Diurnal and seasonal trends in total gaseous mercury flux from three urban ground surfaces

Abstract

Total gaseous mercury flux measurements were carried out over three urban ground surfaces for 1 year in Tuscaloosa, AL, USA. The objective was to provide insight into the characteristics of gaseous mercury flux from urban surface covers. Bare soil, grass, and pavement surfaces were sampled as the most representative terrestrial surfaces throughout Tuscaloosa. Measurements were quantified over diurnal and seasonal periods and relationships were developed between flux from each surface and major meteorological parameters. Averaging data over the entire year, fluxes from each surface were as follows: bare soil (6.48 ng/m −2 h), pavement (0.02 ng/m −2 h), and grass (0.28 ng/m −2 h). Pavement and many grass fluxes were small and arguably indistinguishable from chamber blanks. The soil surface displayed the largest difference between evening and daytime flux, particularly during the spring and summer seasons (i.e., evening low (12 ng/m −2 h) to daytime high (30 ng/m −2 h) during summer). The grass surface showed the largest amount of atmospheric deposition, mainly during the spring and fall periods (up to −2.31 ng/m −2 h), with pavement showing somewhat less (up to −1.05 ng/m −2 h). Bare soil showed very little to negligible deposition. Diurnal flux variance was greater than seasonal flux variance for all surfaces. The regression results demonstrate that despite the highly dissimilar physical and geochemical make-up of pavement, bare soil, and grass, each surface displayed similar responses to time series change in meteorological parameters. However, each surface may be seasonally controlled or limited by different sets of meteorological parameters.