Speciated atmospheric mercury on haze and non-haze days in an inland city in China
Long-term continuous measurements of speciated atmospheric mercury were conducted from July 2013 to June 2014 in Hefei, a midlatitude inland city in eastern central China that experiences frequent haze pollution. The mean concentrations (±standard deviation) of gaseous elemental mercury (GEM), g...
| Main Authors: | , , , , , , , , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2016-11-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://www.atmos-chem-phys.net/16/13807/2016/acp-16-13807-2016.pdf |
| Summary: | Long-term continuous measurements of speciated atmospheric mercury were
conducted from July 2013 to June 2014 in Hefei, a midlatitude inland city in
eastern central China that experiences frequent haze pollution. The mean
concentrations (±standard deviation) of gaseous elemental mercury (GEM),
gaseous oxidized mercury (GOM) and particle-bound mercury (PBM) were
3.95 ± 1.93 ng m<sup>−3</sup>, 2.49 ± 2.41 and
23.3 ± 90.8 pg m<sup>−3</sup>, respectively, on non-haze days, and
4.74 ± 1.62 ng m<sup>−3</sup>, 4.32 ± 8.36 and
60.2 ± 131.4 pg m<sup>−3</sup>, respectively, on haze days. Potential
source contribution function (PSCF) analysis suggested that atmospheric
mercury pollution on haze days was caused primarily by local emissions,
instead of via long-range transport. The poorer mixing conditions on haze
days also favored the accumulation of atmospheric mercury. Compared to GEM
and GOM, PBM was especially sensitive to haze pollution. The mean PBM
concentration on haze days was 2.5 times that on non-haze days due to
elevated concentrations of particulate matter. PBM also showed a clear
seasonal trend; its concentration was the highest in fall and winter,
decreased rapidly in spring and was the lowest in summer, following the same
order in the frequency of haze days in different seasons. On both non-haze
and haze days, GOM concentrations remained low at night, but increased
rapidly just before sunrise, which could be due to diurnal variation in air
exchange between the boundary layer and free troposphere. However, non-haze
and haze days showed different trends in daytime GEM and GOM concentrations.
On non-haze days, GEM and GOM declined synchronously through the afternoon,
probably due to the retreat of the free tropospheric air as the height of the
atmospheric boundary layer increases. In contrast, on haze days, GOM and GEM
showed opposite trends with the highest GOM and lowest GEM observed in the
afternoon, suggesting the occurrence of photochemical oxidation. This is
supported by simple box-model calculations, which showed that oxidation of
GEM to GOM does occur and that the transport of free tropospheric GOM alone
is not large enough to account for the observed increase in daytime GOM. Our
results further postulate that NO<sub>2</sub> aggregation with the HgOH
intermediate may be a potential mechanism for the enhanced production of GOM
during daytime. |
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| ISSN: | 1680-7316 1680-7324 |