How Satellites Can Be Used to Track World Pollution

A version of this story originally appeared on NoCamels – Israeli Environment News

By NoCamels Team
Researchers at Tel Aviv University have managed to produce quality analysis of pollution in major cities around the world – using readings taken in outer space.

Professor Pinhas Alpert of Tel Aviv University's Department of Geophysics and Planetary Sciences and head of the Porter School of Environmental Studies, is turning to three of NASA's high-tech satellites for a comprehensive view of pollutants in the atmosphere.

Using eight years' worth of data collected by the satellites, the researchers tracked pollution trends for 189 megacities; metropolitan hotspots where the population exceeds two million. Fifty-eight of these megacities, including New York City, Tokyo, and Mumbai, have populations that exceed five million.

Their method is the first to provide standardized global testing of pollution levels. Beyond uncovering reliable data about pollution trends, Alpert believes that this monitoring method will also hold countries accountable for their emissions and encourage more environmentally friendly practices.

The smog which often covers megacities is actually a thick atmospheric layer several hundred meters above the earth's surface, comprised of particles of pollutants. It's an environmental hazard and a severe health risk for those living below, who breathe in the particulates, Alpert explains.

To accurately analyze the level of pollution over each megacity, the researchers used data gathered by three aerosol-monitoring satellites, called MODIS-Terra, MODIS-Aqua, and MISR, which NASA launched between the years 2000 and 2002. The combined data these satellites provide constitute an accurate survey of aerosol concentrations a few hundred meters above earth.

Alpert likens the use of three satellites to the traditional Jewish idea of the three-judge panel. "In the Jewish tradition, individual judges don't decide cases. There must be a minimum of three. You need a majority opinion," he says. "By merging the data from three imperfect sensors, their flaws are mostly counterbalanced. In cases where the three sensors show differing signs of pollution levels, more research is required."

Northeast China, India, the Middle East, and Central Africa are currently leading in pollution increase. Bangalore, India, for example, has a 34 percent average increase in aerosol concentration between 2002 and 2010. Ibdan, Nigeria, was also part of that group. Europe and Northeast and Central North America are seeing the largest decreases in aerosol concentrations overall. Among the cleanest cities were Houston, Texas, with a 31 percent decrease over the time period; Curitiba, Brazil, with a 26 percent decrease; and Stockholm, Sweden, with a 23 percent decrease.

Some American cities were on the list of increased pollution levels, including Portland with a 53 percent average increase and Seattle with a 32 percent average increase, but Alpert believes these numbers reflect the multiple wildfires that have been plaguing 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.

A standardized approach to smog analysis is made difficult by often unreliable data from monitoring stations, the reluctance of politicians or government ministries to offer accurate numbers on pollution, and even a complete lack of monitoring in major parts of the world, says Alpert. When it comes to international treaties aimed at reducing pollution, this measurement method could help to keep all countries accountable for their promises by tracking compliance in an equitable way. Cities that successfully decrease pollution could be applauded for their efforts and stand as a positive example to follow, he suggests.

Professor Alpert's research, which was done with graduate student Olga Shvainshteinand and Dr. Pavel Kishcha, was published in the American Journal of Climate Change.

Photo by Metro Transportation Library and Archive<