NASA is flying planes low over the US to make maps of air pollution sources

A white plane is seen on a runway. It has a NASA sign on its tail.

We've reached a point when scientists can easily gauge levels of greenhouse gases or other air pollutants just by measuring their concentrations in the atmosphere. However, with these measurements alone, it is not necessarily obvious where the pollution actually comes from. 

How could we tell which specific neighborhoods in a city, for example, spawn the most carbon dioxide? That's important information because only then can scientists start figuring out how to mitigate greenhouse gas emissions, especially as Earth continues to warm due to human-driven climate change.