The browser you are using is not supported by this website. All versions of Internet Explorer are no longer supported, either by us or Microsoft (read more here: https://www.microsoft.com/en-us/microsoft-365/windows/end-of-ie-support).

Please use a modern browser to fully experience our website, such as the newest versions of Edge, Chrome, Firefox or Safari etc.

Natascha Kljun. Photo.

Natascha Kljun

Professor

Natascha Kljun. Photo.

Eddy Covariance Flux Measurements of Gaseous Elemental Mercury Using Cavity Ring-Down Spectroscopy

Author

  • Ashley M. Pierce
  • Christopher W. Moore
  • Georg Wohlfahrt
  • Lukas Hörtnagl
  • Natascha Kljun
  • Daniel Obrist

Summary, in English

A newly developed pulsed cavity ring-down spectroscopy (CRDS) system for measuring atmospheric gaseous elemental mercury (GEM) concentrations at high temporal resolution (25 Hz) was used to successfully conduct the first eddy covariance (EC) flux measurements of GEM. GEM is the main gaseous atmospheric form, and quantification of bidirectional exchange between the Earth’s surface and the atmosphere is important because gas exchange is important on a global scale. For example, surface GEM emissions from natural sources, legacy emissions, and re-emission of previously deposited anthropogenic pollution may exceed direct primary anthropogenic emissions. Using the EC technique for flux measurements requires subsecond measurements, which so far has not been feasible because of the slow time response of available instrumentation. The CRDS system measured GEM fluxes, which were compared to fluxes measured with the modified Bowen ratio (MBR) and a dynamic flux chamber (DFC). Measurements took place near Reno, NV, in September and October 2012 encompassing natural, low-mercury (Hg) background soils and Hg-enriched soils. During nine days of measurements with deployment of Hg-enriched soil in boxes within 60 m upwind of the EC tower, the covariance of GEM concentration and vertical wind speed was measured, showing that EC fluxes over an Hg-enriched area were detectable. During three separate days of flux measurements over background soils (without Hg-enriched soils), no covariance was detected, indicating fluxes below the detection limit. When fluxes were measurable, they strongly correlated with wind direction; the highest fluxes occurred when winds originated from the Hg-enriched area. Comparisons among the three methods showed good agreement in direction (e.g., emission or deposition) and magnitude, especially when measured fluxes originated within the Hg-enriched soil area. EC fluxes averaged 849 ng m–2 h–1, compared to DFC fluxes of 1105 ng m–2 h–1 and MBR fluxes of 1309 ng m–2 h–1. This study demonstrated that a CRDS system can be used to measure GEM fluxes over Hg-enriched areas, with a conservative detection limit estimate of 32 ng m–2 h–1.

Publishing year

2015-01-21

Language

English

Pages

1559-1568

Publication/Series

Environmental Science and Technology

Volume

49

Issue

3

Document type

Journal article

Publisher

The American Chemical Society (ACS)

Topic

  • Meteorology and Atmospheric Sciences
  • Geosciences, Multidisciplinary

Status

Published

ISBN/ISSN/Other

  • ISSN: 1520-5851