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Open Access , 4 erential op- ff Discussions Chemistry and Physics Atmospheric , J. A. Thornton 4 , T. P. Riedel source is anthropogenic (Thornton et al., 3 • 10136 10135 erent salt contents were performed in a Teflon ff , R. Sander mixing ratio. Besides bromine, large amounts of chlo- x 2,* cult to measure directly, resulting in a challenge to infer ). A strong activation of halogens was found at high NO ffi 2 1 and BrO, ClO, OClO and Cl atoms were simultaneously mea- NO 2 + NO , BrNO ce, Exeter, UK 2 ffi = , J. C. Buxmann 1 x , and C. Zetzsch , ClNO 2 2 , Br 2 This discussion paper is/has beenand under Physics review (ACP). for Please the refer journal to Atmospheric the Chemistry corresponding final paper in ACP if available. Atmospheric Chemistry Research Unit, UniversityInstitut of für Bayreuth, Umweltphysik, Bayreuth, University Germany ofAir Heidelberg, Chemistry Heidelberg, Germany Department, Max-Planck InstituteUniversity for of Chemistry, Washington, Mainz, Seattle, Germany USA now at: Met O a significant fraction of2010). the Although tropospheric the mechanisms Cl of halide activation, namely the conversion of inactive 1 Introduction Due to their high reactivity, bromineof and the chlorine atmosphere. have a In strong contrast impacttroposphere to on the seems the situation to chemistry in be the dominatedchlorinated stratosphere, by their species natural presence sources are in the such di a as budget of sea total spray. reactive Especially chlorine in the lower atmosphere. Recent studies suggest that CAABA/MECCA 0-D box model,took which the aerosol was liquid adapted wateragree to content reasonably and the with composition chamber the intoprerequisites conditions account. observations for The and halogen and model release, provide such results chloride as important contents the information as time about well profiles as of the the the aerosol aerosol pH. bromide and ozone depletion by reactive halogenbe species a released function from ofrine the the aerosol, have initial was been NO found releasedCl to in our smogsured chamber. Time by profiles various of techniquestical the (chemical absorption halogen ionization spectrometry species mass coupledraphy spectrometry, with of di a hydrocarbon multi-reflection tracersand cell and for flame gas ionization Cl chromatog- detection). and Measurements OH, are employing compared cryogenic to preconcentration calculations by the Experiments on saltchamber aerosol under with tropospheric di oxides light (NO conditions withmixing various ratios, initial even contents in of samples nitrogen with lower bromide contents such as road salts. The Abstract Atmos. Chem. Phys. Discuss., 14, 10135–10166,www.atmos-chem-phys-discuss.net/14/10135/2014/ 2014 doi:10.5194/acpd-14-10135-2014 © Author(s) 2014. CC Attribution 3.0 License. The influence of nitrogen oxidesactivation on of the bromide and chlorideaerosol in salt S. Bleicher U. Platt 1 2 3 4 * Received: 6 March 2014 – Accepted: 11Correspondence March to: 2014 C. – Zetzsch Published: ([email protected]) 22 AprilPublished 2014 by Copernicus Publications on behalf of the European Geosciences Union. 5 20 25 15 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | + (R8) (R9) (R1) (R2) (R3) (R4) (R5) (R6) (R10) (R7a) (R7b) (R13) (R14) (R15) (R12c) (R11a) (R11b) (R12a) (R12b) 0.85 and ∼ with OH (e.g. 2 Cl, Br) can be activated by molecules is under discus- = x is photolyzed rapidly (photolysis rates can (R11)(overall) is reported to be ectively deplete ozone catalytically due to its / 2 ff 10137 10138 O O 2 2 H H + + during nighttime and its hydrolysis and dissociation to H M 5 (aq) 2 2 + O 2 3 X XY(aq) O 2 3 Br O + → → + 5 − + − − HNO 2 O X Y 2 2 O 2HNO XO → + + N O + OClO 2ClO HOX HOX(aq) + + . →

+ M 2 → H H 2 − Br → → 2X → + O

2 X 2 XO on aqueous surfaces (George et al., 1994; Schütze et al., 2002): O 2 + + X (aq) 2 + 2Br + O HOX(aq) Cl 3 − 3 H → + + → → H NO OH + ClO O + + → 3 HO → 2 + hν + + 5 + O + 3 2 → − (aq) + Br ClOO BrCl (aq) O + 3 3 2 2 2 During the daytimeatoms, the which gaseous rapidly react halogen with molecules ozone: areX photolyzed to two halogen X X surfaces, which was alsosuch observed ice surfaces in and nature aerosolby droplets (Pratt the can et be production caused al., ofand by 2013) N nitrogen NO The oxides, in acidification particular of NO is known that theand pH-value (Betts Zetzsch, and 2001) Mackenzie, and 1951;impact Fickert the on et the bromide al., activation to 1999; cycles.sion. chloride Especially da Recently, Lopez-Hilfiker the ratio Rosa et role (Behnke al. of (2012)of et NO and gaseous al., Wren chlorine et 1999) and al. have (2013) bromine an found molecules the production from NaCl/NaBr-doped and acidified ice Hippler et al., 2006): NO halides into reactive halogen species (e.g. halogen oxides), are not fully understood, it N Nitric acid can also be formed during daytime by the reaction of NO However, the first halogen moleculesdissolved (indicated by ozone X (aqueous or species Y Hunt are et indicated al., 2004): by “aq”) even duringO nighttime (e.g. O XO HOX(aq) self-reaction: 2BrO The formed bromine oxide is known to e → → HOX(aq) The branching ratio offormation Reactions of (R11a) OBrOHowever, and under Br the is influencebe considered of found to light in Br be thedepletion unimportant Supplement). of ozone In (Atkinson is the even etand faster. mixed Then al., an case BrO intermediate 2007). may of OClO alsoClO: additional molecule. react OClO with activated ClO in chlorine, to turn the form reacts a with BrBrO chlorine atom atoms back to → OClO XO radicals may also reactare with the hydroperoxyl driver radicals of to Reaction form (R7) hypohalide after acids,XO their which uptake into the aqueous phase: HOX 5 5 10 15 20 25 10 15 20 25 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ; 1 − 7.8 s = 1 (R20) (R21) (R16) (R22) (R17) (R23) (R18) (R19) − a K Cl due to (Cox and 2 = molecule 1200 W, Osram 3 × cm Br or X,Y and Cl budgets, both Br. The production of 12 x = = − on halide aqueous phase value of HOBr (p 10 5 a Cl. One reason is the faster × O K = 2 Cl and Y = alters the NO 2 8.6 at 274 K for HOBr, Shilov, 1938). = Teflon chamber (FEP 200A, DuPont) with a Br than for X K 3 = − 3 10140 10139 et al. (2008) in the polluted subtropical marine (aq) ff NO + . In this chamber we are able to simulate the mixed + H 1 + − (Finlayson-Pitts, 1983). A further minor source is the + Br is favored over X H (aq) (aq) 3 = − 3 − + (aq) , which accrues in the reaction of XO and NO (aq) 3 Cl − − NO M + Cl NaNO Cl + 2 + (aq) 2 + + 3 Br − HOX(aq) Cl

XNO + XNO → is possible as well (Behnke et al., 1997), but at a slower rate compared BrCl(aq) 2 NOCl HONO 2 (aq) → O (aq) → Br 3 2 → − → → H M ect the troposphere’s oxidizing capacity. Recently, a few hundred ppt of → Br ff (aq) + O + 2 XNO − (aq) + 2 H X − NaCl have been measured in the middle of North America (Boulder, Colorado) by (aq) have a faster uptake to the aqueous phase than HOX (e.g. Hanson et al., 1996; → (aq) + + NO 2 Br − + 3 3 3 5 + + 2 Cl O Additionally, heterogeneous reactions are known to influence the halogen chem- 2 2 2 on halide surfaces: Cl ClNO Thornton et al.important (2010) class and of over heterogeneous continentalexample such reactions Europe as provides the (Phillips well-known chloride conversion etsurfaces: of to One al., molecular example the chlorine 2012). is to aqueous the bromine A phase on well-known further halide conversion of molecular chlorine to bromine of which a at 273 K for HOCl,Additionally the (Morris, release 1966), of X,Y andwater a phase p reaction constantscan (Fickert be et accelerated al., by 1999). XNO Lewis, 1979; In Sander polluted et areas al., the 1981): activation XO release of one moleculea containing self-accelerating two autocatalytic halogen activationplosion” atoms of (Platt into halides and the and Janssen, gasthe thus 1995; phase halogen is explosion Hönninger results occurs et called in ratheruptake al., “halogen for of X 2004). ex- HOBr Under compared remote to conditions HOCl, due to the higher p The aquatic uptake of one molecule containing one halogen atom and the subsequent BrCl(aq) Br XNO and the formation ofet HONO al., from 1997): an uptake of NOCl intoNOCl the aqueous phase (Scheer aqueous and gaseous chemistryBleicher, of 2012). the The tropospheric lightHMI1200GS) mixed of below boundary the seven layer chamber medium (see is filtered also pressure by arc glass lamps (Schott, Tempax, (7 3 mm thickness) 2 Instrumental setup and methods The experiments were performed ina a 3.7 surface m to volume ratio of 3.5 m XNO Uptake of ClNO to NOCl (Frenzel et al.,1998).NO The most important sourcereaction of of NOCl is chlorine the atomsDeMore reaction et with of al., 2 nitrogen 1997). monoxide (2.19 George et al., 1994): N XNO Deiber et al., 2004) and its hydrolysis also provides protonsistry needed (summarized by by Reaction Rossi, (R7). 2003).leads to E.g. a the direct uptake transition of of N the halides to gaseous photolabile reservoir species (e.g. This heterogeneous activation mechanism was originallyFinlayson-Pitts proposed et al. and (1989) investigated and by confirmedBehnke in an (1992) aerosol and smog chamber Behnke byin Zetzsch et a and al. wetted-wall (1993, flow-tube 1997) byClNO2 Frenzel for has et chlorine been al. and observed (1998),boundary investigated by including layer. in Ostho It X detail alters. The production of ClNO 5 5 10 10 20 15 15 20 25 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | and x 99 %, erential > ff ) with high 10 − 10 ) and measured erential pressure ) and a molybde- 50 %. The nebu- 2 ff 2 × erential optical ab- > 5 ff and HONO albeit at ∼ of chloride and 1.5 to 3 1 − 0.90 between 300–405 nm) ∼ NaCl (Sigma-Aldrich, 1 R − ). We have to note that sedimented 3 − ciency of mechanism (a) is a scientific m ffi 3 10142 10141 in mechanism Reaction (R7), (b) the light loss due 2 ects on the chemistry are also discussed in a recent ff ) as compensation in all experiments where DOAS was 1 Kr neutralizer and a condensation nucleus counter (TSI, − 85 0.995 between 335 and 360 nm) to achieve a path length of . According to the Köhler theory (e.g. Wex et al., 2005) the con- R > 1 . A slight overpressure (around 0.5 Pa), measured by a di − 4 statistical error of a single spectral fit was taken as an estimate of the of bromide. The particle size distributions were measured by a particle 1 σ − Kern DKRF400X-P). The salt aerosol was generated by an ultra-sonic neb- + was injected from gas cylinders (Rießner Gase, 101 ppm in N -time) of ca. 5.5 h in our chamber by neglecting a coagulation loss for these large 800 ppt. The integrated output light intensity after passing the White cell is propor- 2 ∼ During the experiments, the bromide concentration was varied for two reasons: (a) The temperature and the relative humidity (RH) were measured at three heights 500 ppb of CH 0.01 % NaBr) and various concentrations of NaBr (Merck, Suprapur) ranging from /e of tional to the integrationTo time minimize light of loss, the we DOASbromide used spectra content low (300 and aerosol mmolL thus concentrationsapplied. (lwc influences Ozone the was sensitivity. generated by(Rießner an electrical Gase, discharge 99.996 (Sorbios, %) GSGNO and 12) in measured oxygen by UVby absorption chemiluminescence (Ecophysics, (Thermo CLD Scientific, 88p,a CLD 49i). photolytic 700) converter with (Ecophysics, two PLC types 860, of mainly converters: sensitive to NO 288 m. This led totively. a The mean BrO 4 and OClOdetection detection limit. limit Optional of broadband 40 aluminum pptwere mirrors and ( used 150 ppt, to respec- observea shorter a light larger path. variety For of ClO species the chosen e.g. light ClO, path O of 32 m results in a detection limit with chloride to BrCl insteadto of the Br Mie-scattering bysorption the spectrometer aerosol (DOAS). within the Whilequestion light the (b) path e has of ain the technical detail di origin. by Buxmann Theoverview. The et DOAS instrument al. system was (2012) hasa equipped and with already base a Buxmann been length multi-reflection (2012), of described mirrors cell and 2 (Layertec, (White, m here 1976) diagonal with we through give the a chamber short using highly reflective dielectric siderable uncertainty for thechamber computer set-up modeling and applied thepaper wall in by e Hoch this et study. al. A (2014). comparable the influence of bromide on the activation of chloride by recombination of HOBr(aq) aerosol, although not measurable, contributes to the chemistry, which results in a con- to the liquid water content (lwc, given in m about 400 nm, with300 resulting mmolL ion concentrationsclassifier of (TSI, 6.1 3071) molL with a 3020) with custom written software forfor scanning multiple the charges size (see distributions and alsoFig. for Balzer, correction 2012). 2. Typical Higher particle salt distributionssedimentation are concentrations (Siekmann, shown would in 2008). lead For(1 to the bigger given particles particle andparticle diameter sizes. thus we Since to found the particles a a were faster lifetime liquid at the given RH, their total volume equals ulizer (Quick Ohm QUV-HEVlized FT25/16-A, stock solution 35 of W, bi-distilled 1.63< water MHz) contained at 1 gL RH 0.42 to 86.4 mgL centration of salt in the stock solution determines the aerosol particle diameter to ∼ pressure sensor (Kalinsky Elektronikdiminished DS1) the and intrusion controlled of ambient byoverpressure, air. a the Since volume the clean specified chamber air above volume was flowby is measured knowing system, dependent at the on 0.5 dilution Pa the flow di andin measuring the the dark depletion of (Bendix an hydrocarbon inert analyzer, tracer model like 8201) methane or n-perfluorohexane. (Driesen appendix for photolysis frequencies). Thephase lamps after of ignition this lasting solara for simulator shift three have of a minutes the heat-up spectrum. and To causing avoidshuttered an for an influence the increase on first the minutes of experiment, after intensityheat-up. the ignition. solar The and The simulator chamber shutter was was was filled removed promptly with after zero the air, containing less than 500 ppt of NO and a water layer of 2 cm depth to achieve tropospheric light conditions (see Fig. 1 and 5 5 25 20 10 15 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ) 1 (1) − s 3 is the − 1 D) pho- − 1 at typical 10 s 1 1 × − − 7.1 at ozone mixing = 1 ) − 2 values derived from 1 molecule loss process and Re- -perfluorohexane) we − 3 is exponential and ne- 3 (NO n 0.015 ppbs s j 2 3 ∼ cm − 12 10 − ) (2) × 10 n , × 6.7 ) (3) as parameters. Using the obtained n ... = , 0 ) 2.7 = 1, actinometry ( t 2 ] -pentane, 2,2-dimethylbutane, 2,2,4,4- ... = = 2 2 n 1 i 1, k (NO = j i ,( i 10144 10143 as a simplification (which is reasonable since ) and [Cl ,( i i 2 (Cl j [Cl][HC] i Cl, [Cl][HC] k i : − Cl, t count of HC species) to get the both unknowns [Cl] and [OH] i k is the source and the I reactions with hydrocarbons are the = we normalize the previously measured lamp spectrum by the 2 i c n X 1 + − − s 2 ] 3 2 − [OH][HC] i )[Cl 10 [BrO] 2 1 OH, × k k (Cl 2 − represents other ozone sinks and j actinometry, since the chlorine molecule has a broad absorption maximum in 2.4 = 2 = species. 2 c ] = i x = 3 ) t linear equations ( photolysis were found to agree with NO 2 t d -mixing ratios in the chamber and a humidity dependent loss due to the O( t n d Additionally used in a measurement campaign was a chemical ionization mass spec- Hydrocarbons (HC), which can be important sinks for reactive halogens, were mea- The measurement of the ozone temporal variation allows us to estimate the BrO 2 d[O 3 d (Cl d[Cl] d[HC] for all experimental times − of NO concentration assuming that Reaction (R10)action is (R11a) the is dominant the O rate-limiting step: num converter (used in the CLD 700 instrument), which is sensitive to a broad spectrum trometer (CIMS), which wasspecies. described by All Kercher instruments, ettubes except al., as 2009 the short to GC, as observe possible werebromine non-radical with compounds connected like (1–3 m BrO to length). or the Chemical HOBr on conversion chamber instrument of and highly by inlet reactive Teflon surfaces is a well known chlorine photolysis frequency (Fig. 1). The Cl within an acceptable deviation of less than 6 %. where photolysis of Cl sinks of atomic Cl.glecting Assuming the that time the dependencethe photolytic HC of decay are HC of in Cl exponential function excess) of we time are with ablej to solve Eq. (3) analytically. The solution is a bi- ozone photolysis. In this spectralthe region NO the chlorine actinometrythe is UV more with precise its maximum than the at behavior 330 nm of (e.g. chlorine Maric atoms et basically al., follows 1993). the In equation: the irradiated chamber, This technique was alsoflux in employed the to UV determine rangeon by the the chlorine solar actinometry. chemistry UV simulator’s by light actinic below forming photon 330 nm excited has state a oxygen high impact atoms and hence OH radicals by sigmoidal functions. The time derivatives ofof the fitted functions allow us to solve the set tetramethylbutane, toluene) andcould an indirectly determine inert theknown dilution concentrations as standard of the OH radical ( in and clock selected Cl method experiments radicals. (RCM, onlyThe This Zetzsch since measured method and the HC is Behnke, HC time 1992). species profiles It influence were was the interpolated used halogen by chemistry. appropriate exponential and/or O tolysis channel of ozone. Tothe estimate separately the BrO measured mixing dilutionfrom ratio the rate from ozone Eq. (but curve (1), not by we smoothing the eliminated it wall using loss) the Savitzky–Golaysured and algorithm. by removed the gas noise chromatographyionization (Siemens detector, Sichromat with 2,the custom Al-PLOT decay built column of nitrogen a 50 m, cold special flame trap injected enrichment). HC By mixture measuring ( where second order rate constant ofnated Reaction chamber (R11a). we In observe an aratios empty, but typical below humidified ozone 1 and ppm. loss illumi- This of value max. includes 0.02 ppbs a wall loss of max. 5 5 20 15 10 20 25 15 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | x 1 of − OH 3 − + m X 3 → m , and NO ciently Cal- x 11 ffi − 10 × and contains particles 3 − NaCl into a humid cham- mixing ratios. Although the m mixing ratio of 500 ppt. The 1 x 3 − 2 after 30 min of illumination. As m -mixing ratios we discuss four 1 9 x , containing 7 − − 3 − 10 101 325 Pa, and a RH of 60 %. The × = mixing ratios were adapted to the con- 700 ppb) and UV radiation of our solar 58 ppts x p ∼ − 0. The loss of ozone accelerated in the day mixing ratio of 515 ppt in case of its entire Cl) results in a good agreement with the ex- NaBr and 1 gL -case. Before starting the experiment, by in- x = = x 1 t 10146 10145 − 293 K, = for X 1 T − chloride in the aerosol phase according to the Köhler 1 − represents wall losses. The gas phase was initialized with 60 %) and ozone ( 1 bromide. The model in its original state overpredicts the con- > − s 1 − 5 − Br and 0.02 s , while the ozone and NO 4 = 10 × could allow a maximal Br CH experiment with DOAS , we found that the addition of two reactions to the model HOX in the dark. and 6.1 molL 1 3 x 2 for X − 1 1 X 1 − − − cients and references, is available in the Supplement. Photolysis frequencies → ffi Q + 0.12 s = We switched the solar simulator on at We compared our measurements to simulations with version 3.0 of the chemical box 0.01 ppbs k time conditions and reached a peak value of 300 mmolL theory. The particle concentration reachedliquid 1650 water. cm The particletration size per distribution cm isactivation. shown The in nighttime Fig. chemistry(508 2a. ppb), which (R1, The induces R2 bromide a completeozone concen- and mixing loss R19) ratio of was the started nearly initial− constant by NO with injection a (dilution-corrected) of loss ozone rate of less than high levels of humiditysimulator. ( Therefore the possibility ofadditional remaining wall organic release from of formernebulized BrO experiments a was and stock minimized solution duringber of the (50 86.4 % mgL actual rel. experiment. humidity Here at we 293 K), which should result in a bromide concentration of From a series ofexperimental runs experiments in with detail: two variousparameters experiments except initial (which are their NO quite initialexperiments comparable with NOx in the almost mixing CIMS all ratio) instrument. with the3.1 DOAS instrument and Low two NO The first experiment (Fig.jection 3) is of a the low salt NO aerosols, the chamber was cleaned photochemically by introducing the system. 3 Results and discussion constants are fast, this approximation is conservative since it does not add halogens to ( perimental data over a wide range of initial ozone and NO 500 nmolmol ditions of individual experiments. Thechloride initial and composition of 0.3 molL the aerosolcentrations was of 6.1 HOX molL species onthe the cost DOAS of and the XO thewalls compared act CIMS to as a the experiments source results of (seeiments. gained active After from Sect. halogens testing due 3). various to possibilities theHOX We to deposits assume of include HX a that from simplified previous the wall exper- source chamber Q, such as ficiencies. All photolysis valuesage are of the scaled lamps with (amore a new than lamp single 600 has factor ca.were operating which four kept hours). times represents constant more during the The the intensitytion photolysis whole than term model an frequencies of simulation. old and For 1.3 lamp ozone, with the a constant scaling destruc- factor scenario in the modelmodeled was aerosol set has to awith liquid water a content radius of ofchemistry, 5 we 0.2 µm. activated In chlorineand addition and in bromine to the multiphase aerosol the particles. chemistry standardrate A in coe list ozone, of the methane, the gas chemical HO phase reactionswere used calculated in this for study, including theshown in solar Fig. simulator 1 by and building the a cross sections scalar of product the of molecules the weighted by spectrum the quantum ef- it is important to keep the inlet short, asmodel it CAABA/MECCA was (Chemistry demonstrated by As Liao Aculating et Boxmodel the al. Application/Module (2011). E Chemistry ofrun for the 144 min, Atmosphere) with by output every Sander 6 s. et To represent al. our laboratory (2011). conditions, The the “LAB” model was problem and can even result in a complete loss of BrO (Neuman et al., 2010). Therefore 5 5 25 20 15 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | x 3 2 to − de- 3 cient 3 NaCl cm ffi 4 1 − 10 × mixing ratio 2 -mixing ratio of x might be caused -derivative (slope 3 1 − species. The model x -mixing ratio of 78 ppb x 60 ppb, once we started ∼ 3, and the shutter was still in comparison to BrCl, was − 2 85 ppt is coincident with the O reached a plateau of about 40 ppt, ± 2 ; its distribution is shown as curve B in 3 300 − would allow a maximum Br = m 1 3 − 10148 10147 m 10 mixing ratio of 500 ppt must have been su − 2 10 case and between 0.5 and 2 ppt in a moderate NO × x scenario. The dark chemistry started with an injection of x set of 200 ppt was subtracted, since it was obviously an arte- ff hydrolysis (mechanism Reactions R16–R18 and R7). After the 3 erence to the observed ozone loss of 55 ppt s ff . According to the model, a large fraction of bromide was activated experiment, we injected aerosol into a purged and humid cham- 2 x NaBr. The aerosol reached a particle concentration of 1.8 experiment with DOAS ions needed by Reaction (R7) via Reactions (R2) and (R3). 1 x − + . The di , causing the exponential loss of the previously constant NO 1 3 − was nearly consumed, the activating mechanism changed to Reactions (R14), radical, had an almost constant, but slightly falling mixing ratio around 50 ppt, anti- 2 2 To decide about the dominant activation mechanism, we show a simulation run with 770 ppb O of 150 ppb. The solar simulator was switched on at minute As in the lowber NO (55 % rel. humidityand at 86.4 293 mgL K) by nebulizingwith a a stock solution liquid containing water 1Fig. content gL 2. of The bromide 5 content of3.65 300 ppb, mmolL while the chloridein content the would case allow a of maximum fullcorresponding Cl to halide a activation. Figure high-NO 5 shows time profiles from this experiment, by the low amounts ofare sinks below in 0.5 ppt theatmosphere, surrounding in measured air. a by Typical low RCM OH with values NO injected in HCs. our chamber 3.2 High NO two orders of magnitudewhile lower. the Furthermore, peak of Br gaseousHO HOBr was around 70 ppt.correlated The to major HOBr. precursor The of total HOBr,consumer loss the of of methane methane could was be therine calculated OH atoms to had radical 12 a with ppb. minor its Theis contribution main mixing formaldehyde, here. since ratio One it of important is 5–10 a oxidationing ppt, product main ratio while sink of was chlo- for methane bromine calculated atoms to to be form a HBr. The plateau HCHO of mix- 300 ppt. The high OH levels are explained (R15) and (R7). Thisof is indicated the by aerosol proton pH.chlorine consumption, With to causing a an the maximum accelerated model ofof rise we below chlorine 5 might atoms ppt roughly was ClO(not BrCl, and quantify shown), which below the despite 3 reached ppt extent the 2–4 OClO. ppt lower of The photolysis here, activated main frequency while precursor of the Cl mixing ratio of Cl NO directly through BrNO via mechanism Reactions (R6) and(e.g. (R7) Fickert needs et an al., acidificationto 1999). of activate The the the NO aqueous entire phase provide bromide the via H Reactions (R16)–(R18) or to form enoughthe HNO same starting conditions inimportant Fig. 4. trigger Herein species plotted vs. areplausibly the the reproduces total calculated the mixing mixing experiment ratios in ratio of termsand of like the gaseous the loss ozone Br of decay, the NO BrO mixing ratio tionship in Eq. (1) toof calculate 12 ppts the contribution ofby bromine chlorine to atoms, which the were ozoneconstants not loss monitored leading to during to a the ozone value experiment. lossmuch However, reaction faster due compared to to bromine. chlorine It (e.g. is Reaction well-known that R10 an and activation R12) of bromide and directly are fact remaining after the previousorganic, chamber purge. has During the been cleaningformaldehyde detected phase signal remaining in was below formthe the of mean salt formaldehyde detection aerosol by limitwith experiment. of the narrow In band DOAS-instrument. this dielectric The mirrors experiment,the (335–360 absorption the nm) for cross DOAS sensitive section whitemight detection of have of cell been OClO BrO. the was Since is measurable equipped indicatorremained within for below the an a same activation mean of spectral detection chloride. range, However, limit OClO this of species 150 ppt, and we may follow the simple rela- of the ozone time profile);pletion the peak maximum. of A [BrO] fractionin of the a observed previous BrO highbackground was level ozone released of by chamber 200 ppt the purgethe of chamber BrO-mixing without BrO walls ratio aerosol an in o the and chamber remained during as the dark a phase. stable Thus, from expected, the measured BrO concentration was correlated to the O 5 5 25 15 20 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ) 3 2 2 2 1 − after erent ff 2 544 ppt was still ± 2 according and BrNO after 100 s. 3 1.15 ppbs 2 2 species is the − from the XNO x 5 0, the loss of NO O (Soller et al., 2002) 2 = 3 t erent periods of halogen and XNO ff x and produce XNO is available in gas phase. For 2 2 to X and NO 78 ppt in the middle of both ozone mixing ratio, which reached its max- 3 ± 2 44 ppt (while the total BrO maximum of reached its maximum of 11.5 ppb 6 min ± while NO 2 5 O 2 10150 10149 (originating from the photolysis of HONO) was (which was converted to HONO on the droplet x x was consumed, we observed a rapid acceleration 2 case, the model reasonably reproduces the experiment by the model in Fig. 5. The slight increase of ClNO x 49.3%). Since this was a nighttime formation we assume . We performed two experiments to demonstrate di / , which is heterogeneously converted to ClNO 2 2 ). Both maxima can be related to di 5 1 − O 2 and Br 2 and XNO 513 ppt at the point of the second ozone depletion maximum. The OClO 2 1.25 ppbs ± − consumption. Once NO mixing ratio to a plateau of 1.5 ppb was observed afterwards. . The halogen atoms react with ozone and NO 2 to NO. In daytime conditions, after opening the shutter at 2 2 2 33 ppt was reached two minutes before). The ClO mixing ratio was 2770 ± Br, Reaction (R16) replenishes the bromide in the aerosol droplets by uptake and As well as in the low NO = concentrations Cl the beginning of illumination is correlated with the production of N the dark chamber, werect observed mixing bromine ratio in ofthe the 50.7% occurrence gas of phase mechanism (bothbromine Reactions isotopes may trigger (R4)–(R8). in the Such the auto-catalyticconditions, nighttime cor- halide we activation formed observed cycles a gaseous during rapid increase dawn.imum of In of the daytime Br 6.1 ppb afterlater. 7 min Both of maxima illumination. occurred Cl whilestill NO present in high mixing ratios. This verifies the calculation of the halogen species mechanisms of halogen activation andperiments conversion where of done active on halogen aa species. single Both day, fraction causing ex- some of remainingFig. old reaction 6). products aerosol and In from theseruns the early and experiments first thus the experiment contained chambersurface to was HC during not and influence the cleaned NO the before aerosol second the injection chamber run for the (see first run). After the injection of ozone into X dissociation. In a comprehensive view,formation the of sink nitrate for in most the NO droplets. 3.3 CIMS runs A CIMS measurementspecies, may i.e. give X information about the direct precursors of X, XO Also a continued lossis of predicted chloride by during the nighttime model.and In by NO daytime forming conditions almost both 30 nitryl ppbto species of are Reaction ClNO photolysed (R16). to The X leads photodissociation to of the XNO photolytic steady state of N following this pathway and a constant mixing ratio of 3.65 ppb of BrNO by the production ofon N the particle surface (Reaction R19). The model calculates a total loss of bromide self-reaction and reaction with ClO,consumed, forming and OClO. the After mixing 18the min, ratios NO the of ozone the was halogen totally oxides declined. A slightcompared to increase most of of thehalogen measured species oxides (Fig. species 6). are Thevalues simulated quite are mixing comparable ratios lower. of to This the ment, the may probably experiment, be by although caused the the by chamber OClO a walls. The higher consumption supply of of ozone bromine starts in at the nighttime experi- depletion maxima had a remarkable rounduct shape. of Since OClO ClO is and a BrOprecursors: direct (Reaction the reaction prod- decrease R12), of its BrO shapeof and can a the be coincident BrO explained rise by of profilemation ClO. the appears The by behavior trapezoidal consumption to of behavior of be the ozone a by atomic consequence Br of at stationary the beginning states and involving its its consumption for- by of the ozone loss, whichand reached 13 min two ( noticeable maximaactivation. after The 9.5 first min is ( mostcated likely by caused an by observed a BrO high841 mixing involvement ratio of of bromine 764 atoms, indi- at the first ozone depletionvalue maximum of with 4114 a rising tendency,mixing reaching ratio almost time twice series the with a maximum of 6907 of NO rapidly accelerated and the losspresent, of no ozone became halogen slightly oxides steeper.ror; could While however be NO we observed assume within thatthe the mechanism NO statistical Reactions (R16)–(R18) measurement was er- responsible for kept closed. Small light leaks around the shutter led already to a noticeable photolysis 5 5 25 15 20 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | , ff x OH + erence -levels. x ff measure- x . These follow 10 − 10 values. Even at low x × erences between the , where the salt was 1 ff 5 − -converter was constant ∼ x , the activation of chlorine is 0.63. The ozone loss depends − cases bromide and chloride is − Br x init + ] x species and the high XO mixing ra- x . Furthermore, the presence of chlorine 2 ln([NO and BrCl 10 ppb non-methane HC, measured by FID), × − < 10152 10151 Cl ect the maximum ozone decay linearly in the re- 0.223 , which results in an accelerated consumption of + reaction. cycle. This can also be seen by injecting HCs (red ff x 2 may occur already in the dark, driven by dissolved (8.5 ppb) remained in the gas phase after the light = 2 − 3 2 2 on halogen activation is not restricted to acidification, max NO erences are their bromide content and the liquid water x ) ff t + d + / ] H , the activation of halides from the solid phase is dependent experiments showed a strong activation of chloride even in mechanisms. Although bromide eases the release of chloride 3 x + x x . It caused a heterogeneous release of bromine (Reactions R20–R22) HONO ff ) in the night and daytime; in high NO → 3 O 2 mixing ratio. An overview of this dependence is shown in Fig. 7, where the H x + , XNO values, the model predicts faster ozone decay (red fit). We explain this di 2 2 x In all cases the activation of bromide was found to be preferred over chloride. An The relatively low CIMS-signals of both HO and bromine wouldas have methane significant in impact highly on polluted the coastal tropospheric regions. ozone Only level a as few well studies exist (e.g. Ostho XNO activated utterly by NO due to the equilibriumnot between necessarily Br dependent onsalt the showed. bromide High concentration,cases NO as where measurements on the road conditions concentration could of be bromide presentthey on was are roads, a in which possible source the are of de-iced lower continental by ClNO millimolar NaCl-salts range. in winter Such time; initial activation of bromideozone. to The acidification Br of the aerosolHowever, liquid the phase is influence often of provided bybut NO nitrogen leads oxides. also to a heterogeneous release of photolabile reservoir species (i.e. NO since HCs slow down theto ozone an depletion ozone by production scavenging ofdots). the Following the halogens the RO to model HX calculations andin one due can a define ppt a noticeable rangeozone. release from Moreover, of chlorine 0.5 this ppb overview ofactivation demonstrates in NO salt characteristic droplets di andthe salt pans dependence shown on in NO Buxmannon et the al. liquid (2012); water additionally layers to on the crystals. strongly on of thefunction initial in nitrogen Fig. oxides 7. mixing Modelgood ratio runs agreement as with with it similar the is startingNO experiments shown conditions at by (empty moderate the black and dots) blackby high fitting are HC NO impurities in in the lower ppb range ( a logarithmic curve: (d[O taken from commercial roadiments salt, without an a addition strong of ozone HC depletion were carried is out observed. at a Most lwc exper- of tial NO maximum ozone decay ofAdditionally 42 shown are experimental model runs runsshare is with a similar plotted initial common vs. conditions. chloride their Allmean concentration of initial diameter. our in NO The experiments the maincontent. stock di solution According and to a modelthe common calculations bromide particle and content experimental andgarded runs the range. (full lwc pink Even a diamonds) at bromide levels as low as 1.5 mmolL reactions. 4 Summary and conclusions Generally speaking, the result of an experimental run is strictly dependent on the ini- phase and canReaction occur (R23) on non-saturated duringwas aerosol the observed only. particle after (B) generation thement The aerosol must by supply injection the lead of for CLD(not to chloride the 700 shown), bigger by second instrument which run. particles, indicates with2NO a (C) the which 1 The molybdenum : 1-conversion NO NO and thus excludes the heterogeneous tios measured by DOAS led us to introduce the previously mentioned HOX to X was switched o out of fresh aerosol,a which production was of injected HONOseveral indicators in was for observed preparation the during ofhalted occurrence with the the of the stop aerosol subsequent Reaction of injection aerosol run. (R23): injection; period. (A) Also Reaction (R23) the There provides chloride production are to of the aerosol HONO photolysis. A large fraction of Cl 5 5 25 15 20 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | → M) + ( from the 2 2 NO + NaCl ratio on the / in the presence of 3 and HNO 2 -aerosol, J. Aerosol Sci., 24, 115– 4 SO 2 , 2007. Na / previously. The model in its current stage x http://opus4.kobv.de/opus4-ubbayreuth/files/1370/ 10154 10153 . . However, the influence of the chamber walls needs x has likely decreased by 30 to 50 % in Europe and North , 2004. 2 with NaCl solution: bulk and aerosol experiments, J. Geophys. 5 10.5194/acp-7-981-2007 O by Halide containing droplets, Atmos. Chem. Phys., 4, 1291–1299, 2 2 We would like to thank R. von Glasow, F. Siekmann and J. Wittmer for de- (last access: 1 March 2014), 2012. is consumed, the mechanism changes to HOX and precedes the activa- M), J. Chem. Soc. Faraday T., 1, 75, 2649–2661, 1979. x Diss.pdf and BrONO + ( + 2 2 and wet pure NaCl and wet mixed NaCl 5 10.5194/acp-4-1291-2004 -catalysed production of halogenated radicals, J. Atmos. Chem., 34, 87–99, 1999. O − 2 Once NO ClONO phase, J. Aerosol Sci., 32, S311–S312, 2001. ClONO doi: Ravishankara, A. R., Kolb,data C. for E., use andPropulsion Molina, in Laboratory M. California stratospheric Institute J.: modeling, of Chemical Technology Pasadena, Evaluation kinetics California, number 1–266, and 1997. photochemical 12, JPL Publication 97-4, Jet tolysis, Part 3. – Pressure and temperature dependence of the reaction: ClO acid solutions of bromine and bromate ions, Can. J.sis, Chem., 29, University 666–677, of 1951. Bayreuth,Bleicher available at: versity of Heidelberg, Heidelberg, Germany, 2012. plosions in smog chamber312–326, 2012. experiments above a model salt pan, Int. J. Chem. Kinet., 44, Br N 116, 1993. reaction of gaseous N Res., 102, 3795–3804, 1997. in einer Smogkammer, Ph.D. thesis, University of Bayreuth, Bayreuth, Germany, 2012. of the photochemical degradation of22, chemicals 1113–1120, in 1988. the presence of aerosols, Atmos. Environ., Jenkin, M. E., Rossi, M.spheric J., chemistry: and Troe, Volume J.: III EvaluatedPhys., kinetic – 7, and 981–1191, gas photochemical doi: phase data for reactions atmo- of inorganic halogens, Atmos. Chem. tion cycle via thereasonably protons reproduces provided chamber experiments by in NO vation terms and of its ozone dependence loss on and NO to halogen be acti- considered as a secondary liquid phase in the model in upcoming work. amounts of tropospheric NO America, it has(Hilboll increased et by al., more 2013),especially than which chlorine in might a the influence factor atmosphere,investigated the according of in to total future our 2 amount studies. findings. in This of should reactive Asia be bromine further since and the mid-1990 s et al., 2008; Phillips et al., 2012), which do not allow a global budget. Even though, Deiber, G., George, Ch., Le Calvé, S., Schweitzer,DeMore, F., W. and B., Sander, Mirabel, S. Ph.: P., Golden, Uptake D. study M., of Hampson, R. F., Kurylo, M. J., Howard, C. J., da Rosa, M. and Zetzsch, C.: Influence of pH and halides on halogen species in the aqueous Cox, R. A. and Lewis, R.: Kinetics of chlorine oxide radical reactions using modulated pho- Bleicher, S.: Zur Halogenaktivierung im deliquestzenten Aerosol und in Salzpfannen, Ph.D. the- Buxmann, J., Balzer, N., Bleicher, S., Platt, U., and Zetzsch, C.: Observations of bromine ex- Betts, R. H. and Mackenzie, A. N.: Formation and stability of hypobromous acid in perchloric Buxmann, J.: Bromine and Chlorine Explosion in a Simulated Atmosphere, Ph.D. thesis, Uni- Behnke, W., Elend, M., Krüger, U., and Zetzsch, C.: The influence of NaBr Behnke, W., George, C., Scheer, V., and Zetzsch, C.: Production and decay of ClNO Behnke, W., Scheer, V., and Zetzsch, C.: Formation of ClNO Balzer, N.: Kinetische Untersuchungen der Halogen-Aktivierung einer simulierten Salzpfanne Behnke, W., Holländer, W., Koch, W., Nolting, F., and Zetzsch, C.: A smog chamber for studies Atkinson, R., Baulch, D. L., Cox, R. A., Crowley, J. N., Hampson, R. F., Hynes, R. G., References unit 763. Acknowledgements. tailed discussions. We also thank the Deutsche Forschungsgemeinschaft for funding research Supplementary material related to thishttp://www.atmos-chem-phys-discuss.net/14/10135/2014/ article is available online at acpd-14-10135-2014-supplement.pdf 5 5 30 25 20 15 10 20 15 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | , over O on 2 2 , Nature, 2 with H , 2014. 2 : high pressure erent European 2 ff : simultaneous, in 5 NO O and ClONO + 2 , 2010. 5 O 2 10.5194/acp-5-3357-2005 erential Optical Absorption ff , J. Phys. Chem., 70, 3798– ◦ and BrCl via uptake of HOBr , 2012. 2 , J. Phys. Chem. A, 102, 1329–1337, 2 10.5194/amt-7-199-2014 , 2009. , and Cl 2 , 2012. , Br 10.5194/acp-10-6503-2010 2 10155 10156 man, D., Quinn, P. K., Dibb, J. E., Stark, H., ff 10.1029/2012GL051912 , ClNO by chemical ionization mass spectrometry, Atmos. 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A., Pöhler, D., General, S., Zielcke, J., Platt, U. and Janssen, C.: Observation and role of the free radicals NO 5 30 20 25 15 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | to red. ) compared to ff 11 − NaBr, resulting in 10 1 − × NaCl and 86.4 mgL 1 − 10160 10159 ). 10 − 10 × Measured actinic photon flux in comparison to the sun in mid summer in Germany, Initial particle size distributions of the experiments discussed below. Both aerosols were a common maximum at nearlythe at DOAS 400 instrument, nm. where Run the Athe particle Mie was concentration scattering. one was The of kept content therun lower of first B to liquid aerosol (5 water test experiments was the with thus light lower loss in by run A (7 Fig. 2. calculated by Tropospheric Ultraviolet &1999) Visible and Radiation to Model a (TUV,for Madronich previous 15 and publication years. (Palm Flocke, The et glass al., filter 1997) is with subject a to solarization, glass which filter moves that the had UV-cuto been in use Fig. 1. generated from the same stock solution of 1 gL Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | has

2

4 3 ) s / b p p ( t d / ] H C [ d , t d / ] O [ d 1 2 3 4 0 0 0 0 0 . . . . 0 .

0 0 0 0

0 - - - -

2 2 3 ) t p p ( ] O H , r B O H , O r B , O N , O N r B [ 0 0 0 0 0 0 0 0 0 0 5 4 3 2 1 0 0 0 5 0 0 0 2 4 6 O r 0 - - - r B B 0 0 ) O t 0 1 H 4 to HOBr after the NO p scenario. A part of the BrO 2 p 2 (

3 x O O s l t e H i 0 t c 0 d 0 8 d e / C 3 ] p / 1 4 s ]

H X 3 O r C [ B 0

d 0 s O 5 0 u 2 [ 3 1 o e O s d t N n a r d o / g 0

] B 0 r ) 3 2 0 o t 1 O 2 [ 1 n a l d i H O u p N m i

m s 0

r ( 0 9 a

l o s 8 7 6 5 4 3 e O

r H p l o s o r e A 0 m 10162 10161 i 6

B

t X

3 O O ) 0 0 0 d O 2 3 l e O N N r C u s O a e m 0 ( 0

5 2 1 r O O r r B

B B

) 3 2 1 0 1 2 - - n 0 0 0 0 0 0 i 0 0 0 0 0 0 0 0 0 0 0 0 m 2 0 1 1 1 1 (

1 1 2 1 1 4 3

1

O

-

e

H

X

X 3 m i ) t p p ( ] O X [ 3 ) b p p ( ] O N , O [ t l O C r N 2 r l B B 0 C r 5 B O 2 H O N 0 species coming from the loss of bromide of the liquid phase. The modeled BrO 2 1 0 3

x 0 0 0 0

1 1 1 1

) t p p ( o i t a r g n i x i m Model calculation of the experiment shown in Fig. 3. Time profiles are plotted in the Activation of bromide and its impact on ozone in a low NO almost completely been consumed andbe is seen in indicated the by right a figure. fast consumption of protons as it can Fig. 4. left figure, whilegaseous in Br the right figure the data of the first 30 min is plotted against the gained reaches a stationary stateand at confirms 350 a ppt low after level of 35The OClO min change of with 3 of a ppt, the well slower below activation decrease the regime detection than during limit the of “day experiment the time” DOAS from instrument. BrNO mixing ratio (200 ppt) waswas subtracted stable under as night an time artifact conditions. from the previous chamber purge, since it Fig. 3. Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | is still x species. x begins in the dark 2 almost imperceptible: the . 2 1 − s 4 − scenario. Although the values of 10 x × . A rapid loss of ozone was observed 2 and XNO 5 O 10164 10163 2 under light conditions, thus forming the observable XO 2 scenario with a large activation of chloride. The loss of NO x Model calculation of halogen activation in a high NO mixing ratio raises right after the day time conditions are switched on while NO High NO 2 ClNO ozone depletion are comparable tobe the explained experiment, the with simulation wall ismide sources 3–5 in min from the delayed. previous This liquid experiments. can phaseratios A as would higher observed. explain simulated In a the content faster logarithmic of consumption scale of bro- is ozone the and photolysis of higher ClNO OClO mixing Fig. 6. Fig. 5. after the consumption of NO The remarkable round shapeBrO of and OClO ClO, which can are be both explained trapezoids. by the time profiles of its precursors available and declines after with its photolytic life time of 3 and can be explained by the production of N Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | x 1 − NaCl 1 − as a prod- (road salt) x 1 bromide and − 1 − and HOBr) and 2 . The open symbols are 9 , red circles – 0.3 molL − 10 − 10 concentration for 1 gL × 10 x was heterogeneously converted × x were reached while NO 2 , cyan dots – 5.2 mmolL 9 − and Cl 2 10 × bromide and lwc 5 10166 10165 1 bromide and lwc 5 − 1 − bromide and lwc 5 1 − , green triangles – salt pan experiments from Buxmann et al., 2012, and additional VOC injected, blue triangles – 1.5 mmolL 10 10 − . The maximum values of Br − 1 − 10 10 s × 3 × and HOCl). The chamber contained a sum of 25 ppb of HONO and NO − erent bromide contents and variations of other parameters. The full symbols 2 ff 10 ers from the experiment due to VOC impurities in the zero air which slow down × ff , orange asterisks – 52 mmolL 2 9 − = , ClNO 2 CIMS measurement of HONO and the direct precursors of BrO (Br 10 Dependence of the maximum ozone loss on the initial NO × (HONO) model runs with initial parameters correspondingto to the the full experiments. black The circles, blackthe while curve model the was red fitted di curve wasthe fitted halogen to chemistry. the The open salt black pan circles. experiments In are the slowed low down range due to low rel. humidity. bromide and lwc 5 pink diamonds – 0.03 molL lwc 5 Fig. 7. ClO (Cl to HONO. Itsj decay during daytime conditions suits the measured photolysis frequency of from ambient air impurities. During the aerosol injection, NO uct of HONO. Fig. 8. are experiments: black circles – 0.3 molL aerosol with di bromide and lwc 5