Unless you completely avoided modern society in August and September, you helped make this map.

If you were in a car, bus or train with a combustion engine, if you were in an electric vehicle that was charged using non-renewable energy or if you consumed something that was shipped to you on an actual ship—chances are, you contributed to this global composite of nitrogen dioxide (NO₂) made using data from ESA’s Sentinel-5P satellite.

NO₂ is a nasty-smelling, gaseous pollutant that is mostly the byproduct of the combustion process. It is, unsurprisingly, not good for you.

In a city, almost all of the NO₂ in the air comes from vehicle exhaust. Outside the urban environment, NO₂ is emitted in large quantities by power plants, factories and anything else that uses combustion as a matter of course. Basically, if you are burning fossil fuels to do anything, you’re creating NO₂.

Local hotspots of NO₂ around India and China

And, as we all know, humankind burns quite a lot of fossil fuels to do all sorts of things. (At the risk of entering a rabbit hole, I might even point out that the creation and publication of this here blog post involved burning some fossil fuels.) NO₂ is nearly everywhere.

Most of the highest concentrations of NO₂ in this composite are in big cities—Tehran, Moscow, Lima, Mexico City, Beijing, Seoul, Jakarta. So, at first glance, a view of the world using just NO₂ looks somewhat like a population map. But it’s not. One of the dots in the map above, for example, is the town of Korba, India. The population of Korba is about 360,000, yet the highest concentrations of NO₂ levels around Korba in this composite were higher than all but two American cities (New York and Los Angeles). Why? Korba has industry. Power plants, mines (that produced 711,921,000 tons of coal in 2015) and factories kicked out this NO₂.