Study of Urban Population and Air Pollution Uncovers Regional Discrepancies

Through the help of satellite observations, NASA scientists have released the first-ever study to examine just how much more air pollution people living in large cities are exposed to compared to those living in less populous areas.

In particular, the study focused on nitrogen dioxide, a common pollutant produced through the burning of fossil fuels considered a clear proxy for urban air quality, in regards to the United States, Europe, China and India.

Published in Environmental Science and Technology, the study reveals how pollution-population relationships vary based on what region of the world the city is located. For example, the researchers discovered that a city of 1 million in Europe averages NO2 rates six times higher than a city of the same size in India -- a variation reflected in differences in variables such as industrial development, per capita emissions and geography.

The findings were based on data collected by the Ozone Monitoring Instrument on NASA's Aura satellite, which measures NO2 levels in the atmosphere throughout the world. Using this data, they determined the annual mean concentration of the gas near the ground in some of the Northern Hemisphere's major polluting regions, not including "outliers," such as power plants.

With this map of pollution concentration in place, the researchers then overlayed it with maps of population density data.

The results showed that for every urban area of 1 million people, NO2 concentrations averaged 0.98 parts per billion (US), 1.33 ppb (Europe), 0.68 ppb (China) and 0.23 ppb (India).

This divergence was mimicked in cities with populations of 10 million people as well, totaling 2.55 ppb (US), 3.86 ppb (Europe), 3.13 ppb (China) and 0.53 ppb (India).

Going forward, study lead Lok Lamsal of NASA's Goddard Space Flight Center says that while further research is needed in order to clearly define the reasons behind these regional disparities, population and pollution measurements like this one are "potentially useful for developing future inventories and formulating air pollution control policies."