For a fuil list of publications, visit the Atmospheric Research Lab's page: http://instaar.colorado.edu/arl/publications.html
Surface-Atmosphere Ozone fluxes at Summit, Greenland
Previous research in Polar Regions has demonstrated that chemical and physical interactions between the snowpack and the overlaying atmosphere have a substantial impact on the composition of the atmosphere. Deposition and scavenging of gases and aerosols result in the accumulation of a chemical reservoir that subsequently, under conditions of increasing temperature and solar irradiance can turn into a photochemically active reactor. These reactions result in the formation of radicals, the release of chemicals into the atmospheric surface layer, and consequently influence concentrations and budgets of important tropospheric trace gases.
Recent observations of photochemical depletion of ozone in firn air, diurnal ozone trends in the surface layer, tethered balloon vertical profile data and estimates of photochemical ozone production all imply that ozone deposition to the snowpack depends on parameters including the quantity and composition of deposited trace gases, solar irradiance and snow temperature. Consequently, ozone surface fluxes in Polar Regions are expected to have snow photochemical, diurnal and seasonal dependencies and to overall be more complex and possibly larger than considerations in global atmospheric models. Current literature does not reflect these conditions and ozone flux estimates to year-round snow are contradictory and are suspected to have large errors.
The objective of this research is to study the diurnal and seasonal ozone deposition to the year-round snowpack and investigate dependencies of ozone deposition on environmental and snow photochemical conditions. This study will employ sensitive flux measurement approaches by eddy correlation, by the tower gradient method and by measurements of ozone in the interstitial air. Field measurements will be performed during three experiments at Summit, Greenland during a wide variety of environmental and seasonal conditions.
Development of Ship-Borne Eddy Correlation Ozone Flux Measurements
Over the past century tropospheric ozone has been steadily increasing. A further future rise is anticipated due to increasing anthropogenic emissions of ozone precursor compounds including carbon monoxide, reactive hydrocarbons and nitrogen oxides. Increased ozone levels are of concern for both plant and animal life on Earth. Furthermore, the added portion of tropospheric ozone is estimated to contribute ~ 13 % to anthropogenic greenhouse gas forcing, which places ozone the third most important greenhouse gas after CO2 and methane (IPCC, 2001). Assessments of future ozone and development of ozone control strategies require accurate descriptions of both sources and sinks of ozone for incorporation in global atmospheric chemistry models that develop predictions of future ozone trends from anticipated changes in fossil fuel emissions, land use and global environmental change. A constraining parameter in the improvement of these models is the inaccurate description of ozone fluxes over the Earth's oceans. Current literature data is very limited and lacks dependencies of the ozone deposition rate on the ocean's biological, chemical and physical properties. The sparseness of these data is mainly due to the fact that, until very recently, direct ozone ocean flux studies from ship-borne platforms were technically impossible. Previous data mostly resulted from laboratory experiments, enclosure studies and a few ambient level measurements with tower observations in coastal regions. Over the past ten years, intensive research efforts in ship-based eddy covariance measurements (ECM) have resulted in technical advances where ship motion can be monitored and corrected from 3D sonic anemometer turbulence data. These methods have now successfully been applied to ECM of the air-sea flux of carbon dioxide. Similar to carbon dioxide, ozone can be captured for ECM with a selective, fast response chemiluminescence instrument. In this research it is proposed to build and deploy a highly sensitive and fast response ozone analyzer for air-sea ozone flux ECM. This experiment will complement established technology for ECM from a ship platform. Besides the testing of this new technique, the plethora of concurrent chemical, physical and biological ocean water measurements will offer an opportunity to investigate, for the first time, the variations and biological dependencies of ocean ozone fluxes.
A synthesis of existing and new observations of air-snowpack exchanges to assess the Arctic Tropospheric Ozone Budget
Investigation of ozone photochemistry in lower free troposphere continental outflow traveling over the North Atlantic
Air-sea gas transfer over the Southern Ocean in GasEx III
A study of biomass burning and anthropogenic impacts on Arctic tropospheric chemistry using measurements at Summit, Greenland, as part of the POLARCAT International Polar Year Project
Sesquiterpene Emissions from Vegetation: Sesquiterpene Emissions from Natural, Urban and Agricultural Vegetation in the United States
The potential contribution of biogenic volatile organic compound (BVOC) emissions to atmospheric secondary organic aerosol has been a matter of speculations and scientific debates for more than 40 years. Research during the past 10 years has slowly manifested this role of BVOCs in aerosol formation. However our understanding of contributing plant species, chemical compounds and the environmental atmospheric conditions that trigger biogenic aerosol formation are far from allowing us to derive desired quantitative assessments of the role of BVOC to the formation of secondary aerosol.
Sesquiterpene (SQT) hydrocarbon emissions have been observed from many types of natural and agricultural vegetation. Of all BVOC studied so far, SQT have the highest (almost quantitative) yields of aerosol products. Due to their high reactivity and relatively low vapor pressure, SQT are easily lost and overseen in common chemical analysis procedures. Consequently, to date most reports on SQT have been qualitative and of preliminary nature. These preliminary studies indicate that SQT are emitted at sufficient levels to be the dominant source of secondary organic aerosol in at least some regions. Over the past two years a designated SQT calibration instrument was built, which subsequently was used for investigating and calibration of SQT measurement techniques. In this new project it is now proposed to apply quantitative techniques for the study of biogenic SQT emissions. SQT fluxes will be investigated from the dominant vegetation in natural, agricultural and urban landscapes in the U.S. Vegetation will be surveyed by environmentally controlled enclosure experiments (leaf cuvette and branch enclosure). Emission samples will be collected on inorganic solid adsorbents and SQT will be identified and quantified in the field by thermal desorption/gas chromatography with mass spectrometry and flame ionization detection. Secondly, SQT emission rates will be investigated in their response to ambient parameters such as temperature and light for developing seasonal emission estimates.