Atmospheric effects of large fires: spring 2000 Cerro Grande, NM (Los Alamos) fire

Large wildfires (that is, greater than a few thousand acres) have the potential to release significant quantities of combustion products that can impact atmospheric concentrations at sites distant from the fire area. These combustion products can include: particulate material with associated trace metals and radioactivity; carbon, sulfur and nitrogen oxides; hydrocarbons; and oxygenated species such as aldehydes, ketones and carboxylic acids. In addition to the effects wildfires may have on atmospheric species, the proximity of these fires to human population raises health concerns. Examples of such fires are the Mexican/Central American fires in 1998, the Indonesian fires in 1997, and recent fires at sensitive sites such Los Alamos, NM and Hanford, WA. The latter two fires are of particular concern because they had the potential for the release of radioactive materials.

In this report we present data from the Cerro Grande Fire near Los Alamos, NM. The fire began June 7, 2000 as a controlled burn by the U.S. National Park Service in Bandelier National Monument and quickly became uncontrolled, eventually consuming almost 50,000 acres, destroying over 200 homes and structures, and threatening sensitive areas at Los Alamos National Laboratory. Sampling was conducted about 16 km downwind from the fire in Española, NM from June 12-17. The fire was contained shortly thereafter but continued to burn within the containment area. Analyses were performed for condensation nuclei, PM10, PM2.5, gross a radioactivity, trace metals and soluble anions in particulate material, hydrocarbons, ozone, NOx, and low molecular weight carbonyl compounds and carboxylic acids. Preliminary results indicate low gross alpha activity on particulates, which also was independent of particle size. The presence of the smoke plume was evident through high condensation nuclei counts, and slightly elevated levels of volatile organic compounds occurred during the smokier periods. Several trace metals (Zn, Cd, Mo, Cr, Pb, and Hg) were enhanced on smaller particles relative to non-fire conditions. NOx levels were generally higher during the fire and increased when smokier episodes occurred. When compared to a similar site in the region, the ozone concentrations and behavior showed little impact from the fire. Oxygenated hydrocarbons increased from 2-4x during the fire relative to a similar site under clean air conditions.