Vertical distribution of mercury, CO, ozone, and aerosol scattering coefficient in the Pacific Northwest during the spring 2006 INTEX-B campaign

In the spring of 2006, we measured the vertical distribution of gaseous elemental mercury (GEM), CO, ozone, and aerosol scattering coefficient in the Pacific Northwest concurrent with NASA's INTEX-B campaign. Seven profiles from the surface to 6 km were conducted from 12 April to 8 May along with one flight in the Seattle-Tacoma boundary layer. Ozone had a bimodal distribution with the lower mode occurring primarily in the mixed layer and the higher mode occurring in the free troposphere. In the free troposphere, the mixing ratios (1 - σ ) of GEM, CO, ozone, and aerosol scattering coefficient were 1.52 (0.165) ng/m³, 142 (14.9) ppbv, 78 (7.7) ppbv, and 3.0 (1.8) Mm^-1, respectively. GEM and CO were correlated in the high ozone mode (r² = 0.30) but were uncorrelated in the lower mode (r² = 0.05). Three flights observed enhancements of GEM and CO with good correlations and with regression slopes (0.0067 (±0.0027) ng/m₃/ppbv by ordinary least squares regression and 0.0097 (±0.0018) ng/m₃ /ppbv by reduced major axis regression) slightly higher than previous observations of enhancements due to Asian industrial long-range transport (LRT). The influence of Asian LRT is supported by back trajectories and a global chemical transport model. In the Seattle-Tacoma boundary layer flight, CO was uncorrelated with GEM, which reflects relatively weaker local GEM sources. On three flights, pockets of air were observed with strong inverse GEM-ozone and ozone-CO correlations (in contrast to all data), which is evidence of upper tropospheric/lower stratospheric (UTLS) influence. An extrapolation of the GEM-CO and GEM-ozone slopes suggests the UTLS can be depleted of GEM.