The floating particles on this page depict microscopic particulate pollution called PM2.5. The number of particles you see here represents the upper limit for “good” air quality, as defined by the United States Environmental Protection Agency: 12 micrograms per cubic meter over 24 hours. This is pollution in New York City on the worst air quality day this year. Hazardous particulate concentrations reached 41 µg/m 3 during the highest hour, a level that would be considered “unhealthy for sensitive groups.” Compare that to the air in California last year, when a thick blanket of smoke from the Camp Fire descended across the Bay Area . Particulate pollution hit nearly 200 µg/m 3 , well within the “very unhealthy” range when people are advised to limit outdoor activity. But that spike pales in comparison with the recent air quality crisis in northern India: On the most polluted day last month, […]