OH Radical and Chlorine Atom Kinetics of Substituted Aromatic Compounds: 4-Chlorobenzotrifluoride (p-ClC₆H₄CF₃)

Abstract

The mechanisms for the OH radical and Cl-atom gas-phase reaction kinetics of substituted aromatic compounds remains a topic of atmospheric and combustion chemistry research. 4chlorobenzotrifluoride (para-chlorobenzotrifluoride, p-ClC6H4CF3, PCBTF) is a commonly used substituted aromatic volatile organic compound (VOC) in solvent-based coatings. As such, PCBTF is classified as a volatile chemical product (VCP) whose release into the atmosphere potentially impacts air quality. In this study, rate coefficients, k1, for the OH + PCBTF reaction were measured over the temperature ranges 275-340 K and 385-940 K using low-pressure discharge flow-tube reactors coupled with a mass spectrometer detector in the ICARE/CNRS (Orléans, France) laboratory. k1(298-353 K) was also measured using a relative rate method in the thermally regulated atmospheric simulation chamber (THALAMOS; Douai, France). k1(T) displayed a non-Arrhenius temperature dependence with a negative temperature dependence between 275 and 385 K given by k1(275-385 K) = (1.50  0.15)  10 -14 exp((705  30)/T) cm 3 molecule -1 s -1 , where k1(298 K) = (1.63  0.03)  10 -13 cm 3 molecule -1 s -1 and a positive temperature dependence at elevated temperatures given by k1(470-950 K) = (5.42  0.40)  10 -12 exp(-(2507  45) /T) cm 3molecule -1 s -1 . The present k1(298 K) results are in reasonable agreement with two previous 296 K (760 Torr, syn. air) relative rate measurements. The rate coefficient for the Cl-atom + PCBTF reaction, k2, was also measured in THALAMOS using a relative rate technique that yielded k2(298 K) = (7.8  2)  10 -16 cm 3 molecule -1 s -1 . As part of this work, the UV and infrared absorption spectra of PCBTF were measured (NOAA; Boulder, CO, USA). On the basis of the UV absorption spectrum, the atmospheric instantaneous UV photolysis lifetime of PCBTF (ground level, midlatitude, Summer) was estimated to be 3-4 days, assuming a unit photolysis quantum yield. The non-Arrhenius behavior of the OH + PCBTF reaction over the temperature range 275 to 950 K is interpreted using a mechanism for the formation of an OH-PCBTF adduct and its thermochemical stability. The results from this study are included in a discussion of the OH radical and Cl atom kinetics of halogen substituted aromatic compounds for which only limited temperature dependent kinetic data are available.

Rate coefficients for the gas‐phase OH + furan (C4H4O) reaction between 273 and 353 K

“…Both apparatuses have been used in the past and only brief descriptions of the experimental setups and methods are given herein. [15][16][17][18] 2.1 Chamber relative rate measurements: THALAMOS THALAMOS consists of three main components, (i) a cuboid Teflon reactor, 0.6 m 3 , housed in a climatic thermostatic cage (climatic box VT-4100, Vötsch industrietechnik, Germany) providing temperature regulation between 231 and 453 K, (ii) a set of 10 UV-A (PL-L 24 W/10/4P, Philips, Netherlands), and 10 UV-C (HNS-L 24 W 2G11, Osram, UK) photolysis lamps, equally spaced around the Teflon chamber inside the climatic box and (iii) FTIR and SIFT-MS detection setups.…”

“…The uncertainty in thermochemistry calculations is estimated to be less than 5 kJ mol −1 for the studied reactions. 16 Yuan et al 29 have previously theoretically studied the kinetics and the reaction mechanism for reaction 1. In our thermochemical approach the reaction pathways enthalpy, entropy and free energy, ΔH, ΔS and ΔG, were calculated as a function of temperature to evaluate the OH-furan adduct thermodynamic stability over the temperature range of the present kinetic measurements and determine that our measured k 1 (T) values correspond to the forward rate coefficient.…”

“…HONO was synthesized online by adding 0.1 M aqueous NaNO 2 dropwise (∼0.5 mL min −1 ) into ∼50 mL of 0.5 or 1 M aqueous solution of H 2 SO 4 . 16 NO 2 impurity levels were continuously monitored via FTIR. Pressure was measured by 100 and 1000 Torr calibrated pressure sensors.…”

“…Two apparatuses were used to perform relative rate experiments: (a) The thermostated Teflon chamber “THALAMOS” (IMT NE) equipped with in‐line FTIR spectroscopy and SIFT‐MS was used to measure k 1 (273–353 K) at 760 Torr (syn. air) 15,16 and (b) the photochemical reactor (PCR, UoC) coupled with FTIR spectroscopy 16–18 was used to measure k 1 (296 K). Both apparatuses have been used in the past and only brief descriptions of the experimental setups and methods are given herein 15–18 …”

Advances in Atmospheric Chemical and Physical Processes

“…Initiation of the VOC oxidation process is primarily driven by the sunlight-derived OH radical but also via reactions involving other oxidants. Papers in this virtual special issue include studies of the initiation reactions of VOC species by OH, Cl, − O 3 , , NO 3 , and HCO, as well as by direct photolysis . Chamber studies, in which the products of a VOC oxidation process are identified and quantified, are also prevalent; two studies quantify the formation of secondary organic aerosol (SOA) in the reaction of OH or NO 3 with monoterpenes, , while a combined experimental/theoretical study shows that methylmethanimine oxidation via the OH radical is unlikely to compete with atmospheric hydrolysis of this species .…”