Scientists using NASA satellites and computer models have shown that pollutants from Central American biomass burning can influence air quality and climate in the United States.

A NASA-funded study published in the July 26, 2006 Journal of Geophysical Research-Atmospheres found that during April-May 2003, large amounts of smoke, which include aerosols -- tiny particles suspended in the air -- from biomass burning in the Yucatan Peninsula and southern Mexico reached Texas, Oklahoma, and other areas in the southeastern United States.



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Image above: These images from the Moderate Resolution Imaging Spectroradiometer (MODIS) on the Terra and Aqua satellites on May 9-12, 2003, shows the transport of smoke plumes. Red dots indicate the location of fires. Credit: Jun Wang and Sundar Christopher/University of Alabama-Huntsville

The smoke plumes degraded visibility and air quality in coastal regions along the Gulf of Mexico and resulted in the greatest concentration of small particulate matter in southern Texas since 1998. By blocking incoming sunlight, the smoke plumes also cooled surface air temperatures over land. But higher in the atmosphere the smoke absorbed solar radiation and warmed temperatures. This created a circulation pattern that trapped smoke aerosols in the lower atmosphere, worsening air quality.

The researchers used a newly developed computer model to simulate the transport and effects of smoke in the atmosphere and on the Earth's surface. The model couples aerosol properties with meteorology and uses hourly smoke emission data from the NASA-led Fire Locating and Monitoring of Burning Emissions (FLAMBE) project. FLAMBE is a joint effort by NASA, the U.S. Navy, the National Oceanic and Atmospheric Administration and university partners to develop smoke aerosol forecasting models for the benefit for the global weather community.

Image right: This May 11, 2003, Sea-viewing Wide Field-of-view Sensor (SeaWiFS) image shows that much of the country's weather was dominated by a low-pressure system centered near Lake Michigan. The system carried smoke from the fires across Central America into the Gulf Coast states and northern Caribbean. The grayish haze just left of the bottom center of this image is smoke from the fires burning in Central America. Credit: NASA

"Although this computer model is not currently used in air-quality and weather forecasting, it is superior to other models for this purpose because it explicitly accounts for the diurnal variation of smoke emission from biomass burning fires and the radiative impacts of aerosols so that their impact on meteorology can be studied," said study co-author Sundar Christopher of the University of Alabama, Huntsville, Ala.

Comparisons with ground-based observations and imagery from NASA's Moderate Resolution Imaging Spectroradiometer (MODIS) on the Terra and Aqua Earth Observing System satellites showed that the model accurately simulated the impact of smoke on air temperature and the amount of sunlight absorbed and scattered through the atmosphere.



Image right: The top image shows clouds with low aerosol concentrations and few large droplets that do not scatter light well, and allow much of the Sun's light to pass through and reach the surface. The bottom image shows clouds with high aerosol concentrations that provide the nucleation points necessary for the formation of many small liquid water droplets. Up to 90 percent of visible light is reflected back to space by such clouds without reaching Earth's surface. Credit: NASA

MODIS data was particularly useful in determining how aerosols from the Central American fires affected the amount of sunlight passing through the atmosphere, which can impact surface and atmospheric temperatures. "MODIS data allows us to capture the meteorological impacts of smoke and aerosols, especially important during the tropical dry season each spring when biomass burning peaks and pollutants are transported to the United States," said Christopher.

Smoke particles and aerosols scatter incoming sunlight while black carbon aerosols absorb solar radiation, affecting the atmospheric temperature profile. In turn, this alters evaporation and cloud formation. Smoke particles also often act as cloud condensation nuclei -- small particles on which water vapor condenses and forms clouds -- influencing the formation and distribution of rainfall. When combined with certain weather patterns, these aerosols can also have a significant impact on local and regional air quality according to the study.

This work demonstrated a new capability to improve air quality and climate forecasts, but researchers need to learn more about how smoke and aerosols impact clouds. "New satellite data, including that from the joint NASA and French Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation satellite, should help us better understand cloud microphysical processes and how aerosols impact cloud formation," said Christopher. Combining this information with improved computer models will help scientists better understand the role of smoke and aerosols on the climate to improve forecasts, even when the pollutant source is thousands of miles away.

The authors of this and a previous related study included former NASA Earth System Science fellow Jun Wang of Harvard University; Sundar A. Christopher and U. Nair, University of Alabama-Huntsville; Jeffrey Reid, Naval Research Laboratory; Jenny Hand, Colorado State University; Jim Szykman, NASA Langley Research Center; and Elaine Prins, University of Wisconsin.

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Mike Bettwy
Goddard Space Flight Center