HR: 12:00h
AN: A32A-05    [Abstracts]
TI: Soil emissions of nitrogen trace gases in the Mojave Desert under elevated carbon dioxide: implications for regional tropospheric chemistry.
AU: * Sparks, J P
EM: jps66@cornell.edu
AF: Cornell, E149 Corson Hall, Ithaca, NY 14853 United States
AU: McCalley, C K
EM: ckm27@cornell.edu
AF: Cornell, E149 Corson Hall, Ithaca, NY 14853 United States
AU: Jin, V L
EM: vjin@wsu.edu
AF: Washington State University, PO Box 644236, Pullman, WA 99164 United States
AU: Evans, R D
EM: rdevans@wsu.edu
AF: Washington State University, PO Box 644236, Pullman, WA 99164 United States
AB: Understanding the exchange and transformation of compounds at the biosphere - atmosphere boundary is critical to predict the consequences of global change on future atmospheric composition. We present here observations of nitrogen trace-gas efflux from Mojave Desert soils under ambient and elevated CO₂ conditions. Measurements were conducted at the Nevada Desert Free Air CO₂ Enrichment Facility (FACE) north of Las Vegas, Nevada, USA. Previous results from this site have demonstrated that elevated CO₂ has increased microbial functional diversity and, therefore, potentially altered the magnitude and composition of trace nitrogen gas efflux. A shift in emission between the ozone precursor NO and aerosol-producing ammonia under elevated CO₂ would have profound influences on atmospheric composition and global temperature forcing. Nitrogen effluxes from the soil were quantified using a custom-built reduction system and traditional electron-capture chromatography to quantify fluxes of NH₃, NO, NO_y, and N₂ O. Under ambient CO₂ conditions, soil emissions were dominated by emissions of NO (0.35 nmol m^-2 s^-1) with smaller emissions of non-NO NO_y compounds and NH₃ (0.074 and 0.053 nmol m^-2 s^-1, respectively). After a seven-year elevated CO₂ treatment of 550 ppmv, soil emissions are now dominated by ammonia (0.22 nmol m^-2 s^-1) with smaller emissions of NO (0.13 nmol m^-2 s-^-1) and non-NO NO_y (0.05 nmol m-2 s-1). If the shift from NO to NH₃ soil emission under elevated CO₂ observed in this study were common across arid lands globally, the potential would exist, depending on the ensuing atmospheric chemistry, to shift regional emissions from precursors of tropospheric ozone production to precursors of secondary organic aerosols. Such a shift could potentially alter the regional atmosphere from a positive (NO induced tropospheric ozone production) to a negative global temperature forcer (increased aerosol production and cloud formation) independent of carbon dioxide concentrations.
DE: 0305 Aerosols and particles (0345, 4801, 4906)
DE: 0315 Biosphere/atmosphere interactions (0426, 1610)
DE: 0365 Troposphere: composition and chemistry
DE: 0426 Biosphere/atmosphere interactions (0315)
DE: 0469 Nitrogen cycling
SC: Atmospheric Sciences [A]
MN: Fall Meeting 2005