New Article from The Wall Street Journalinfographic_sourcesAccording to the World Health Organization, air pollution is “any contamination of the indoor or outdoor environment by any chemical, physical or biological agent that modifies the natural characteristics of the atmosphere.”  Some of the most common components of air pollution are particulate matter, ground-level ozone, nitrogen dioxide, sulfur dioxide and carbon monoxide.


There are different ways to measure and report air pollution. In Delhi, measurements from the U.S. Embassy air quality monitor come in the form of an AQI- a single number to express overall air quality. Measurements from other sources in Delhi are usually shown as a list of numbers showing the measurements of individual components of air pollution (these can be converted into AQI).  Some monitoring stations report measures in real time, others in daily or annual mean concentration of pollutants.


The World Health Organization has set safe thresholds for particular pollutants. In the case of particulate matter, no safe threshold has been established (there is evidence that it is harmful at any level) so the benchmark is as low as possible: 10 μg/m3 annual mean.  For perspective, WHO data showed D