Atmospheric hydrogen peroxide and organic hydroperoxides during PRIDE-PRD'06, China: their concentration, formation mechanism and contribution to secondary aerosols

W Hua,A Hofzumahaus,Y Kondo,K Kita,N Takegawa,Z M Chen,Y Miyazaki,C C Chang,M Hu,C Y Jie,H L Wang,Y H Zhang,K D Lu

doi:10.5194/acp-8-6755-2008

Abstract

Abstract. Atmospheric hydrogen peroxide (H2O2) and organic hydroperoxides were measured from 18 to 30 July in 2006 during the PRIDE-PRD'06 campaign at Backgarden, a rural site located 48 km north of Guangzhou, a mega-city in southern China. A ground-based instrument was used as a scrubbing coil collector to sample ambient air, followed by on-site analysis by high-performance liquid chromatography (HPLC) coupled with post-column derivatization and fluorescence detection. The H2O2 mixing ratio over the 13 days ranged from below the detection limit to a maximum of 4.6 ppbv, with a mean (and standard deviation) of (1.26±1.24) ppbv during the daytime (08:00–20:00 LT). Methyl hydroperoxide (MHP), with a maximum of 0.8 ppbv and a mean (and standard deviation) of (0.28±0.10) ppbv during the daytime, was the dominant organic hydroperoxide. Other organic peroxides, including bis-hydroxymethyl hydroperoxide (BHMP), peroxyacetic acid (PAA), hydroxymethyl hydroperoxide (HMHP), 1-hydroxy-ethyl hydroperoxide (1-HEHP) and ethyl hydroperoxide (EHP), were detected occasionally. The concentration of H2O2 exhibited a pronounced diurnal variation on sunny days, with a peak mixing ratio in the afternoon (12:00–18:00 LT), but lacked an explicit diurnal cycle on cloudy days. Sometimes a second peak mixing ratio of H2O2 was observed during the evening, suggesting that H2O2 was produced by the ozonolysis of alkenes. The diurnal variation profile of MHP was, in general, consistent with that of H2O2. The estimation indicated that in the morning the H2O2 detected was formed mostly through local photochemical activity, with the rest probably attributable to vertical transport. It is notable that relatively high levels of H2O2 and MHP were found in polluted air. The unexpectedly high level of HO2 radicals detected in this region can account for the production of hydroperoxides, while the moderate level of NOx suppressed the formation of hydroperoxides. High concentrations of hydroperoxides were detected in samples of rainwater collected in a heavy shower on 25 July when a typhoon passed through, indicating that a considerable mixing ratio of hydroperoxides, particularly MHP, resided above the boundary layer, which might be transported on a regional scale and further influence the redistribution of HOx and ROx radicals. It was found that hydroperoxides, in particular H2O2, play an important role in the formation of secondary sulfate in the aerosol phase, where the heterogeneous reaction might contribute substantially. A negative correlation between hydroperoxides and water-soluble organic compounds (WSOC), a considerable fraction of the secondary organic aerosol (SOA), was observed, possibly providing field evidence for the importance of hydroperoxides in the formation of SOA found in previous laboratory studies. We suggest that hydroperoxides act as an important link between sulfate and organic aerosols, which needs further study and should be considered in current atmospheric models.

Highlights

A series of hydroperoxides, including hydrogen peroxide (H2O2) and organic hydroperoxides (ROOH), such as methylhydroperoxide (MHP, CH3OOH), hydroxymethyl hydroperoxide (HMHP, HOCH2OOH), 1-hydroxy-ethyl hydroperoxide (1-HEHP, CH3CH(OH)OOH), peroxyacetic acid (PAA, CH3C(O)OOH) and ethylhydroperoxide (EHP, CH3CH2OOH), have been measured in the atmosphere since the measurement of organic hydroperoxides was pioneered in the 1980s by Hellpointner and Gab (1989)
The organic peroxides bis-hydroxymethyl hydroperoxide (BHMP) and PAA were often detected, and HMHP, 1-HEHP and EHP were occasionally detected, but all these species were present at only several-decade pptv level under these experimental conditions
The mixing ratios of H2O2 and Methyl hydroperoxide (MHP) are in agreement with those reported in the literature with H2O2 ranging between 0.5 ppbv and 5 ppbv and MHP ranging between several pptv and 2.7 ppbv worldwide respectively (Hellpointner and Gab, 1989; Hewitt and Kok, 1991; Das and Aneja, 1994; Watkins et al, 1995a, b; Jackson and Hewitt, 1996; Sauer et al, 1997, 2001; O’Sullivan et al 1999; Morgan and Jackson, 2002; Moortgat et al, 2002; Grossmann et al, 2003; Lee et al, 1993, 1995, 1998, 2000, 2008; Francois et al, 2005; Xu and Chen, 2005; Walker et al, 2006; Kim et al, 2007)

Summary

Introduction

A series of hydroperoxides, including hydrogen peroxide (H2O2) and organic hydroperoxides (ROOH), such as methylhydroperoxide (MHP, CH3OOH), hydroxymethyl hydroperoxide (HMHP, HOCH2OOH), 1-hydroxy-ethyl hydroperoxide (1-HEHP, CH3CH(OH)OOH), peroxyacetic acid (PAA, CH3C(O)OOH) and ethylhydroperoxide (EHP, CH3CH2OOH), have been measured in the atmosphere since the measurement of organic hydroperoxides was pioneered in the 1980s by Hellpointner and Gab (1989). These reactive species play significant roles in atmospheric processes, such as acid precipitation, cycling of HOx radicals, and formation of secondary organic aerosol (SOA). Several laboratory studies have revealed that secondary organic aerosol (SOA) can be formed from isoprene and its gas-phase oxidation products through acidcatalyzed heterogeneous oxidation with hydrogen peroxide, a remarkably close analogy with atmospheric secondary sulfate formation (Claeys et al, 2004; Boge et al, 2006; Kroll et al, 2006)

Objectives

Methods

Results

Conclusion