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Turbulent transport and chemistry of halogens in the Arctic boundary layer

The Arctic is undergoing rapid environmental changes in response to atmospheric warming. The most dramatic and consequential changes in the Arctic are the loss of perennial sea ice and the formation of seasonal ice. The changes are causing impacts and feedbacks on the chemistry and the chemical composition as well as aerosol physical and chemical characteristics in the Arctic boundary over the ocean and the coastal environments. One example of such changes is the rapid, catalytic destruction of ozone by halogens that is routinely observed in the Arctic during the spring when low air temperature and stably stratified air layers provide favorable conditions for complete ozone depletion. Mercury also concomitantly undergoes rapid depletion events in the Arctic boundary layer. Thus, this lecture will summarize the findings of a field campaign that took place in Utqiaġvik, Alaska during March to May 2016. The goal of the field campaign was to develop a quantitative understanding of the impacts of halogens on the chemistry in the Arctic boundary layer. To achieve the goal, air turbulence and air chemistry measurements were made at several levels above the snowpack using a 12-meter tower as the platform to deploy 8 sonic anemometers and air intakes. Atmospheric stable conditions and intermittent turbulence dominated the lower atmosphere. Such atmospheric states modulated the transport of halogens from the snowpack to the overlying atmosphere. Eddy covariance methods were employed to estimate the turbulent transport of halogens. Also, gradient diffusion methods were employed to determine the atmospheric transport of halogens in the Arctic boundary layer using a one-dimensional numerical model. Different eddy diffusivity formulations were developed and tested to determine the most reliable method to estimate the atmospheric transport of halogens based on the gradient diffusion approach included in the one-dimensional model. Comparisons of model outputs with observations were carried out to determine the strength of sources, sinks, and recycling of halogens in the Arctic boundary layer.