Think about a weather model as being like 100 overlapping window screens, like the kind that keep bugs out of your house, stacked into the sky. All of those overlaps create thousands of crossover points at different levels throughout the stack. “At each one of those little intersections of those wires, we're solving these equations: How much change is there?” says Stan Benjamin, senior weather modeling scientist at NOAA Global Systems Laboratory and branch leader for development of HRRR. “It's lots of computations to be able to put all that together and see how all these different aspects of the atmosphere—and actually parts of the earth system—are affecting each other.”
So if you’re looking at the HRRR-Smoke map, on that same left-hand menu, click on “Near Surface Smoke.” This gives you smoke concentrations at about 8 meters off the ground, which are indicated on a light-blue-to-purple color scale at top right on the map. As you might expect, California is currently covered in a smoky haze—purple and red is scary-bad, while light blue indicates fairly low concentrations, measured in micrograms per cubic meter of air. But if you zoom out to the entire US, you’ll see that smoke has traveled clear across the country, landing in New York. These are tiny amounts, to be sure, but they’re there.
Scientists still have much to learn about Covid-19, but, says Jessica McCarty, a geographer and fire scientist at Miami University, “We know that there's linkages between people who live in highly-polluted areas and their likelihood of getting any type of respiratory illness, as well as viral infections.” Smog from cars, for instance, remains a major threat to human health.