LEADX-2005: A system study of near-surface winter tropospheric processes near Barrow, Alaska

In the Arctic, a set of vigorous and linked near-surface tropospheric processes commence in March with polar sunrise and continue until the snow melts in late May. In ways not fully understood, these processes produce ozone (ODE) and mercury (MDE) depletion events, the latter responsible for the introduction of mercury into the coastal marine and terrestrial arctic environments. The processes require a sea ice cover, open leads, diamond dust events, snowfall, and the presence of a snowpack on both land and sea. In March, 2005 we conducted a campaign (LEADX-2005) to investigate this suite of processes in the coastal strip near Barrow, Alaska. During a 17-day period when the coastal flaw lead was active and open, 30 scientists from more than 10 institutions made a set of coordinated measurements on, near, and inland from the lead. Measurements included continuous observations of surface weather, reactive halogens using MAX-DOAS, and near-surface mercury concentrations. Spot measurements of ozone and VOCs were made at the lead in a variety of ice and weather conditions. Airborne measurements were made using unmanned aerial vehicles (UAVs), tethered balloons, and kites. Deposited and newly fallen snow was sampled for ions, halogens, and mercury content on a daily basis on transects running from the lead inland several kilometers. Results suggest ozone depletion and mercury deposition occur at the regional (order 100 km) rather than local scale, but are confined to a thin layer of marine air (order 100 m). The processes evolve with time, the seasonal rise in air temperature, and the evolution of the snow pack, but considerable uncertainty remains as to the ultimate fate of the constituents (chiefly Hg) upon the completion of snow melt in the environment due to re-emission processes. From LEADX-2005 and follow-on studies we hope to develop a more systematic understanding of how these linked processes work across time and space.