Ozonolysis of methyl oleate monolayers at the air–water interface: oxidation kinetics, reaction products and atmospheric implications

Pfrang, Christian; Sebastiani, Federica; Lucas, Claire O. M.; King, Martin D.; Hoare, Ioan D.; Chang, Debby P.; Campbell, Richard A.

doi:10.1039/c4cp00775a

Cited by 49 publications

(64 citation statements)

References 39 publications

(65 reference statements)

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“…Therefore, the retention of the organic character at the air-water interface differs fundamentally between the different surfactant species: the fatty acids studied form products with a yield of ∼ 20 % that are stable at the air-water interface while the NO 3 -initiated oxidation of the methyl ester rapidly removes the organic character from the surface of the aqueous droplet. A similar difference (King et al, 2009;Pfrang et al, 2014;Sebastiani et al, 2015) between methyl ester and parent fatty acid has been found for the ozonolysis of d 34 OA and d 33 MO, but the retention of 20 % of organic material at the air-water interface is even more surprising for the more highly reactive nitrate radicals. The film-forming potential of the reaction products thus strongly depends on the head group properties.…”

Section: Head Groupsupporting

confidence: 63%

“…Nitrate radicals, NO 3 , were produced in situ from the reaction of O 3 with NO 2 . O 3 was generated by the exposure of molecular oxygen to UV light (the procedure has been described elsewhere; Pfrang et al, 2014). [NO 3 ] was regulated by changing the flow rate of NO 2 in the range 0.045-0.23 dm 3 min −1 while [O 3 ] was kept constant at 3.9 ppm (i.e.…”

Section: Gas Deliverymentioning

confidence: 99%

“…The molecules chosen for this study are oleic acid (OA), palmitoleic acid (POA), methyl oleate (MO) and stearic acid (SA). OA (King et al, 2004(King et al, , 2009, POA (Huff Hartz et al, 2007;Pfrang et al, 2011), MO (Hearn et al, 2005;Zahardis and Petrucci, 2007;Xiao and Bertram, 2011;Pfrang et al, 2014;Sebastiani et al, 2015) and SA (Sobanska et al, 2015) are popular model systems for atmospheric surfactants. MO, the methyl ester of OA, is a main component of biodiesel (chemical name: fatty acid methyl esters, or FAME; Wang et al, 2009) likely leading to an increased atmospheric abundance in the future since up to 7 % of FAME is added to standard petroleum diesel in the EU to reduce greenhouse gas emissions; higher proportions of FAME in petroleum diesel (10 % FAME sold as "B10" and 20 % FAME sold as "B20") as well as pure FAME ("B100") have become increasingly common fuel alternatives across a number of European countries including Germany, France and Finland.…”

Section: Introductionmentioning

confidence: 99%

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Nighttime oxidation of surfactants at the air–water interface: effects of chain length, head group and saturation

et al. 2018

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Reactions of the key atmospheric nighttime oxidant NO 3 with organic monolayers at the air-water interface are used as proxies for the ageing of organic-coated aqueous aerosols. The surfactant molecules chosen for this study are oleic acid (OA), palmitoleic acid (POA), methyl oleate (MO) and stearic acid (SA) to investigate the effects of chain length, head group and degree of unsaturation on the reaction kinetics and products formed. Fully and partially deuterated surfactants were studied using neutron reflectometry (NR) to determine the reaction kinetics of organic monolayers with NO 3 at the air-water interface for the first time. Kinetic modelling allowed us to determine the rate coefficients for the oxidation of OA, POA and MO monolayers to be (2.8 ± 0.7) × 10 −8 , (2.4 ± 0.5) × 10 −8 and (3.3 ± 0.6) × 10 −8 cm 2 molecule −1 s −1 for fitted initial desorption lifetimes of NO 3 at the closely packed organic monolayers, τ d,NO 3 ,1 , of 8.1 ± 4.0, 16 ± 4.0 and 8.1 ± 3.0 ns, respectively. The approximately doubled desorption lifetime found in the best fit for POA compared to OA and MO is consistent with a more accessible double bond associated with the shorter alkyl chain of POA facilitating initial NO 3 attack at the double bond in a closely packed monolayer. The corresponding uptake coefficients for OA, POA and MO were found to be (2.1±0.5)×10 −3 , (1.7±0.3)×10 −3 and (2.1±0.4)×10 −3 , respectively. For the much slower NO 3 -initiated oxidation of the saturated surfactant SA we estimated a loss rate of approximately (5 ± 1) × 10 −12 cm 2 molecule −1 s −1 , which we consider to be an upper limit for the reactive loss, and estimated an uptake coefficient of ca. (5 ± 1) × 10 −7 . Our investigations demonstrate that NO 3 will contribute substantially to the processing of unsaturated surfactants at the air-water interface during nighttime given its reactivity is ca. 2 orders of magnitude higher than that of O 3 . Furthermore, the relative contributions of NO 3 and O 3 to the oxidative losses vary massively between species that are closely related in structure: NO 3 reacts ca. 400 times faster than O 3 with the common model surfactant oleic acid, but only ca. 60 times faster with its methyl ester MO. It is therefore necessary to perform a case-by-case assessment of the relative contributions of the different degradation routes for any specific surfactant. The overall impact of NO 3 on the fate of saturated surfactants is slightly less clear given the lack of prior kinetic data for comparison, but NO 3 is likely to contribute significantly to the loss of saturated species and dominate their loss during nighttime. The retention of the organic character at the air-water interface differs fundamentally between the different surfactant species: the fatty acids studied (OA and POA) form products with a yield of ∼ 20 % that are stable at the interface while NO 3 -initiated oxidation of the methyl ester MO rapidly and effectively removes the organic character (≤ 3 % surface-active products). The film-forming potential of r...

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Section: Head Groupsupporting

confidence: 63%

Section: Gas Deliverymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Nighttime oxidation of surfactants at the air–water interface: effects of chain length, head group and saturation

et al. 2018

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“…Led by Christian Pfrang from Reading University, UK, the team studied the oxidation, by ozone, of organic monolayers at the air-liquid interface as a proxy for what is happening on the surface of aerosol droplets in clouds. 3 The interest arises from the fact that the lifetime of the droplets, which influences how much heat from sunlight gets to the lower atmosphere, is affected by their coating with organic material. The team showed that the surface reactions were much faster than could have been predicted before as methyl oleate has an atmospheric lifetime of just a few minutes.…”

Section: Neutron Reflectometrymentioning

confidence: 99%

Neutrons for industry

2014

Chemistry & Industry

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“…We found that flash photolysis at 193 nm has not been attempted before for the generation of NO 3 , despite what is stated in Table II.19 in : the experiments referred to were only performed at 248 nm rather than 193 nm . We thus conducted the experiments presented here to establish if this method is a suitable source for NO 3 and can be applied for future experimental studies at the air–water interface (compare for an example of such experiments at the air–water interface).…”

Section: Introductionmentioning

confidence: 99%

Kinetic Studies of Nitrate Radicals: Flash Photolysis at 193 nm

Becerra

Pfrang

2016

Int. J. Chem. Kinet.

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Nitrate radicals, NO3, were produced for the first time by 193 nm laser flash photolysis of N2O5 and HNO3. Detection was achieved due to NO3's strong absorption at 622.7 nm confirmed by measurements of the absorption spectrum in the range of 617–625 nm using both NO3 precursors. Time‐resolved kinetic studies allowed the determination of room temperature rate coefficients for the reactions of NO3 with 2‐methylbut‐2‐ene and NO2 of (1.28 ± 0.11) × 10−11 and (8.4 ± 1.2) × 10−13 cm3 molecule−1 s−1, respectively. The rate coefficients compare well to previous measurements with alternative techniques, suggesting that the reported method is valid and may be applied in follow‐up studies. The rate coefficient for 2‐methylbut‐2‐ene is compared to previous measurements and predictions for the alkene as well as the related alkenol. The new data are consistent with a previously suggested deactivation of the reactive site of the double bond if adjacent to an OH group. A calculated atmospheric lifetime for 2‐methylbut‐2‐ene with respect to NO3‐initiated oxidation of less than 3 min suggests predominant removal by NO3 in the atmosphere.

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Ozonolysis of methyl oleate monolayers at the air–water interface: oxidation kinetics, reaction products and atmospheric implications

Cited by 49 publications

References 39 publications

Nighttime oxidation of surfactants at the air–water interface: effects of chain length, head group and saturation

Nighttime oxidation of surfactants at the air–water interface: effects of chain length, head group and saturation

Neutrons for industry

Kinetic Studies of Nitrate Radicals: Flash Photolysis at 193 nm

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