EGU Journal Logos (RGB) Open Access Open Access Open Access Advances in Annales Nonlinear Processes Geosciences Geophysicae in Geophysics Open Access Open Access Natural Hazards Natural Hazards and Earth System and Earth System Sciences Sciences Discussions Open Access Open Access Atmos. Chem. Phys., 13, 5671–5683, 2013 Atmospheric Atmospheric www.atmos-chem-phys.net/13/5671/2013/ doi:10.5194/acp-13-5671-2013 Chemistry Chemistry © Author(s) 2013. CC Attribution 3.0 License. and Physics and Physics Discussions Open Access Open Access Atmospheric Atmospheric Measurement Measurement Techniques Techniques Discussions Open Access Newly observed peroxides and the water effect on the formation and Open Access removal of hydroxyalkyl hydroperoxides in the ozonolysis of Biogeosciences Biogeosciences isoprene Discussions D. Huang, Z. M. Chen, Y. Zhao, and H. Liang Open Access Open Access State Key Laboratory of Environmental Simulation and Pollution Control, College of Environmental Sciences and Climate Engineering, Peking University, Beijing 100871, China Climate of the Past of the Past Correspondence to: Z. M. Chen ([email protected]) Discussions Received: 5 January 2013 – Published in Atmos. Chem. Phys. Discuss.: 25 February 2013 Open Access Open Access Revised: 4 May 2013 – Accepted: 15 May 2013 – Published: 12 June 2013 Earth System Earth System Dynamics Dynamics Abstract. The ozonolysis of alkenes is considered to be an lows them to become involved in atmospheric chemical pro- Discussions important source of atmospheric peroxides, which serve as cesses, e.g., SOA formation and radical recycling. oxidants, reservoirs of HOx radicals, and components of sec- Open Access ondary organic aerosols (SOAs). Recent laboratory investi- Geoscientific Geoscientific Open Access gations of this reaction identified hydrogen peroxide (H2O2) Instrumentation Instrumentation and hydroxymethyl hydroperoxide (HMHP) in ozonolysis 1 Introduction Methods and Methods and of isoprene. Although larger hydroxyalkyl hydroperoxides (HAHPs) were also expected, their presence is not currently Peroxides, including hydrogenData peroxide Systems and organic perox- Data Systems supported by experimental evidence. In the present study, ides, are considered to be important trace compounds in the Discussions Open Access Open Access we investigated the formation of peroxides in the gas phase atmosphere due to their multiple roles as oxidants (Calvert et Geoscientific ozonolysis of isoprene at various relative humidities on a al., 1985) and reservoirs ofGeoscientific radicals (HOx, RO2) (Wallington time scale of tens of seconds, using a quartz flow tube re- and Japar, 1990; Lightfoot et al., 1991; Vaghjiani and Rav- Model Development Model Development actor coupled with the online detection of peroxides. We de- ishankara, 1990; Hatakeyama et al., 1991; Atkinson et al., Discussions tected a variety of conventional peroxides, including H2O2, 1992; Spittler et al., 2000; Ravetta et al., 2001). Furthermore, they can harm vegetation (Hewitt et al., 1990; Pellinen et al., HMHP, methyl hydroperoxide, bis-hydroxymethyl hydroper- Open Access Open Access oxide, and ethyl hydroperoxide, and interestingly found three 2002) and are known toHydrology be important componentsand of sec- Hydrology and unknown peroxides. The molar yields of the conventional ondary organic aerosols (SOAs) (Bonn et al., 2004; Docherty peroxides fell within the range of values provided in the lit- et al., 2005; Hallquist et al.,Earth 2009; System Chen et al., 2011). In the Earth System erature. The three unknown peroxides had a combined molar laboratory, organic peroxides areSciences known to be major prod- Sciences yield of ∼ 30 % at 5 % relative humidity (RH), which was ucts of the photooxidation of isoprene by the OH radical Discussions Open Access comparable with that of the conventional peroxides. Unlike under NOx-free conditions (Miyoshi et al., 1994;Open Access Paulot et H2O2 and HMHP, the molar yields of these three unknown al., 2009). Using the iodometric spectrophotometric method, Surratt et al. (2006) quantitatively reported that total organic Ocean Science peroxides were inversely related to the RH. On the basis of Ocean Science experimental kinetic and box model analysis, we tentatively peroxides account for 25–60 % of SOA mass formed from Discussions assigned these unknown peroxides to C2−C4 HAHPs, which the photooxidation of isoprene. Some model results suggest are produced by the reactions of different Criegee intermedi- that organic peroxides are even more important than car- Open Access ates with water. Our study provides experimental evidence boxylic acids as SOA contributors (Bonn et al.,Open Access 2004). Kroll for the formation of large HAHPs in the ozonolysis of iso- et al. (2006) suggested that the decrease in SOA mass dur- Solid Earth prene (one of the alkenes). These large HAHPs have a suffi- ing the photooxidation of isopreneSolid may Earth be attributed to the ciently long lifetime, estimated as tens of minutes, which al- chemical reactions of organic peroxides. There are no known Discussions primary sources of peroxides. An important pathway for their Open Access Open Access Published by Copernicus Publications on behalf of the European Geosciences Union. The Cryosphere The Cryosphere Discussions 5672 D. Huang et al.: Hydroxyalkyl hydroperoxides in the ozonolysis of isoprene formation is considered to be the bimolecular reaction be- In the present study, we detect more peroxide types in the tween RO2 and HO2 radicals, while RO2 radicals are mainly reaction of ozone and isoprene in the gas phase to evaluate formed from the OH radical-initiated photooxidation of alka- the reaction mechanism of Criegee intermediates with water, nes and alkenes under low NOx conditions (e.g., Atkinson et and we study the peroxide yield dependence on the relative al., 2006). Another pathway for the formation of hydroper- humidity. We conduct simulations for the ozonolysis of iso- oxides is the ozonolysis of alkenes (e.g., Becker et al., 1990; prene in a quartz flow tube reactor with a reaction time of Hewitt et al., 1990; Gab¨ et al., 1995; Neeb et al., 1997; Sauer tens of seconds at ten different relative humidities, using an et al., 1999; Lee et al., 2000; Tobia and Ziemann, 2001). A online HPLC detection for the peroxides. A variety of perox- peak in the concentration of peroxides was found at night in ides have been identified and quantified or semi-quantified, field measurements (Hua et al., 2008), providing evidence for in particular organic peroxides. A box model is used to sim- the important contribution from the ozonolysis of alkenes. ulate the HAHPs’ formation process, and simultaneously to Scheme 1 illustrates a summary of the major known steps study the effect of water on the formation and removal of in the ozonolysis of alkenes. The formation of peroxides is HAHPs. related to the reactions of Criegee intermediates, i.e., iso- merization (R3b), reaction with water (R4a1), and reaction with organic acid (R4a2); whereas the decomposition of per- 2 Experimental oxides follows pathways of R4b1, R4a11, R4a12, R4a13, 2.1 Chemicals and R4a14. Considering the ubiquity of water molecules in the atmosphere, water plays a principal role in hydrox- Isoprene (Fluka, 99.5 %), ultrapure water (18 M, Milli- yalkyl hydroperoxide (HAHP) formation via the reaction of pore), acetonitrile (Tedia, spectroscopically pure, ≥ 99.9 %), R4a1 (Gab¨ et al., 1985; Hatakeyama and Akimoto, 1994; N2 (≥ 99.999 %, Beijing Haikeyuanchang Practical Gas Ryzhkov and Ariya, 2004, 2006). In theoretical studies, Cre- Company Limited, Beijing, China), and O2 (≥ 99.999 %, huet et al. (2001) suggested that the CH2OO biradical, the Beijing Haikeyuanchang Practical Gas Company Limited, simplest Criegee intermediate, would have a two-step reac- Beijing, China) were used as received. The source and tion with H2O, first generating HMHP and then decompos- purity of authentic standards for synthesising peroxides ing. Aplincourt and Anglada (2003a) showed that the most are: H2O2 (Acros, 35 wt. %), formaldehyde (Riedel-delaen, favourable pathway for the reaction of water and the isoprene 36.5 wt. %), acetaldehyde (Amethyst, 40 wt. %), glycoalde- Criegee intermediate is the formation of HAHP. The HAHP hyde (Aldrich, crystalline), propanal (Fluka, 99.7 %), glyoxal would decompose into the corresponding carbonyl and H2O2 (Sigma-Aldrich, 40 wt. %), formic acid (Alfa Aesar, 97 %), (Atkinson and Arey, 2003). Very recently, Welz et al. (2012) acetic acid (Alfa Aesar, 99.9985 %), glycolic acid (Sigma- directly determined unexpectedly large rate constants for the Aldrich, 99 %), propionic acid (Alfa Aesar, 99 %), acetone reactions of the Criegee intermediate with SO2 and NO2, (Fluka, 99.7 %), hydroxyacetone (Fluka, 90 %), 2-Br-ethanol indicating that Criegee intermediates may be important ox- (Alfa Aesar, 97 %), 3-Br-1-proponol (Alfa Aesar, 97+ %), idants for SO2 and NO2. Vereecken et al. (2012) presented and 1-Br-2-proponol (Aldrich, 70 %). a series of loss pathways for the stabilised Criegee interme- diate, and found that its loss was dominated by its reaction 2.2 Apparatus and procedure with H2O, NO2, and SO2, for which H2O is the most effi- cient scavenger. A flow tube reactor (100 cm length, 5 cm inner diameter, There have been only a few chamber studies focusing on quartz wall) equipped with a water jacket for temperature hydrogen peroxide and the C1–C3 hydroperoxide formation control was employed for performing ozonolysis experi- in the ozonolysis