Measurements of GEM fluxes and atmospheric mercury concentrations (GEM, RGM and Hg p) from an agricultural field amended with biosolids in Southern Ont., Canada (October 2004–November 2004)

Abstract

Five weeks of gaseous elemental mercury (GEM), reactive gaseous mercury (RGM) and particle bound mercury (Hg p) concentrations as well as fluxes of GEM were measured at Maryhill, Ontario, Canada above a biosolids amended field. The study occurred during the autumn of 2004 (October–November) to capture the effects of cool weather conditions on the behaviour of mercury in the atmosphere. The initial concentration of total mercury (Hg) in the amended soil was relatively low (0.4 μg g −1±10%). A micrometeorological approach was used to infer the flux of GEM using a continuous two-level sampling system with inlets at 0.40 and 1.25 m above the soil surface to measure the GEM concentration gradient. The required turbulent transfer coefficients were derived from meteorological parameters measured on site. The average GEM flux over the study was 0.1±0.2 ng m −2 h −1(±one standard deviation). The highest averaged hourly GEM fluxes occurred when the averaged net radiation was highest, although the slight diurnal patterns observed were not statistically significant for the complete flux data series. GEM emission fluxes responded to various local events including the passage of a cold front when the flux increased to 2 ng m −2 h −1 and during a biosolids application event at an adjacent field when depositional fluxes peaked at −3 ng m −2 h −1. Three substantial rain events during the study kept the surface soil moisture near field capacity and only slightly increased the GEM flux. Average concentrations of RGM (2.3±3.0 pg m −3), Hg p (3.0±6.2 pg m −3) and GEM (1.8±0.2 ng m −3) remained relatively constant throughout the study except when specific local events resulted in elevated concentrations. The application of biosolids to an adjacent field produced large increases in Hg p (25.8 pg m −3) and RGM (21.7 pg m −3) concentrations only when the wind aligned to impact the experimental equipment. Harvest events (corn) in adjacent fields also corresponded to higher concentrations of GEM and Hg p but with no elevated peaks in RGM concentrations. Diurnal patterns were not statistically significant for RGM and Hg p at Maryhill.