NASA¹s WB-57 aircraft in Houston in spring 2011; the Single Particle Soot Photometer is on the lower left in the aircraft pallet in the foreground. Members of the David Fahey team include: Ru-Shan Gao (far left), Anne Perring (third from left), Laurel Watts (fourth from left), Fahey (fifth from left) and Joshua Schwarz and Ryan Spackman (not pictured). Photo courtesy David Fahey

In hot pur-soot

Researchers monitor black carbon levels

By Kristin Bjornsen

Soot from coal burned in China ends up as haze over Hawaii—in concentrations that rival urban centers. “These are some of the highest levels of black carbon that we’ve seen in remote areas like the middle of the Pacific Ocean,” CIRES Fellow and NOAA scientist David Fahey said. “It likely flowed over from Asia.”

The burning of coal, diesel, biofuel, such as firewood, and biomass (for example, agricultural waste, forests and grasslands) releases black carbon, a fine particulate that makes up soot. Because these tiny particles penetrate deep into the lungs, long-term exposure can cause emphysema, chronic bronchitis and asthma, while the organic byproducts that often coat the particles may raise cancer risk. In terms of global climate, black carbon is also an important heat-trapping agent, absorbing solar radiation and affecting cloud formation.

State-of-the-art monitoring of soot is now giving researchers an unprecedented look at its global distribution and behavior. “We’re interested in exactly how much there is, where it came from and what its fate is,” Fahey said. As part of the HIAPER (High-Performance Instrumented Airborne Platform for Environmental Research) Pole-to-Pole Observations of Carbon Cycle and Greenhouse Gases study, Fahey and his team outfitted NCAR’s long-range jet with a soot photometer. On five missions

between January 2009 and September 2011, the plane will have flown more than 40,000km on each circuit between latitudes 67°S to 85°N—roller-coastering from 0.5km to 8.5km, continuously sampling the air. “This gives us a wealth of information about the vertical, ‘ground to the top of the atmosphere’ distribution of materials,” Fahey said.

The data are essential for improving model predictions, which currently have black-carbon uncertainty factors of 10 to 100, Fahey said. “A lot of air pollution and climate science hinges on models, so they need to accurately reflect the atmosphere and not some fantasy planet,” he said. “These fundamental observations can feed into the models so the projected values are closer to reality.”

Fahey’s team also took lower-elevation measurements, which are more relevant to the air we breathe,

in the Los Angeles region, as part of the CalNex 2010 project (see The lowdown on CalNex). These yielded heartening results. Despite a steady increase in the use of diesel in L.A., black carbon concentrations are lower now than in 1965 because of government regulations. “Without such stringent standards, L.A. could have looked more like what you see in the Pearl River Delta in China, where levels are up to 10 times higher,” Fahey said.

The work being done by Fahey and others will help policy makers decide how to best achieve such reductions. “If we know how much black carbon there is, we can ask, ‘How many people are breathing this? Is that bad for them? How bad? Where are the hot spots?’” Fahey said. “And since this is happening in all the world’s cities, everybody has to act in concert to reverse the systematic effects.”