CAPPS takes off

The sources of Southern California smog are identified in a unique survey

Southern California is as famous for its smog as it is for its otherwise pleasant weather. But where does the smog come from?

In a new survey that employs revolutionary technology, scientists at Scripps Institution of Oceanography at UC San Diego have begun to assess Southern California's potential for future climate change and better understand the origins of its air pollution through the California AUAV Air Pollution Profiling Study (CAPPS).

CAPPS, which began data collection on April 2, features the use of autonomous unmanned aerial vehicles (AUAVs) that can gather a suite of meteorological data as they fly through clouds and aerosol masses in Southern California skies. When flying in formation, the aircraft can provide researchers with an unprecedented three-dimensional view of clouds and aerosol masses in the atmosphere.

Scripps Atmospheric and Climate Sciences Professor V. Ramanathan, CAPPS' lead scientist, said the characteristics of Southern California climate and meteorology ranging from its dry weather to its tendency to trap rather than export smog could make it especially prone to climate change consequences such as accelerated snowmelt in area mountains and dimming at ground level.

"These monthly flights will provide unprecedented data for evaluating how long-range transport of pollutants including ozone, soot, and other particulates from the northwest United States, Canada, east Asia, and Mexico mix with local pollution and influence our air quality and regional climate, including the early melting of snow packs," he said.

The data-gathering flights originate at Dryden Flight Research Center,  located on the grounds of Edwards Air Force Base near Palmdale, Calif. The missions are expected to continue through January 2009, offering researchers a chance to view seasonal variations in air pollution.

Ramanathan's team revolutionized the gathering of atmospheric data in 2006 when the researchers first successfully deployed the aircraft in the Maldives AUAV Campaign (MAC). Miniaturized instruments on the aircraft, which flew in stacked formations of three, measured a range of properties such as the quantity and size of the aerosols on which cloud droplets form. The instruments also recorded variables such as temperature, humidity and the intensity of light that permeates clouds and masses of smog. It was the first time such comprehensive measurements were made at a low cost relative to traditional manned flights.

The Scripps researchers have used data from MAC and other field campaigns to observe that a pervasive mass of air pollution in south and east Asia, commonly referred to as the "atmospheric brown cloud," can disrupt rainfall patterns and cause cooling at ground level but warming at higher altitudes. The cloud typically contains a mix of dust, sulfates and soot and other forms of black carbon. These aerosols are primarily the products of agricultural biomass burning, use of wood- and cow dung-burning stoves in rural homes, and the use of coal in home heating.

Ramanathan linked the brown cloud to an observed acceleration of glacial melt in the Himalayas. Himalayan glaciers provide billions of people in Asia with their drinking water.

In CAPPS, the Scripps team hopes to determine how much of Southern California's air pollution comes from Asia, Mexico and from regions north of California. Scientists routinely observe aerosol masses traveling across the Pacific Ocean to the West Coast but are still trying to understand the effects of that pollution. The imported smog is only one of several sources of atmospheric aerosols in Southern California, joining local auto and industrial emissions and smoke from wildfires. Researchers have seen evidence that this air pollution can mix with falling snow and accelerate its melt when sunlight hits and warms the "dirty" snow in mountain watersheds.

The California Energy Commission's Public Interest Energy Research (PIER) program will use CAPPS results in an analysis of the potential future economic and ecological consequences of Southern California air pollution. Scientists also hope to combine CAPPS results with satellite data to better understand the role of aerosols at a larger regional scale.

The aircraft will profile atmospheric conditions at altitudes ranging between 2,000 and 12,000 feet. Because of Federal Aviation Administration regulations that prohibit unmanned aircraft from flying in public airspace, the flight paths will be limited to military airspace, which is exempted from FAA rules. The researchers hope to conduct the flights at least once a month or as often as every two weeks depending on resource availability. The Scripps team also hopes to gather data on a situational basis such as during wildfires.

Primary funding of CAPPS comes from the California Energy Commission. Additional support comes from NASA.

Robert Monroe