|DISCOVER-AQ instrumentation deployment strategy. Source: NASA. Click to enlarge.|
This summer two NASA research airplanes will fly over the Baltimore-Washington region and northeast Maryland as part of a mission to enhance the capability of satellites to measure ground-level air quality from space. The flights will be supported by the US Environmental Protection Agency (EPA) and will aid EPA in monitoring pollutants.
The project—Deriving Information on Surface conditions from Column and Vertically Resolved Observations Relevant to Air Quality (DISCOVER-AQ)—will help researchers develop a three-dimensional view of how air pollutants are distributed and move between different levels of the atmosphere throughout the day. The fundamental challenge for satellites measuring air quality is to distinguish between pollution near the surface and pollution higher in the atmosphere. Measurements from aircraft, in combination with ground-based measurements, offer a key perspective that makes such distinctions easier to make.
Twelve to fourteen flights are planned throughout July using two primary planes. Ground-based instruments will offer a critical view of the same patches of air the aircraft are monitoring from above. Test flights begin as early as 27 June followed by up to 14 flights during July using two NASA planes. Sampling will focus on an area extending from Beltsville, Md., to the northeastern corner of Maryland in a pattern that follows major roadway traffic corridors.
Ground sites maintained by the Maryland Department of the Environment form the backbone of the surface network. These sites will supplemented by additional instrumentation provided by NASA, EPA, Howard University, Pennsylvania State University, the University of Maryland-Baltimore County, and Millersville University in Pennsylvania. In the air, NASA investigators will be joined by colleagues from the National Center for Atmospheric Research, the University of California-Berkeley, and the University of Innsbruck in Austria.
The P-3B, a four-engine turboprop that returned recently from a deployment to the Arctic, will carry a suite of nine instruments, while a smaller two-engine UC-12 (military version of the King Air) will carry two instruments.
Both aircraft will measure ozone and a mixture of soot and PM. Other instruments on the P-3B will measure pollutants that lead to the formation of ozone such as nitrogen dioxide and formaldehyde. A third aircraft, a Cessna operated by the University of Maryland, will also participate in the campaign.
While the UC-12 will cruise at high-altitudes—about 26,000 feet—the P-3B will fly corkscrew patterns over six ground stations in Maryland that will bring the plane from its highest altitude of about 15,500 feet to as low as 1,000 feet from the surface.
The two instruments aboard the UC-12 will look down at the surface, much like a satellite instrument might, and measure particles and trace gases. The P-3B, in contrast, will sample the air it flies through, allowing it to take samples from a variety of altitudes.
The July flights are the first leg of a broader five-year campaign that will bring the aircraft to Houston and other polluted regions during upcoming years.
Measuring pollution from space. Overall, the World Health Organization estimates that air pollution causes some 2 million premature deaths globally per year. Pollutants can spark a whole range of diseases including asthma, cardiovascular disease, and bronchitis.
Since many countries, including the United States, have large gaps in ground-based networks of air pollution monitors, experts look toward satellites to provide a global perspective. Satellites have attempted to collect information about the main air pollutants that affect human health for more than a decade, yet they have struggled to achieve accurate measurements of the pollutants in the air near the surface.
Most satellite instruments can’t distinguish pollution close to the ground from that high in the atmosphere. In addition, clouds can block the view. And bright land surfaces, such as snow, desert sand, and those found in certain urban areas can mar measurements.
We’re better with some pollutants than others, but broadly speaking we have difficulty distinguishing between pollutants high in a given column of air, which we can see quite well with satellites, and pollutants at the surface.— Kenneth Pickering, DISCOVER-AQ’s project scientist
As a result, questions remain about the vertical distribution of pollutants. How far up in the atmosphere are morning and evening spikes in pollution associated with rush hour noticeable? How does ozone, which peaks near the surface in afternoon, behave at other altitudes throughout the day? When is the best time of the day for satellites to measure various pollutants?
The problem is particularly pronounced for pollutants that are abundant at the surface and higher in the atmosphere. For example, a “code red” air-quality day during the summer might produce very high concentrations of ozone in the bottom few kilometers of the atmosphere, yet generate a change of a mere 1 or 2 percent to a total column of ozone.
Studies suggest that discrepancies of as much as 30 to 50% exist between estimates of ground nitrogen dioxide inferred from the Ozone Monitoring Instrument (OMI), an instrument on NASA’s Aura satellite launched in 2004, and measurements from ground-based instruments.
Scientists will use information collected during the DISCOVER-AQ campaign to improve measurements from existing satellites and to help establish parameters for future NASA satellite missions that will monitor air quality.