atmosphere

Article Rate Constants for the Reaction of OH Radicals with Hydrocarbons in a Smog Chamber at Low Atmospheric Temperatures

Lei Han *,‡ ID , Frank Siekmann and Cornelius Zetzsch *,‡

Atmospheric Chemistry Research Laboratory, University of Bayreuth, 95447 Bayreuth, Germany; [email protected] * Correspondence: [email protected] (L.H.); [email protected] (C.Z.) ‡ Current address: Department of Multiphase Chemistry, Max Planck Institute for Chemistry, 55128 Mainz, Germany.



Received: 18 July 2018; Accepted: 14 August 2018; Published: 18 August 2018


Abstract: The photochemical reaction of OH radicals with the 17 hydrocarbons n-butane, n-pentane, n-hexane, n-heptane, n-octane, n-nonane, cyclooctane, 2,2-dimethylbutane, 2,2-dimethylpentane, 2,2-dimethylhexane, 2,2,4-trimethylpentane, 2,2,3,3-tetramethylbutane, benzene, toluene, ethylbenzene, p-xylene, and o-xylene was investigated at 288 and 248 K in a temperature controlled smog chamber. The rate constants were determined from relative rate calculations with toluene and n-pentane as reference compounds, respectively. The results from this work at 288 K show good agreement with previous literature data for the straight-chain hydrocarbons, as well as for cyclooctane, 2,2-dimethylbutane, 2,2,4-trimethylpentane, 2,2,3,3-tetramethylbutane, benzene, and toluene, indicating a convenient method to study the reaction of OH radicals with many hydrocarbons simultaneously. The data at 248 K (k in units of 10−12 cm3 s−1) for 2,2-dimethylpentane (2.97 ± 0.08), 2,2-dimethylhexane (4.30 ± 0.12), 2,2,4-trimethylpentane (3.20 ± 0.11), and ethylbenzene (7.51 ± 0.53) extend the available data range of experiments. Results from this work are useful to evaluate the atmospheric lifetime of the hydrocarbons and are essential for modeling the photochemical reactions of hydrocarbons in the real troposphere.

Keywords: OH radicals; smog chamber; rate constant; hydrocarbons; low temperatures

1. Introduction Great quantities of volatile organic compounds (VOCs) are emitted into the atmosphere from both anthropogenic and natural sources. Their atmospheric concentrations are influenced by chemical reactions in the atmosphere, where the main removal pathway for alkanes and alkylated aromatics occurs through chemical oxidation by OH radicals [1,2]. In the past few decades, many studies have been focused on the atmospheric reaction of OH radicals with alkanes and aromatics [3–13] since these kinetic data are important to estimate the lifetime of the VOCs in the atmosphere. Smog chamber studies have started in the 1950s after the London smog episode [14]. At the beginning, they were designed mainly to study the gas-phase reactions with ozone and the chemistry of NOx in the troposphere and the formation of aerosol from the gaseous pollutants [15–17]. Later research concentrated on the reactions of VOCs with OH radicals and their role in ozone formation and photochemical smog [18–20]. Despite intensive research on gas-phase kinetics during the last decades, comparatively little is known about the reactivity of OH radicals with VOCs below room temperature, especially for larger molecules [4,21–23]. Based on the standard atmospheric values specified by the International Civil Aviation Organization (ICAO), the sea level temperature is 288 K [24] and

Atmosphere 2018, 9, 320; doi:10.3390/atmos9080320 www.mdpi.com/journal/atmosphere Atmosphere 2018, 9, 320 2 of 16 drops by approximately 6.5 K per kilometer of altitude up to the tropopause [14]. However, very few hydrocarbons have been investigated at temperatures below 290 K, which are representative of the troposphere. The understanding of kinetics at low temperature is of great importance to understand the real atmospheric degradation of organic compounds. There has been theoretical research about the reaction of OH with hydrocarbons [6,25,26], giving guidance to understand the kinetics at low temperatures. Subsequent to an extensive review on the reactions of alkanes and cycloalkanes with OH by Atkinson [27], there are only a few studies below room temperature. DeMore and Bayes [4] measured the relative rate constant of n-butane, n-pentane, and other cyclic hydrocarbon at temperatures down to 233 K. Harris and Kerr [21] developed a flow reactor system to study the relative rate constant of OH radicals with n-pentane, 2,2-dimethylbutane, and several other hydrocarbons, over a temperature range of 243–328 K. Talukdar et al. [22] measured the rate constant of n-butane and n-pentane over the temperature range of 212–380 K by using the pulsed photolysislaser induced fluorescence (PP-LIF) technique. Li et al. [28] studied n-octane, n-nonane, and n-decane relative to 1,4-dioxane at temperatures down to 240 K and Crawford et al. [29] studied the reactions of OH radicals with n-hexane and n-heptane at 240–340 K. Wilson et al. [30] studied the reactions of several alkanes and cycloalkanes with hydroxyl radicals in a photochemical glass reactor with GC/MS detection at temperatures down to 241 K. Cyclooctane and other alkanes were studied by Sprengnether et al. [31] at temperatures down to 237 K in a high-pressure flow reactor with LIF detection, and by Singh et al. [32] in a discharge flow reactor at temperatures down to 240 K. Tully et al. [23] studied the absolute rate constant of OH radicals with benzene and toluene at temperature down to 213 K, and Witte et al. [33] obtained similar results for benzene at 239–352 K. Semadeni et al. also studied the OH reactivity of benzene by using toluene as a reference compound at 274–363 K. Mehta et al. [34] measured the rate constant of OH with o- and p-xylene at 240–340 K, by using the relative rate/discharge flow/mass spectrometry (RR/DF/MS) technique. Alarcón et al. [35] used the flash photolysis resonance fluorescence technique (FPRF) to study the reaction of OH radicals with methylated benzenes including p-xylene, delivering an Arrhenius expression of the absolute rate constants between 300 and 350 K. A table with information on the various research conducted at low temperatures is available in Supporting Information (SI, Table S1). In this work, we have investigated the gas phase reaction of OH with several alkanes and aromatic compounds at 288 K (sea level temperature) and 248 K (in the free troposphere this temperature corresponds to a height of approximately 5–8 km, depending on latitude and season [36]). Using n-pentane [27] and toluene [37] as reference compounds, the rate constants for the reactions of OH radicals with the 17 compounds have been obtained at 248 and 288 K. These two compounds are chosen as reference compounds, because their temperature-dependent parameters are well investigated between 220 to 350 K. Those data deliver chemical kinetic information about the temperature range below room temperature, and therefore are supplementary to the existing Arrhenius expression.

2. Experiments

2.1. Description of the Simulation Chamber The simulation chamber is located at the Atmospheric Chemistry Research Laboratory of the University of Bayreuth in a temperature controllable room, where the temperature could be set from 298 K to 248 K with the aid of an inside cooling system in the room and monitored by a thermistor Epcos NTC 50 K, calibrated against a platinum resistance thermometer (Keithley 195A with probe 8693) from −40 ◦C to +30 ◦C. The chamber consists of four cylinder sections made of glass (Duran, Schott, inner diameter 1 m, total height 4 m), yielding a volume of 3.2 m3. Sixteen fluorescent lamps (Osram Eversun, 80 W each, kept at 300 K by an air thermostat) were employed as light sources, irradiating the chamber from the bottom through Teflon film (FEP 200A). The emission spectrum of the lamps has a Gaussian shape with a maximum at 350 nm, it starts at 300 nm and extends beyond 450 nm, containing the emission lines of mercury. The inherent heating effects on the bottom caused by the lamps led to a Atmosphere 2018, 9, 320 3 of 16 Atmosphere 2018, 9, x FOR PEER REVIEW 3 of 16 verticalthe middle temperature of the chamber gradient, to enhancing accelerate the furthe mixingr efficiency.mixing. The Sensors temperature in the middle regulation and upper leads part to variationsof the chamber of ±1 measured K in the refrigerated the temperature laboratory. and a ventilator A schematic was diagram installed of in th thee simulation middle of the chamber chamber is shownto accelerate below further (Figure mixing. 1). The temperature regulation leads to variations of ±1 K in the refrigerated laboratory. A schematic diagram of the simulation chamber is shown below (Figure1).

1 m FEP Teflon film

0.4 m

Temperature OH precursor and sensors hydrocarbons

0.5 m Gas-phase Bypass air analysis by GC

Ventilator 1.2 m

FEP Teflon film

16 Fluorescent lamps (Osram Eversun)

Figure 1. Schematic of the low temperature smog chamberchamber facility. The hydrocarbons were injected into the smog chamber via syringessyringes from two stock mixtures (see text), the gas-phase compounds were sampledsampled throughthrough a a stainless stainless steel steel capillary capillary and and analyzed analyzed by by GC-FID GC-FID with with sample sample enrichment enrichment (see (seebelow). below). Purified Purified air was air was supplied supplied via thevia aidthe ofaid a bypass.of a bypass.

2.2. Instrumentation and Chemical Materials The concentration of of the the hydrocarbons hydrocarbons (startin (startingg with with approx. approx. 20 20 ppb ppb each) each) was was monitored monitored by by a gasa gas chromatograph chromatograph (GC) (GC) with with a aflame flame ionization ionization de detectortector (FID). (FID). It It uses uses an automated cryogenic sample enrichmentenrichment systemsystem with with liquid liquid nitrogen nitrogen [10 [10],], that that has has been been modified modified by substitutingby substituting the 6-portthe 6- valveport valve by two by magnetictwo magnetic valves valves (for detailed(for detailed information information see Figuresee Figure S1 in S1 Supporting in Supporting Information, Information, SI). ASI). gas A samplegas sample of 30 mLof 30 was mL taken was everytaken 30 every min. 30 The min. GC (SichromatThe GC (Sichromat II, Siemens, II, Munich,Siemens, Germany) Munich, Germany)is equipped is withequipped a capillary with a columncapillary (Al2O3-PLOT, column (Al2O3-PLOT, Chrompack/Agilent) Chrompack/Agilent) with 50 with m length 50 m andlength an and an inner diameter of 0.32 mm, using N2 as carrier gas at a column temperature of◦ 190 °C and a inner diameter of 0.32 mm, using N2 as carrier gas at a column temperature of 190 C and a FID FIDtemperature temperature of 270 of◦ C.270 In °C. order In order to inject to theinject 17 the hydrocarbons 17 hydrocarbonsn-butane, n-butane,n-pentane, n-pentane,n-hexane, n-hexane,n-heptane, n- heptane,n-octane, nn-nonane,-octane, cyclooctane,n-nonane, cyclooctane, 2,2-dimethylbutane, 2,2-dimethylbutane, 2,2-dimethylpentane, 2,2-dimethylpentane, 2,2-dimethylhexane, 2,2- dimethylhexane,2,2,4-trimethylpentane, 2,2,4-trimethylpentane, 2,2,3,3-tetramethylbutane, 2,2,3,3-tetr benzene,amethylbutane, toluene, ethylbenzene,benzene, toluene,p-xylene, ethylbenzene,o-xylene, pand-xylene,n-perfluorohexane o-xylene, and (inertn-perfluorohexane standard) simultaneously (inert standard) into thesimultaneously chamber, two into glass the containers chamber, weretwo glassemployed containers as a storage were employed device for as preparing a storage stock device mixtures, for preparing which minimizedstock mixtures, the operating which minimized deviation theduring operating the injection deviation process during (see SIthe Section injection S1). process Methyl (see nitrite SI wasSection self-synthesized S1). Methyl [nitrite38] and was used self- as synthesizeda photochemical [38] and precursor used as of a the photochemical OH radicals. precursor Two gas containersof the OH (1.3radicals. L of each)Two gas were containers connected (1.3 in Lseries of each) to approximate were connected a constant in series concentration to approximate of OH a constant (see Figure concentration S2 in SI). of OH (see Figure S2 in SI).

Atmosphere 2018, 9, 320 4 of 16

2.3. Calculation of the Reaction Rate Constant of OH with Hydrocarbons In this study, the relative rate method was used to calculate the rate constant of the OH radical with the hydrocarbons. Assuming that the decrease of hydrocarbons in the chamber is caused by the reaction with OH radicals and by the dilution from the gas sampling process, one gets the following simple reaction scheme: kHC HC + OH →OHproducts (1)

k HC →dilloss (2) to be described by the differential equation

d[HC] = −kHC [OH]·dt − k ·dt (3) [HC] OH dil where [HC] and [OH] represent the concentration of hydrocarbon and OH radicals at time t, HC respectively, kOH, is reaction rate constant of target hydrocarbon with OH and kdil includes other changes that cause the decrease of the hydrocarbons (e.g., dilution, wall adsorption). By using n-perfluorohexane (PFH) as an internal standard, we corrected the hydrocarbon data for the dilution of the chamber contents by the gas consumption of the gas analyzers for ozone and NOx, eliminating the second term from Equation (3). Integration then leads to the simple equation

 0 Z HC 0 HC ln  0 = kOH [OH]dt (4) HC t where [HC’]t and [HC’]0 are the dilution-corrected concentrations of the target hydrocarbon at time t and time zero, respectively, according to [HC’] = [HC] [PFH]0/[PFH]. The presence of several hydrocarbons in the same experiment opens the opportunity to select one of those as a reference compound (REF), in order to eliminate the time integral of OH and to obtain HC REF relative rate constants, kOH/kOH , from the equation:

 0  0 HC kHC REF t = OH t ln  0 REF ln  0 (5) HC 0 kOH REF 0 where [REF’]t and [REF’]0 are the (by PFH, see above) dilution-corrected concentrations of the reference compound (n-pentane and toluene in this study) at time t and time zero, respectively. From the plots of ln([HC’]t/[HC’]0) versus ln([REF’]t/[REF’]0), straight lines are expected with zero intercept, and the slopes represent the relative rate constants. Based on the known reaction rate constant of the reference REF HC compound, kOH , the OH reaction rate constant of the target hydrocarbon kOH can be calculated.

3. Results In relative rate constant measurements, the FID peak area represents the concentration of each sampling point. Figure2 shows the hydrocarbon concentrations (corrected for dilution) from one single experiment at 288 K. Following Equation (5), one can get a straight line from a plot of ln([HC’]0/[HC’]t) of the hydrocarbons versus ln([REF’]0/[REF’]t) for the reference compound in most cases. Three experiments were carried out at 288 K, and two experiments were performed at 248 K. The rate constants were calculated from the experimental data from all runs at each temperature (Figure3 for straight-chain hydrocarbons, with toluene as reference compound). Table1 summarizes results obtained for the reaction from OH with the hydrocarbons at 288 K and the results at 248 K are summarized in the supporting material (Table S2), using n-pentane and toluene as reference compounds, respectively. Atmosphere 2018, 9, x FOR PEER REVIEW 5 of 16

Atmosphere 2018, 9, x FOR PEER REVIEW 5 of 16 Atmosphere 2018, 9, 320 5 of 16 n-butane 1 n-pentane 2,2-dimethylbutane n-butanen-hexane 1 n-pentane2,2-dimethylpentane 2,2-dimethylbutanen-heptane n-hexanebenzene 2,2-dimethylpentane2,2,4-trimetylpentane n-heptane 2,2-dimethylhexane 0.1 benzene 2,2,3,3-tetramethylbutane 2,2,4-trimetylpentane n-octane 0.1 2,2-dimethylhexane 2,2,3,3-tetramethylbutanecyclooctane n-octanetoluene cyclooctanen-nonane

FID-Area (normalized) tolueneethylbenzene 0.01 n-nonanep-xylene

FID-Area (normalized) ethylbenzeneo-xylene 0.01 p-xylene o-xylene

0246

0246t / h t / h Figure 2. Decrease of hydrocarbon concentrations (normalized by n-perfluorohexane) during a smog chamber run by reaction with OH at 288 K (corresponding information at 248 K is displayed in the FigureFigure 2.2. Decrease ofof hydrocarbonhydrocarbon concentrationsconcentrations (normalized(normalized byby nn-perfluorohexane)-perfluorohexane) duringduring aa smogsmog SI).chamberchamber runrun byby reaction reaction with with OH OH at at 288 288 K K (corresponding (corresponding information information at 248at 248 K is K displayed is displayed in the in SI).the SI).

6 n-Butane n-Butane 6 (a) (b) n-Pentane n-Pentane 5 n-Hexanen-Butane (a) nn-Butane-Hexane (b) n-Heptanen-Pentane nn-Pentane-Heptane 5 n-Octanen-Hexane nn-Hexane-Octane n-Heptane n-Heptane n-Nonane n-Nonane 4 n-Octane n-Octane Cyclooctane Cyclooctane n-Nonane n-Nonane

) 4

t Cyclooctane Cyclooctane c / ) 0 3t c c /

0 3 c ln (

2ln ( 2

1 1

0 01230 0.0 0.5 1.0 1.5 2.0 01230.0 0.5 1.0 1.5 2.0 ln (c0/ct ) Toluene ln (c0/ct ) Toluene ln (c0/ct ) Toluene ln (c0/ct ) Toluene

FigureFigure 3. 3. PlotPlotof of ln( cln(/cc0t/)c oft) straight-chainof straight-chain alkanes alkanes and cyclooctane and cycl versusooctane toluene versus (reference toluene substance). (reference Figure 3. Plot of 0ln(c0/ct) of straight-chain alkanes and cyclooctane versus toluene (reference substance).(substance).a) Data points (a ()a )Data ofData three points points experimental of of threethree experimentalexperimental runs at 288 K; runsruns (b) Data atat 288 288 points K; K; ( b(b of) )Data twoData points experimental points of of two two runsexperimental experimental at 248 K. n runsTheruns at curvature at 248 248 K. K. The ofThe thecurvature curvature data and ofof the thethe non-zero datadata and intercept thethe non-zeronon-zero for -nonaneintercept intercept atfor for 248 n -nonanen K-nonane indicate at at248 experimental 248 K indicateK indicate limitations of adsorption in the sampling capillary of the gas chromatograph. The symbols 5, and experimentalexperimental limitations limitations ofof adsorptionadsorption in the samplingsampling capillarycapillary of of the the gas gas chromatograph. chromatograph. The The distinguish data points from different experimental runs, plots of branched-chain alkanes and aromatic# symbolssymbols ▽ ▽, ○, ○and and □ □ distinguish distinguish datadata pointspoints fromfrom didifffferenterent experimental experimental runs, runs, plots plots of ofbranched- branched- hydrocarbons are displayed in the SI. chainchain alkanes alkanes and and aromatic aromatic hydroc hydrocarbonsarbons are displayed in in the the SI. SI.

At a temperatureTableTable 1. 1. Rate Rate of constants constants 248 K, the forfor initial thethe reaction decrease ofof OHOH by radicals radicals exposure with with to hydrocarbons hydrocarbons OH appeared at at288 to 288 beK. K. delayed for compounds with lower vapor pressures, such as n-nonane (Figure3b) and p-xylene and o-xylene (SI, −12 3 −1 Rate Constant,Constant, ( k(kOHOH ± ±2 σ2σ)/10)/10− 12cm cm s3 s −1 Figure S5b).Compound This is possibly due to adsorption in the sampling capillary of the gas chromatograph Compound a b (stainless steel, 1/16 inch, 5 m long)TolueneToluene that was as notReference heated during a Pentane Pentane the experiments. as as Reference Reference b AverageAverage n-Butanen-Butane 2.28 ± 0.020.02 2.05 2.05 ± ±0.03 0.03 2.16 2.16 ± 0.04 ± 0.04 b n-Pentanen-Pentane 3.84 ± 0.040.04 3.62 3.62 b 3.73 3.73 ± 0.04 ± 0.04 n-Hexanen-Hexane 5.41 ± 0.030.03 5.25 5.25 ± ±0.05 0.05 5.33 5.33 ± 0.06 ± 0.06 n-Heptanen-Heptane 7.10 ± 0.040.04 6.79 6.79 ± ±0.06 0.06 6.94 6.94 ± 0.07 ± 0.07 n-Octane 9.07 ± 0.08 8.62 ± 0.13 8.84 ± 0.15 n-Octane 9.07 ± 0.08 8.62 ± 0.13 8.84 ± 0.15 n-Nonane 12.0 ± 0.4 11.5 ± 0.5 11.8 ± 0.6 n-Nonane 12.0 ± 0.4 11.5 ± 0.5 11.8 ± 0.6

Atmosphere 2018, 9, 320 6 of 16

Table 1. Rate constants for the reaction of OH radicals with hydrocarbons at 288 K.

−12 3 −1 Rate Constant, (kOH ± 2σ)/10 cm s Compound Toluene as Reference a Pentane as Reference b Average n-Butane 2.28 ± 0.02 2.05 ± 0.03 2.16 ± 0.04 n-Pentane 3.84 ± 0.04 3.62 b 3.73 ± 0.04 n-Hexane 5.41 ± 0.03 5.25 ± 0.05 5.33 ± 0.06 n-Heptane 7.10 ± 0.04 6.79 ± 0.06 6.94 ± 0.07 n-Octane 9.07 ± 0.08 8.62 ± 0.13 8.84 ± 0.15 n-Nonane 12.0 ± 0.4 11.5 ± 0.5 11.8 ± 0.6 Cyclooctane 16.1 ± 0.4 15.8 ± 0.5 15.9 ± 0.6 2,2-Dimethylbutane 2.11 ± 0.02 2.04 ± 0.02 2.07 ± 0.03 2,2-Dimethylpentane 3.21 ± 0.03 3.14 ± 0.04 3.18 ± 0.05 2,2-Dimethylhexane 4.74 ± 0.03 4.57 ± 0.04 4.66 ± 0.05 2,2,4-Trimethylpentane 3.48 ± 0.03 3.35 ± 0.03 3.41 ± 0.04 2,2,3,3-Tetramethylbutane 1.01 ± 0.02 0.98 ± 0.01 1.00 ± 0.02 Benzene 1.11 ± 0.02 1.04 ± 0.01 1.08± 0.02 Toluene 5.86 a 5.52 ± 0.06 5.69 ± 0.06 Ethylbenzene 6.95 ± 0.08 6.72 ± 0.15 6.83 ± 0.17 p-Xylene 16.0 ± 0.9 15.4 ± 1.1 15.7 ± 1.4 o-Xylene 15.6 ± 0.7 15.2 ± 0.9 15.4 ± 1.1 a k (toluene) = 1.8 × 10−12 e340/T cm3 molecule−1 s−1 (210–350 K) and 5.86 × 10−12 cm3 molecule−1 s−1 at 288 K [37]; b k (n-pentane) = 2.52 × 10−17 T2e158/T cm3 molecule−1 s−1 (220–760 K) and 3.62 × 10−12 T2e361/T at 288 K [27].

4. Discussion The rate constants for the reactions of the hydrocarbons with OH radicals derived from this study are plotted together with literature data in Arrhenius diagrams for the n-alkanes and cyclooctane (Figure4), branched-chain alkanes (Figure5), and aromatic hydrocarbons (Figure6). In order to compare to previous evaluations, the regression lines from the Arrhenius expressions for each hydrocarbon are displayed in the figures. Detailed explanations and illustrations for the alkanes and cycloalkanes can be found in the review article by Atkinson [27]. Our results demonstrate that the rate constants obtained in the present study generally agree well with the literature data, which prove that the experimental method is reliable. Moreover, the experimental results complement existing gas-phase kinetic data for hydrocarbons in the following points: (1) For n-alkanes, results from this work follow the existing Arrhenius expressions quite well (Figure4). The rate constants decrease as the temperature decreases, showing a positive correlation of temperature with the reactivity. For n-hexane, Atkinson [27] has recommended two Arrhenius − − ± T − − expressions: 1 k (n-hexane) = 2.29 × 10 11 e (442 52)/ cm3 molecule 1 s 1, 2 k (n-hexane) = 2.54 × 10−14 T e−(112 ± 28)/T cm3 molecule−1 s−1. The rate constants obtained from this work at 288 K and 248 K confirm that a third type of Arrhenius expression (k = AT2e−B/T) does also fit to the existing data − T − − ( 3 k = 1.82 × 10 17T2 e361/ cm3 molecule 1 s 1 [27]). More experimental data are needed (especially at high temperatures) to determine a more appropriate temperature dependence relationship from the existing Arrhenius expressions. Data reported by Crawford et al. [29] for n-hexane are away from expression 3 and in case of n-heptane, their data are also lower than the recommended Arrhenius expression, indicating a systematic deviation. When using only n-hexane as reference compound, our result at 248K for n-heptane agrees to the results of Crawford et al. and Wilson et al. (see SI, Figure S6). In addition, we compared the different results when using n-butane, n-pentane, and n-hexane as reference compounds respectively. The calculated rate constant decrease with increasing −12 3 −1 −1 CH2 chains: 7.00 ± 0.19, 6.32 ± 0.14 and 5.47 ± 0.01 (in unit × 10 cm molecule s , result with n-hexane is plotted in SI), respectively (rate constant of reference compounds refers to Atkinson [27]). Since Crawford et al. (n-octane and n-nonane) and Wilson et al. (di- and tri-methylpentanes and n-octane) used higher hydrocarbon molecules as reference compounds, their results of rate constants for n-heptane were expected to be lower than ours. Based on the discussions of this work, there are Atmosphere 2018, 9, 320 7 of 16 several possible Arrhenius expressions for n-hexane, therefore, we choose n-pentane as our reference compound,Atmosphere 2018 for, 9, whichx FOR PEER a more REVIEW comprehensive understanding of temperature-dependence is available.7 of 16 This explains why our data are higher than the existing results. However, more experimental research, especiallywith absolute with measurements absolute measurements is needed to is clarify needed the to real clarify reaction the real rate reactionconstant rate of OH constant radicals of with OH radicalsn-heptane with at lown-heptane temperature. at low Our temperature. results for Our n-octane results and for nn-nonane-octane andare consistentn-nonane arewith consistent previous withresults previous by Li results et al. by [28]. Li et This al. [28 study]. This studyprovides provides more more open open questions questions than than a a comprehensive understandingunderstanding ofof gas-phasegas-phase reactionsreactions ofof OHOH withwith nn-alkanes-alkanes belowbelow 290290 KK untiluntil preciseprecise determinationsdeterminations ofof absoluteabsolute raterate constantsconstants forfor thethe higherhigher alkanesalkanes becomebecome available.available. The result for cyclooctane confirmsconfirms thethe datadata fromfrom SprengnetherSprengnether etet al.al. [[31],31], however,however, datadata atat higherhigher temperaturestemperatures areare desirabledesirable toto validatevalidate thethe ArrheniusArrhenius expressionexpression overover aa widerwider temperaturetemperature range. range. OurOur results for for nn-octane-octane and and n-nonanen-nonane are are consistent consistent with with previous previous results results by Li by et Li al. et [28]. al. [This28]. Thisstudy study will help will helpto provide to provide a more a more comprehensive comprehensive understanding understanding of gas-phase of gas-phase reactions reactions of OH of with OH withn-alkanesn-alkanes below below 290 290K. The K. The result result for forcyclooctane cyclooctane co confirmsnfirms the the data data from from Sp Sprengnetherrengnether et et al. [[31],31], however,however, datadata atat higherhigher temperaturestemperatures areare desirabledesirable toto validatevalidate thethe ArrheniusArrhenius expressionexpression overover aa widerwider temperaturetemperature range.range.

Badwin and Walker (1979) Greiner (1970) Atkinson et al. (1982b) Perry et al. (1976) Harris and Kerr (1988) Atkinson and Aschman (1984) Behnke et al. (1988) Droege and Tully (1986) Abbatt et al. (1990) Behnke et al. (1988) Talukdar et al. (1994) Abbatt et al. (1990) Donahue et al. (1998) Talukdar et al. (1994) DeMore and Bayes (1999) Donahue et al. (1998) Pang et al. (2011) DeMore and Bayes (1999) This work This work Recommendation Recommendation (Atkinson, 2003) (Atkinson, 2003) Fit to k = A e-B/T Fit to k = A e-B/T (Calvert et al., 2008) (Calvert et al., 2008) Arrhenius fit (Pang et al., 2011) 100

) n-Butane -1 ) s n-Pentane -1 -1 s

10 -1 molecule

-3 10 molecule -3 cm -12 cm -12 (10 k (10 k

1 012345 1 012345 1000/T (K-1) 1000/T (K-1) (a) (b)

Figure 4. Cont.

Atmosphere 2018, 9, 320 8 of 16 Atmosphere 2018, 9, x FOR PEER REVIEW 8 of 16

Atkinson et al. (1982a) Atkinson et al. (1982a) Klöpffer et al. (1986) Klein et al. (1984) Behnke et al. (1987) Behnke et al. (1988) Behnke et al. (1988) Koffend and Cohen (1996) Ferrari et al. (1996) Donahue et al. (1998) Koffend and Cohen (1996) DeMore and Bayes (1999) Wilson et al. (2006) Crawford et al. (2011) This work Pang et al. (2011) -B/T * Crawford et al. (2011) Fit to k = A e This work Fit to k = A T e-B/T * Recommendation (Atkinson, 2003) Fit to k = A T 2 e-B/T * Arrhenius expression (* Atkinson, 2003) (Wilson et al., 2006) -B/T Fit to k = A e Fit to k = A e-B/T (Calvert et al., 2008) (Calvert et al., 2008) Arrhenius expression Arrhenius fit (Crawford et al. 2011) (Pang et al., 2011) 100 100 )

n-Hexane ) -1 n-Heptane -1 s s -1 -1 molecule molecule -3 10 -3

cm 10 cm -12 -12 (10 k (10 k

012345 012345 -1 1000/T (K ) -1 1000/T (K ) (c) (d)

Atkinson et al. (1982a) Greiner (1970) Behnke et al. (1988) Atkinson et al. (1982a) Nolting et al. (1988) Behnke et al. (1988) Koffend and Cohen (1996) Nolting et al. (1988) Ferrari et al. (1996) Koffend and Cohen (1996) Coeur et al. (1998) Anderson et al. (2003) Colomb et al. (2004) Wilson et al. (2006) Li et al. (2006) Li et al. (2006) Pang et al. (2011) This work This work Recommendation Recommendation (Atkinson, 2003) (Atkinson, 2003) Arrhenius expression Arrhenius expression (Li et al., 2006) (Li et al., 2006) Arrhenius fit Fit to k = A e-B/T (Pang et al., 2011) (Calvert et al., 2008) Arrhenius expression (Warneck and Williams, 2012)

100 100

) n-Octane -1 ) s n-Nonane -1 -1 s -1 molecule -3 molecule -3 cm -12 cm -12

(10 10 k (10 k 10

012345 012345 1000/T (K-1) 1000/T (K-1) (e) (f)

Figure 4. Cont.

Atmosphere 2018, 9, 320 9 of 16 Atmosphere 2018, 9, x FOR PEER REVIEW 9 of 16

Donahue et al. (1998) Sprengnether et al. (2009) Aschmann et al. (2011) Singh et al. (2013) This work Calvert et al. (2008) Sprengnether et al. (2009) Singh et al. (2013)

) Cyclooctane -1 s -1 molecule -3

cm 10 -12 (10 k

2.0 2.5 3.0 3.5 4.0 4.5 5.0 1000/T (K-1) (g)

Figure 4. Arrhenius plots of the rate data for the reaction of OH radicals with straight-chain alkanes Figure 4. Arrhenius plots of the rate data for the reaction of OH radicals with straight-chain alkanes and cyclooctane in comparison with previous studies [25,39–49]. and cyclooctane in comparison with previous studies [25,39–49]. (2) Figure 5 shows the Arrhenius plot for the reaction of branched-chain alkanes with OH radicals.(2) Figure For5 theshows first time, the Arrheniuswe report the plot rate for cons thetant reaction below of290 branched-chain K for the reactions alkanes of OH with radicals OHwith radicals. 2,2,4-trimethylpentane, For the first time, we2,2-dimethylpentane, report the rate constant 2,2,3,3-tetramethylbutane below 290 K for the reactionsand 2,2- of OHdimethylhexane. radicals with The 2,2,4-trimethylpentane, reaction rate constant 2,2-dimethylpentane,data for 2,2-dimethylbutane, 2,2,3,3-tetramethylbutane 2,2,4-trimethylpentane and and 2,2-dimethylhexane.2,2,3,3-tetramethylbutane The reaction are consistent rate constant with data previous for 2,2-dimethylbutane, results and follow 2,2,4-trimethylpentane the existing Arrhenius andexpressions 2,2,3,3-tetramethylbutane (or non-linear fit) are as consistent well. For with 2,2-dimethylbutane, previous results we and give follow an estimated the existing Arrhenius Arrhenius fit to expressionsk = ATe−B/T (or by non-linear applying fit)the asvalue well. of For activation 2,2-dimethylbutane, energy (B = 445 we K) give estimated an estimated by Kwok Arrhenius and Atkinson fit to −B/T k = ATe[50] andby obtain applying an expression the value of of activation k = 3.33 × energy 10−14 T ( Be–445/= 445T cm K)3 estimatedmolecule− by1 s− Kwok1. For and2,2-dimethylpentane Atkinson [50] −14 −445/T 3 −1 −1 andand obtain 2,2-dimethylhexane, an expression of k calculated= 3.33 × 10 valuesT e(based oncm a moleculestructure-activitys . For relationship 2,2-dimethylpentane (SAR) [51]) at androom 2,2-dimethylhexane, temperature are given calculated for these values two (based compounds on a structure-activityto evaluate the temperature relationship dependence. (SAR) [51]) The at roomresults temperature of 2,2-dimethylpentane are given for fit these well twoto the compounds non-linear fit to provided evaluate theby Badra temperature and Farooq dependence. [52]. A SAR Theestimation results of 2,2-dimethylpentaneis given for 2,2-dimethylhexane, fit well to the and non-linear our data fit providedfall very byclose Badra to the and estimation Farooq [52 ].line. A SARNevertheless, estimation in is order given to for give 2,2-dimethylhexane, a more accurate evaluation and our data of the fall temperature very close to dependence the estimation of 2,2- line.dimethylhexane, Nevertheless, in more order experimental to give a more data accurate are need evaluationed to establish of the the temperature temperature dependence dependence of and 2,2-dimethylhexane,hereafter to develop more the experimental Arrhenius expression data are needed for this to compound. establish the temperature dependence and hereafter to develop the Arrhenius expression for this compound. (3) Regarding the activated aromatic hydrocarbons, our rate data points at 288 K and 248 K coincide well with the existing data points, showing that the rate constant for these reactions had a negative dependence on temperature at T ≤ 298 K, which indicates a coherent pathway of electrophilic addition of the OH radical to the aromatic ring [23]. Combining our results with the available literature data (Figure5), we here give Arrhenius expressions for o-xylene, p-xylene and ethylbenzene: 6.24 × 10−12 e(203 ± 126)/T cm3 molecule−1 s−1, 1.03 × 10−11 e(62 ± 116)/T cm3 molecule−1 s−1 and 6.90 × 10−12 e(8 ± 135)/T cm3 molecule−1 s−1, respectively (SI, Table S3). All previously reported data points for ethylbenzene existed around room temperature, which caused great uncertainties in determining the activation energy. Further investigations at other temperatures lower than 298 K are required to give a more precise evaluation of the Arrhenius expression for ethylbenzene.

Atmosphere 2018, 9, x FOR PEER REVIEW 10 of 16 Atmosphere 2018, 9, 320 10 of 16

Atkinson et al. (1984) Greiner (1970) Harris and Kerr (1988) Atkinson et al. (1984) Badra and Farooq (2015) Bott and Cohen (1991) This work Badra and Farooq (2015) Recommendation This work (Atkinson 2003) Recommendation Non-linear fit (Atkinson, 2003) (Badra and Farooq, 2015) -B/T Non-linear fit Fit to k = A T e (Badra and Farooq, 2015) (estimated from this work) 100 100

) 2,2,4-Trimethylpentane ) 2,2-Dimethylbutane -1 -1 s s -1 -1

10 10 molecule molecule -3 -3 cm cm -12 -12 (10 (10 k k

1 1 012345 012345 -1 1000/T (K-1) 1000/T (K ) (a) (b)

Greiner (1970) Baldwin et al. (1979) Atkinson et al. (1984) Tully et al. (1985) Bott and Cohen (1991) Sivaramakrishnan and Michael (2009) This work Calculation value Fit to k = A T 2 e-B/T (Kwok and Atkinson, 1995) Finlayson Pitts and Pitts (2000) (Cohen, 1991) Badra and Farooq (2015) Recommendation This work (Atkinson, 2003) -B/T SAR estimation k = A T e-B/T Fit to k = A e (Calvert et al., 2008) (Calvert et al., 2008) Non-linear fit Non-linear fit (Badra and Farooq, 2015) (Sivaramakrishnan and Michael, 2009) 100

2,2-Dimethylpentane )

) 2,2,3,3,-Tetramethylbutane -1 -1 s s -1 -1 10

10 molecule molecule -3 3 cm cm -12 -12 (10 (10 k k

1

1 012345 012345 -1 1000/T (K ) 1000/T (K-1) (c) (d)

Figure 5. Cont.

Atmosphere 2018, 9, x FOR PEER REVIEW 11 of 16

Calculation value (Kwok and Atkinson, 1995) This work SAR estimation k = A T2 e-B/T (Calvert et al., 2008) 100

2,2-Dimethylhexane ) -1 s -1

10

Atmosphere 2018, 9, 320 molecule 11 of 16 3 Atmosphere 2018, 9, x FOR PEER REVIEW 11 of 16 cm -12 (10

k Calculation value (Kwok and Atkinson, 1995) This work SAR estimation k = A T2 e-B/T (Calvert et al., 2008) 1 100 012345 1000/T (K-1) 2,2-Dimethylhexane (e) ) -1 s Figure 5. Arrhenius plots-1 of the rate data for the reaction of OH radicals with branched-chain alkanes [47,53–58]. 10 molecule 3 cm

(3) Regarding the activated-12 aromatic hydrocarbons, our rate data points at 288 K and 248 K

coincide well with the existing (10 data points, showing that the rate constant for these reactions had a k negative dependence on temperature at T ≤ 298 K, which indicates a coherent pathway of electrophilic addition of the OH radical to the aromatic ring [23]. Combining our results with the available literature data (Figure 5), 1 we here give Arrhenius expressions for o-xylene, p-xylene and 012345 −12 (203 ± 126)/T 3 −1 −1 −11 (62 ± 116)/T 3 −1 −1 ethylbenzene: 6.24 × 10 e cm molecule 1000/ s T, 1.03(K-1) × 10 e cm molecule s and 6.90 × −12 (8 ± 135)/T 3 −1 −1 10 e cm molecule s , respectively (SI, (Tablee) S3). All previously reported data points for ethylbenzene existed around room temperature, which caused great uncertainties in determining the activationFigureFigure energy. 5.5. ArrheniusArrhenius Further plots plots investigations of of the the rate rate data dataat for other forthe reacti thetemperatures reactionon of OH of radicals lower OH radicals thanwith branched-chain298 with K branched-chainare required alkanes to give a morealkanes[47,53–58]. precise [47,53 evaluation–58]. of the Arrhenius expression for ethylbenzene.

(3) Regarding the activatedHansen aromatic et al. (1975) hydrocarbons, our rate data points at 288 K and 248 K Davis et al. (1975) coincide well with the existing dataPerry et points, al. (1977) showing that the rate constant for these reactions had a Tully et al. (1981) negative dependence on temperatureWahner etat al. T (1983) ≤ 298 K, which indicates a coherent pathway of electrophilic Witte et al. (1986) Hansen et al. (1975) addition of the OH radical to theWallington aromatic et al. (1987) ring [23]. Combining our resultsDavis with et al. (1975) the available Knispel et al. (1990) Perry et al. (1977) literature data (Figure 5), weGoumri here et al. (1991)give Arrhenius expressions for o-xylene,Tully et al. (1981) p-xylene and −12 (203 ± 126)/SemadeniT 3 et al. (1995) −1 −1 −11 (62 ± 116)/T 3 Atkinson and− Aschmann1 −1 (1989) ethylbenzene: 6.24 × 10 e Anderson cm etmolecule al. (2003) s , 1.03 × 10 e cm moleculeKnispel et al. (1990) s and 6.90 × −12 (8 ± 135)/T 3 −1 −1 This work Semadeni et al. (1995) 10 e cm molecule s , respectivelyArrhenius expression (SI, Table S3). All previously reportedAnderson and data Hites (1996)points for (Witte et al., 1986) This work ethylbenzene existed around roomArrhenius temperature, expression which caused great uncertaintiesArrhenius in expressiondetermining the (Semadeni et al., 1995) (Semadeni et al., 1995) activation energy. Further investigationsRecommendation at other temperatures lower than 298 RecommendationK are required to give (IUPAC, 2008) (IUPAC, 2008) a more4 precise evaluation of the Arrhenius expression20 for ethylbenzene.

3 Benzene Toluene Hansen et al. (1975) ) ) -1

-1 Davis et al. (1975) s s Perry et al. (1977) 10

2 -1 -1 Tully et al. (1981) 9 Wahner et al. (1983) 8 Witte et al. (1986) 7 Hansen et al. (1975) Davis et al. (1975) molecule

molecule Wallington et al. (1987) 6 3 3 Knispel et al. (1990) Perry et al. (1977) 5

1 cm cm Goumri et al. (1991) Tully et al. (1981) 0.9 -12 -12 Atkinson and Aschmann (1989) 0.8 Semadeni et al. (1995) 4 Knispel et al. (1990) (10

(10 Anderson et al. (2003)

0.7 k k This work Semadeni et al. (1995) 3 0.6 Arrhenius expression Anderson and Hites (1996) 0.5 (Witte et al., 1986) This work Arrhenius expression Arrhenius expression 0.4 (Semadeni et al., 1995) 2 (Semadeni et al., 1995) 2.5 3.0 3.5Recommendation 4.0 4.5 2.53.03.54.04.55.0Recommendation (IUPAC, 2008) (IUPAC, 2008) -1 -1 4 1000/T (K ) 20 1000/T (K ) (a) (b) 3 Benzene Toluene ) ) -1 -1 s s 10

2 -1 -1 Figure 6. Cont. 9 8 7 molecule

molecule 6 3 3 5

1 cm cm 0.9 -12 -12 0.8 4 (10 (10

0.7 k k 0.6 3 0.5

0.4 2 2.5 3.0 3.5 4.0 4.5 2.53.03.54.04.55.0 1000/T (K-1) 1000/T (K-1) (a) (b)

Atmosphere 2018, 9, 320 12 of 16 Atmosphere 2018, 9, x FOR PEER REVIEW 12 of 16

Doyle et al. (1975) Hansen et al. (1975) Davis (1977) Doyle et al. (1975) Perry et al. (1977) Hansen et al. (1975) Ravishankara et al. (1978) Perry et al. (1977) Nicovich et al. (1981) Davis (1977) Ohta and Ohyama, (1985) Ravishankara et al. (1978) Atkinson and Aschmann (1989) Nicovich et al. (1981) Mehta et al. (2009) Atkinson and Aschmann (1989) Alarcón et al. (2015) Anderson et al. (2003) This work Mehta et al. (2009) Arrhenius expression This work (Alarcón et al., 2015) Arrhenius expression Arrhenius expression (from this work) (this work) 50 50

40 40 o-Xylene p-Xylene

) 30 ) 30 -1 -1 s s -1 -1

20 20 molecule molecule 3 3 cm cm -12 -12 10 10 (10 (10 9 9 k k 8 8 7 7 6 6 5 5 2.6 2.8 3.0 3.2 3.4 3.6 3.8 4.0 4.2 4.4 2.8 3.0 3.2 3.4 3.6 3.8 4.0 4.2 4.4 1000/T (K-1) 1000/T (K-1) (c) (d)

Lloyd et al. (1976) Davis et al. (1977) Ravishankara et al. (1978) Ohta and Ohyama (1985) Anderson et al. (2003) This work Arrhenius expression (from this work) 20

Ethylbenzene ) -1

s 10 -1 9 8 7

molecule 6 3 5 cm -12 4 (10 k 3

2 2.6 2.8 3.0 3.2 3.4 3.6 3.8 4.0 4.2 4.4 1000/T (K-1) (e)

Figure 6. Arrhenius plots of the rate data for the reaction of OH radicals with aromatic hydrocarbons Figure 6. Arrhenius plots of the rate data for the reaction of OH radicals with aromatic hydrocarbons [33,34,59–67]. [33,34,59–67]. 5. Conclusions 5. Conclusions In summary, this study has reported the rate constant of gaseous OH radicals with 17 hydrocarbons In summary, this study has reported the rate constant of gaseous OH radicals with 17 at 288 K and 248 K. The results have proven the capability of our simulation chamber for atmospheric hydrocarbons at 288 K and 248 K. The results have proven the capability of our simulation chamber chemistry study. Data obtained from this work are consistent with previous studies, supplementing the for atmospheric chemistry study. Data obtained from this work are consistent with previous studies, existing database. Our data on n-hexane agree well with the recommended Arrhenius expression supplementing the existing database. Our data on n-hexane agree well with the recommended (k = 1.82 × 10−17 T 2e361/T cm3 molecule−1 s−1 [4]) over the temperature range from 290 to 970 K. Arrhenius expression (k = 1.82 × 10−17 T 2e361/T cm3 molecule−1 s −1[4]) over the temperature range from Using the activation energy recommended by Kwok and Atkinson [50] for 2,2-dimethylbutane from 290 to 970 K. Using the activation energy recommended by Kwok and Atkinson [50] for 2,2- an SAR calculation (B = 445 K), we obtain the Arrhenius expression k = 3.33 × 10−14 T e−445/T dimethylbutane from an SAR calculation (B = 445 K), we obtain the Arrhenius expression k = 3.33 × cm3 molecule−1 s−1. This study reports experimental results for the rate constant of the gas phase 10−14 T e−445/T cm3 molecule−1 s−1. This study reports experimental results for the rate constant of the gas reaction of 2,2-dimethylhexane with OH, extending the homologous series of the 2,2-dimethylalkanes. phase reaction of 2,2-dimethylhexane with OH, extending the homologous series of the 2,2- dimethylalkanes. Data obtained from this study will help to give a more comprehensive understanding to evaluate the atmospheric behavior of this compound.

Atmosphere 2018, 9, 320 13 of 16

Data obtained from this study will help to give a more comprehensive understanding to evaluate the atmospheric behavior of this compound. For aromatic hydrocarbons, we reported the first determination of a rate constant for the reaction of OH radicals with ethylbenzene below the atmospheric sea level temperature (T ≤ 288 K). Our data points agree with the existing results from previous research. Results from this work will help to evaluate the atmospheric degradations of n-alkanes, branched-chain alkanes, and aromatic hydrocarbons with better precision, especially in the lower and middle troposphere.

Supplementary Materials: The following are available online at http://www.mdpi.com/2073-4433/9/8/320/s1, Figure S1: Schematic flowchart of the sample enrichment system connected with gas chromatographic analysis of the gas phase in the smog chamber, Figure S2: Dosage of methyl nitrite into the smog chamber, using a twin of gas containers. This method warrants a fairly constant production of OH, Figure S3: Decrease of the hydrocarbon concentrations (normalized by n-perfluorohexane) by the reaction with OH during a smog chamber run at 248 K, Figure S4: Plots of ln (c0/ct) of hydrocarbons versus toluene (reference substance) from data points of three experimental runs at 288 K, respectively (5, and  distinguish data points from different experimental runs), Figure S5: Plots of ln (c0/ct) of hydrocarbons versus# toluene (reference substance) from data points of two experimental runs at 248 K, respectively (5 and distinguish data points from different experimental runs), Figure S6: Arrhenius plots of the rate constant for# the reaction of OH radicals with n-heptane, Table S1: Studies below room temperature for the reaction of OH radicals with hydrocarbons, Table S2: Rate constants for the reaction of OH radicals with hydrocarbons at 248 K, Table S3: Arrhenius parameters A and B corresponding to the (−B/T) equation kOH = Ae . Author Contributions: Conceptualization, C.Z.; Experiments, L.H. and F.S.; Data Analysis, L.H. and F.S.; Writing-Original Draft Preparation, L.H.; Writing-Review & Editing, L.H., F.S. and C.Z.; Supervision, C.Z.; Funding Acquisition, C.Z. Funding: This research was funded by the European Community through the EUROCHAMP project. This publication was funded by the German Research Foundation (DFG) and the University of Bayreuth in the funding program “Open Access Publishing”. Acknowledgments: This work is in memoriam to Heinz-Ulrich Krüger (†) for his enormous technical support and discussions for the primary data. Conflicts of Interest: The authors declare no conflict of interest.

References

1. Koppmann, R. Chemistry of Volatile Organic Compounds in the Atmosphere. In Handbook of Hydrocarbon and Lipid Microbiology; Springer: Heidelberg, Germany, 2010; pp. 267–277. 2. Atkinson, R. Atmospheric Chemistry of VOCs and NOx. Atmos. Environ. 2000, 34, 2063–2101. [CrossRef] 3. Carter, W.P.L.; Pierce, J.A.; Luo, D.; Malkina, I.L. Environmental Chamber Study of Maximum Incremental Reactivities of Volatile Organic Compounds. Atmos. Environ. 1995, 29, 2499–2511. [CrossRef] 4. DeMore, W.B.; Bayes, K.D. Rate Constants for the Reactions of Hydroxyl Radical with Several Alkanes, Cycloalkanes, and Dimethyl Ether. J. Phys. Chem. A 1999, 103, 2649–2654. [CrossRef] 5. Doyle, G.L.; Lloyd, A.C.; Darnall, K.R.; Winer, A.M.; Pitts, J.N., Jr. Gas Phase Kinetic Study of Relative Rates of Reaction of Selected Aromatic Compounds with Hydroxyl Radicals in an Environmental Chamber. Environ. Sci. Technol. 1975, 9, 237–241. [CrossRef] 6. Greiner, N.R. Hydroxyl Radical Kinetics by Kinetic Spectroscopy. VI. Reactions with Alkanes in the Range 300–500 K. J. Chem. Phys. 1970, 53, 1070–1076. [CrossRef] 7. Hansen, D.A.; Atkinson, R.; Pitts, J.N. Rate Constants for the Reaction of Hydroxyl Radicals with a Series of Aromatic Hydrocarbons. J. Phys. Chem. 1975, 79, 1763–1766. [CrossRef] 8. Koffend, J.B.; Cohen, N. Shock Tube Study of OH Reactions with Linear Hydrocarbons near 1100 K. Int. J. Chem. Kinet. 1996, 28, 79–87. [CrossRef] 9. Nicovich, J.M.; Thompson, R.L.; Ravishankara, A.R. Kinetics of the Reactions of the Hydroxyl Radical with Xylenes. J. Phys. Chem. 1981, 85, 2913–2916. [CrossRef] 10. Nolting, F.; Behnke, W.; Zetzsch, C. A Smog Chamber for Studies of the Reactions of Terpenes and Alkanes with Ozone and OH. J. Atmos. Chem. 1988, 6, 47–59. [CrossRef] 11. Perry, R.A.; Atkinson, R.; Pitts, J.N. Kinetics and Mechanism of the Gas Phase Reaction of Hydroxyl Radicals with Aromatic Hydrocarbons over the Temperature Range 296–473 K. J. Phys. Chem. 1977, 81, 296–304. [CrossRef] Atmosphere 2018, 9, 320 14 of 16

12. Tully, F.P.; Koszykowski, M.L.; Stephen Binkley, J. Hydrogen-Atom Abstraction from Alkanes by OH. I. Neopentane and Neooctane. Symp. Int. Combust. 1985, 20, 715–721. [CrossRef] 13. Atkinson, R. Kinetics and Mechanisms of the Gas-Phase Reactions of the Hydroxyl Radical with Organic Compounds. J. Phys. Chem. Ref. Data 1989. Available online: https://srd.nist.gov/JPCRD/jpcrdM1.pdf (accessed on 8 January 2018). 14. Finlayson, B.J.; Pitts, J.N. Photochemistry of the Polluted Troposphere. Science 1976, 192, 111–119. [CrossRef] [PubMed] 15. Hecht, T.A.; Seinfeld, J.H.; Dodge, M.C. Generalized Kinetic Mechanism for Photochemical Smog. Environ. Sci. Technol. 1974, 8, 327–339. [CrossRef] 16. Pitts, J.N., Jr.; Darnall, K.; Winer, A.; McAfee, J. Mechanisms of Photochemical Reactions in Urban Air. Volume II. Chamber Studies. 1977. Available online: https://cfpub.epa.gov/si/si_public_record_Report. cfm?dirEntryId=40180 (accessed on 8 January 2018). 17. Rohrer, F.; Bohn, B.; Brauers, T.; Brüning, D.; Johnen, F.-J.; Wahner, A.; Kleffmann, J. Characterisation of the Photolytic HONO-Source in the Atmosphere Simulation Chamber SAPHIR. Atmos. Chem. Phys. 2005, 5, 2189–2201. [CrossRef] 18. Zador, J.; Turányi, T.; Wirtz, K.; Pilling, M.J. Measurement and Investigation of Chamber Radical Sources in the European Photoreactor (EUPHORE). J. Atmos. Chem. 2006, 55, 147–166. [CrossRef] 19. Karl, M.; Brauers, T.; Dorn, H.-P.; Holland, F.; Komenda, M.; Poppe, D.; Rohrer, F.; Rupp, L.; Schaub, A.;

Wahner, A. Kinetic Study of the OH-isoprene and O3-isoprene Reaction in the Atmosphere Simulation Chamber, SAPHIR. Geophys. Res. Lett. 2004, 31.[CrossRef] 20. Wang, X.; Liu, T.; Bernard, F.; Ding, X.; Wen, S.; Zhang, Y.; Zhang, Z.; He, Q.; Lü, S.; Chen, J.; et al. Design and Characterization of a Smog Chamber for Studying Gas-Phase Chemical Mechanisms and Aerosol Formation. Atmos. Meas. Tech. 2014, 7, 301–313. [CrossRef] 21. Harris, S.J.; Kerr, J.A. Relative Rate Measurements of Some Reactions of Hydroxyl Radicals with Alkanes Studied under Atmospheric Conditions. Int. J. Chem. Kinet. 1988, 20, 939–955. [CrossRef] 22. Talukdar, R.K.; Mellouki, A.; Gierczak, T.; Barone, S.; Chiang, S.-Y.; Ravishankara, A.R. Kinetics of the Reactions of OH with Alkanes. Int. J. Chem. Kinet. 1994, 26, 973–990. [CrossRef] 23. Tully, F.P.; Ravishankara, A.R.; Thompson, R.L.; Nicovich, J.M.; Shah, R.C.; Kreutter, N.M.; Wine, P.H. Kinetics of the Reactions of Hydroxyl Radical with Benzene and Toluene. J. Phys. Chem. 1981, 85, 2262–2269. [CrossRef] 24. Mohanakumar, K. Stratosphere Troposphere Interactions: An Introduction; Springer: Dordrecht, The Netherlands, 2008; Available online: https://books.google.com.hk/books?hl=zh-TW&lr=&id=pAQDbLQXnksC& oi=fnd&pg=PR7&dq=Stratosphere+Troposphere+Interactions:+An+Introduction&ots=30W_Js-QWU& sig=6KPUegpfd-54aoOID9vU94VTeIM&redir_esc=y#v=onepage&q=Stratosphere%20Troposphere% 20Interactions%3A%20An%20Introduction&f=false (accessed on 8 January 2018). 25. Droege, A.T.; Tully, F.P. Hydrogen Atom Abstraction from Alkanes by Hydroxyl. 5. n-Butane. J. Phys. Chem. 1986, 90, 5937–5941. [CrossRef] 26. Donahue, N.M.; Clarke, J.S. Fitting Multiple Datasets in Kinetics: N-Butane + OH → Products. Int. J. Chem. Kinet. 2004, 36, 259–272. [CrossRef] 27. Atkinson, R. Kinetics of the Gas-Phase Reactions of OH Radicals with Alkanes and Cycloalkanes. Atmos. Chem. Phys. 2003, 3, 2233–2307. [CrossRef] 28. Li, Z.; Singh, S.; Woodward, W.; Dang, L. Kinetics Study of OH Radical Reactions with N-Octane, n-Nonane, and n-Decane at 240–340 K Using the Relative Rate/Discharge Flow/Mass Spectrometry Technique. J. Phys. Chem. A 2006, 110, 12150–12157. [CrossRef][PubMed] 29. Crawford, M.A.; Dang, B.; Hoang, J.; Li, Z. Kinetic Study of OH Radical Reaction with N-Heptane and n-Hexane at 240–340K Using the Relative Rate/Discharge Flow/Mass Spectrometry (RR/DF/MS) Technique. Int. J. Chem. Kinet. 2011, 43, 489–497. [CrossRef] 30. Wilson, E.W.; Hamilton, W.A.; Kennington, H.R.; Evans, B.; Scott, N.W.; DeMore, W.B. Measurement and Estimation of Rate Constants for the Reactions of Hydroxyl Radical with Several Alkanes and Cycloalkanes. J. Phys. Chem. A 2006, 110, 3593–3604. [CrossRef][PubMed] 31. Sprengnether, M.M.; Demerjian, K.L.; Dransfield, T.J.; Clarke, J.S.; Anderson, J.G.; Donahue, N.M. Rate Constants of Nine C6−C9 Alkanes with OH from 230 to 379 K: Chemical Tracers for [OH]. J. Phys. Chem. A 2009, 113, 5030–5038. [CrossRef][PubMed] Atmosphere 2018, 9, 320 15 of 16

32. Singh, S.; de Leon, M.F.; Li, Z. Kinetics Study of the Reaction of OH Radicals with C5–C8 Cycloalkanes at 240–340 K Using the Relative Rate/Discharge Flow/Mass Spectrometry Technique. J. Phys. Chem. A 2013, 117, 10863–10872. [CrossRef][PubMed] 33. Witte, F.; Urbanik, E.; Zetzsch, C. Temperature Dependence of the Rate Constants for the Addition of Hydroxyl to Benzene and to Some Monosubstituted Aromatics (Aniline, Bromobenzene, and Nitrobenzene) and the Unimolecular Decay of the Adducts. Part 2. Kinetics into a Quasi-Equilibrium. J. Phys. Chem. 1986, 90, 3251–3259. [CrossRef] 34. Mehta, D.; Nguyen, A.; Montenegro, A.; Li, Z. A Kinetic Study of the Reaction of OH with Xylenes Using the Relative Rate/Discharge Flow/Mass Spectrometry Technique. J. Phys. Chem. A 2009, 113, 12942–12951. [CrossRef][PubMed] 35. Alarcón, P.; Bohn, B.; Zetzsch, C. Kinetic and Mechanistic Study of the Reaction of OH Radicals with Methylated Benzenes: 1,4-Dimethyl-, 1,3,5-Trimethyl-, 1,2,4,5-, 1,2,3,5- and 1,2,3,4-Tetramethyl-, Pentamethyl-, and Hexamethylbenzene. Phys. Chem. Chem. Phys. 2015, 17, 13053–13065. [CrossRef] [PubMed] 36. Warneck, P. Chemistry of the Natural Atmosphere, 2nd ed.; Academic Press: San Diego, CA, USA, 1999. 37. IUPAC. Preferred Value for Toluene of the IUPAC Task Group on Atmospheric Chemical Kinetic Data Evaluation. Available online: http://Iupac.Pole-Ether.Fr/ (accessed on 8 January 2018). 38. Doumaux, A.R.; Downey, J.J.M.; Henry, J.P.; Hurt, J.M. Preparation of Methyl or Ethyl Nitrite from the Corresponding Alcohols in a Vapor Phase Process. European Patent No. EP0057143B1, 23 January 1981. 39. Donahue, N.M.; Anderson, J.G.; Demerjian, K.L. New Rate Constants for Ten OH Alkane Reactions from 300 to 400 K: An Assessment of Accuracy. J. Phys. Chem. A 1998, 102, 3121–3126. [CrossRef] 40. Abbatt, J.P.D.; Demerjian, K.L.; Anderson, J.G. A New Approach to Free-Radical Kinetics: Radially and Axially Resolved High-Pressure Discharge Flow with Results for Hydroxyl + (Ethane, Propane, n-Butane, n-Pentane) .Fwdarw. Products at 297 K. J. Phys. Chem. 1990, 94, 4566–4575. [CrossRef] 41. Behnke, W.; Holländer, W.; Koch, W.; Nolting, F.; Zetzsch, C. A Smog Chamber for Studies of the Photochemical Degradation of Chemicals in the Presence of Aerosols. Atmos. Environ. (1967) 1988, 22, 1113–1120. [CrossRef] 42. Atkinson, R.; Aschmann, S.M. Rate Constants for the Reaction of OH Radicals with a Series of Alkenes and Dialkenes at 295 ± 1 K. Int. J. Chem. Kinet. 1984, 16, 1175–1186. [CrossRef] 43. Atkinson, R.; Aschmann, S.M.; Carter, W.P.L.; Winer, A.M.; Pitts, J.N. Kinetics of the Reactions of OH Radicals with N-Alkanes at 299 ± 2 K. Int. J. Chem. Kinet. 1982, 14, 781–788. [CrossRef] 44. Ferrari, C.; Roche, A.; Jacob, V.; Foster, P.; Baussand, P. Kinetics of the Reaction of OH Radicals with a Series of Esters under Simulated Conditions at 295 K. Int. J. Chem. Kinet. 1996, 28, 609–614. [CrossRef] 45. Behnke, W.; Nolting, F.; Zetzsch, C. A Smog Chamber Study on the Impact of Aerosols on the Photodegradation of Chemicals in the Troposphere. J. Aerosol Sci. 1987, 18, 65–71. [CrossRef] 46. Coeur, C.; Jacob, V.; Foster, P.; Baussand, P. Rate Constant for the Gas-Phase Reaction of Hydroxyl Radical with the Natural Hydrocarbon Bornyl Acetate. Int. J. Chem. Kinet. 1998, 30, 497–502. [CrossRef] 47. Calvert, J.G.; Derwent, R.G.; Orlando, J.J.; Tyndall, G.S.; Wallington, T.J. Mechanisms of Atmospheric Oxidation of the Alkanes; Oxford University Press: New York, NY, USA, 2008. 48. Atkinson, R.; Aschmann, S.M.; Winer, A.M.; Pitts, J.N. Rate Constants for the Reaction of OH Radicals with a Series of Alkanes and Alkenes at 299 ± 2 K. Int. J. Chem. Kinet. 1982, 14, 507–516. [CrossRef] 49. Pang, G.A.; Hanson, R.K.; Golden, D.M.; Bowman, C.T. High-Temperature Measurements of the Rate Constants for Reactions of OH with a Series of Large Normal Alkanes: N-Pentane, n-Heptane, and n-Nonane. Zeitschrift für Physikalische Chemie 2011, 225, 1157–1178. [CrossRef] 50. Kwok, E.S.C.; Atkinson, R. Estimation of Hydroxyl Radical Reaction Rate Constants for Gas-Phase Organic Compounds Using a Structure-Reactivity Relationship: An Update. Atmos. Environ. 1995, 29, 1685–1695. [CrossRef] 51. Jenkin, M.E.; Valorso, R.; Aumont, B.; Rickard, A.R.; Wallington, T.J. Estimation of Rate Coefficients and Branching Ratios for Gas-Phase Reactions of OH with Aliphatic Organic Compounds for Use in Automated Mechanism Construction. Atmos. Chem. Phys. 2018, 18, 9297–9328. [CrossRef] 52. Badra, J.; Farooq, A. Site-Specific Reaction Rate Constant Measurements for Various Secondary and Tertiary H-Abstraction by OH Radicals. Combust. Flame 2015, 162, 2034–2044. [CrossRef] 53. Atkinson, R.; Carter, W.P.L.; Aschmann, S.M.; Winer, A.M.; Pitts, J.N. Kinetics of the Reaction of Oh Radicals with a Series of Branched Alkanes at 297 ± 2 K. Int. J. Chem. Kinet. 1984, 16, 469–481. [CrossRef] Atmosphere 2018, 9, 320 16 of 16

54. Bott, J.F.; Cohen, N. A Shock Tube Study of the Reactions of the Hydroxyl Radical with Several Combustion Species. Int. J. Chem. Kinet. 1991, 23, 1075–1094. [CrossRef] 55. Baldwin, R.R.; Walker, R.W.; Walker, R.W. Addition of 2,2,3-Trimethylbutane to Slowly Reacting Mixtures of Hydrogen and Oxygen at 480 ◦C. J. Chem. Soc. Faraday Trans. 1 Phys. Chem. Condens. Phases 1981, 77, 2157–2173. [CrossRef] 56. Finlayson-Pitts, B.J.; Pitts, J.N., Jr. Chemistry of the Upper and Lower Atmosphere: Theory, Experiments, and Applications, 1st ed.; Academic Press: San Diego, CA, USA, 1999. 57. Sivaramakrishnan, R.; Michael, J.V. Rate Constants for OH with Selected Large Alkanes: Shock-Tube Measurements and an Improved Group Scheme. J. Phys. Chem. A 2009, 113, 5047–5060. [CrossRef][PubMed] 58. Cohen, N. Are Reaction Rate Coefficients Additive? Revised Transition State Theory Calculations for OH + Alkane Reactions. Int. J. Chem. Kinet. 1991, 23, 397–417. [CrossRef] 59. Ravishankara, A.R.; Wagner, S.; Fischer, S.; Smith, G.; Schiff, R.; Watson, R.T.; Tesi, G.; Davis, D.D. A Kinetics Study of the Reactions of OH with Several Aromatic and Olefinic Compounds. Int. J. Chem. Kinet. 1978, 10, 783–804. [CrossRef] 60. Anderson, R.S.; Czuba, E.; Ernst, D.; Huang, L.; Thompson, A.E.; Rudolph, J. Method for Measuring Carbon Kinetic Isotope Effects of Gas-Phase Reactions of Light Hydrocarbons with the Hydroxyl Radical. J. Phys. Chem. A 2003, 107, 6191–6199. [CrossRef] 61. Semadeni, M.; Stocker, D.W.; Kerr, J.A. The Temperature Dependence of the OH Radical Reactions with Some Aromatic Compounds under Simulated Tropospheric Conditions. Int. J. Chem. Kinet. 1995, 27, 287–304. [CrossRef] 62. Wallington, T.J.; Neuman, D.M.; Kurylo, M.J. Kinetics of the Gas Phase Reaction of Hydroxyl Radicals with Ethane, Benzene, and a Series of Halogenated Benzenes over the Temperature Range 234–438 K. Int. J. Chem. Kinet. 1987, 19, 725–739. [CrossRef] 63. Knispel, R.; Koch, R.; Siese, M.; Zetzsch, C. Adduct Formation of OH Radicals with Benzene, Toluene, and Phenol and Consecutive Reactions of the Adducts with NOx and O2. Berichte der Bunsengesellschaft für Physikalische Chemie 1990, 94, 1375–1379. [CrossRef] 64. Goumri, A.; Pauwels, J.F.; Devolder, P. Rate of the OH + C6H6 + He Reaction in the Fall-off Range by Discharge Flow and OH Resonance Fluorescence. Can. J. Chem. 1991, 69, 1057–1064. [CrossRef] 65. Anderson, P.N.; Hites, R.A. OH Radical Reactions: The Major Removal Pathway for Polychlorinated Biphenyls from the Atmosphere. Environ. Sci. Technol. 1996, 30, 1756–1763. [CrossRef] 66. Ohta, T.; Ohyama, T. A Set of Rate Constants for the Reactions of OH Radicals with Aromatic Hydrocarbons. Bull. Chem. Soc. Jpn. 1985, 58, 3029–3030. [CrossRef] 67. Atkinson, R.; Aschmann, S.M. Rate Constants for the Gas-Phase Reactions of the OH Radical with a Series of Aromatic Hydrocarbons at 296 ± 2 K. Int. J. Chem. Kinet. 1989, 21, 355–365. [CrossRef]

© 2018 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).