ACD Studies Globe-Trotting Chemicals
When massive forest fires in Indonesia released nearly a billion tons of hazardous gases into the air in 1997, scientists investigated the chemicals that were emitted and their potential impact on the global environment. They also became interested in the global impacts of other types of emissions, including the effect that increasing industrial activities and growing automotive trafficless tightly regulated in many Asian countries than in the United Statescould have on North America.
Industrial emissions can have far-flung atmospheric effects.
These types of questions formed the genesis of the Intercontinental Transport and Chemical Transformation 2K2 project. Last spring, ITCT researchers used both aircraft and ground-based instruments in a field campaign to measure a wide range of chemical species over the U.S. West Coast and adjacent areas of the Pacific Ocean. The project, led by NOAA with the participation of NCAR and 32 other government, university, and industry research centers, was designed to measure and track chemicals as they are transported across the Pacific Ocean to the United States.
The goal of ITCT is to understand the intercontinental transport of chemicals such as ozone, carbon monoxide, and nitrogen oxides, as well as airborne particles, or aerosols (see sidebar on pollutants, page 6). In addition to studying the transport of chemicals, the project also examines their impact on climate and air quality.
Several studies have been conducted on pollutants that travel from the East Coast of the United States toward Europe and from the western coast of Asia toward the United States. But according to Peter Hess of the Atmospheric Chemistry Division, this West Coast study is the first of its kind. Unlike earlier West Coast studies that have used localized measurements, ITCT marks the first time incoming pollutants have been measured and analyzed along the entire length of the coast.
MOZART sets the tune
Using meteorological fields and chemical emissions as inputs, NCAR scientists Peter Hess and Jean-Francois Lamarque applied a sophisticated computer model to forecast events when Asian chemical emissions strongly impact the West Coast of the United States. Although various models were used in the ITCT field project, the team turned to the Model for Ozone and Related Chemical Tracers 2 (MOZART-2) to forecast the complex chemistry of Asian emissions.
Of particular interest in the ITCT project were pollutant transport eventsdistinct, measurable layers of pollutants (like ozone) in contained, well-defined areas. These events are comparatively easy to track and measure.
The researchers used MOZART, along with other global and regional models, to map predicted pollutant event locations and plan flight paths to intercept these events. Then planes were sent into the troposphere to measure chemical levels and confirm the forecasted pollutant events.
Impact of Asian emissions
Only a few events with distinctly elevated levels of Asian pollutants were detected and measured by the researchers on the airplanes. Most of these occurred in very thin layers but with pollutant concentrations elevated over twice the background levels. However in many locations, like Los Angeles, local factors, such as factory emissions, are of much greater concern than transcontinental pollutants, explains Peter.
Model calculations suggest the impact of Asian-based pollution is generally less than 2025% of local pollutant levels on the West Coast. However, an increase in Asian pollutants might offset the effects of more stringent restrictions on U.S. pollutants.
Researchers will use models like MOZART to determine if 2002 was a normal year for the transport of Asian pollutants to the United States. Another question for investigation is the effect of atmospheric events like this years El Niño on the transport of chemicals.
The Intercontinental Chemical Transport ExperimentNorth America (INTEX-NA) will be an extension of the ITCT 2K2 project. This experiment, to be performed over North America in 2004 and 2006, is designed to examine the atmospheric chemical budget of the United States. The project would measure both outgoing pollutant events, primarily from the East Coast, and incoming pollutant events, primarily to the West Coast. Ellen Leslie