scholarly journals Rate coefficients for reactions of OH with aromatic and aliphatic volatile organic compounds determined by the Multivariate Relative Rate Technique

2020 ◽  
Author(s):  
Jacob T. Shaw ◽  
Andrew R. Rickard ◽  
Mike J. Newland ◽  
Terry J. Dillon
Keyword(s):  
Volatile Organic Compounds ◽  
Organic Compounds ◽  
Relative Rate ◽  
Ozone Production ◽  
Rate Coefficients ◽  
Phase Reaction ◽  
Volatile Organic ◽  
Simultaneous Study ◽  
Oxidation Chemistry ◽  
Alkyl Benzenes

Abstract. The multivariate relative rate method was applied to a range of volatile organic compounds (VOC) reactions with OH. This previously published method (Shaw et al., 2018b) was improved to increase the sensitivity towards slower reacting VOC, broadening the range of compounds which can be examined. A total of thirty-five room temperature relative rate coefficients were determined; eight of which have not previously been reported. Five of the new reaction rate coefficients were for large alkyl substituted monoaromatic species recently identified in urban air masses, likely with large ozone production potentials. The new results (with kOH (296 K) values in units of 10–12 cm3 molecule−1 s−1) were: n-butylbenzene, 11 (± 4); n-pentylbenzene, 7 (± 2); 1,2-diethylbenzene, 14 (± 4); 1,3-diethylbenzene, 22 (± 4) and 1,4-diethylbenzene, 16 (± 4). Interestingly, whilst results for smaller VOC agreed well with available structure activity relationship (SAR) calculations, the larger alkyl benzenes were found to be less reactive than the SAR prediction, indicating that our understanding of the oxidation chemistry of these compounds is still limited. kOH (296 K) rate coefficients (in units of 10–12 cm3 molecule−1 s−1) for reactions of three large alkanes with OH were also determined for the first time: 2-methylheptane, 9.1 (± 0.3); 2-methylnonane, 11.0 (± 0.3) and ethylcyclohexane, 14.4 (± 0.3), all in reasonable agreement with SAR predictions. Rate coefficients for the twenty-seven previously studied OH + VOC reactions agreed well with available literature values, lending confidence to the application of this method for the rapid and efficient simultaneous study of gas-phase reaction kinetics.

scholarly journals Rate coefficients for reactions of OH with aromatic and aliphatic volatile organic compounds determined by the multivariate relative rate technique

2020 ◽  
Vol 20 (16) ◽  
pp. 9725-9736
Author(s):  
Jacob T. Shaw ◽  
Andrew R. Rickard ◽  
Mike J. Newland ◽  
Terry J. Dillon
Keyword(s):  
Relative Rate ◽  
Ozone Production ◽  
Rate Coefficients ◽  
Phase Reaction ◽  
Air Masses ◽  
Volatile Organic ◽  
Aromatic Species ◽  
Simultaneous Study ◽  
Oxidation Chemistry ◽  
Alkyl Benzenes

Abstract. The multivariate relative rate method was applied to a range of volatile organic compound (VOC) reactions with OH. This previously published method (Shaw et al., 2018) was improved to increase the sensitivity towards more slowly reacting VOCs, broadening the range of compounds which can be examined. A total of 35 room temperature relative rate coefficients were determined, eight of which have not previously been reported. Five of the new reaction rate coefficients were for large alkyl substituted mono-aromatic species recently identified in urban air masses, likely with large ozone production potentials. The new results (with kOH (296 K) values in units of 10−12 cm3 molec.−1 s−1) were n-butylbenzene, 11 (±4); n-pentylbenzene, 7 (±2); 1,2-diethylbenzene, 14 (±4); 1,3-diethylbenzene, 22 (±4); and 1,4-diethylbenzene, 16 (±4). Interestingly, whilst results for smaller VOCs agreed well with available structure–activity relationship (SAR) calculations, the larger alkyl benzenes were found to be less reactive than the SAR prediction, indicating that our understanding of the oxidation chemistry of these compounds is still limited. kOH (296 K) rate coefficients (in units of 10−12 cm3 molec.−1 s−1) for reactions of three large alkanes with OH were also determined for the first time: 2-methylheptane, 9.1 (±0.3); 2-methylnonane, 11.0 (±0.3); and ethylcyclohexane, 14.4 (±0.3), all in reasonable agreement with SAR predictions. Rate coefficients for the 27 previously studied OH + VOC reactions agreed well with available literature values, lending confidence to the application of this method for the rapid and efficient simultaneous study of gas-phase reaction kinetics.

scholarly journals Sources and photochemistry of volatile organic compounds in the remote atmosphere of western China: results from the Mt. Waliguan Observatory

2013 ◽  
Vol 13 (5) ◽  
pp. 11745-11788 ◽  
Author(s):  
L. K. Xue ◽  
T. Wang ◽  
H. Guo ◽  
D. R. Blake ◽  
J. Tang ◽  
...  
Keyword(s):  
Air Pollution ◽  
Volatile Organic Compounds ◽  
Organic Compounds ◽  
Late Spring ◽  
Chemical Mechanism ◽  
Ozone Production ◽  
Western China ◽  
Air Masses ◽  
Eurasian Continent ◽  
Volatile Organic

Abstract. The chemistry of the natural atmosphere and the influence by long-range transport of air pollution are key issues in the atmospheric sciences. Here we present two intensive field measurements of volatile organic compounds (VOCs) in late spring and summer of 2003 at Mt. Waliguan (WLG, 36.28° N, 100.90° E, 3816 m a.s.l.), a baseline station in the northeast part of Qinghai-Tibetan Plateau. Most VOC species exhibited higher concentrations in late spring than in summer. A typical diurnal variation was observed with higher nighttime levels, in contrast to results from other mountainous sites. Five different air masses were identified from backward trajectory analysis showing distinct VOC speciation. Air masses originating from the central Eurasian continent contained the lowest VOC levels compared to the others that were impacted by anthropogenic emissions from China and the Indian sub-continent. The data were compared with the TRACE-P (Transport and Chemical Evolution over the Pacific) data to examine the inflow and outflow of air pollution over the China sub-continent. The results show that the free troposphere over China may be affected by the inflow from the Eurasian continent in spring, and the emissions in China may not have a significant influence on the free tropospheric outflow. A photochemical box model based on the Master Chemical Mechanism (version 3.2) and constrained by a full suite of measurements was developed to probe the photochemistry of atmosphere at WLG. Our results show net ozone production from in-situ photochemistry during both late spring and summer. Oxidation of nitric oxide (NO) by the hydroperoxyl radical (HO2) dominates the ozone production relative to the oxidation by the organic peroxy radicals (RO2), and the ozone is primarily destroyed by photolysis and reactions with the HOx(HOx = OH + HO2) radicals. Ozone photolysis is the predominant primary source of radicals (ROx = OH + HO2 + RO2), followed by the photolysis of oxygenated VOCs and hydrogen peroxides. The radical losses are governed by the self and cross reactions among the radicals. The findings can provide insights into the background chemistry and the impacts of pollution transport on the pristine atmosphere over the Eurasian continent.

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