

Among the cleanest cities were Houston, with a 31 per cent decrease over the time period; Curitiba, Brazil, with a 26 per cent decrease; and Stockholm, Sweden, with a 23 per cent decrease.

Researchers led by Pinhas Alpert of Tel Aviv University's Department of Geophysics and Planetary Sciences tracked pollution trends for 189 megacities ¿ metropolitan hotspots where the population exceeds 2 million.

Their method, published in the American Journal of Climate Change, is the first to provide standardised global testing of pollution levels.

Researchers found that the thickest layers of global smog caused by traffic, industry, and natural minerals, among other factors are found over the world's megacities.

Some American cities were on the list of increased pollution levels, including Portland with a 53 per cent average increase and Seattle with a 32 per cent average increase, but Alpert believes these numbers reflect the multiple wildfires that have been happening in the region in the second half of the period examined.

In the future, he hopes to develop a method for separating such natural causes of pollution from man-made pollutants for more accurate data.