Using Passive Air Samplers to Quantify Vertical Gaseous Elemental Mercury Concentration Gradients Within a Forest and Above Soil. Issue 15 (26th July 2021)

• Record Type: Journal Article
• Authors: Quant, M. Isabel; Feigis, Michelle; Mistry, Shreya; Lei, Ying Duan; Mitchell, Carl P. J.; Staebler, Ralf; Di Guardo, Antonio; Terzaghi, Elisa; Wania, Frank
• Is Part Of: Journal of geophysical research. Volume 126:Issue 15(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-07-26
• Subjects: mercury -- flux -- vertical concentration gradient -- atmosphere -- vegetation uptake -- passive air sampler; Atmospheric physics -- Periodicals; Geophysics -- Periodicals; 551.5
• DOI: 10.1029/2021JD034981
• Languages: English
• ISSNs: 2169-897X

Abstract

Abstract: Gaseous elemental mercury (GEM), the primary form of mercury (Hg) in the atmosphere, can undergo bidirectional exchange with the Earth's surface, with uptake in growing vegetation constituting the dominant atmospheric deposition process. Whereas direction and magnitude of this exchange can be determined using micrometeorological and chamber techniques, these approaches are complex, costly and labor‐intensive, and often only yield fluxes over relatively short time‐scales at few sites. We demonstrate that an inexpensive and easy‐to‐use passive air sampler can identify and quantify vertical GEM concentration gradients on scales ranging from centimeters to tens of meters over long time periods (up to 1.5 years) and with coarse temporal resolution (monthly to seasonally). Samplers were deployed above clean and contaminated soil and through a deciduous forest canopy at two sites in Southern Ontario. Significant and seasonally variable gradients of GEM concentrations, both increasing and decreasing with height above ground, were observed and can be explained through the influence of factors such as soil contamination, canopy growth, temperature, solar irradiance, and snow cover. At a minimum, the sampler can identify the GEM flux direction, but, when combined with the Modified Bowen Ratio method, can also be used to estimate the evaporative GEM flux from mercury‐contaminated soil. We further demonstrate the application of the approach to contaminated site assessment, using a field in Brescia, Italy, known to contain elevated levels of Hg in soil. By allowing for cost‐effective measurements at multiple sites and over extended time periods, passive sampling complements existing techniques for studying atmosphere‐surface exchange of GEM. Key Points: Passive air samplers can be used to record vertical gradients of gaseous elemental mercury (GEM) concentration at different height scales Sampling rate should be adjusted for wind speed to accurately capture the vertical GEM concentration gradient Modified Bowen Ratio method allows for estimation of long‐term average GEM evaporation flux from contaminated soil