Project Abstracts :

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.

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Study of Air Transport and Photochemistry in the North-Atlantic Region by Hydrocarbon Analysis at Pico Island, Azores

Several recent large-scale atmospheric chemistry experiments have demonstrated that intercontinental transport of air pollution has a remarkable impact on regional air quality and that synoptic transport of pollution from Asia to North America as well as from North America to Western Europe needs to be considered in the understanding and management of air quality in these continents.  While these episodic campaigns have yielded information of such transport phenomena, the desired improvement of our understanding of the occurrence, seasonality and control of long-range air transport requires continuous, year-round measurements at coastal and remote marine monitoring sites.
The PICO-NARE monitoring station is located near the summit of Pico Island in the Azores, Portugal, and has been developed by Michigan Technological University (R. Honrath) and the University of the Azores (P. Fialho).  NARE, the North Atlantic Regional Experiment, is part of the Intercontinental Transport and Chemical Transformation (ITCT) project of the International Global Atmospheric Chemistry (IGAC) program.  The particular goals of PICO-NARE are to quantify the impact of exported ozone, nitrogen oxides, and black carbon on the regional atmosphere and to identify the atmospheric transport and photochemical history of the encountered air samples.  PICO-NARE is a receptor site for transport from North America as well as from Europe and Africa and has been shown to be a very suitable location for research on long-range transport and atmospheric chemistry from these diverse source regions.
Current measurements at PICO-NARE include carbon monoxide, ozone, Black Carbon, and meteorological parameters.  Further measurements that will commence in 2002 are JNO2, NO, NO2, and NOy. A constraining gap in the interpretation of data is the current lack of hydrocarbon measurements.  This project addresses this need:  We propose to develop continuous (every 2 hours), on-site measurements of volatile organic compounds (VOC) by an automated gas chromatograph (GC) with low parts-per-trillion detection limits.  The GC instrument will rely on established sample collection and injection procedures by multi-stage solid adsorbent concentration with thermal desorption.  Analysis will be performed by two parallel columns with flame ionization and photoionization detection.  Monitored system parameters and GC data will be transferred via ftp to our Boulder laboratory.  Quantified VOC will include ethane, ethene, acetylene, propane, propene, methyl-propane, butane, butadiene, methylbutane, dimethylpropane, pentane, isoprene, benzene, toluene, methyl chloride and methyl chloroform, and possibly selected oxygenated hydrocarbons such as acetaldehyde, methanol, acetone and long-chain aldehydes.
Ambient mixing ratios and relative ratios of selected hydrocarbon pairs will be monitored and used as a sensitive tool to derive information on photochemical history and atmospheric transport from emission sources to when the sample was collected.  Furthermore, analysis of short-lived compounds, such as isoprene and ethene, is a valuable tool for identifying upslope air originating from vegetated areas of Pico and the marine boundary layer.  Correlation of VOC with the observation of the other analyzed gases (see above) and Black Carbon will be investigated.
The measurements proposed in this study will add significant characterization of atmospheric intercontinental transport in the North Atlantic Region.  VOC analysis will decipher air mass history, photochemical properties and enhance data analysis capabilities of current measurements.  This study will support observations for the year 2004 intensive ITCT-2K4, INTEX-NA and EXPORT-E2 field campaigns and provide a means for extension and interpolation of their results to the seasonal and annual domain.

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What are the Expected Changes in Tropospheric Ozone from Reduced Snow Cover?

In this proposed research, we are studying processes that determine the removal of ozone from the atmosphere, in particular the uptake (or release) of ozone by the snow pack.  The past century has seen significant increases in ozone levels in the troposphere.  The increase of ozone is caused by the photochemical formation of ozone from hydrocarbons and nitrogen oxides.  These changes have important impacts on society because enhanced atmospheric ozone levels result in reduced crop yields, health problems and greenhouse warming.  Consequently, an improved understanding of the processes that control the exchange of ozone between the atmosphere and the Earth’s surface is important for predictions of future tropospheric ozone levels.  A particular research need is in the area of snow  atmosphere interactions.  This project will investigate the fluxes of ozone in and out of the snow and the parameters that control these fluxes.  The ozone fluxes will subsequently be used with satellite-derived snow cover maps to assess the effect of snow-covered landscapes on the tropospheric ozone budget.  Snow land cover has been and continues to change dramatically as can be seen by remote sensing data.  The consequences of the changing snow cover on the tropospheric ozone cannot be assessed with the current knowledge of ozone snow-atmosphere interactions.

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Sesquiterpenoid Compound Emissions from Vegetation :
Chemical Analysis Technique for Ambient Measurements of the Contribution to the Formation of Ozone and Aerosols

 An analytical technique for the measurement of sesquiterpenoid compounds (SQT) emitted from vegetation will be developed.  SQT are of special interest because of their suspected participation in aerosol-forming processes and heterogeneous reactions in the atmosphere.  SQT have been identified in plant emissions in numerous studies.  However, their role in atmospheric processes remains uncertain.  This uncertainty is mainly due to the lack of analytical capabilities and experimental measurements of their atmospheric reactions, ambient concentrations, and fluxes.  These compounds pose a challenge to the analytical chemist, and many questions regarding their reliable analysis remain unresolved.
 In this proposed project, methodology for the reliable measurement of SQT will be developed.  This will allow improvements in the data quality of these compounds in 1) experimental enclosure systems such as cuevettes, branch enclosures and chamber experiments and 2) at the ambient level, such as by ambient monitoring, tower gradient flux measurements or relaxed eddy correlation methods.
 A calibration system will be built to generate well-defined gas-phase concentrations of individual SQT and SQT mixtures.  This system will be based on capillary diffusion and will deliver steady output concentrations of the target compounds.  A gas chromatography/flame ionization detection instrument will provide automated and continuous on-line monitoring of the system output.  The calibration system will be designed to allow addition of potential analytical interferences to the analytes, such as water and ozone, in order to study the effects of these atmospheric components on the SQT recovery rate and the analytical precision and accuracy. Sampling, storage and analysis methods using either whole air sampling techniques into bags and canisters and collection onto solid adsorption cartridges will be investigated for their analytical suitability.
 The developed analytical method will be further tested by preliminary measurements of ambient SQT mixing ratios.  These measurements will be performed at a well characterized research site (such as Oak Ridge, TN or Fernbank Forest, Atlanta, GA) where high overall biogenic volatile organic compound (BVOC) fluxes with a significant SQT contribution are expected.  This project will provide a platform to further research the non-isoprene portion of BVOC fluxes and will be an important contribution to the elucidation of how BVOC participate in the atmospheric formation of oxidants and aerosols.

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Sesquiterpenoid Compound Emissions from Vegetation :
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.

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Trace Gas Deposition Processes in the Arctic Boundary Layer

This proposal is concerned with data analyses and modeling activities to gain further insights on the processes governing atmospheric trace gas dynamics, in particular ozone in the Arctic boundary layer. The proposed research activities will lead to improvements in the predictive understanding of tropospheric ozone and other trace gases, which can exert a critical influence in the Arctic chemical and radiative balance. Our studies are motivated to derive further understanding of trace gas deposition rates and will achieve the following objectives:

  1. to investigate the most appropriate methods for estimating trace gas transport in the surface layer of the Arctic atmosphere,
  2. to evaluate the suitability of electrochemical ozone sonde data for deriving ozone deposition rates,
  3. to study and quantify ozone deposition rates at selected Arctic sites based on ozonesonde routinely obtained at selected Arctic sites,
  4. and to define the atmospheric conditions when maximum ozone surface deposition rates take place in the Arctic boundary layer.

These objectives will be addressed through a combination of data analyses and modeling studies employing three data sets deemed to be of high quality. During spring 2000, we obtained high frequency data at Alert, Nunavut, Canada and Summit, Greenland, Denmark. These two data sets, involving vertical meteorological and chemical profiles from towers and tethered balloons, will be analyzed within the framework of investigating the most appropriate methods to derive trace gas fluxes between the surface and overlying atmosphere and/or vice versa. Additional scientific outputs of these activities relate to the turbulent length scales associated with trace gas fluxes in the Arctic boundary layer. Knowledge of turbulent scales is critically essential to understand the atmospheric layer impacted by trace gas emissions from the Arctic snowpack. The third data set involves the archived data from ozonesondes released at selected sites throughout the Arctic. We propose to employ these extensive historical data to develop a one-dimensional model to derive ozone deposition rates to the snowpack surface. Estimated deposition rates will provide upper threshold values that can then be incorporated in regional and/or global models to constrain ozone budgets in the Arctic troposphere. The proposed research will lead to a simple modeling parameterization to routinely derive ozone deposition rates based on the World Meteorological Organization (WMO) ozone monitoring network, and thus provide critical information to decipher the processes governing ozone temporal changes in the Arctic boundary layer. Understanding of ozone dynamics is crucial to define the contribution of ozone in the chemical and radiative balance of the Arctic. Given the recent discovery that the Arctic snowpack represents a substantial source of gases such as nitric oxide, nitrogen dioxide, nitrous acid and formaldehyde, this project will also yield methodologies to deduce fluxes of these important trace gases based on ambient (profile) concentrations.

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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.

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