In:
Atmospheric Chemistry and Physics, Copernicus GmbH, Vol. 19, No. 1 ( 2019-01-09), p. 315-325
Abstract:
Abstract. Mercury (Hg) bound to fine aerosols (PM2.5-Hg) may undergo photochemical
reaction that causes isotopic fractionation and obscures the initial isotopic
signatures. In this study, we quantified Hg isotopic compositions for 56
PM2.5 samples collected between 15 September and 16 October 2015 from
Beijing, China, among which 26 were collected during daytime (between 08:00
and 18:30 LT) and 30 during night (between 19:00
and 07:30 LT). The results show that diel variation was statistically
significant (p 〈 0.05) for Hg content, Δ199Hg and
Δ200Hg, with Hg content during daytime (0.32±0.14 µg g−1) lower than at night (0.48±0.24 µg g−1) and Δ199Hg and Δ200Hg
values during daytime (mean of 0.26 ‰±0.40 ‰ and
0.09 ‰±0.06 ‰, respectively) higher than during
nighttime (0.04 ‰±0.22 ‰ and 0.06 ‰±0.05 ‰, respectively), whereas PM2.5 concentrations and
δ202Hg values showed insignificant (p 〉 0.05)
diel variation. Geochemical characteristics of the samples and the air mass
backward trajectories (PM2.5 source related) suggest that diel variation
in Δ199Hg values resulted primarily from the photochemical
reduction of divalent PM2.5-Hg, rather than variations in emission
sources. The importance of photoreduction is supported by the strong
correlations between Δ199Hg and (i) Δ201Hg
(positive, slope = 1.1), (ii) δ202Hg (positive,
slope = 1.15), (iii) content of Hg in PM2.5 (negative),
(iv) sunshine durations (positive) and (v) ozone concentration (positive)
observed for consecutive day–night paired samples. Our results provide
isotopic evidence that local, daily photochemical reduction of divalent Hg is
of critical importance to the fate of PM2.5-Hg in urban atmospheres and
that, in addition to variation in sources, photochemical reduction appears to
be an important process that affects both the particle mass-specific
abundance and isotopic composition of PM2.5-Hg.
Type of Medium:
Online Resource
ISSN:
1680-7324
DOI:
10.5194/acp-19-315-2019
DOI:
10.5194/acp-19-315-2019-supplement
Language:
English
Publisher:
Copernicus GmbH
Publication Date:
2019
detail.hit.zdb_id:
2069847-1
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