Mysterious diel cycles of mercury emission from soils held in the dark at constant temperature

• Published in: Atmospheric environment (1994) Vol. 42; no. 21; pp. 5424 - 5433
• Main Authors: Zhang, Hong, Lindberg, Steve E., Kuiken, Todd
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01.07.2008; Elsevier Science
• Subjects: AIR; Air/surface exchange; Applied sciences; ATMOSPHERIC CHEMISTRY; Atmospheric pollution; Chemical composition and interactions. Ionic interactions and processes; DAILY VARIATIONS; Earth, ocean, space; ENVIRONMENTAL SCIENCES; Exact sciences and technology; External geophysics; Global biogeochemistry; Heavy metal; MERCURY; Meteorology; Pollutants physicochemistry study: properties, effects, reactions, transport and distribution; Pollution; PROBES; SEASONAL VARIATIONS; SOILS; SOLAR RADIATION; WEATHER; Global biogeochemistry; Air/surface exchange; Atmospheric chemistry; Solar radiation; Heavy metal; Light effect; geochemical cycle; air-ground interface; heavy metals; mercury; Temperature effect; Environmental factor; solar radiation; Operating conditions; Controlled environment study; Flux density; Gas exchange; Emission measure
• ISSN: 1352-2310; 1873-2844
• DOI: 10.1016/j.atmosenv.2008.02.037

It is well known that mercury (Hg) emission from soils is largely controlled by solar radiation and soil temperature, exhibiting diel cycles that closely follow diel variations of solar radiation. To study soil Hg emission processes, we conducted experiments by measuring soil Hg emission fluxes under controlled conditions in the laboratory with a dynamic flux chamber using outside ambient air as flushing air. Unexpectedly, we observed consistent, recurring diel cycles of Hg emissions from dry soils held at constant temperature in the dark in our laboratory. The peaks of the emissions also seemed subject to some seasonal variation and to respond to local weather conditions with lower flux peaks in wintertime and on cloudy or rainy days. Finally, much lower soil Hg emission fluxes were observed in the presence of Hg-free zero air than in the presence of outside ambient air. It is hypothesized that some unidentified air-borne substance(s) in the ambient air might be responsible for the observed diel cycles of soil Hg emission. Further elaborate mechanistic investigations are clearly needed to test the initial working hypotheses and uncover the cause for this interesting, mysterious phenomenon. The present work and recent finding of enhancement of Hg emissions from soil and mineral particles by O 3 seem to point to a research need to probe the possible role of near-ground atmospheric chemistry in Hg air/soil exchange.