- Jim Crawford
- Brent Holbren
- Cassie Stearns
- David Doughty
You don't need a time traveling DeLorean to get a clear picture of air quality near the Earth's surface, In fact, your best bet is to take the DISCOVER-AQ approach. They use sun photometers, LIDAR, tethered and untethered ozone sondes… and almost a DeLorean. NASA EDGE breathes easier after talking to Jim Crawford (DISCOVER-AQ, Principle Investigator,) Brent Holbren (Co-Investigator) and several of the folks at the Beltville, MD ground station. Unfortunately, the Co-Host still can't remember what the acronym stands for. Fortunately, he can always rewind the video.
CHRIS: Welcome to NASA EDGE.
BLAIR: An inside and outside look at all things NASA.
CHRIS: We’re here at NASA Langley Research Center in Hampton, Virginia. We’re going to be talking about Discover-AQ.
BLAIR: And I’m hoping to actually discover what this massive acronym, Discover, stands for in the process.
CHRIS: Yeah. In a few minutes I’ll be talking to Jim Crawford, who’s the Principal Investigator. I’m going to ask him that very same question.
BLAIR: And I’m going to be flying on the P3. So, I’ll be able to ask some of the other researchers what it stands for as well.
CHRIS: You’re flying on what?
BLAIR: The P3, one of the planes, flying is part of Discovery-AQ.
CHRIS: How did you get that gig?
BLAIR: Well, it’s not who you know… no. It’s not what you know, it’s who you know.
[Chris & Blair laughing]
CHRIS: I tell you what. You see, right then and there, it kind of scares me. Did you let him know the about the magnetospherence level that you produce?
CHRIS: Because, there’s a lot of instruments on board that plane. If you corrupt the data, the whole mission is a wash.
BLAIR: I honestly thought the health form would rule out the entire flight. I think they were more focused on that but I’m also stopping at the Beltsville, Maryland ground station.
BLAIR: So, I’ll ask them there too.
[train whistle in background]
CHRIS: Tell you what, you go prepare for that; I’ll go talk to Jim. You’re watching NASA EDGE.
BLAIR: An inside and outside look at all things NASA.
CHRIS: We’ve got a train whistle blowing here.
BLAIR: Whoo hoo.
CHRIS: Welcome to NASA EDGE.
JACKY: An inside and outside look…
FRANKLIN: At all things NASA.
BLAIR: Oh, that’s going to leave a mark.
CHRIS: We’re here with Jim Crawford, Principal Investigator for Discover-AQ. Jim, what does Discover-AQ stand for?
JIM: It is a fairly tortured acronym. Discover-AQ stands for Deriving Information on Surface conditions from COlumn and VErtically Resolved Observations Relevant to Air Quality.
CHRIS: Sounds like a dissertation.
JIM: There will be enough information out of this project to cover many dissertations. The number of students involved and scientists, we expect a lot of papers and results to come out of this.
CHRIS: Give us the big picture. What’s Discover-AQ all about?
JIM: Discover-AQ came from a realization at NASA that we have satellites that can see constituents in the atmosphere that have to do with air quality but can’t see them in a way that’s good enough to ascertain what’s happening at the surface where people are being exposed to poor air quality. From a regulatory standpoint, the EPA, and other regulators want to understand what’s happening right here where you and I are standing.
JIM: They’re not even interested in as high as maybe a few thousand feet above our head. So, trying to protect health is about what you’re breathing now, not about what’s present higher in the atmosphere.
CHRIS: And satellites have a tough time of detecting that here.
JIM: Well, pollution aloft versus pollution at the surface is difficult for satellites because they’re looking down from space through the entire atmosphere.
JIM: They’re measuring the total amount of constituent throughout that column. Within that column, the pollution is distributed. And trying to determine how much of it is at low versus aloft is a particularly vexing problem. The satellite collects that one piece of information, that total amount in the atmosphere. But, how do we tease apart the way it’s distributed?
JIM: You have to put yourself at different vantage points to be able to do that.
BLAIR: To cover those different vantage points, I’ve put together a few crude models to illustrate the assets that you might find at a particular ground station. The first vantage point we get from the sun photometer, which is run here by Dr. Xavier The instrument actually looks directly through the column of atmosphere directly at the sun.
BRENT: Basically, we know the energy at the top of the atmosphere, very precisely in discreet wavelengths that are basically window for aerosols. This little device measures the energy coming in at the bottom of the atmosphere. And the difference is due to either absorption or scattering by particles in the atmosphere. And we come up with a quantity that we call aerosol optical depth.
CHRIS: Looking at pollution, what types of pollution are we looking at? Is this aerosol gases?
JIM: Well, from a regulatory standpoint, there are two things that are regulated very heavily. That’s particulate matter, we call it aerosols in the atmosphere.
JIM: And particularly the small aerosols; things that when you breath can reach deep into your lungs. Think of it as a natural secondhand smoke.
JIM: And then ozone… ozone is not emitted in pollution but it results from the chemical outplay of the degradation of emissions. Ozone is a highly reactive gas. We tend to think of it as the thing in the stratosphere that protects us from ultraviolet light but down low, near the surface, it’s a reactive gas that when you ingest it into your lungs, it reacts with tissues. It causes damage, not just to people but to ecosystems. Agricultural productivity is also degraded by the presence of ozone.
BLAIR: Another asset is the untethered Ozone Sonde. Sonde being the French word for Science. We release this Ozone Sonde into the same column of atmosphere. Oh, I guess I should have thought about how to recover that.
CASSIE: So what happens with the ozone sondes is that there’s a pump on the ozone sonde that draws in air as the balloon is rising. That air will react with the chemical solution that’s inside the sonde. That chemical reaction creates a current, which we then measure. We’re basically getting real time measurements. At this point in the atmosphere, this is the concentration of ozone. We put contact information in there so if it comes down in somebody’s backyard, they can give us a phone call. Hopefully, we can make arrangements to pick it up, at the very least, we can say, it’s not going to hurt you. You can stop panicking now.
BLAIR: The tethered ozone sonde actually covers the area of the column from the ground up to 500 feet. And, oh look, we have a special guest, Researcher Jim Crawford is here to run camera during a tethered ozone sonde assent. Release the sondes! Data is looking good.
DAVID: The thing we’re measuring right now is aerosol spectrum. What that tells us is for a given size how many aerosols are present. Aerosols mean, of course, a little particle of dust.
DAVID: This instrument measures aerosols from about 200 nanometers up to 20 micrometers. We’re able to provide a profile very low down to compare with what the airplane measures between 1,000 and 5,000 feet.
BLAIR: After taking off from NASA Wallops, the P3 follows a specific predetermined flight plan covering each of the Discover-AQ ground stations. And then, obeying all laws of science and physics, the P3 flies in over the tethered sonde at 5,000 ft, begins a corkscrew motion safely all the way down to 1,000 ft. gathering data and then heads off to the next ground station.
JIM: A satellite looks at particles due to their scattering. The light comes in the atmosphere, and just like in haze, you can see the light being scattered.
CHRIS: Right, right.
JIM: So, they have to ascertain how much particulate matter is there based on a scattering signal. But that scattering signal is a wet signal. And the wetter the particle, the bigger it is and the more it…
JIM & CHRIS: …scatters.
JIM: We have to understand not only the amount of particles in the atmosphere but what their affinity for water is. Are they ones that like to be wet or one that tend to shun water? We also have to worry about what they’re made of; sulfate aerosols from burning coal…
JIM: …and things like that will tend to reflect light. Black carbon particles from a diesel engine, for instance, will absorb light. So, the difference in the way a particle interacts with light is important as well as whether it grows in a humidified environment.
CHRIS: That’s why you have so many instruments to measure that?
JIM: If you saw the aerosol rack on the plane, seventeen instruments all looking at something different.
BLAIR: Discover-AQ also uses automobiles to collect data on Interstate I-95. No Mr. Scientist, that’s not a time machine that’s a regular car fitted with LIDAR to collect data for Discovery-AQ. Be careful merging onto 95.
BLAIR: So the LIDAR-mobile or the Discover-AQ mobile, what kind of equipment is this?
BRENT: Well, this kind of embodies in a mobile form what we have spread throughout the network. This is a sun photometer.
BRENT: That’s a LIDAR. There are about 10 LIDARs in the network that are basically sending a green, pulse of light vertically, measuring how long it takes to be returned. That timing gives us the position of where the aerosols are suspended in the atmosphere. These two, with a fixed ground sites are working together mobile. So, we’re driving the length of I-95 up to the Delaware line, turning around, coming back and doing these profiles, getting extinction basically over the I-95 corridor.
BLAIR: The cool part about Discover-AQ is that all these assets operate at the same time, gathering lots of data in the column. And how do we make all these assets available on the ground? With help from our partners, like Howard University, and other participating institutions.
CHRIS: The first stop is the Baltimore, Washington D.C. area, you’re going to be traveling west across the country. What are some of the sights you’re going to be looking at?
JIM: First of all, I would say that question comes to us, why do you need to go to other locations?
JIM: Think of Baltimore, Washington as that area on the East Coast that represents that endemic problem of the East Coast generates its own pollution but it also receives everyone else’s pollution as it makes its way across the continent because of weather patterns, and the general flow of the atmosphere is from west to east.
JIM: Maryland represents an opportunity to look at local emissions in the context of also what’s coming from upstream. Houston represents a very different condition. We want to see the variety of factors that drive air quality. So, in Houston, you’re looking at a place where the petrochemical industry is highly concentrated. The emissions that come from that, lead to a chemical mixture that is actually quite different than you would find in Maryland.
JIM: Finally, we find places like the Central Valley of California where the wintertime is when air quality has a big problem. Particulate matter can come from the direct burning of substances; anything from wood burning to crop burning to actually the corps in the Central Valley and dust being blown up by wind. All of that particulate matter in the wintertime is squeezed into a very thin atmospheric layer without the heating of the sun as much as you get in the summer. Things mix into a much smaller volume and that ends up concentrating it to a much higher concentration. It’s a difficult problem.
CHRIS: Jim, I want to thank you so much. Good luck on your mission.
CHRIS: The next 4 or 5 years are going to be wonderful to see. I can’t wait to read all the papers down the road.
JIM: That’s right. We’re looking forward to it.
CHRIS: You’ve heard it from Jim. You’re watching NASA EDGE an inside and outside look at all things NASA.
BLAIR: I thought these were data-gathering instruments but it was pointed out to me that these are the international colors of safety, not science, so they won’t be gathering any data.
BLAIR: Whew! Ah, it’s hot up there. I haven’t been this hot since I was roofing back at Shawshank. Whew.
BLAIR: Whew. And for the record, nothing about this air quality needs to be discovered. Whew.
BLAIR: Lawn maintenance shed, now here’s some equipment I can relate to. [equipment humming] Not exactly.
Page Editor: Blair Allen