Multiphase Chemistry of Highly Oxidized Molecules: The Case of Organic Hydroperoxides
2016; Elsevier BV; Volume: 1; Issue: 4 Linguagem: Inglês
10.1016/j.chempr.2016.09.015
ISSN2451-9308
Autores Tópico(s)Air Quality and Health Impacts
ResumoSignificant quantities of highly oxidized molecules (HOMs), such as organic hydroperoxides, are formed from the oxidation of biogenic compounds. In this issue of Chem, Dommen and coworkers highlight the fast decomposition of HOMs in the condensed phase, which can potentially affect the chemical and physical properties of secondary organic aerosol (SOA). Significant quantities of highly oxidized molecules (HOMs), such as organic hydroperoxides, are formed from the oxidation of biogenic compounds. In this issue of Chem, Dommen and coworkers highlight the fast decomposition of HOMs in the condensed phase, which can potentially affect the chemical and physical properties of secondary organic aerosol (SOA). The largest mass fraction of atmospheric fine particulate matter (PM2.5, aerosol with aerodynamic diameters ≤ 2.5 μm) is generally organic and is dominated by secondary organic aerosol (SOA) formed from gas-phase oxidation of volatile organic compounds (VOCs). SOA plays an important role in cloud formation, visibility, and health. Biogenic VOCs (BVOCs), such as 2-methylbuta-1,3-diene (isoprene) and monoterpenes, are typically the most abundant SOA precursors, especially in regions of dense terrestrial vegetation. Recent developments of novel reagent ion chemistries, such as nitrate (NO3−), for chemical ionization mass spectrometers has allowed for the identification of previously unresolved gaseous highly oxidized molecules (HOMs).1Ehn M. Thornton J.A. Kleist E. Sipilä M. Junninen H. Pullinen I. Springer M. Rubach F. Tillmann R. Lee B. et al.Nature. 2014; 506: 476-479Crossref Scopus (1078) Google Scholar HOMs, initially observed from the oxidation of several biogenic VOCs, form at unexpectedly high yields.1Ehn M. Thornton J.A. Kleist E. Sipilä M. Junninen H. Pullinen I. Springer M. Rubach F. Tillmann R. Lee B. et al.Nature. 2014; 506: 476-479Crossref Scopus (1078) Google Scholar It has been suggested that their abundances are sufficient to explain the observed particle growth rates in both laboratory and field studies and to contribute significantly to SOA formation.1Ehn M. Thornton J.A. Kleist E. Sipilä M. Junninen H. Pullinen I. Springer M. Rubach F. Tillmann R. Lee B. et al.Nature. 2014; 506: 476-479Crossref Scopus (1078) Google Scholar, 2Tröstl J. Chuang W.K. Gordon H. Heinritzi M. Yan C. Molteni U. Ahlm L. Frege C. Bianchi F. Wagner R. et al.Nature. 2016; 533: 527-531Crossref Scopus (417) Google Scholar The formation of HOMs is proposed to primarily occur through peroxy radical (RO2) intramolecular hydrogen shifts followed by rapid reaction with O2, sometimes also called “autoxidation.”1Ehn M. Thornton J.A. Kleist E. Sipilä M. Junninen H. Pullinen I. Springer M. Rubach F. Tillmann R. Lee B. et al.Nature. 2014; 506: 476-479Crossref Scopus (1078) Google Scholar HOMs are expected to contain a wide range of chemical functional groups, including alcohols, hydroperoxides, epoxides, or carbonyls.2Tröstl J. Chuang W.K. Gordon H. Heinritzi M. Yan C. Molteni U. Ahlm L. Frege C. Bianchi F. Wagner R. et al.Nature. 2016; 533: 527-531Crossref Scopus (417) Google Scholar Consequently, HOMs have very low vapor pressures and could react and/or condense nearly irreversibly onto aerosol surfaces.1Ehn M. Thornton J.A. Kleist E. Sipilä M. Junninen H. Pullinen I. Springer M. Rubach F. Tillmann R. Lee B. et al.Nature. 2014; 506: 476-479Crossref Scopus (1078) Google Scholar Although the importance of HOMs in the formation of new particles and SOA was revealed in previous studies,1Ehn M. Thornton J.A. Kleist E. Sipilä M. Junninen H. Pullinen I. Springer M. Rubach F. Tillmann R. Lee B. et al.Nature. 2014; 506: 476-479Crossref Scopus (1078) Google Scholar, 2Tröstl J. Chuang W.K. Gordon H. Heinritzi M. Yan C. Molteni U. Ahlm L. Frege C. Bianchi F. Wagner R. et al.Nature. 2016; 533: 527-531Crossref Scopus (417) Google Scholar the molecular structures, formation pathways, and fate of HOMs still remain uncertain. Potential multiphase (heterogeneous) reactions—such as decomposition via photolysis or reactive uptake, oligomerization (or accretion reactions), and radical reactions induced by decomposition or photolysis—are likely to be important and could further affect the chemical and physical properties of SOA (Figure 1). For instance, rapid acid-catalyzed uptake of epoxide products (e.g., 2-methyl-2,3-epoxy-1,4-butanediol: β-IEPOX) to aerosol was demonstrated to yield subsequent SOA formation from the oxidation of isoprene.5Surratt J.D. Chan A.W.H. Eddingsaas N.C. Chan M. Loza C.L. Kwan A.J. Hersey S.P. Flagan R.C. Wennberg P.O. Seinfeld J.H. Proc. Natl. Acad. Sci. USA. 2010; 107: 6640-6645Crossref Scopus (681) Google Scholar Lee et al.6Lee B.H. Mohr C. Lopez-Hilfiker F.D. Lutz A. Hallquist M. Lee L. Romer P. Cohen R.C. Iyer S. Kurtén T. et al.Proc. Natl. Acad. Sci. USA. 2016; 113: 1516-1521Crossref Scopus (198) Google Scholar have also reported that organonitrates formed from the oxidation of isoprene and/or monoterpenes undergo gas-particle partitioning and are rapidly depleted in the condensed phase (lifetimes ∼ 2−4 hr). Among the wide range of products, organic hydroperoxides (ROOHs) represent a significant fraction of SOA generated from the oxidation of BVOCs. ROOHs are formed via multi-step gas-phase oxidation and autoxidation, introducing multiple ROOH functional groups.1Ehn M. Thornton J.A. Kleist E. Sipilä M. Junninen H. Pullinen I. Springer M. Rubach F. Tillmann R. Lee B. et al.Nature. 2014; 506: 476-479Crossref Scopus (1078) Google Scholar Because of the low binding energy of the O–O bond induced by the electron-donating R group, ROOHs are well known to undergo thermal homolytic cleavage.4Tong H. Arangio A.M. Lakey P.S. Berkemeier T. Liu F. Kampf C.J. Brune W.H. Pöschl U. Shiraiwa M. Atmos. Chem. Phys. 2016; 16: 1761-1771Crossref Scopus (111) Google Scholar Recent studies have suggested that ROOHs condense onto particles and can play a central role in the formation and aging of SOA. For instance, ROOHs formed from the oxidation of BVOCs were proposed as precursors to the formation of organosulfates7Mutzel A. Poulain L. Berndt T. Iinuma Y. Rodigast M. Böge O. Richters S. Spindler G. Sipilä M. Jokinen T. et al.Environ. Sci. Technol. 2015; 49: 7754-7761Crossref Scopus (114) Google Scholar, 8Riva M. Budisulistiorini S.H. Chen Y. Zhang Z. D’Ambro E.L. Zhang X. Gold A. Turpin B.J. Thornton J.A. Canagaratna M.R. Surratt J.D. Environ. Sci. Technol. 2016; 50: 9889-9899Crossref Scopus (82) Google Scholar and oligomers8Riva M. Budisulistiorini S.H. Chen Y. Zhang Z. D’Ambro E.L. Zhang X. Gold A. Turpin B.J. Thornton J.A. Canagaratna M.R. Surratt J.D. Environ. Sci. Technol. 2016; 50: 9889-9899Crossref Scopus (82) Google Scholar through multiphase reactions (Figure 1). In addition, Tong et al.4Tong H. Arangio A.M. Lakey P.S. Berkemeier T. Liu F. Kampf C.J. Brune W.H. Pöschl U. Shiraiwa M. Atmos. Chem. Phys. 2016; 16: 1761-1771Crossref Scopus (111) Google Scholar have observed substantial formation of OH radicals from the hydrolysis of SOA and reported that the chemical reactivity and aging of SOA are strongly enhanced by the presence of water and iron (Fe2+). Although these studies have suggested that ROOH is a reactive species in the aerosol phase, leading to a large variety of products, the associated chemical mechanisms and kinetics still remain unknown. Dommen and co-workers3Krapf M. El Haddad I. Bruns E.A. Molteni U. Daellenbach K.R. Prévôt A.S.H. Dommen J. Chem. 2016; 1: 603-616Abstract Full Text Full Text PDF Scopus (109) Google Scholar have now investigated the abundance and fate of hydroperoxide-containing HOMs in the condensed phase produced from the ozonolysis of 2,6,6-trimethylbicyclo[3.1.1]hept-2-ene (α-pinene). The results reported in this issue of Chem reveal that such compounds contribute to a large mass fraction of SOA and undergo rapid decomposition (within a timescale shorter than 1 hr) in the aerosol phase. As shown in previous studies,9Epstein S.A. Blair S.L. Nizkorodov S.A. Environ. Sci. Technol. 2014; 48: 11251-11258Crossref Scopus (85) Google Scholar subsequent photolytic degradation of SOA was observed, which could further affect the chemical composition and the aerosol mass generated from the ozonolysis of α-pinene. However, experimental results from this study reveal that rapid photolysis of SOA is not due to the presence of the hydroperoxide functional groups. Indeed, the estimated photolysis rate of ROOHs is significantly lower than the photolytic loss rate of SOA generated from the ozonolysis of α-pinene. These results reveal that other functional groups, such as carbonyls, most likely act as chromophores in the photodegradation of HOMs.3Krapf M. El Haddad I. Bruns E.A. Molteni U. Daellenbach K.R. Prévôt A.S.H. Dommen J. Chem. 2016; 1: 603-616Abstract Full Text Full Text PDF Scopus (109) Google Scholar Dommen and co-workers3Krapf M. El Haddad I. Bruns E.A. Molteni U. Daellenbach K.R. Prévôt A.S.H. Dommen J. Chem. 2016; 1: 603-616Abstract Full Text Full Text PDF Scopus (109) Google Scholar also suggest that the rapid decomposition of hydroperoxide-containing HOMs in the condensed phase could affect particle growth. It is worth noting that a recent study has reported the rapid decomposition of gas-phase organic hydroperoxides formed from the photooxidation of isoprene in the presence of acidified sulfate aerosols and estimated that at least 50% of 2-hydroperoxy-2-methylbut-3en-1-ol and 2-hydroperoxy-3-methylbut-3en-1-ol (ISOPOOH) taken up into acidified aerosols react and form more volatile species that evaporate.10Liu Y. Kuwata M. McKinney K.A. Martin S.T. Phys. Chem. Chem. Phys. 2016; 18: 1595-1600Crossref Google Scholar The implication is that the global importance of hydroperoxide-containing HOMs in the formation of new particles and SOA might have been over-predicted in recent works.3Krapf M. El Haddad I. Bruns E.A. Molteni U. Daellenbach K.R. Prévôt A.S.H. Dommen J. Chem. 2016; 1: 603-616Abstract Full Text Full Text PDF Scopus (109) Google Scholar The findings reported in this study3Krapf M. El Haddad I. Bruns E.A. Molteni U. Daellenbach K.R. Prévôt A.S.H. Dommen J. Chem. 2016; 1: 603-616Abstract Full Text Full Text PDF Scopus (109) Google Scholar highlight the significant reactivity of hydroperoxide-containing HOMs in the condensed phase. However, as suggested in previous works, aerosol constituents including aerosol water, sulfate, or metals (e.g., iron) could significantly influence the integrity of HOMs and affect the chemical composition, aging, or toxicity of SOA.4Tong H. Arangio A.M. Lakey P.S. Berkemeier T. Liu F. Kampf C.J. Brune W.H. Pöschl U. Shiraiwa M. Atmos. Chem. Phys. 2016; 16: 1761-1771Crossref Scopus (111) Google Scholar, 5Surratt J.D. Chan A.W.H. Eddingsaas N.C. Chan M. Loza C.L. Kwan A.J. Hersey S.P. Flagan R.C. Wennberg P.O. Seinfeld J.H. Proc. Natl. Acad. Sci. USA. 2010; 107: 6640-6645Crossref Scopus (681) Google Scholar, 6Lee B.H. Mohr C. Lopez-Hilfiker F.D. Lutz A. Hallquist M. Lee L. Romer P. Cohen R.C. Iyer S. Kurtén T. et al.Proc. Natl. Acad. Sci. USA. 2016; 113: 1516-1521Crossref Scopus (198) Google Scholar, 7Mutzel A. Poulain L. Berndt T. Iinuma Y. Rodigast M. Böge O. Richters S. Spindler G. Sipilä M. Jokinen T. et al.Environ. Sci. Technol. 2015; 49: 7754-7761Crossref Scopus (114) Google Scholar, 8Riva M. Budisulistiorini S.H. Chen Y. Zhang Z. D’Ambro E.L. Zhang X. Gold A. Turpin B.J. Thornton J.A. Canagaratna M.R. Surratt J.D. Environ. Sci. Technol. 2016; 50: 9889-9899Crossref Scopus (82) Google Scholar, 9Epstein S.A. Blair S.L. Nizkorodov S.A. Environ. Sci. Technol. 2014; 48: 11251-11258Crossref Scopus (85) Google Scholar, 10Liu Y. Kuwata M. McKinney K.A. Martin S.T. Phys. Chem. Chem. Phys. 2016; 18: 1595-1600Crossref Google Scholar For example, it might be expected that the lifetimes of hydroperoxide-containing HOMs are even shorter than those estimated by Dommen and co-workers,3Krapf M. El Haddad I. Bruns E.A. Molteni U. Daellenbach K.R. Prévôt A.S.H. Dommen J. Chem. 2016; 1: 603-616Abstract Full Text Full Text PDF Scopus (109) Google Scholar and the presence of acidified aerosol could catalyze the decomposition of HOMs.5Surratt J.D. Chan A.W.H. Eddingsaas N.C. Chan M. Loza C.L. Kwan A.J. Hersey S.P. Flagan R.C. Wennberg P.O. Seinfeld J.H. Proc. Natl. Acad. Sci. USA. 2010; 107: 6640-6645Crossref Scopus (681) Google Scholar, 8Riva M. Budisulistiorini S.H. Chen Y. Zhang Z. D’Ambro E.L. Zhang X. Gold A. Turpin B.J. Thornton J.A. Canagaratna M.R. Surratt J.D. Environ. Sci. Technol. 2016; 50: 9889-9899Crossref Scopus (82) Google Scholar, 10Liu Y. Kuwata M. McKinney K.A. Martin S.T. Phys. Chem. Chem. Phys. 2016; 18: 1595-1600Crossref Google Scholar Therefore, heterogeneous reactions of HOMs warrant further study for better characterization of the impact of such chemistry on the chemical and physical properties of SOA under atmospheric conditions. In addition, given the large reactivity of organic hydroperoxides and the analytical methods currently used,3Krapf M. El Haddad I. Bruns E.A. Molteni U. Daellenbach K.R. Prévôt A.S.H. Dommen J. Chem. 2016; 1: 603-616Abstract Full Text Full Text PDF Scopus (109) Google Scholar, 10Liu Y. Kuwata M. McKinney K.A. Martin S.T. Phys. Chem. Chem. Phys. 2016; 18: 1595-1600Crossref Google Scholar an under-estimation of the contribution of such compounds to SOA formation should not be ruled out and warrants further study. ROOHs could yield highly oxidized products in SOA but could also generate significant quantities of volatile species, which could further contribute to SOA formation and/or to the oxidative capacity of the atmosphere. Assessing the global importance of HOMs in the formation of new particles and SOA is urgently needed to help bring predictions of organic particle concentrations closer to ambient observations in the atmosphere. Labile Peroxides in Secondary Organic AerosolKrapf et al.ChemOctober 13, 2016In BriefParticles in the atmosphere affect the climate and are a major factor for premature deaths. Peroxide-containing highly oxygenated molecules may constitute an important class of compounds for the formation of new particles and secondary organic aerosols. However, they are found to be labile and decay with half-lives of less than an hour at room temperature. This significantly alters the oxidation state and volatility of organic aerosols, thereby affecting their impact on health and climate. Full-Text PDF Open Archive
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