Hovering above the iconic Hollywood sign is Southern California’s other icon: smog. After decades of gains fighting the menace, LA is now losing ground, clocking a 10 percent rise in deaths from ozone pollution between 2010 and 2017. Cars, of course, are the major contributor to smog, but vehicles (and power plants and industry and airports) also put out an invisible menace—the CO 2 that's warming the planet.

Problem, though: You can't just train a satellite on LA to quantify the emissions coming from each street. For one, you’d have a hard time telling vehicle sources of CO 2 from trees along the road, which are respirating their own carbon dioxide. Plus, the wind is blowing the greenhouse gas all over the place, so it’d be hard to tell the origin of a plume in a gusty day.

So instead of relying on satellites alone, a group of researchers combed through data from a dizzying number of publicly available sources, looking at everything from traffic patterns to utilities data to air pollution reporting, to quantify the emissions from not just every road but every building in the nearly 5,000 square miles of the Los Angeles megacity. Such an incredible resolution could help the city focus its carbon mitigation efforts, for instance bolstering public transport to relieve particularly congested roadways. The larger quest is to build a block-by-block forecasting system for cities around the country—monitoring emissions hour by hour, month by month, year by year—to get smarter about tackling emissions for the health of the public and the planet.

Patrick Brooks Patrick Brooks

This project is an extension of a larger system called Vulcan, which quantified emissions on a kilometer scale across the US. For that the researchers pulled in data like federal traffic statistics and registration records for cars in every country. “It uses carbon monoxide emissions reporting, local air pollution reporting, monitored data of power plants,” says Kevin Gurney, a climate scientist at Northern Arizona University. He’s the lead author on a new paper describing the LA project. “It merges that with where all the railroads are, where all the roads are, where all the buildings are from FEMA.”

Matt Simon covers cannabis, robots, and climate science for WIRED.