In honor of Brown’s first-ever Climate Week, environmental epidemiologist Allan Just sits down with us to explain how his team uses NASA satellite data to measure hyper-local temperatures and air pollution. Discover why these precise measurements are vital for public health, especially for those on common medications that can unexpectedly increase vulnerability to extreme heat.
How does heat and air pollution affect neighborhoods in the same city differently?
Just: Individual neighborhoods can be warmer or cooler, and that varies. It depends on how many trees there are, and how much pavement there is, and whether you're near a body of water, or whether there's a major roadway that goes through.
We see, for example, that people that live in a valley are experiencing worse air pollution on average than people who live up on a hill. And it sort of makes sense when you think about it because the air gets trapped and it can stay there. So when you have some sort of local emission source or you have long range transport of air pollutants that are coming down, they can settle close to the surface, and then that's what you're breathing and it may not get moved out by wind or other patterns.
We're doing lots of studies in which we're using the location of an individual's specific address or the school that their children attend or we're considering the location of every nursing home in the Northeast. So there are many studies in which we're trying to drill down into those very, very specific quantities.
Typically, research into heat and air pollution has used much less specific temperature readings, from airports and weather stations, but your satellite data is different.
We have used kind of a broad brush to assign what we think people are exposed to and have not always tracked that different neighborhoods are experiencing different temperatures. We think that when we get more specific, we've been underestimating the burden.
By bringing in data from NASA satellites, those satellites are telling us things like the temperature of the surface of the earth, and we're also bringing in information about land cover, how much vegetation there is, the amount of people nearby.
We're bringing together lots of different kinds of information and we're training up a model so that we can have a better reconstruction where we don't have those direct measurements. All of that layered information helps them make precise predictions about how hot it was at any spot in the United States.
With air pollution, there's even fewer of those regulatory-grade, high-quality monitors that are measuring air pollution. Many US counties don't even have a single measurement, and when we just use the nearest monitor, we're accepting quite a bit of error in the measurement that we're assigning. And then that error means that if we try to relate what someone is being exposed to what they're actually breathing, we get the answer slightly wrong.
And so there's particular value in reconstructing what people breathe or what they're feeling, where they live, where they work and play.
How do these satellites capture information about air pollution?
One of the main satellite measures that we work with is called aerosol optical depth, and what the satellite is detecting is that the particles that we're concerned about, because they impact human health, they're also what cause smog. They scatter the light and instead of having the ability to see a distant mountain range when it's polluted, we're not able to see as far, we have less visibility. In the same way, the NASA satellites are looking at how light that ought to be reflected off of the surface gets scattered by the particles that are in that atmospheric column. That's the quantity that we're taking into understanding the exposure that's happening down near the surface where you and I breathe because somewhere above us, between here and space, is enough of this particle aerosols that it's scattering the light.