Carboxylate Ion Availability at the Air–Water Interface

Enami, Shinichi; Fujii, Toshitsugu; Sakamoto, Yosuke; Hama, Tetsuya; Kajii, Yoshizumi

doi:10.1021/acs.jpca.6b08868

Cited by 54 publications

(65 citation statements)

References 87 publications

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“…The underlying process is genuinely interfacial, because γ(NO2)e is significantly enhanced by cationic surfactants, weakly depressed by anionic surfactants, and unaffected by hydrophobic 1-octanol. [44][45][46][51][52] Significantly, our results are consistent with the γ(NO 2 ) e ∼ 10 -4 values measured on ∼3 mM NaCl droplets in a cloud chamber, [53][54] a finding that remained unexplained vis-à-vis the γ(NO2)w < 1 × 10 -7 value previously measured on pure water, and consequently ignored by the atmospheric chemistry community. In short, in the presence of dense aerosols, such as those that develop in urban smog at noon, reaction R2 can become competitive with the photolysis of NO 2 (g), R3:…”

Section: The Disproportionation Of Nitrogen Dioxide On Aqueous Aerososupporting

confidence: 90%

Detecting Intermediates and Products of Fast Heterogeneous Reactions on Liquid Surfaces via Online Mass Spectrometry

Colussi¹,

Enami²

2018

Preprint

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One of the research priorities in atmospheric chemistry is to advance our understanding of heterogeneous reactions and their effect on the composition of the troposphere. Chemistry on aqueous surfaces is particularly important in this regard because of their ubiquity and expanse. They range from the surfaces of oceans (360 million km2), cloud and aerosol drops (~10 trillion km2) to the fluids lining the human lung (~200 m2). Typically, ambient air contains reactive gases that may affect human health, influence climate and participate in biogeochemical cycles. Despite their importance, reactions between gases and solutes at air-aqueous interfaces are not well understood. New, surface-specific techniques are required that detect and identify the intermediates and products of such reactions as they happen on liquids. This is a tall order because genuine interfacial reactions are faster than mass diffusion into bulk liquids, and may produce novel species at low concentrations. Herein, we review evidence that validates online pneumatic ionization mass spectrometry of liquid microjets dosed by reactive gases as a technique meeting such requirements. Next, we call attention to results obtained by this approach on reactions of ozone, nitrogen dioxide and hydroxyl radicals with various solutes on aqueous surfaces. The overarching conclusion is that the outermost layers of aqueous solutions are unique media, where equilibria shift and reactions proceed faster than, in some cases along different pathways from the bulk liquids. The fact that the rates and mechanisms of reactions at air-aqueous interfaces may not be deduced from experiments in bulk liquids opens new conceptual frameworks and lines of research, and adds an overlooked dimension to atmospheric chemistry.

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Section: The Disproportionation Of Nitrogen Dioxide On Aqueous Aerososupporting

confidence: 90%

Detecting Intermediates and Products of Fast Heterogeneous Reactions on Liquid Surfaces via Online Mass Spectrometry

Colussi¹,

Enami²

2018

Preprint

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“…times smaller than those at m/z 431 (and 433) from OA at [1-octanol] = [OA] = 100 mM reveals that 1-octanol is much less reactive than OA toward CIs, although both species are expected to have similar affinities for aqueous surfaces. 25,32,43,[69][70] The C 23 ethers and esters produced in each case, by having similar mass and structures (see This finding is in line with gas-phase reaction rate constants of CIs + HCOOH/CH 3 COOH, which approach collisionally controlled values: k ≥ 10 -10 cm 3 molecule -1 s -1 , 22 vs. the much smaller values for CIs + methanol/2-propanol. 48,50,68 Tobias and Ziemann have reported that rate constants of gas-phase C 13 CIs reactions with various species increase in the order: water < methanol < 2-propanol < formaldehyde < formic acid < heptanoic acid, over a 10 4…”

Section: Page 3 Of 23 Acs Paragon Plus Environmentsupporting

confidence: 64%

“…31 Previous experiments in our laboratory have demonstrated that mass spectral signal intensities are proportional to interfacial ion populations. [31][32]36 We have shown that mass spectra: (1) are not affected by the weak local electric fields at the tip of the grounded nozzle, [37][38] (2) correspond to species generated by reactions taking place in the outermost interfacial layers of the microjets. 29,[31][32][39][40] The limited exposures of unambiguously identified by the characteristic M/M+2 = 3/1 signal ratios arising from natural abundance 35 Cl: 37 Cl::0.75:025 isotopes.…”

Section: Page 3 Of 23 Acs Paragon Plus Environmentmentioning

confidence: 99%

Reactions of Criegee Intermediates with Alcohols at Air–Aqueous Interfaces

Enami

Colussi

2017

J. Phys. Chem. A

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The fate of Criegee intermediates (CIs) from the gas-phase ozonolysis of unsaturated organic compounds in the troposphere is largely controlled by their reactions with water vapor. We recently found that against all expectations carboxylic acids compete at millimolar concentrations with water for CIs at the air-liquid interface of aqueous organic media. This outcome is consistent with both the low water concentration in the outermost interfacial layers and the enrichment of the competing acids therein. Here we show, via online electrospray mass spectrometric detection, that CIs generated in situ in the fast ozonolysis of sesquiterpenes (CH) on the surface of water:acetonitrile microjets react with n ≥ 4 linear alcohols CHOH to produce high molecular weight C ethers in one step. The OH group of 1-octanol proved to be ∼25 times less reactive than that of n-octanoic toward CIs at the same bulk molar concentration, revealing that the reactivity of hydroxylic species depends on both acidities and interfacial affinities. CI interfacial reactions with surface-active hydroxylic species, by bypassing water, represent shortcuts to molecular complexity in atmospheric aerosols.

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“…This was demonstrated by the well-defined RCOO − (R = n-alkyl) mass signals versus pH titration curves (inflection points at pK a (RCOOH) = 4.8) obtained from aqueous RCOOH solutions [14,37,38,[41][42][43][44][45]. Well-defined pK a (RCOOH) = 4.8 titration curves imply that the sampled layers have well-defined proton activities [46].…”

Section: Products Of Gas-liquid Reactions Are Mainly Formed On Liquidmentioning

confidence: 87%

Detecting Intermediates and Products of Fast Heterogeneous Reactions on Liquid Surfaces via Online Mass Spectrometry

Colussi

Enami

2019

Atmosphere

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One of the research priorities in atmospheric chemistry is to advance our understanding of heterogeneous reactions and their effect on the composition of the troposphere. Chemistry on aqueous surfaces is particularly important because of their ubiquity and expanse. They range from the surfaces of oceans (360 million km2), cloud and aerosol drops (estimated at ~10 trillion km2) to the fluid lining the human lung (~150 m2). Typically, ambient air contains reactive gases that may affect human health, influence climate and participate in biogeochemical cycles. Despite their importance, atmospheric reactions between gases and solutes on aqueous surfaces are not well understood and, as a result, generally overlooked. New, surface-specific techniques are required that detect and identify the intermediates and products of such reactions as they happen on liquids. This is a tall order because genuine interfacial reactions are faster than mass diffusion into bulk liquids, and may produce novel species in low concentrations. Herein, we review evidence that validates online pneumatic ionization mass spectrometry of liquid microjets exposed to reactive gases as a technique that meets such requirements. Next, we call attention to results obtained by this approach on reactions of gas-phase ozone, nitrogen dioxide and hydroxyl radicals with various solutes on aqueous surfaces. The overarching conclusion is that the outermost layers of aqueous solutions are unique media, where most equilibria shift and reactions usually proceed along new pathways, and generally faster than in bulk water. That the rates and mechanisms of reactions at air-aqueous interfaces may be different from those in bulk water opens new conceptual frameworks and lines of research, and adds a missing dimension to atmospheric chemistry.

show abstract

Carboxylate Ion Availability at the Air–Water Interface

Cited by 54 publications

References 87 publications

Detecting Intermediates and Products of Fast Heterogeneous Reactions on Liquid Surfaces via Online Mass Spectrometry

Detecting Intermediates and Products of Fast Heterogeneous Reactions on Liquid Surfaces via Online Mass Spectrometry

Reactions of Criegee Intermediates with Alcohols at Air–Aqueous Interfaces

Detecting Intermediates and Products of Fast Heterogeneous Reactions on Liquid Surfaces via Online Mass Spectrometry

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