Abstract
Abstract. Methyl hydroperoxide (MHP), one of the most important organic peroxides in the atmosphere, contributes to the tropospheric oxidizing capacity either directly as an oxidant or indirectly as a free radical precursor. In this study we report measurements of MHP from seven field campaigns at urban, suburban and rural sites in China in winter 2007 and summer 2006/2007/2008. MHP was usually present in the order of several hundreds of pptv level, but the average mixing ratios have shown a wide range depending on the season and measuring site. Primary sources and sinks of MHP are investigated to understand the impact of meteorological and chemical parameters on the atmospheric MHP budget. The MHP/(MHP+H2O2) ratio is also presented here to examine different sensitivities of MHP and H2O2 to certain atmospheric processes. The diurnal cycle of MHP/(MHP+H2O2), which is out of phase with that of both H2O2 and MHP, could imply that MHP production is more sensitive to the ambient NO concentration, while H2O2 is more strongly influenced by the wet deposition and the subsequent aqueous chemistry. It is interesting to note that our observation at urban Beijing site in winter 2007 provides evidence for the occasional transport of MHP-containing air masses from the marine boundary layer to the continent. Furthermore, the contribution of MHP as an atmospheric oxidant to the oxidizing capacity of an air parcel is assessed based on the "Counter Species" concept.
Highlights
Peroxides play an important role in atmospheric processes
Atmospheric Methyl hydroperoxide (MHP) concentrations at urban, suburban and rural sites of China were measured during 7 observations
Two conclusions can be drawn from the investigation of the MHP/(MHP+H2O2) ratio: (i) the diurnal variation of the MHP/(MHP+H2O2) ratio is out phase of the temporal profiles of H2O2 and MHP, indicating a preferential depletion of H2O2 to MHP during the night and early morning; and (ii) the elevated MHP/(MHP+H2O2) ratios in PKU-summer 2008, when mitigation of atmospheric pollution was implemented in Beijing, suggests that MHP is more sensitive to NO than H2O2
Summary
Peroxides (hydrogen peroxide and organic peroxides) play an important role in atmospheric processes They are among the principle oxidants in their own right, primarily as important oxidants of SO2 in cloud or rain droplets (Penkett et al, 1979; Martin et al, 1981; Calvert et al, 1985), and act as temporary reservoirs for important oxidizing radicals (Madronich and Calvert, 1990; Lightfoot et al, 1992). As one of the main organic peroxides in the atmosphere, methyl hydroperoxide (MHP, CH3OOH) has a longer lifetime and a lower solubility in water, compared to H2O2 (Cohan et al, 1999; Wang and Chen, 2006). MHP contributes to the formation of water-soluble organic compounds (WSOC) and atmospheric secondary sulfates (Claeys et al, 2004; Boge et al, 2006; Kroll et al, 2006; Hua et al, 2008)
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