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.
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.
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:
- To investigate the most appropriate methods for estimating trace gas transport in the surface layer of the Arctic atmosphere,
- To evaluate the suitability of electrochemical ozone sonde data for deriving ozone deposition rates,
- To study and quantify ozone deposition rates at selected Arctic sites based on ozonesonde routinely obtained at selected Arctic sites,
- 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.