Supplement of Detailed characterizations of the new Mines Douai comparative reactivity method instrument via laboratory experiments and modeling

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1 uppleent o Atos Meas Tech, 8, 57 55, 05 doi:0594/at suppleent Authors 05 CC Attribution 0 License uppleent o Detailed characterizations o the new Mines Douai coparative reactivity ethod instruent via laboratory experients and odeling V Michoud et al Correspondence to: Dusanter sebastiendusanter@ines-douair and V Michoud vincentichoud@ines-douair The copyright o individual parts o the suppleent ight dier ro the CC-BY 0 licence

2 uppleentary aterial : Coparison between easured and calculated total OH reactivity values or two dierent gas ixtures: Non-Methane Hydrocarbons NMHCs and Oxygenated VOCs OVOCs Figure : catter plot o calculated-to-easured OH reactivity or two dierent gas ixtures: NMHCs top panel and OVOCs botto panel at pyrrole to OH ratios o 9 and 8, respectively Cheical copositions o these ixtures are given in table The easured OH reactivity corresponds to the total OH reactivity easured by MD-CM and corrected or changes in huidity between C and C and or not operating the instruent under pseudo irst order conditions Correction or dilution is not perored since it is accounted or in the calculated OH reactivity Table : Cheical coposition o the OVOC and NMHC ixtures pecies OVOC ixture Mixing ratios pp pecies NMHC ixture Mixing ratios pp Methanol 5 Acetonitrile 06 Acetaldehyde 4 Acrylonitrile 05 Acetone 450 Benzene 096 Methyl Ethyl Ketone 40 Toluene 09 -Methyluran 5 EthylBenzene 080 Acrolein 48,,4-TriethylBenzene 05 Methacrolein 65 tyrene 07 Methyl Vinyl Ketone 54 Alpha-Pinene 07 -Methyl--buten--ol 060 Methyl ulur 4

3 Table : eactions included in the siple echanis see section o the ain anuscript eactions Biolecular rate constants c olecules - s - H + O = HO 75x0 - OH + VOC = O 50x0 - OH + Pyrrole = O x0-0 * O + O = 4x0 - * O + HO = 5x0 - O + NO = O+NO 77x0 - O + O = HO the oration o a product is not accounted or in the echanis 9x0-5 In addition to the reactions shown in Table, inorganic reactions ro IUPAC 00 have been added in the echanis, leading to a total o 4 reactions

4 uppleentary aterial : Experients perored to investigate the NO artiact in the presence o VOC reactivity addition o ethane and isoprene Figure : Changes in C ΔC = C expected C easured as a unction o NO in the reactor with red and without blue addition o a VOC These experients have been conducted using two dierent standards ethane and isoprene selected or their dierent kinetic rate constants with OH and c olecules - s -, respectively The concentrations added were 7 pp and 46 ppb or ethane and isoprene, respectively, leading to calculated OH reactivity values o and 66 s -, respectively Experients

5 ade using isoprene have been conducted at two dierent Pyrrole-to-OH ratios 6 and to test the inluence o this paraeter on the NO artiact in the presence o a VOC Dierences observed in the NO artiact when VOCs are added in the reactor are within experiental uncertainties 9-%, except when NO is low during the isoprene experient ade at a pyrrole-to-oh ratio o No clear inluence o the Pyrrole-to-OH ratio or o the VOC reactivity has been ound on the aplitude o the NO artiact uppleentary aterial : Coparison between real and apparent Pyrrole-to- OH ratios Figure : Coparison between real and apparent pyrrole-to-oh ratios or siulations conducted under dry conditions with the siple echanis presented in section o the ain anuscript Apparent pyrrole-to-oh ratios are calculated using Eq, where C is the initial concentration o pyrrole and C the inal concentration when OH has been ully reacted in the siulations This apparent ratio provides the aount o OH that has reacted with pyrrole This igure shows that running the CM instruent at an apparent pyrrole-to-oh ratio o 5-5 leads to a real ratio o approxiately 05-5 The ain anuscript and this suppleentary aterial always reer to the apparent pyrrole-to-oh ratio since it is the easurable quantity uppleentary aterial 4: Experiental easureents o the OH ixing ratio inside the CM reactor Experients were conducted to deterine the OH ixing ratio inside the reactor A large aount o isoprene pp was injected inside the reactor in absence o pyrrole with ercury lap ON or without ercury lap OFF OH production Isoprene was onitored by the PT-ToFM instruent at /z 69 iulations were conducted using MCM to ensure that this level o isoprene allows scavenging ore than 97% o OH in the reactor The OH ixing ratio present within the reactor can be derived ro the decrease o isoprene when the OH production is turned ON This OH ixing ratio, reerred as OH experient, was

6 deterined at two dierent pyrrole-to-oh ratios o 6 and 8 The level o OH quantiied experientally ro C-C, ie the aount o OH reacting with pyrrole, is reerred as OH estiated CM and is copared to the total ixing ratio o OH deterined experientally In addition, the OH ixing ratio necessary to reproduce the experiental C-C odulation with the odel is reerred as OH odel The three OH ixing ratios are shown in Fig 4 As seen in this igure, OH experient is higher than the level deterined ro the C-C odulation but only slightly lower ~0-0% than OH odel within experiental uncertainties However, the aount o isoprene injected inside the reactor ay not be high enough to scavenge all the OH radicals i a segregation occurs between the reactants see suppleentary aterial 8 oe OH ight still react with HO, leading to a slight underestiation o OH experients Fro these results, we consider that OH ixing ratios set in the odel to siulate the experiental C-C odulations are representative o the real ixing ratio in the reactor Figure 4: Coparison between OH ixing ratios deterined experientally OH experient, blue diaonds, calculated ro the C-C odulation OH estiated CM, red squares, and estiated ro the odel OH odel, green triangles at two dierent pyrrole-to-oh ratios 6 and 8 Error bars are the easureent precision Large error bars -68% are ound since these OH easureents correspond to dierences o tens o ppb or an initial ixing ratio o isoprene o approxiately pp

7 uppleentary aterial 5: Inluence o huidity on the NO artiact siulation results Figure 5: Coparison between siulations perored to investigate the NO artiact under dry open sybols and huid illed sybols conditions These siulations were conducted at three dierent pyrrole-to-oh ratios o 5-6 blue diaonds, green triangles, and 8-9 red squares, using the siple echanis and huid conditions corresponding to a relative huidity o 00% A sall decrease o ΔC is observed at each pyrrole-to-oh ratio This can be explained by an enhanceent o the reaction rate o HO + HO in the presence o water, reducing the secondary oration o OH, hence the NO artiact

8 uppleentary aterial 6: Inluence o adding a gas standard on the NO artiact siulation results Figure 6: iulated changes in C ΔC = C expected C siulated as a unction o NO This igure shows siulations ade with open circles and without illed circles adding a gas standard These siulations were conducted with the MCM echanis at a pyrrole-to- OH ratio o 4 The gas standards are isoprene 46 ppb and ethane 7 pp, leading to additional OH reactivities o 66 and s -, respectively

9 uppleentary aterial 7: Inluence o the VOC biolecular rate constant on the correction actor experiental results Figure 7: Experiental investigations o the bias caused by not operating the instruent under pseudo irst-order conditions Coparison o calculated true OH reactivity to CM easureents during the addition o a gas standard into the reactor at a pyrrole-to-oh ratio o 4 esults ro the addition o ive dierent gas standards Isoprene: red squares, Propene: green triangles, Ethene: orange triangles, Propane: purple circles, and Ethane: blue diaonds These gas standards are characterized by reaction rate constants with OH o 0 0-0, 9 0 -, , 0 -, and c olecules - s -, respectively uppleentary aterial 8: Potential inluence o reactant segregation on the siulations One hypothesis to explain the dierences observed between easureents and siulations or the bias caused by not operating the instruent under pseudo irst-order conditions is a potential segregation o reactants coing ro two dierent injectors OH and HO on one side and pyrrole + reactive trace gases on the other side To account or this segregation ie inhoogeneity in the reactor, we doubled the reaction rate constants o cross- and selreactions o radicals ie HO +OH and HO +HO, assuing that these reactions are avored by inhoogeneities inside the reactor since all the radicals are injected ro the sae injector Figure 8 shows a coparison between base siulations and siulations including reactant segregation as a unction o the pyrrole-to-oh ratio Laboratory derived correction actors are also shown These siulations suggest that segregation cannot explain the disagreeent since a larger dierence is ound when copared to experiental observations

10 Figure 8: Coparison o siulated and easured correction actors required to correct or not operating the instruent under pseudo irst order conditions Correction actors are shown as a unction o the Pyrrole-to-OH ratio Measured correction actors blues circles, as well as error bars, are the sae than in Fig 7 The siulated correction actors ste ro siulations conducted using the siple echanis blue open diaonds and the siple echanis including the segregation eect green open diaonds uppleentary aterial 9: Potential inluence o O +OH reactions on the siulations A recent study has proposed the reaction o CH O with OH as a potential sink o CH O in the reote atosphere Fittschen et al, 04 ince high radical concentrations are produced in the CM reactor, radical-radical reactions ay have an iportant ipact on the CM easureents We have, thereore, tested the addition o the reaction between peroxy radicals and OH in the siple echanis, assuing a reaction rate constant siilar to the one o CH O deterined by Bossolasco et al 04 Figure 9 shows the coparison between the correction actors derived ro base siulations and siulations including the ast O +OH reactions as a unction o the pyrrole-to-oh ratio The addition o this reaction in the cheical echanis leads to an increase o the correction actor and worsen the coparison

11 Figure 9: Coparison o the siulated and easured correction actors required to correct or not operating the instruent under pseudo irst order conditions Correction actors are shown as a unction o the Pyrrole-to-OH ratio Measured correction actors blues circles, as well as error bars, are the sae than in Fig 7 The siulated correction actors ste ro siulations conducted using the siple echanis blue open diaonds and the siple echanis including O +OH reactions green open diaonds The reaction rate constant or O +OH was set to c olecules - s -, corresponding to the rate constant o the reaction o CH O + OH Bossolasco et al, 04 uppleentary aterial 0: Potential inluence o uncertainties associated to radical-radical reaction rate constants on the siulations Fro the two previous tests 8-9, it appears that enhancing radical-radical reaction rates leads to an increase o the correction actors, which worsen the odel-experient coparison One can iagine that an overestiation o reaction rate constants o these reactions can contribute to the discrepancies observed between easureents and siulations To test the inluence o uncertainties associated to radical-radical reaction rate constants, siulations were perored with a reduction o 0% and 50% o the reaction rate constant or HO +OH Figure 0 shows the coparison between easured correction actors, base siulations, and siulations where a reduction o the reaction rate constant was ade This igure shows that a decrease o the HO +OH reaction rate constant allows to decrease the odeled correction actors and to get a better agreeent with experiental observations However, a reduction o the rate constant by 0% is not suicient to reconcile easureents and siulations Even a reduction o 50%, which is very unlikely, leads to siulated correction actors that are still slightly higher than the easureents Thereore, the uncertainty o reaction rate constants o radical-radical reactions cannot totally explain the discrepancies between siulations and easureents

12 Figure 0: Coparison o the siulated and easured correction actors required to correct or not operating the instruent under pseudo irst order conditions Correction actors are shown as a unction o the Pyrrole-to-OH ratio Measured correction actors blues circles, as well as error bars, are the sae than in Fig 7 The siulated correction actors ste ro siulations conducted using the base siple echanis blue open diaonds and the siple echanis odiied to relect a slower reaction rate constant or HO +OH green open diaonds: 0% reduction, red open diaonds: 50% reduction uppleentary aterial : Potential inluence o a higher proportion o HO copared to OH on the siulations In all the siulations presented in the ain paper and above, we assued siilar concentrations o HO and OH since water photolysis produces siilar aounts o these radicals However, it is likely that a larger aount o OH radicals is lost on the walls o the injector copared to HO Thereore, a HO to-oh ratio higher than unity ight be observed inside the reactor The inluence o a higher proportion o HO copared to OH has been tested with the siple echanis by setting initial HO concentrations higher by 0% than OH concentrations Figure shows the coparison between easured values, base siulations, and siulations where initial HO concentrations are higher than initial OH concentrations by 0% A higher proportion o HO leads to higher siulated correction actors, which worsen the coparison

13 Figure : Coparison o siulated and easured correction actors required to correct or not operating the instruent under pseudo irst order conditions Correction actors are shown as a unction o the Pyrrole-to-OH ratio Measured correction actors blues circles, as well as error bars hardly visible, are the sae than in Fig 7 The siulated correction actors ste ro siulations conducted using the siple echanis assuing the sae concentration or OH and HO blue open diaonds and 0% ore HO than OH green open diaonds uppleentary aterial : Potential inluence o O inside the reactor on the siulations All the siulations presented in this work have been perored without O However, photolysis o O ro the ercury lap eission at 849 n ay occur inside the reactor and ay lead to the oration o a signiicant aount o O In this context, the inluence o O was tested or both the pseudo irst order correction and the NO artiact The O ixing ratio was set at 00 ppb in the siulations, which corresponds to the ixing ratio easured using an ozone analyzer Environneent-A, odel O-4M at the exhaust o the reactor under dry conditions and the ercury lap ON Figure shows the coparison between easured correction actors required to correct or not operating the instruent under pseudo irst order conditions, base siulations, and siulations where initial O ixing ratios were set to 00 ppb This igure shows that the presence o O has alost no ipact on the siulated correction actors This can be explained by the act that the kinetic rate constant or the reaction between Pyrrole and O is seven orders o agnitude lower than the rate constant or the reaction between Pyrrole and OH while initial ixing ratios o O are only a actor to 9 higher than initial OH ixing ratios Furtherore, these siulations indicate that the ipact o the O + HO OH reaction has only a sall ipact on CM siulations, probably due to a slow reaction rate, even with high ixing ratios o HO 7-0 ppb and O 00 ppb inside the reactor

14 Figure : Coparison o siulated and easured correction actors required to correct or not operating the instruent under pseudo irst order conditions Correction actors are shown as a unction o the Pyrrole-to-OH ratio Measured correction actors blues circles, as well as error bars, are the sae than in Fig 7 The siulated correction actors ste ro siulations conducted using the base siple echanis blue open diaonds and the siple echanis where the initial ixing ratio o O was set to 00 ppb green open diaonds Figure displays the coparison between experiental and siulated results or the NO artiact iulations were perored using the MCM echanis and initialized with an O ixing ratios o 00 ppb This igure shows that the presence o ozone leads to a decrease o the NO artiact by approxiately 5%, independent o the pyrrole-to-oh ratio

15 Figure : Coparison o laboratory observations to odel siulations or the NO artiact Experiental illed sybols and solid lines and siulated open sybols and dashed or dotted lines results are shown or the changes in C ΔC = C expected C easured as a unction o NO Experiental values are the sae than in Fig 5 Model values are ro siulations ade using the base MCM echanis open lighter sybols and dashed lines and the MCM echanis where the initial O concentrations was set to 00 ppb open darker sybols and dotted lines uppleentary aterial : Potential inluence o a lower proportion o HO copared to OH on the siulations As described in the suppleent, a signiicant ixing ratio o O ~00 ppb is produced inside the reactor ro the photolysis o O Thereore, the ozone produced can lead to a production o OH inside the reactor ro its photolysis O + hν O D + O ollowed by O D + H O OH This OH source is ree o HO production I a non-negligible raction o OH coes ro this OH source, then the OH ixing ratio ay be higher than HO Thereore, the inluence o a lower proportion o HO copared to OH was also tested with the siple echanis by setting initial HO concentrations lower by 5% than OH concentrations Figure displays the coparison between easured values, base siulations, and siulations where HO concentrations were set lower by 5% than OH concentrations This igure shows that a lower proportion o HO leads to lower siulated correction actors However, it cannot ully explain the discrepancies Furtherore, a uch lower proportion o HO copared to OH is not likely since the photolysis o H O inside the injector will likely bring a larger aount o HO copared to OH inside the reactor, which would partly balance the absence o HO production ro O photolysis It is worth noting that a reduction o HO by 5% would also result in a reduction o the NO artiact by approxiately 6% using the MCM echanis not shown

16 Figure : Coparison o siulated and easured correction actors required to correct or not operating the instruent under pseudo irst order conditions Correction actors are shown as a unction o the Pyrrole-to-OH ratio Measured correction actors blues circles as well as error bars are the sae than in Fig 7 The siulated correction actors ste ro siulations conducted using the siple echanis assuing the sae concentration or OH and HO blue open diaonds and a 5% lower proportion o HO copared to OH green open diaonds uppleentary aterial 4: Assessent o OH reactivity uncertainties To assess the total uncertainty o abient OH reactivity easureents it is necessary to take into account errors associated to each quantity involved in the OH reactivity calculations Eq, including the dierent corrections When we account or the dierent corrections, the inal OH reactivity is calculated by the ollowing equation: C C C C koh k p C F D C C C Where k OH is the inal total OH reactivity, C, C and C the concentrations o pyrrole at dierent easureent steps see the ain anuscript, ΔC the change in C due to the NO artiact, ΔC the change in C due to a dierence in H between C and C, k the reaction rate constant o pyrrole with OH, F the correction actor to apply or not operating the instruent under pseudo irst-order conditions, and D the correction actor or dilution o abient air inside the reactor Considering that uncertainties are only due to PT-M easureents o pyrrole concentrations, the above equation can be rearrange to express it in ters o easured signals only or uncertainty deterinations and not or reactivity quantiication: p

17 F D X k k r p OH 7 9 Where,,, and are the pyrrole signals recorded by the PT-M at /z 68 during the dierent easureent steps, Δ and Δ the changes in pyrrole signals due to the NO artiact and changes in relative huidity, respectively, F the PTM sensitivity to pyrrole, 9 and 7 the signals at /z 9 H O + and /z 7 H O + H O, respectively, and X r the noralization actor accounting or the huidity dependence o the PT-M sensitivity deterined experientally as described by Hansen et al 05 Making the assuption that the noralization o pyrrole signals by H O + and H O + H O does not bring additional errors, the ters producing uncertainties in the easureents are:,,, Δ, Δ, k p,, F, and D Assuing that these variables are independent, we can calculate the total uncertainty or OH reactivity easureents using the ollowing equation: n xi xn x u xi U,, Applied to the total OH reactivity easureents, this gives the ollowing equations: p r D p r F p r kp r p r p r p r D F k X F k X D k X D F X F D k X F D k X D F k X U air ince the statistics or PT-M signals ollow a poissonian distribution De Gouw and Warneke, 007:,, and These ters represent the rando error precision o the PT-M easureents To calculate the precision on OH reactivity

18 easureents, it is thereore possible to consider only these three uncertainties as non-zero in the above equations Ters leading to systeatic errors are: k p,, F, and D Their relative uncertainties σ are described below: k kp p is estiated ro the literature to be 8% Dillon et al, 0 is calculated as the relative standard deviation o pyrrole calibrations perored during the capaigns and in the laboratory, and ro the uncertainty on the pyrrole standard σ o 5% is estiated to be % F is calculated ro the standard deviation o correction actors obtained or F dierent standards and within a restrained range o pyrrole-to-oh ratios 4- assuing that the pyrrole-to-oh dependence o F on this range o ratios is sall The corresponding relative uncertainty is 9% D is calculated ro uncertainties associated to dierent low rates PT-M D sapling, reactor exhaust, addition o N and pyrrole that are controlled by ass low controllers estiated at % The overall relative uncertainty to the dilution is estiated to be % Finally, uncertainties or Δ and Δ are given below: Δ is calculated using the ollowing equation: p 9 9 see equation ro the ain anuscript, where p is the slope o the linear relationship observed between the pyrrole signal and the 7/9 ratio ince the uncertainty on the 7/9 ratio is negligible ~005%, it is assued that depends only on the error associated to the slope and is estiated, ro laboratory and ield experients, to be % - Δ is calculated using a quadratic regression depending on NO: a' NO b' NO The relative uncertainty or Δ is estiated by propagating errors on the deterinations o a and b and on the NO easureents: U NOeasureent rel paraetrization NO U Errors associated to the deterinations o a and b are estiated using the σ conidence intervals o the quadratic regression see Fig 4 These errors are ound to be dependent on the NO ixing ratio

19 The error on NO easureents is estiated using the speciication given by the constructor or the NO x analyzer Thero Environental Instruents, odel 4C, ie a liit o detection o 04 ppb, and a relative precision o 4% deterined experientally LOD U NOeasureent relative precision NO The overall relative uncertainty or this correction regarding the NO ixing ratio is shown in Fig 4 Figure 4: Change in C as a unction o NO The solid line corresponds to an estiated ΔC using the quadratic regression deterined experientally or a pyrrole-to-oh ratio o 8, or which the largest uncertainties are expected The dashed lines display the σ conidence interval calculated using errors associated to a and b

20 Figure 4: Trend o with NO The relative uncertainty or this correction is estiated by propagating errors associated to the deterinations o a and b quadratic regression o ΔC=NO and the easureent error on NO

21 eerences Bossolasco, A, Faragó, E P, choeaecker, C, and Fittschen, C: ate constant o the reaction between CH O and OH radicals, Che Phys Lett, 59, 7, 04 De Gouw, J and Warneke, C: Measureents o volatile organic copounds in the Earth s atosphere using proton-transer reaction ass spectroetry, Mass pectro ev, 6, 57, 007 Dillon, T, Tucceri, M, Dulitz, K, Horowitz, A, Vereecken, L, and Crowley, J: eaction o Hydroxyl adicals with C4H5N Pyrrole: Teperature and Pressure Dependent ate Coeicients, J Phys Che A, 6, , doi:00/jp4x, 0 Fittschen, C, Whalley, L K, Heard, D E: The eaction o CHO adicals with OH adicals: A Neglected ink or CHO in the eote Atosphere, Environ ci Technol, 48, 4, , 04 Hansen, F, Blocquet, M, choeaecker, C, Léonardis, T, Locoge, N, Fittschen, C, Hanoune, B, tevens, P, inha, V, and Dusanter, : Intercoparison o the coparative reactivity ethod CM and pup-probe technique or easuring total OH reactivity in an urban environent, Atos Meas Tech Discuss, 8, , doi:0594/atd , 05