ABOVE THE SAN JOAQUIN VALLEY -- A pair of NASA airplanes crisscrossing the sky and doing stomach-turning loops are giving scientists a 3-D look at winter air pollution in a way they've never seen before.
The flights are part of a five-year, $30 million mission called DISCOVER-AQ, an effort to help researchers develop the next generation of satellites to measure air pollution from space.
Jim Crawford, the mission's lead investigator from NASA's Langley Research Center in Virginia, explains how the airplanes work with monitoring stations on the ground to provide a better understanding of how air pollution forms and mixes.
The valley's unique geography — flat land ringed by mountains — and stagnant winter weather are the perfect lab for pollution research, Crawford said: "This is a great place to come."
The valley is the second of four places in the United States where scientists are using the aircraft and ground stations to learn about pollution formation.
One of the planes, a four-engine P-3B Orion, has attracted considerable attention with its low-level passes and circles over and around valley cities. Instruments on the plane measure the air quality at altitudes from less than 1,000 feet to about 9,000 feet.
At the same time, a smaller plane cruises at about 26,000 feet, using lasers and reflected light to simulate how an orbiting satellite sees the atmosphere over the valley.
Tuesday was the fifth of 10 scheduled DISCOVER-AQ flights over the region, and the last before a weather front came through to help clean the air. When flights resume, perhaps as early as this weekend, scientists hope to examine how pollution forms from a clean slate and worsens with time in the region. "We arrived here at an ideal time for us," Crawford said.
Winter soup
Winter weather in the valley creates an accumulation of very fine dust and chemical particles, compared with the summer, when chemicals that create ozone are more prevalent. But conditions can change daily or hourly.
Ground stations operated by the San Joaquin Valley Air Pollution Control District and the California Air Resources Board give air-quality regulators a snapshot of what's happening on Earth's surface. Satellites that pass over once a day offer a glimpse at the atmosphere at that time.
But satellites in space cannot distinguish whether pollution is in the upper atmosphere, near the surface, or somewhere in between.
"Trying to make a judgment about what the regulator wants to know — which is what you're breathing on the ground — and teasing that apart is not the easiest thing to do right now with satellites," Crawford said.
NASA's project is filling the gap.
The P-3B is festooned with probes that suck air as it climbs and descends. The probes connect to eight instruments that identify chemicals in the air and their concentrations at different altitudes. Scientists get a real-time look at the gunk that blankets the valley between winter storms.
David Lighthall, health science adviser for the valley air district, said the research will help his agency better predict pollution problems for the region's residents.
"They're laying the foundation for an improved model for both ozone and PM-2.5 (fine particles)," Lighthall said. "From these studies, they're collecting fine-grained meteorological information over time, to get different combinations of information that we can relate to our ground-level observations."
By improving computer models to match atmospheric and ground-level data, "we'll have a better ability to predict what we're going to see under specific sets of conditions," he added.
Each of the P-3B's 7½-hour missions takes off in the morning from NASA's Dryden Aircraft Operations Facility in Palmdale and flies a course that includes stomach-turning spirals over Bakersfield, Porterville, Hanford, Huron, Tranquillity and Fresno. It repeats that course two more times, providing data from the morning, midday and afternoon as conditions change.
Up, up and away
The scientific instruments aboard the plane showed that Tuesday was a particularly dirty day. As the airplane descended, the machines showed a sharp rise in the chemicals and particles at altitudes of less than 2,000 feet. The meters then dropped off as the airplane climbed.
That corresponded with the view from the cockpit, where a layer of gray-brown haze was trapped at less than 2,000 feet.
"Boy, I'm glad I don't live here," said Alan Fried, a senior researcher from the University of Colorado at Boulder. His job on the plane is to monitor formaldehyde with a machine called an infrared spectrometer.
Since the valley missions began Jan. 16, Crawford added, "we've seen the particulate levels over Bakersfield double over the past six days."
That changed Wednesday, the first of several days when weather fronts stirred things up to clean the atmosphere. The fronts not only give Crawford and the other researchers a break from a hectic flight schedule, but set the stage for a new set of measurements when flights resume.
"We are looking forward to sort of resetting the situation and watch it happen again," Crawford said.
The team will have plenty of chances to reset situations during its five-year mission. DISCOVER-AQ research began with flights over Baltimore and Washington, D.C., in the summer of 2011. This fall, the research team will move on to Houston. The research will wrap up with a fourth city or region in 2014.
All that data — including the measurements from 180 spirals over the valley cities — "will prepare us to make better observations from space, as well as determine the best mix of observations to have at the surface when we have new satellites in orbit," Crawford said. He added that NASA expects to launch its newest generation of air-quality satellite, called TEMPO, in 2017.
A smarter satellite can help air-quality regulators understand how pollution develops and forms at different levels of the atmosphere.
"Ultimately, from space you don't want to just say it's polluted or it's not," Crawford said. "You want to know the degree to which it's polluted, and you want the satellite to help you find models to strategize what emissions can be addressed to make things better."
On the Net: http://discover-aq.larc.nasa.gov.
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