Journal article

Oxidation of elemental Hg in anthropogenic and marine airmasses

Timonen H, Ambrose J, Jaffe D ...see all

Atmospheric Chemistry and Physics, vol. 13, issue 5 (2013) pp. 2827-2836

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Mercury (Hg) is a neurotoxin that bioaccumulates in the food chain.
Mercury is emitted to the atmosphere primarily in its elemental form,
which has a long lifetime allowing global transport. It is known that
atmospheric oxidation of gaseous elemental mercury (GEM) generates
reactive gaseous mercury (RGM) which plays an important role in the
atmospheric mercury cycle by enhancing the rate of mercury deposition to
ecosystems. However, the primary GEM oxidants, and the chemical
composition of RGM are poorly known. Using speciated mercury
measurements conducted at the Mt. Bachelor Observatory since 2005 we
present two previously unidentified sources of RGM to the free
troposphere (FT). Firstly, we observed elevated RGM concentrations,
large RGM/GEM-ratios, and anti-correlation between RGM and GEM during
Asian long-rang transport events, demonstrating that RGM is formed from
GEM by in-situ oxidation in some anthropogenic pollution plumes in the
FT. During the Asian pollution events the measured RGM/GEM-enhancement
ratios reached peak values, up to similar to 0.20, which are
significantly larger than ratios typically measured (RGM/GEM < 0.03) in
the Asian source region. Secondly, we observed very high RGM levels -
the highest reported in the FT - in clean air masses that were processed
upwind of Mt. Bachelor Observatory over the Pacific Ocean. The high RGM
concentrations (up to 700 pgm(-3)), high RGM/GEM-ratios (up to 1), and
very low ozone levels during these events provide observational evidence
indicating significant GEM oxidation in the lower FT in some conditions.

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