Impacts of aerosols on the chemistry of atmospheric trace gases: a case study of peroxides and HO<sub>2</sub> radicals
Field measurements of atmospheric peroxides were obtained during the summer on two consecutive years over urban Beijing, which highlighted the impacts of aerosols on the chemistry of peroxide compounds and hydroperoxyl radicals (HO<sub>2</sub>). The major peroxides were determined to be...
| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2013-11-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | http://www.atmos-chem-phys.net/13/11259/2013/acp-13-11259-2013.pdf |
| Summary: | Field measurements of atmospheric peroxides were obtained
during the summer on two consecutive years over urban Beijing, which highlighted the impacts of aerosols on the chemistry of peroxide compounds and
hydroperoxyl radicals (HO<sub>2</sub>). The major peroxides were determined to be
hydrogen peroxide (H<sub>2</sub>O<sub>2</sub>), methyl hydroperoxide (MHP), and
peroxyacetic acid (PAA). A negative correlation was found between
H<sub>2</sub>O<sub>2</sub> and PAA in rainwater, providing evidence for a conversion
between H<sub>2</sub>O<sub>2</sub> and PAA in the aqueous phase. A standard gas phase
chemistry model based on the NCAR Master Mechanism provided a good
reproduction of the observed H<sub>2</sub>O<sub>2</sub> profile on non-haze days but
greatly overpredicted the H<sub>2</sub>O<sub>2</sub> level on haze days. We attribute
this overprediction to the reactive uptake of HO<sub>2</sub> by the aerosols,
since there was greatly enhanced aerosol loading and aerosol liquid water
content on haze days. The discrepancy between the observed and modeled
H<sub>2</sub>O<sub>2</sub> can be diminished by adding to the model a newly proposed
transition metal ion catalytic mechanism of HO<sub>2</sub> in aqueous aerosols.
This confirms the importance of the aerosol uptake of HO<sub>2</sub> and the
subsequent aqueous phase reactions in the reduction of H<sub>2</sub>O<sub>2</sub>. The
closure of HO<sub>2</sub> and H<sub>2</sub>O<sub>2</sub> between the gas and aerosol phases
suggests that the aerosols do not have a net reactive uptake of
H<sub>2</sub>O<sub>2</sub>, because the conversion of HO<sub>2</sub> to H<sub>2</sub>O<sub>2</sub> on
aerosols compensates for the H<sub>2</sub>O<sub>2</sub> loss. Laboratory studies for the
aerosol uptake of H<sub>2</sub>O<sub>2</sub> in the presence of HO<sub>2</sub> are urgently
required to better understand the aerosol uptake of H<sub>2</sub>O<sub>2</sub> in the
real atmosphere. |
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| ISSN: | 1680-7316 1680-7324 |