This study will involve the systematic sampling of snow in northern Alaska during the critical springtime period when ozone depletion events (ODE) and mercury deposition events (MDE) take place. It has been known for sometime that unusual chemistry takes place during sunrise at high northern latitudes, in which chemistry involving bromine leads to boundary layer ozone destruction, and deposition of mercury. The details of the source of the bromine and the exact chemical mechanisms are still under study. The deposition of mercury is a potential environmental hazard, and thus it is important to understand the details of the processes. This study will attempt to quantify the functional dependence of mercury deposition and halogen abundance on distance from the ocean source region, meteorology, and other factors. This project leverages the existence of the Barrow Arctic Mercury Study (BAMS) that will provide infrastructure and detailed chemical and physical measurements at Barrow, Alaska, and will extend BAMS through geographical sampling of snow in the region south and west of Barrow. In addition, satellite observations of bromine monoxide (BrO) will be used to track the evolution of ozone depletion events and to help plan the snow sampling periods.
The snow samples will be collected along three transects between Barrow, Wainwright, and Atqasuk. The three villages form a triangle with legs approximately 100 km long. Barrow and Wainwright sit on the shore of the Arctic Ocean, while Atqusuk lies inland. The hypothesis that the chemistry responsible for ozone depletion and mercury deposition is limited by availability of bromide ion in the snow will be rigorously tested by this experiment. Studies will be performed after sunrise, but well before the active ozone depletion period, near equinox when depletion chemistry is very active, and late in the spring when ozone depletion has ended but snow remains on the ground. The snow will be sampled for a number of quantities including mercury, ions and the deuterium and oxygen isotopic composition of water. These measurements will allow the quantification of the target quantities (mercury and bromide) as well as species that will aid in correlating specific snow layers at the different sites.
This project will improve understanding of the mechanism of mercury deposition and be of benefit to the inhabitants of regions impacted by this springtime phenomenon. The spatial extent and intensity of mercury deposition will be studied in the region. This will lead to better understanding of the global mercury budget. The budget provides graduate student support, and the PIs intend to make presentations on their research at the three remote villages bounding the study region, thereby improving public understanding of the relevant issues.
