While NASA aircraft were circling the skies in California's San Joaquin Valley in January and February measuring air pollution, a Penn State team was on the ground making sure the numbers added up.
On some days, the mountains trapped enough of the pollution that the researchers were there to measure that they couldn't see the mountains from the foothills of the Sierra Nevada. That may sound like a place to avoid on days when the air quality index climbs into the unhealthy zones. But, the Penn State meteorology team is seeking those hot spots out as part of a five-year study to improve NASA's ability to monitor air quality from satellites.
The Penn State researchers' role in the project is acting as ground control, or, as meteorology professor Anne Thompson put it, "ground truthing." Even though it might seem like pollution and ozone should be easy to detect and measure from a satellite, clouds can literally create white space in the data that satellites are trying to capture.
Doug Martins, a research associate working on the project, said that in fact satellites are "notoriously limited for their ability to see what's going on at the surface. That's where we live, that's where we breathe.
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"If NASA puts a satellite in orbit, what they want to retrieve is what's going on at the surface. But, looking down they have to look through a lot of atmosphere in order to see the surface, so their signal gets kind of squelched by everything that's going on in the atmosphere."
So, the Penn State team shipped its mobile research unit known as NATIVE - Nittany Atmospheric Trailer and Integrated Validation Experiment - from its home at Rock Springs near the Ag Progress Days grounds across the country to California.
That project gives researchers real-time data on levels of carbon monoxide, sulfur dioxide, nitrogen compounds, ozone and methane to help NASA better understand and forecast air quality. It's also helping NASA develop the ability to monitor global air quality from space and track where pollution comes from and how that changes over time. That will provide valuable information to policy-makers.
"You want to monitor this because you want to see how humans are impacting the atmosphere," Martins said. "Meteorology doesn't respect political borders or state borders. ... So, where is the pollution coming from? In order to answer those questions, you need to monitor this pollution."
The data is also part of long-term predictions related to climate change. Some of the pollution that is being emitted are greenhouse gases and will affect the climate, said Thompson, who is part of Penn State's Earth and Environmental Systems Institute.
"Pollution variability translates into climate variability," she said.
In addition to the sources of pollutions there are natural variabilities that affect the levels of pollutants.
"So it might be a wet year and some of the pollution gets washed away. Other years, these large scale oscillations might aggravate things. In any one given year, it can make things better in one place and worse in another," Thompson said.
And human behavior has an impact, too, as was seen in 2009 when nitrogen oxides dropped with the economy.
California was the most recent stop for NATIVE, but the high-tech trailer was in the Baltimore/Washington, D.C., area in summer 2011. Next up for the NASA project - known as DISCOVER-AQ or Deriving Information on Surface conditions from Column and Vertically Resolved Observations Relevant to Air Quality - is Houston in September 2013, with the final destination to be decided in time for the summer 2014 season.
"Each site was chosen because it has a unique chemical environment, unique sources of the pollutants," Thompson said. "But they also have unique meteorology that aggravates the pollution problem."
In the San Joaquin Valley, for example, a combination of agriculture and oil wells has an impact on the air in a valley that's stuck between two mountain ranges. On chilly days, when farmers were using diesel-powered equipment to warm their orange groves, the levels of reactive nitrogen would spike.
To take the measurements, the Penn State team used what are known as ozonesondes to measure ozone, temperature, humidity and pressure. A sonde is carried on a large weather balloon that ascends into the stratosphere (100,000 feet above ground), transmitting data back to the ground before the balloon bursts. Another instrument allows for remote sensing of aerosol particles by shooting a green laser into the atmosphere. Based on the return light, the researchers can tell the quantity of aerosol particles in the atmosphere.
Those measurements were taken as a NASA plane flew past the team three times a day to allow for comparisons of measurements from the sky and the ground. Eventually, if the satellites can get global measurements, scientists will be able to track pollution.
The pilot on one trip, Martins noted, described it as looking into a bowl of smog soup, because the mountains trapped the pollutants in the bowl.
"We want to know what the ingredients in the soup are - fingerprint the causes," Thompson said.
As the Penn State team collected the data, that information was shared with the team on the plane making the rounds for hours. Using the ground data they improve their algorithm and fine tune their measuring.
The data is publicly available and free to researchers and anyone who is interested. For more information about the project, including data, visit http://discover-aq.larc.nasa.gov/ and http://ozone.met.psu.edu.
Anne Danahy is a writer with Penn State's Earth and Environmental Systems Institute.
Editor's note: The Focus on Research column highlights different research projects being conducted at Penn State. Each column will feature the work of a different researcher from across all disciplines.