BIOLOGICAL INPUT TO VISIBILITY-REDUCING AEROSOL-PARTICLES IN THE REMOTE ARID SOUTHWESTERN UNITED-STATES

Source contributions of contemporary biological material to remote airsheds of the arid southwestern United States are described. Combined inputs of epicuticular plant waxes and airborne microorganisms range from winter minimum (11.3-26.9 ng/m3) to summer maximum ambient mass concentrations (21.2-41.4 ng/m3). Concentrations of aromatic resin acids (i.e., dehydroabietic acid and 13-isopropyl-5-alpha-podocarpa-6,8,11,13-tetraen-16-oic acid) plus a thermally matured wood smoke marker (i.e., retene) range from 1.2 to 9.6 ng/m3. Minimum levels of the resin acids and wood smoke marker are observed for the sparse desert vegetation site (low elevation), and maximum levels are found for the transition site of ponderosa pine and pinyon/juniper forest (high elevation). The total wood smoke mass contributions were estimated by using the ambient mass concentrations of both the aromatic resin acid and wood smoke tracers. Based on these estimates, combustion of conifer biomass (e.g., natural wildfires, camp fires, home heating) is an important component of the organic emission source inventory for this desert region.