Characterization of mercury concentration at a costal site under marine, continental and land-sea-breeze flow regimes

Long term speciated atmospheric mercury (Hg) observations, from the Outlying Landing Field (OLF) site in the vicinity of Pensacola, Florida, provides a dataset that allows characterization of Hg concentrations under marine, continental and land-sea breeze flow regimes. The OLF site is a part of the Southeastern Aerosol Research and Characterization Study (SEARCH) network and speciated Hg observations are available during a five year period of 2005-2009. Observations include surface concentrations of gaseous elemental Hg (Hg⁰), reactive gaseous mercury (RGM), particle-bound Hg (HgP), ozone (O₃), carbon monoxide (CO), sulfur dioxide (SO₂) and surface meteorology. Observations of surface meteorology were utilized for classifying the atmospheric flow into marine, continental and land-sea-breeze regimes. Differences in mean diurnal patterns, mean concentrations and amplitude of diurnal variation for Hg⁰, RGM and HgP concentrations were examined for the three flow regimes. Observations show that surface mercury concentrations are different for marine air mass in comparison to air masses associated with continental and land-sea-breeze flows. Marine air masses are found to have higher average concentrations of Hg⁰ and lower concentrations of RGM and HgP. Furthermore, the amplitude of diurnal variation for all the species is found to be diminished for marine air masses. Prior studies suggest that halogen chemistry could play an important role in oxidation of Hg0 to RGM in the marine boundary layer. Initial results from the present study suggest the production of RGM in the marine air mass is small compared to situations of continental flow and land-sea-breeze circulations. Note that in the latter case, the role of local emissions of RGM needs to be considered in addition to photochemical production.