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We conducted an urban-scale analysis of the contribution of gas phase stabilized-Criegee intermediates (sCIs) to atmospheric sulphate aerosol (SO42−) formation across four seasons in the Greater Tokyo Area (GTA) using the regional chemical transport model, the community multiscale air quality modelling (CMAQ) system. We analysed the seasonal and temporal trend of sCI formation in three areas: Tokyo Bay (urban), suburban, and mountainous areas. In all three areas, the sCI concentrations were high in the morning (7 a.m.) and early evening (6 p.m.) owing to the high frequency of vigorous traffic activities causing intense alkene emissions. The results suggest that more than 90% of the sCIs generated in the target areas are consumed by the unimolecular decomposition of sCIs themselves or by reactions with water, which are consistent with estimates from previous kinetic analysis studies targeting other regions. The contribution of sCIs to SO42−formation estimated in this study was a maximum of 0.25% in the rural area, which is approximately 10-fold lower than that of previous studies. The results of the sCI loss pathway analysis suggested that the unimolecular decomposition of sCIs and the reaction between sCIs and water contribute comparably to the loss of sCIs, which caused less of an effect of sCIs on SO42−formation compared with that in previous studies.

1,2,4-Trioxolanes, known as secondary ozonides (SOZs), are key products of ozonolysis of biogenic terpenoids. Functionalized terpenoid-derived SOZs are readily taken up into atmospheric aerosols; however, their condensed-phase fates remain unknown. Here, we report the results of a time-dependent mass spectrometric investigation into the liquid-phase fates of C10and C13SOZs synthesized by ozonolysis of a C10monoterpene alcohol (α-terpineol) in water:acetone (1:1 = vol:vol) mixtures. Isomerization of Criegee intermediates and bimolecular reaction of Criegee intermediates with acetone produced C10and C13SOZs, respectively, which were detected as their Na+-adducts by positive-ion electrospray mass spectrometry. Use of CD3COCD3, D2O, and H218O solvents enabled identification of three types of C13SOZs (aldehyde, ketone, and lactol) and other products. These SOZs were surprisingly stable in water:acetone (1:1) mixtures at T= 298 K, with some persisting for at least a week. Theoretical calculations supported the high stability of the lactol-type C13SOZ formed from the aldehyde-type C13SOZ via intramolecular rearrangement. The present results suggest that terpenoid-derived SOZs can persist in atmospheric condensed phases, potentially until they are delivered to the epithelial lining fluid of the pulmonary alveoli via inhaled particulate matter, where they may exert hitherto unrecognized adverse health effects.

Organic hydroperoxides (ROOHs) play key roles in the atmosphere as a reactive intermediate species. Due to the low volatility and high hydrophilicity, ROOHs are expected to reside in atmospheric condensed phases such as aerosols, fogs, and cloud droplets. The decomposition mechanisms of ROOHs in the liquid phase are, however, still poorly understood. Here we report a temperature-dependent kinetics and theoretical calculation study of the aqueous-phase decompositions of C12or C13α-alkoxyalkyl-hydroperoxides (α-AHs) derived from ozonolysis of α-terpineol in the presence of 1-propanol, 2-propanol, and ethanol. We found that the temporal profiles of α-AH signals, detected as chloride-adducts by negative ion electrospray mass spectrometry, showed single-exponential decay, and the derived first-order rate coefficient kfor α-AH decomposition increased as temperature increased, e.g., k(288 K) = (5.3 ± 0.2) × 10−4s−1, k(298 K) = (1.2 ± 0.3) × 10−3s−1, k(308 K) = (2.1 ± 1.4) × 10−3s−1for C13α-AHs derived from the reaction of α-terpineol Criegee intermediates with 1-propanol in the solution at pH 4.5. Arrhenius plot analysis yielded an activation energy (Ea) of 12.3 ± 0.6 kcal mol−1. Eaof 18.7 ± 0.3 and 13.8 ± 0.9 kcal mol−1were also obtained for the decomposition of α-AHs (at pH 4.5) derived from the reaction of α-terpineol Criegee intermediates with 2-propanol and with ethanol, respectively. Based on the theoretical kinetic and thermodynamic calculations, we propose that a proton-catalyzed mechanism plays a central role in the decomposition of these α-AHs in acidic aqueous organic media, while water molecules may also participate in the decomposition pathways and affect the kinetics. The decomposition of α-AHs could act as a source of H2O2and multifunctionalized species in atmospheric condensed phases.

We report the results of a mass spectrometric study of the effects of atmospherically relevant metal ions on the decomposition of α-hydroxyalkyl-hydroperoxides (α-HHs) derived from ozonolysis of α-terpineol in aqueous solutions. By direct mass spectrometric detection of chloride adducts of α-HHs, we assessed the temporal profiles of α-HHs and other products in the presence of metal ions. In addition, reactions between α-HHs and FeCl2in the presence of excess DMSO showed that the amount of hydroxyl radicals formed in a mixture of α-terpineol, O3, and FeCl2was 5.7 ± 0.8% of the amount formed in a mixture of H2O2and FeCl2. The first-order rate constants for the decay of α-HHs produced by ozonolysis of α-terpineol in the presence of 5 mM acetate buffer at a pH of 5.1 ± 0.1 were determined to be (4.5 ± 0.1) × 10–4s–1(no metal ions), (4.7 ± 0.2) × 10–4s–1(with 0.05 mM Fe2+), (4.7 ± 0.1) × 10–4s–1(with 0.05 mM Zn2+), and (4.8 ± 0.2) × 10–4s–1(with 0.05 mM Cu2+). We propose that in acidic aqueous media, the reaction of α-HHs with Fe2+is outcompeted by H+-catalyzed decomposition of α-HHs, which produces the corresponding aldehydes and H2O2, which can in turn react with Fe2+to form hydroxyl radicals.

We demonstrate continuous measurement of carbon dioxide (CO2) in the atmosphere using quartz-enhanced photoacoustic spectroscopy (QEPAS) at 2.008 μm with a fiber-coupled distributed-feedback laser. The QEPAS sensor is composed of a quartz tuning fork with a resonance frequency f0of 12.4 kHz. The photoacoustic second-harmonic (2f) signal resulting from CO2absorption was detected using a digital lock-in amplifier. The photoacoustic signal is proportional to the laser power. The limit of detection at an absorption line of 4980.13161 cm−1with a line strength of 3.87 × 10−22cm2molecule−1cm−1was 12 parts per million with an integration time of 10 s. The results of the continuous monitoring of ambient CO2using the QEPAS sensor corresponded to those obtained using a nondispersive IR sensor. The QEPAS sensor exhibited a suitable performance for field measurements of the CO2mixing ratio.

Ozonolysis of unsaturated organic species with water produces α-hydroxyalkyl-hydroperoxides (α-HHs), which are reactive intermediates that lead to the formation of H2O2and multifunctionalized species in atmospheric condensed phases. Here, we report temperature-dependent rate coefficients (k) for the aqueous-phase decomposition of α-terpineol α-HHs at 283–318 K and terpinen-4-ol α-HHs at 313–328 K. The temporal profiles of α-HH signals, detected as chloride adducts by negative-ion electrospray mass spectrometry, showed single-exponential decay, and the derived first-order kfor α-HH decomposition increased as temperature increased, e.g., k(288 K) = (4.7 ± 0.2) × 10–5, k(298 K) = (1.5 ± 0.4) × 10–4, k(308 K) = (3.4 ± 0.9) × 10–4, k(318 K) = (1.0 ± 0.2) × 10–3s–1for α-terpineol α-HHs at pH 6.1. Arrhenius plot analysis yielded activation energies of 17.9 ± 0.7 (pH 6.1) and 17.1 ± 0.2 kcal mol–1(pH 6.2) for the decomposition of α-terpineol and terpinen-4-ol α-HHs, respectively. Activation energies of 18.6 ± 0.2 and 19.2 ± 0.5 kcal mol–1were also obtained for the decomposition of α-terpineol α-HHs in acidified water at pH 5.3 and 4.5, respectively. Theoretical kinetic and thermodynamic calculations confirmed that both water-catalyzed and proton-catalyzed mechanisms play important roles in the decomposition of these α-HHs. The relatively strong temperature dependence of ksuggests that the lifetime of these α-HHs in aqueous phases (e.g., aqueous aerosols, fog, cloud droplets, wet films) is controlled not only by the water content and pH but also by the temperature of these media.

In the atmosphere, most biogenic terpenes undergo ozonolysis in the presence of water to form reactive α-hydroxyalkyl-hydroperoxides (α-HHs), and the lifetimes of these α-HHs are a key parameter for understanding the processes that occur during the aging of atmospheric particles. We previously reported that α-HHs generated by ozonolysis of terpenes decompose in water to give H2O2and the corresponding aldehydes, which undergo hydration to form gem-diols. Herein, we report that this decomposition process was dramatically accelerated by acidification of the water with oxalic, acetic, hexanoic, cis-pinonic, or hydrochloric acid. In acidic solution, the temporal profiles of the α-HHs, detected as their chloride adducts by electrospray mass spectrometry, showed single-exponential decays in the pH range from 4.1 to 6.1, and the first-order rate coefficients (k) for the decays increased with decreasing pH. The lifetime of the α-HH derived from α-terpineol was 128 min (k= (1.3 ± 0.4) × 10–4s–1) at pH 6.1 but only 8 min (k= (2.1 ± 0.1) × 10–3s–1) at pH 4.1. Because the rate coefficients increased as the pH decreased and the increase depended on pH rather than on the properties of the acid, we propose that the decomposition of the α-HHs in water was specifically catalyzed by H+. Fast H+-catalyzed decomposition of α-HHs could be an important source of H2O2and multifunctionalized compounds found in ambient atmospheric particles.

A detailed inventory was taken of evaporative emissions from parked gasoline vehicles in the Kanto region of Japan, 2015, based on the theoretical model to evaluate the amount of evaporative emissions. The inventory showed that evaporative emissions were high in metropolitan and urban areas because of the large populations in these areas and the high vehicle parking frequency. Using the new inventory, the sensitivity of evaporative emissions to the concentration of tropospheric ozone and secondary organic aerosol was evaluated using the chemical transport modeling solver, the community multiscale air quality modeling system (CMAQ), coupled with the weather research and forecasting (WRF) model. The calculation results showed that the evaporative emissions from permeation through fuel related parts were more significant in the generation of the tropospheric ozone than those from fuel tank venting. This was because the permeation emissions included a high proportion of high maximum incremental reactivity value components, such as aromatics. Neither of the evaporative emission types were significant secondary organic aerosol generators. Whole reduction of the evaporative emissions contributed an approximate 3 ppb decrease in tropospheric ozone in urban areas during the daytime. This information will contribute to the volatile organic compound (VOC) management strategy employed by governments worldwide.

The α-hydroxyalkyl-hydroperoxides [R–(H)C(−OH)(−OOH), α-HH] produced in the ozonolysis of unsaturated organic compounds may contribute to secondary organic aerosol (SOA) aging. α-HHs’ inherent instability, however, hampers their detection and a positive assessment of their actual role. Here we report, for the first time, the rates and products of the decomposition of the α-HHs generated in the ozonolysis of atmospherically important monoterpenes α-pinene (α-P), d-limonene (d-L), γ-terpinene (γ-Tn), and α-terpineol (α-Tp) in water/acetonitrile (W/AN) mixtures. We detect α-HHs and multifunctional decomposition products as chloride adducts by online electrospray ionization mass spectrometry. Experiments involving D2O and H218O, instead of H216O, and an OH-radical scavenger show that α-HHs decompose into gem-diols + H2O2rather than free radicals. α-HHs decay mono- or biexponentially depending on molecular structure and solvent composition. e-Fold times, τ1/e, in water-rich solvent mixtures range from τ1/e= 15–45 min for monoterpene-derived α-HHs to τ1/e> 103min for the α-Tp-derived α-HH. All τ1/e’s dramatically increase in <20% (v/v) water. Decay rates of the α-Tp-derived α-HH in pure water increase at lower pH (2.3 ≤ pH ≤ 3.3). The hydroperoxides detected in day-old SOA samples may reflect their increased stability in water-poor media and/or the slow decomposition of α-HHs from functionalized terpenes.

Acidity changes the physical properties of atmospheric aerosol particles and the mechanisms of reactions that occur therein and on the surface. Here, we used surface-sensitive pneumatic ionization mass spectrometry to investigate the effects of pH on the heterogeneous reactions of aqueous α-terpineol (C10H17OH), a representative monoterpene alcohol, with gaseous ozone. Rapid (≤10 μs) ozonolysis of α-terpineol produced Criegee intermediates (CIs, zwitterionic/diradical carbonyl oxides) on the surface of water microjets. We studied the effects of microjet bulk pH (1–11) on the formation of functionalized carboxylate and α-hydroxy-hydroperoxide chloride adduct (HH–Cl–) products generated by isomerization and hydration of α-terpineol CIs, respectively. Compared with the signal at pH ≈ 6, the mass spectral signal of HH–Cl–was less intense under both basic and more acidic conditions, whereas the intensity of the functionalized carboxylate signal increased with increasing pH up to 4 and then remained constant. The decrease of HH–Cl–signals at bulk pH values of >6 is attributable to the accumulation of OH–at the air–water interface that suppresses the relative abundance of hydrophilic HH and Cl–. The present study suggests that α-terpineol in ambient aqueous organic aerosols will be converted into much lower volatile and potentially toxic organic hydroperoxides during the heterogeneous ozonolysis.

Ozone readily reacts with olefins with the formation of more reactive Criegee intermediates (CIs). The transient CIs impact HOxcycles, and they play a role in new particle formation in the troposphere. Oxidation by O3occurs both in the gas-phase, in the liquid phase, and at air–water and air–aerosol interfaces. In light of the importance of O3in environmental and engineered chemical transformations, we have investigated the ozonolysis mechanisms of a triolefin C15-alcohol, nerolidol (Nero, a biogenic sesquiterpene), at the air–water interface in the presence of acetonitrile. Surface-sensitive pneumatic ionization mass spectrometric detection of α-hydroxy-hydroperoxides and functionalized carboxylates, generated by the hydration and isomerization of CIs, respectively, enables us to evaluate the relative reactivity of each C=C toward O3. In addition, we compare bulk-phase ozonolysis chemistry to similar reactions taking place at the air–water interface. Our experimental results show that O3reacts primarily with the (CH3)2C=CH– and −(CH3)C=CH– moieties (>∼98%), while the O3attack on the terminal −HC=CH2site (<∼2%) is a minor pathway during both interfacial and bulk ozonolysis. The presence of functionalized-carboxylates on interfaces but not in bulk-phase reactions with O3indicates that the isomerization of the CIs is not hindered at the air–water interface due to the lower availability of water .

Biogenic monoterpenes are major sources of Criegee intermediates (CIs) in the troposphere. Recent studies underscored the importance of their heterogeneous chemistry. The study of monoterpene CI reactions on liquid surfaces, however, is challenging due to the lack of suitable probes. Here, we report the first mass spectrometric detection of the intermediates and products, which include labile hydroperoxides, from reactions of CIs of representative monoterpenes (α-terpinene, γ-terpinene, terpinolene, d-limonene, α-pinene) with water, cis-pinonic acid (CPA) and octanoic acid (OA) on the surface of liquid microjets. Significantly, the relative yields of α-hydroxy-hydroperoxides production from CIs hydration at the gas–liquid interface—α-terpinene (1.00) ≫ d-limonene (0.18) > γ-terpinene (0.11) ∼ terpinolene (0.10) ≫ α-pinene (0.01)—do not track the rate constants of their gas-phase ozonolyses. Notably, in contrast with the inertness of the other CIs, the CIs derived from α-terpinene ozonolysis readily react with CPA and OA to produce C20and C18ester hydroperoxides, respectively. Present results reveal hitherto unknown structural effects on the reactivities of CIs at aqueous interfaces.

Secondary organic aerosol (SOA) found in polluted mega-cities contains benzoic acid (BA) as a major organic acid in addition to a variety of species including alkenes. In polluted air, ozone could be a major oxidizer for SOA and induces subsequent reactions involving Criegee intermediates (CIs, carbonyl oxide, RR′C•–O–O•/RR′C═O+–O–) formed by the −C═C– + O3reaction at the gas/liquid interface. The possibility that abundant BA could be an effective scavenger of CIs at the interface remains to be investigated by direct experiments. Here, we showed that amphiphilic BA is able to compete with water molecules for the CIs produced in the prompt ozonolysis of β-caryophyllene on the surface of a water/acetonitrile solvent microjet by generating hitherto uncharacterized C22ester hydroperoxide products. Competition between BA vs octanoic acid vs cis-pinonic acid toward CIs reveals that BA is a much less-efficient scavenger of CIs on aqueous organic surfaces. We attribute it to the surface-specific orientation of BA at the gas/liquid interface, where the reactive −C(O)OH group is fully hydrated and not available for CIs generated at the topmost layers.

We developed a mid-IR laser absorption spectrometer for ambient carbon monoxide (CO) measurement that uses a 4.69 µm interband cascade laser with wavelength modulation spectroscopy. The CO concentration was measured with a reproducibility of 0.4‰ (1s) over a 7-h period. Measurements of CO in outside air with a temporal resolution of 1 s were conducted successfully on the Kashiwa campus of The University of Tokyo over 4 days without trouble.We developed a mid-IR laser absorption spectrometer for ambient carbon monoxide that uses a 4.69 µm interband cascade laser with wavelength modulation spectroscopy. CO concentration was measured with reproducibility 0.4‰ (1s) over a 7-h period. Measurements of CO in outside air with a temporal resolution of 1 s were conducted successfully on the Kashiwa campus of The University of Tokyo over 4 days without trouble.

For the real-time measurements of volatile organic compounds (VOCs) in vehicle exhaust, we employed a vacuum ultraviolet single-photon ionization time-of-flight mass spectrometer (VUV-SPI-TOFMS). Exhaust measurements from gasoline and diesel engine vehicles were performed using a chassis dynamometer. Hydrocarbons such as alkylbenzenes, alkenes, alkanes, and dienes were the major organic compounds present in both gasoline and diesel engine exhaust. The concentrations of organic compounds in gasoline exhaust were higher under running conditions than during idling. The VOC concentrations in diesel exhaust were higher during idling than during running conditions. The VUV-SPI-TOFMS measured composition and emission profiles of many hydrocarbons, including aliphatics and aromatics, in vehicle exhaust simultaneously with real time response.

We measured nitrous oxide (N2O) concentration by mid-infrared wavelength modulation spectroscopy at a wavelength of 3.87 μm. Mid-infrared laser light from difference frequency generation in a fiber-coupled direct-bonded quasi-phase-matched LiNbO3-ridge-waveguide module is obtained using a diode-pumped Nd-doped yttrium alminum garnet (Nd:YAG) laser at 1064 nm together with a distributed feedback diode laser at 1466 nm. The absorption line of N2O centered at 2583.39 cm-1(3.871 μm), which originates from the first overtone band of the $\nu_{1}$ asymmetric stretching mode, is measured by second-harmonic wavelength modulation spectroscopy detection. The limits of N2O detection measured by wavelength modulation spectroscopy are found to be 150 ppbv using a 29.9 m Herriott multipass cell at a pressure of 12 kPa. We demonstrated the real-time monitoring of atmospheric N2O using our developed spectrometer with a difference-frequency-generation mid-infrared laser light source.

Using mid-infrared laser direct absorption spectroscopy with a quantum cascade laser light source, we investigated the room-temperature pressure broadening of nitrous oxide (N2O) in carbon dioxide (CO2) over the 1273.7–1277.2 cm−1wavenumber range for the ν1symmetric stretching mode. The five measured absorption profiles of N2O were analyzed with Voigt functions. The CO2pressure broadening coefficients ranged from 0.091(3) cm−1atm−1for the P(13) line to 0.125(2) cm−1atm−1for the P(9) line.

The yields of IO radical from the reaction of CH3I with Cl atom in the presence of O2were determined as functions of total pressure from 5 to 250 Torr of N2diluent and temperature over the range of 278 to 328 K using cavity ring-down spectroscopy. The yields are pressure and temperature dependent. The rate constants and product branching ratios of the reaction of CH2I radical with O2were investigated. We determined a rate constant of (1.28±0.22)×10−12cm3molecule−1s−1at 298 K (2σ uncertainty) for this reaction. Theoretical calculations were performed to determine energetics of the reactions of CH2I + O2and CH2Br + O2. The present results suggest that non-negligible IO radicals will be formed from the reactions of CH3I/CH2I2+ OH/Cl/NO3at atmospheric conditions.

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Vacuum ultraviolet single-photon ionization time-of-flight mass spectrometry (VUV-SPI-TOFMS) has been applied for the detection of chlorobenzene, o-dichlorobenzene, and o-chlorophenol as surrogates for polychlorinated dibenzo-p-dioxine/furans (PCDD/F). The photoionization mass spectra of these compounds appear to be fragmentation free in the ionization processes by the VUV-SPI at 10.2 eV (121.6 nm). Quantum chemical calculations support no fragmentation in the photoionization of chlorobenzene derivatives at around 10 eV. The absolute photoionization cross-sections of chlorobenzene, o-dichlorobenzene, and o-chlorophenol were estimated at 10.2 eV. The photoionization cross-section is an important parameter in the detection of chlorobenzene derivatives by the single-photon ionization technique. The detection limit for chlorobenzene is on the order of tenth parts-per-billion volume (ppbv) in the present experimental setup.

The products of SiH4decomposition on the surface of various filaments were directly detected by using vacuum ultraviolet (VUV) photo-ionization mass spectrometry under collision-free conditions. SiH2and SiH3were detected at filament temperatures of approximately Tf∼1300 K, where silicide formation on the filament was observed. At higher temperatures, the SiH2and SiH3signal intensities decreased and Si atom signal increased. It was confirmed that the Si atoms were the main species desorbed from the tungsten filament at Tf>1700 K. H atoms were also detected as a direct desorbed species from the filament by using the [2+1] resonance enhanced multi-photon ionization (REMPI) method combined with time-of-flight (TOF) mass spectrometry. Gas phase chemical reactions of SiH4with desorbed radicals (Si and H atoms) were also investigated. Si2H6, Si2H4and Si2could be detected as products of gas phase reactions. A chemical kinetic mechanism starting with Si+SiH4and H+SiH4reactions was proposed to explain the formation of Si2H6and Si2H4.

Si2H2 species were produced through the 193 nm excimer laser photolysis of Si2H6. Time-resolved photoionization mass spectrometry was employed to study the reaction kinetics of Si2H2. The lower limit of self-reaction of Si2H2 was estimated, k(Si2H2 + Si2H2) ≥ (1.7 ± 0.5) × 10⁻¹⁰ cm³ molecule⁻¹ s⁻¹, through analysis of the decay traces. This rate constant was independent of a total pressure on the entire pressure range (ptotal = 1–7 Torr). No reaction of Si2H2 with H2, CH4, SiH4, and Si2H6 was confirmed. The decay rates of Si2H2 reacting with O2, NO, and HCl exhibit negative dependence on the total pressure. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 136–141, 2001

Organic compounds present in diesel exhaust were measured using vacuum ultraviolet single photon ionization time-of-flight mass spectrometry while heating the inlet line at high and low temperatures. Increases in signal intensities were observed when the inlet was heated at 623 K because of enhanced volatilization of the organic fraction emitted in the particle phase.

Pressure dependence of vinylperoxyl radical formation in the reaction of the vinyl radical with molecular oxygen has been studied using a laser photolysis/cavity ring-down spectroscopy technique. The absorption spectra of vinyl radical and the product in the reaction were measured in the same spectral range from 439 to 465 nm. Varying the third body carrier gas of Ar from 10 to 120 Torr had obvious effect on the production of the vinylperoxyl radical.

Multiphoton ionization at 157.6 nm using F2laser has been used for the detection of benzene, toluene, and chlorobenzene. In all the photoionization spectra, the fragment ion signal intensities were stronger than those of the molecular ions. The detection limits of the compounds are discussed in terms of the multiphoton ionization schemes of the compounds.

For Abstract see ChemInform Abstract in Full Text.

For Abstract see ChemInform Abstract in Full Text.