NO2 quantum yields from ultraviolet photodissociation of methyl and isopropyl nitrate

Carbajo, P. Gorrotxategi; Orr-Ewing, Andrew J.

doi:10.1039/c001425g

Cited by 19 publications

(13 citation statements)

References 42 publications

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“…Figure 6 plots the transient absorption spectrum (averaged between t = 0.1 and t = 0.7 ms) of the photodissociation of isopropyl nitrate (C 3 H 7 ONO 2 ) at 266 nm. This reaction was recently shown to produce NO 2 with unity yield [13] at the experimental conditions used here (6.5 or 10 Torr, T = 300 K). Using the known initial concentration of isopropyl nitrate, its absorption cross-section at 266 nm, and the photolysis fluence, we expect to detect NO 2 products at concentrations of 2.23 -3.47•10 12 cm -3 .…”

Section: Effective Path Lengthmentioning

confidence: 99%

Time-resolved broadband cavity-enhanced absorption spectroscopy for chemical kinetics.

Sheps¹,

Chandler²

2013

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Experimental measurements of elementary reaction rate coefficients and product branching ratios are essential to our understanding of many fundamentally important processes in Combustion Chemistry. However, such measurements are often impossible because of a lack of adequate detection techniques. Some of the largest gaps in our knowledge concern some of the most important radical species, because their short lifetimes and low steady-state concentrations make them particularly difficult to detect. To address this challenge, we propose a novel general detection method for gas-phase chemical kinetics: time-resolved broadband cavity-enhanced absorption spectroscopy (TR-BB-CEAS). This all-optical, non-intrusive, multiplexed method enables sensitive direct probing of transient reaction intermediates in a simple, inexpensive, and robust experimental package. 4 ACKNOWLEDGMENTSWe thank Dr. David Osborn (8353) and Dr. Steven S. Brown (NOAA, Boulder, CO) for helpful discussions regarding cavity-enhanced optical methods and experimental design. We also thank Dr. Craig Taatjes (8353) for the use of lab space and for the loan of a YAG laser and optics. 5

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Section: Effective Path Lengthmentioning

confidence: 99%

Time-resolved broadband cavity-enhanced absorption spectroscopy for chemical kinetics.

Sheps¹,

Chandler²

2013

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“…This is in agreement with the recent report for a NO 2 quantum yield of unity from photodissociation of methyl and isopropyl nitrate. [58] In the presence of O 2 , the H and HCO radicals formed from reactions 11 and 13b, will rapidly react with O 2 , resulting in the formation of HO 2 , H 2 O 2 and OH (reactions [16][17][18], and the oxidisation of NO 2 into HNO 3 (reaction 20) and HO 2 NO 2 (reaction 21). HC(O)O 2 was reported to be the intermediate product in the HCO þ O 2 reaction, and it can decompose rapidly to CO and HO 2 because of its instability (reactions 19).…”

Section: Reaction Mechanisms Based On Observed Products Photolysis Mementioning

confidence: 99%

Photochemical reactions of methyl and ethyl nitrate: a dual role for alkyl nitrates in the nitrogen cycle

Chen

Zhang

2011

Environ. Chem.

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Environmental context. Alkyl nitrates are considered to be important intermediates in the atmospheric hydrocarbons-nitrogen oxides-ozone cycle, which significantly determines air quality and nitrogen exchange between the atmosphere and the Earth's surfaces. The present laboratory study investigates reaction products of alkyl nitrates to elucidate their photochemical reaction mechanisms in the atmosphere. The results provide a better understanding of the role played by alkyl nitrates in the atmospheric environment.Abstract. Alkyl nitrates (ANs) are important nitrogen-containing organic compounds and are usually considered to be temporary reservoirs of reactive nitrogen NO x (NO 2 and NO) in the atmosphere, although their atmospheric fates are incompletely understood. Here a laboratory study of the gas-phase photolysis and OH-initiated reactions of methyl nitrate (CH 3 ONO 2 ) and ethyl nitrate (C 2 H 5 ONO 2 ), as models of atmospheric ANs, is reported with a focus on elucidating the detailed photochemical reaction mechanisms of ANs in the atmosphere. A series of intermediate and end products were well characterised for the first time from the photochemical reactions of methyl and ethyl nitrate conducted under simulated atmospheric conditions. Notably, for both the photolysis and OH-initiated reactions of CH 3 ONO 2 and C 2 H 5 ONO 2 , unexpectedly high yields of HNO 3 (photochemically non-reactive nitrogen) were found and also unexpectedly high yields of peroxyacyl nitrates (RC(O)OONO 2 , where R ¼ H, CH 3 , CH 3 CH 2 ,y) (reactive nitrogen) have been found as CH 3 C(O)OONO 2 in the C 2 H 5 ONO 2 reaction or proposed as HC(O)OONO 2 in the CH 3 ONO 2 reaction. Although the yields of HNO 3 from the ANs under ambient conditions are likely variable and different from those obtained in the laboratory experiments reported here, the results imply that the ANs could potentially serve as a sink for reactive nitrogen in the atmosphere. The potential for this dual role of organic nitrates in the nitrogen cycle should be considered in the study of air quality and nitrogen exchange between the atmosphere and surface. Finally, an attempt was made to estimate the production of HNO 3 and peroxyacyl nitrates derived from NO x by ANs as intermediates in the atmosphere.

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“…It is also shown that there in minimal overlap with HONO and no overlap in the spectrum at all with PAN. It has been shown (Carbajo and Orr-Ewing, 2010;Talukdar et al, 1997) the UV-LEDs do not possess however. Both systems suffer some overlap with NO 3 radicals and BrONO 2 , more so in the case of PCL optics than for UV-LEDs.…”

Section: Possible Photolytic Interferences Of Blcsmentioning

confidence: 99%

“…non ozone) oxidants of NO. These perturbations have been used to infer the existence of oxidants such as peroxy radicals, or halogen oxides in the atmosphere (Bauguitte et al, 2012;Cantrell et al, 2003;Frey et al, 2015). The concentration of NO x varies from > 100 ppb (parts per billion) next to roads (Carslaw, 2005;Pandey et al, 2008) to low ppt (parts per trillion) in the remote atmosphere (Lee et al, 2009).…”

Section: Introductionmentioning

confidence: 99%

“…Measured NO 2 concentrations are higher than would be expected from the observed NO, O 3 , JNO 2 along with reasonable concentrations of other oxidants (peroxy radicals, halogen oxides). Various explanations have been posited in order to overcome the apparent oxidation gap, typically relying on a mystery unmeasured oxidant, or pushing known chemistry into theoretical realms by theorizing high turnover of short-lived species which may only have been measured in trace quantities (Cantrell et al, 2003;Frey et al, 2013Frey et al, , 2015Hosaynali Beygi et al, 2011). An alternative explanation would be an unknown interference on the NO 2 measurement increasing its apparent concentration.…”

Section: Introductionmentioning

confidence: 99%

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Interferences in photolytic NO<sub>2</sub> measurements: explanation for an apparent missing oxidant?

Reed¹,

Evans²,

Carlo³

et al. 2015

Preprint

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Abstract. Measurement of NO2 at low concentrations is non-trivial. A variety of techniques exist, with the conversion of NO2 into NO followed by chemiluminescent detection of NO being prevalent. Historically this conversion has used a catalytic approach (Molybdenum); however this has been plagued with interferences. More recently, photolytic conversion based on UV-LED irradiation of a reaction cell has been used. Although this appears to be robust there have been a range of observations in low NOx environments which have measured higher NO2 concentrations than might be expected from steady state analysis of simultaneously measured NO, O3, JNO2 etc. A range of explanations exist in the literature most of which focus on an unknown and unmeasured "compound X" that is able to convert NO to NO2 selectively. Here we explore in the laboratory the interference on the photolytic NO2 measurements from the thermal decomposition of peroxyacetyl nitrate (PAN) within the photolysis cell. We find that approximately 5 % of the PAN decomposes within the instrument providing a potentially significant interference. We parameterize the decomposition in terms of the temperature of the light source, the ambient temperature and a mixing timescale (∼ 0.4 s for our instrument) and expand the parametric analysis to other atmospheric compounds that decompose readily to NO2 (HO2NO2, N2O5, CH3O2NO2, IONO2, BrONO2, Higher PANs). We apply these parameters to the output of a global atmospheric model (GEOS-Chem) to investigate the global impact of this interference on (1) the NO2 measurements and (2) the NO2 : NO ratio i.e. the Leighton relationship. We find that there are significant interferences in cold regions with low NOx concentrations such as Antarctic, the remote Southern Hemisphere and the upper troposphere. Although this interference is likely instrument specific, it appears that the thermal decomposition of NO2 within the instrument's photolysis cell may give an explanation for the anomalously high NO2 that has been reported in remote regions, and would reconcile measured and modelled NO2 to NO ratios without having to invoke novel chemistry. Better instrument characterization, coupled to instrumental designs which reduce the heating within the cell seem likely to minimize the interference in the future, thus simplifying interpretation of data from remote locations.

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NO2 quantum yields from ultraviolet photodissociation of methyl and isopropyl nitrate

Cited by 19 publications

References 42 publications

Time-resolved broadband cavity-enhanced absorption spectroscopy for chemical kinetics.

Time-resolved broadband cavity-enhanced absorption spectroscopy for chemical kinetics.

Photochemical reactions of methyl and ethyl nitrate: a dual role for alkyl nitrates in the nitrogen cycle

Interferences in photolytic NO<sub>2</sub> measurements: explanation for an apparent missing oxidant?

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NO2 quantum yields from ultraviolet photodissociation of methyl and isopropyl nitrate

Cited by 19 publications

References 42 publications

Time-resolved broadband cavity-enhanced absorption spectroscopy for chemical kinetics.

Time-resolved broadband cavity-enhanced absorption spectroscopy for chemical kinetics.

Photochemical reactions of methyl and ethyl nitrate: a dual role for alkyl nitrates in the nitrogen cycle

Interferences in photolytic NO&lt;sub&gt;2&lt;/sub&gt; measurements: explanation for an apparent missing oxidant?

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Interferences in photolytic NO<sub>2</sub> measurements: explanation for an apparent missing oxidant?