The distribution and speciation of mercury in the free troposphere of the Pacific Northwest

Mercury (Hg) is a potent neurotoxin which has accumulated in aquatic ecosystems and has led to increased neurological and developmental health risks for wildlife and humans worldwide. This dissertation aims to improve our understanding of the global mercury cycle by investigating its distribution and chemistry in the free troposphere.;A Hg speciation system was deployed at the summit station of Mt. Bachelor, OR (2.7 km asl) (MBO). It measured gaseous elemental mercury (GEM), reactive gaseous mercury (RGM), and particulate mercury (PHg) from May-Aug 2005. The system detected RGM up to 600 pg/m3, or 40% of the total airborne Hg. The high RGM was not due to anthropogenic emissions, but was produced in situ. The GEOS-Chem chemical transport model (CTM) was unable to reproduce the magnitude of the highest RGM concentrations using the assumed OH and ozone oxidation mechanisms.;The vertical distribution of mercury in the Pacific Northwest was investigated with an aircraft campaign in 2006 during the INTEX-B campaign. Three of the eight flights observed significant enhancements of GEM and CO in the free troposphere. The enhancement ratios (0.0067 (+/-0.0027) ng/m3 /ppb) were consistent with previous observations of Asian industrial influence at MBO and in Okinawa, Japan. Backtrajectories and GEOS-Chem CTM simulations supported Asian long range transport as the source of the influence.;A technique was developed to measure RGM in an aircraft. In this technique, RGM is measured by difference and simultaneously is directly collected on a denuder. The system was tested in the laboratory with an RGM proxy, (HgCl 2 at ∼500 pg/m3), and the agreement of the denuder-difference techniques was 15% (+/-13%, relative percent difference). The instrument was tested in five flights from the surface to 5 km. A linear correlation of all denuder-difference data had a slope of 0.41. RGM enhancements (200-500 pg/m3) were observed with varying relationships to ozone and water vapor which suggests that upper tropospheric influence is not a controlling factor. There was no mean vertical trend in total Hg (GEM + RGM) up to 5 km. The only factor common to all high RGM, was low aerosol scattering (<2 M/m).