Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ” to X 2 that has 2 1 within the instru- 2 environments which x measurements and (2) , Higher PANs). We ap- 2 0.4 s for our instrument) 2 2 ∼ , and L. J. Carpenter etc. A range of explanations exist , BrONO 2 2 1,2 NO J , , IONO 3 2 concentrations such as Antarctic, the remote , J. D. Lee NO 28699 28700 x 2 3,4 O 3 selectively. Here we explore in the laboratory the measurements from the thermal decomposition of 2 2 , CH 5 O concentrations than might be expected from steady state 2 into NO followed by chemiluminescent detection of NO be- 2 2 , P. Di Carlo ,N 2 1,2 at low concentrations is non-trivial. A variety of techniques exist, 2 NO 2 (HO 2 , M. J. Evans : NO ratio i.e. the Leighton relationship. We find that there are significant in- 1 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. Wolfson Atmospheric Chemistry Laboratories, Department of Chemistry, University of York, NCAS, School of Earth andCentre Environment, of University Excellence of CEMTEPs, Leeds, Universita’ Leeds, degli LS2 studi 9JT, UK di L’Aquila, ViaDipartmento Vetoio, 67010 di Coppito, Scienze Fisiche e Chimiche, Universita’ degli studi di L’Aquila, Via Vetoio, ing prevalent. Historically this conversion hashowever used this a has catalytic been approach plagued (Molybdenum); withbased interferences. on More recently, UV-LED photolytic irradiation conversion ofto be a robust reaction there cell have has been been a used. range Although of observations this in appears low NO with the conversion of NO Abstract Measurement of NO have measured higher NO analysis of simultaneously measured NO, O in the literature mostthat of is which focus able on to an convert unknown NO and to unmeasured NO “compound measurements: explanation for an apparent missing oxidant? C. Reed 1 Heslington, York, YO10 5DD,2 UK 3 L’Aquila, Italy 4 67010 Coppito, L’Aquila, Italy Received: 6 October 2015 – Accepted: 7Correspondence October to: 2015 J. – D. Published: Lee 23 ([email protected]) OctoberPublished 2015 by Copernicus Publications on behalf of the European Geosciences Union. interference on the photolytic NO and expand the parametric analysisreadily to to other NO atmospheric compounds that decompose Interferences in photolytic NO Atmos. Chem. Phys. Discuss., 15, 28699–28747,www.atmos-chem-phys-discuss.net/15/28699/2015/ 2015 doi:10.5194/acpd-15-28699-2015 © Author(s) 2015. CC Attribution 3.0 License. peroxyacetyl nitrate (PAN) withinof the the photolysis PAN decomposes cell. withinference. We the We find instrument parameterize that providing the approximatelysource, a decomposition 5 the potentially in % significant ambient terms inter- temperature of and the a temperature mixing of timescale the ( light ply these parameters toinvestigate the the global output impact of of this a interference on global (1) atmospheric the NO model (GEOS-Chem) to ment’s photolysis cell may give an explanation for theNO anomalously ratios high without NO having tocoupled invoke novel to chemistry. instrumental Better instrument designs characterization, which reduce the heating within the cell seem likely terferences in cold regions with low NO the NO Southern Hemisphere and theinstrument upper specific, it troposphere. appears Although that this the thermal interference decomposition is of likely NO been reported in remote regions, and would reconcile measured and modelled NO 5 10 15 20 25 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ) is C 3 ◦ (1) . x (R3) etc.) x 2 NO 2 plays a cen- x . This exploits 3 , due to the rapid 2 on aerosol surfaces ) with NO (Dalsøren 2 5 O which is predominantly , HONO, HO 2 ), carbon monoxide (CO) 5 x 4 (Kley et al., 1981). O 2 2 and RO (Leighton, 1961), in Eq. (1). 2 ,N itself poses a public health risk φ 3 and PAN (Reactions R4 and R5) 2 from polluted to remote regions is 2 x . NO 2 to form NO M (R5) is a climate gas (Wang et al., 1995), ad- 3 100 ppb (parts per billion) next to roads + 3 O (R4) 2 > 2 C (Kleindienst, 1994). ◦ et al., 2006), and QCL – Quantum Cascade H 28701 28702 NO ff 2 + 26 • − P) (R1) 3 C(O)O 3 varies from with OH and the hydrolysis of N O( C(O)OO x 2 3 CH is removed from the atmosphere on a timescale of around + x species in the remote atmosphere have been made over the  CH x M (R2) NO M + → → + 2 3 2 2 φ O and the reaction NO and O O NO = 2 + NO →  + • ] 3 + and is lost by its reaction with NO 2 2 into steady state and assuming that these three reactions are the only M • O 410nm) and peroxy-acetyl precursors such as acetaldehyde) and are subsequently 2 but includes small contributions from NO O 2 OH  + ] x 2 NO < + [ ( → P) 2 3 NO cient, because NO NO hv [ NO 1 O( NO j ffi + CHO C(O)OO + k 2 3 3 + + The concentration of NO During the daytime there is fast cycling between NO and NO Measurements of NO = 2 3 versely impacts human health (Mauzerallto ecosystem et damage al., (Ainsworth 2005; et Skalska al.,is 2012; et produced Ashmore, al., through 2005; Hollaway 2010) the et reaction and al., of leads 2012). peroxy It radicals (HO and volatile organic compoundsNO (VOCs). with HO It is(Stieb both et produced al., through 2002). the Thus understanding reaction the of sources, sinks and distribution of NO tral role in theand chemistry hydroxyl of (OH) the radical troposphere, concentrations. O mainly through its impact on ozone (O and Isaksen, 2006;agent Lelieveld in et the atmosphere al., (Crutzen,of 2004). 1979; other Levy The key II, atmospheric 1972) OH constituents as radical such it controls as is the methane concentration (CH the primary oxidizing concentrations is crucial for many aspects of tropospheric chemistry. NO of central importance to understanding the composition of thephotolysis troposphere. of NO O O 1 NO Placing NO chemistry occurring leads to the Leighton relationship, (Carslaw, 2005; Pandey etmosphere al., (Lee et 2008) al., 2009). tonot Direct low e transport of ppt NO (parts per trillion) in the remote at- a day by the reaction of NO The quantities in the relationshipbeen are interpreted to readily signify measured missing and (i.e.have non deviations been ozone) from oxidants used unity of NO. to have These inferoxides perturbations in the the existence atmosphere of (Bauguitte et oxidants al., such 2012; as Cantrell et peroxy al., radicals, 2003; or Frey et halogen al., 2015). (Brown et al., 2004; Dentenervoir and species Crutzen, such 1993; as Riemer peroxy-acetylin nitrate et both are al., NO made 2003). in Instead, polluted reser- transported regions to (which are remote high regions where they thermallyCH breakdown to release the NO NO to minimize the interferenceremote in locations. the future, thus simplifying interpretation of data from 1 Introduction Accurate quantification of atmospheric nitrogen oxide (NO CH The equilibrium between peroxy-acetyl radicals, NO is highly temperature sensitive. Thus the PAN lifetime changes from 30last min 40 at years. 25 MultipleKajii, in-situ 2003), techniques Cavity are Ring available Down such (Ostho as LIF (Matsumoto and (Bridier et al., 1991) to 5.36 years at Laser (Tuzson et al.,has 2013). been However, based probably on the the chemiluminescent most reaction extensively between used NO approach and O 5 5 10 15 20 10 15 25 20 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | (R6) mea- 2 if it is first 2 measurement 2 ering concentrations ff to NO converter (of either signal. 2 2 is proportional to the NO present in the air to be measured. Then, reaction occurs and the decay of 2 2 3 O along with reasonable concentrations concentrations are higher than would NO to NO converter. Now, only NO present 2 + 2 to NO + 2 ∗ 2 NO into NO photolytically (Ryerson et al., 2000), J 2 , 28704 28703 3 systems to investigate the interference on the x ) signal giving the NO ), to yield a signal which is linearly proportional to (Reaction R6) which generates a vibrationally ex- x ∗ 2 have been successfully made in a range locations 3 2 (NO 2 erent NO ff NO , the sample flows through the NO 2 + (Drummond et al., 1985). The photons emitted are detected by 3NO (R8) 600nm) (R7) from PAN. In Sect. 5 we evaluate the impact of this interference 3 + 2 > ( 3 converter/chemiluminescence systems. In Sect. 4 we analyse the 2 ) locations, such as Antarctica and in the open ocean have at times ∗ 2 hv MoO x converters are described in Sect. 2.2. In Sect. 2.3 and the LIF instrument allows the concentration of NO + NO 2 → 2 2 molecule which decays into its ground state through the release of a photon 2 → 2 measurements and on the Leighton relationship through the use of a global NO 3 2 O 3NO to NO → + + ∗ 2 ∗ 2 Here we explore the potential of PAN to interfere with chemiluminescence NO Measurements of NO and NO With NO chemiluminescence analysers it is also possible to analyse NO This forms the basis of theFontijn chemiluminescence analysis et of al., NO (Drummond 1970; etphotons al., Kelly emitted 1985; by et the al., decay 1980; of excited Peterson NO and Honrath,a cooled 1999). photomultiplier The tube number (PMT)the of with fluorescence the lifetime sample of under the low NO pressure (to maximize before reaction with O the number density of NO in the sample gasconverted (Fontijn to et NO, al., either 1970). catalytically (typically(Villena heated et Molybdenum) al., as 2012), in or Reaction byexploiting (R8) converting Reaction NO (R1). Mo be expected from the observed NO, O of other oxidants (peroxyposited radicals, in order halogen to oxides). overcomeunmeasured the Various oxidant, apparent explanations or oxidation have pushing gap, known typically been high chemistry relying turnover into on of theoretical a short-lived species realms mystery which bytities may theorizing only (Cantrell have et been measured al., inalternative 2003; trace explanation quan- Frey would et be al., an 2013, unknown 2015; interference Hosaynali on Beygi the et NO al., 2011). An of PAN into NO measurement of NO on NO model and provide conclusions in Sect. 6. 2 Experimental details In Sect. 2.1 wesis. describe The the NO two chemiluminescenceused instruments to used provide for a theduction reference analy- of analysis PAN is bygeneration acetone described. in photolysis We Sect. in describe 2.5. Sect. ourof Then 2.4. protocol PAN in interference We for tests Sect. provide and pro- 2.6 details residence we time of describe tests the the in zero experimental Sect. air methodology 2.7. identified an unexplained imbalance inHosaynali the Beygi Leighton et relationship (Cantrell al., et 2011). al., Measured 1997; NO potential for errors with di increasing its apparent concentration. surements. In Sect. 2 weIn provide some Sect. details 3 of we the experimental describe studies the undertaken. results of experiments introducing di the sample flow is switchedin to bypass the the sample NO issubtracted detected from the in NO the chemiluminescence reaction. The NO signal is then the reaction between NO and O using the chemiluminescence technique (Huntrieserterson et and al., Honrath, 2007; 1999; Leemote Zhang et (low et al., NO 2009; al., Pe- 2008). However, measurements made in re- cited NO NO (Reaction R7) (Clyne et al., 1964). NO NO To measure NO and NO type) to the reaction chamber where the NO 5 5 20 25 15 10 20 25 10 15 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | , y 4 1 / − ect its ff analyser analyser analyser x x x are measured 2 on channel 1 (NO) on channel 1 (NO) 1 1 − − 2.5 pptv. per channel at ambient ∼ 1 − analyser (Sect. 2.1.1) – on x 1.0 pptv. converter with a total sample flow ∼ 2 ectively two separate NO chemilumi- ff with the other to provide a constant, fast x erent instrument designs; a switching mode ff 28705 28706 . Alternatively, a single channel can be used with 2 converter and a total sample flow of 1 standard L min 2 ciency is by internal automatic gas phase titration of NO ) respectively. The 1 min LOD is ffi x analyser x ). The wetted surfaces of the instrument are constructed of 1 with the NO signal measured with the BLC lamps active and in- analyser from Air Quality Design, Inc. (AQD) is a custom dual x analyser . ) respectively. The 1 min LOD is 1 2 x x x − analyser, also from AQD, operates similarly to the lab NO converter e x fluxes on an airborne platform at reduced pressure. However, in this 2 measurement – the other 60 % of the duty cycle is devoted to NO (40 %) x converter are primarily because of the high sample flow rates needed to 2 converters – commonly referred to as Blue Light Converters (BLCs). Two 2 converters 2 2 to form NO 3 The nominal sensitivity of the instrument is 3.5 and 4.0 cpsppt Both instruments are calibrated for NO by internal, automatic standard addition. Cal- The nominal sensitivity of the instrument is 8.3 and 11.6 cpsppt Both instruments feature independent mass flow controlled sample flows on each measurement (1 Hz) of NOthe and BLC NO in a switching modeNO so and that NO it is active for only 40 % of the duty cycle to provide nescence instruments working in parallel.share Both identical channels duplicate have equipment; identical ozonizers, flowthe MFCs, paths PMTs same and etc. vacuum Both pump channels –immediately share an in front Edwards of XDS the 35i. MFCble One flow to control/low channel analyse pressure is NO side equipped with of with one the channel, system. a It and BLC is NO possi- channel instrument designed forThe fast dual response channel and design means very that low there limit are of e detection (LOD). and channel 2 (NO and NO The laboratory NO inch PFA tubing, with the exception of 316 stainless steelibration unions/MFC for internals. NO whilst sampling zero air. 2.1.1 Laboratory NO 2.1.2 Aircraft NO with some alterations touse make on it the suited ground. to Itwith aircraft the can operation exception therefore but of be the which considered BLCpowerful do UV-diodes which analogous which not is to require a of active the a Peltier/forced air-cooling laborder non-standard controlled to design NO by maintain in a an that PID operating it in temperaturefor uses close six this to more NO ambient. The special requirements study the sample flow rate was a constant 1 standard L min with O active as described by (Lee et al., 2009). Artefacts in both NO and NO measure NO The aircraft NO temperature and pressure. and channel 2 (NO 2.2 NO Photolytic converters forQuality the Design two and chemiluminescent2004, 2007). manufactured systems Systems according were have also to supplied been by their developed subsequently Air proprietary (Pollack et standards al., (Buhr, 2011; (Sect. 2.1.2) on which only temperature controlled BLC experiments werechannel performed. (NO and NO which the majority of the experiments were performed and the “aircraft” NO and a parallel mode with 100 %of duty 2 standard cycle L of min the NO with 40 % duty cycle of the NO by connection of aAtmospheric catalytic Observatory converter GAW to station themodes (Lee were inlet et used as al., in is order 2009). the to In set-up replicate these at di experiments the both Cape Verde and to measuring zero (20 %). In this case the second channel might be used for NO similar instruments were employed; the “laboratory” NO 2.1 Instrumentation Chemiluminescent measurements were performed usingsign dual Inc. channel Air (Golden, Qualitytolytic Colorado, De- NO USA) instruments equipped with UV-LED based pho- 5 5 25 20 10 15 15 10 20 25 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | > (2) (3) C. It ◦ is the quan- φ ), 2 (cm to NO over a narrow 2 2 is the temperature (Sander ciently the power is used. T ffi measurement to that provided is the spectral photon flux 2 ) depending on the combination ciency be acceptable under these 1 ffi F − ), 300 Torr) and therefore lower residence 1 − ∼ is the residence time within the photolysis ). t 1 C and without Peltier cooling reach 77 ), and so, the rate of production of additional 0.2...0.6 s ◦ − j 28708 28707 ( = 2 i j ) t 6.5s ] converter were carried out at ambient temperature = Ox 4 inch Swagelok fittings acting as an inlet and outlet 2 photo-dissociation, and [ / j k λ 2 − , gives a sample residence time of 0.60 s resulting in d 1 ) jt ( − T is the absorption cross section of NO , λ ), lower pressure ( exp σ ( , gives a sample residence time of 0.96 s. Additional lamp end 1 ciency of the standard BLC with a sample flow of 1 ), − − φ − 1 ffi ) 1 − value of the converter is practically determined by the irradiant T h , was 22 to 42 % (  j λ nm C, 1 atm. t ( is the rate constant (s ◦ 1 ] 1 (Ryerson et al., 2000). ciency of 93 % ( − σ − 2 ) ffi s j Ox C, 1 atm. λ [ 2 ( ◦ jt − k [Ox] is the concentration and rate constant of any oxidant that reacts with F k + Z max min jt λ λ  = C. All experiments were carried out at with sample gas at ambient temperature and = ) ciency is determined by Eq. (2) where ◦ The volume of this illuminated sample chamber is 10 mL which, with a standard The conversion e The volume of this illuminated sample chamber is 16 mL which, with a standard flow Photolytic converters employ Reaction (R1) to convert NO T ffi ( a conversion e flow rate of 1 standard L min was therefore possible topower control supplied to the the internal Peltier temperature elements via of the the temperature controller. BLC by varying the photolysis power of the UV emitting elements and how e et al., 2011). The 2.2.1 Standard BLC Standard BLCs consist of two endsCorp) housing the within UV-LEDs (1 W, a 395 nm, heata UV central Hex, sink Norlux section with to rubber which gaskets forming is an air-tight attached seal. a Within the cooling centre section fan. The ends are bolted to of lamp units used whilst45 the external temperature of the converter was typically 34 to pressure; 20 2.2.2 High power BLC The high power BLCrate of (1.5 the standard L aircraft min instrumenttime, is to designed that to of operateaircraft. the at For standard a this reason BLC higher a to flow greaterNichia number allow Corp] (six) fast are of used time more in powerful resolution UV-LEDs orderconditions. [2 measurements that W, The 395 the from nm, lamps conversion an e aresame placed highly evenly along UV two reflectivelamps sides Teflon are of with actively a inlets (Peltier) cylindrical cooled at cavity to of opposing 47 the ends. The high power BLC tum yield (dimensionless) of NO 1 standard L min by molybdenum catalysts (Ridleye et al., 1988; Ryerson et al., 2000). The conversion cell. Here NO to form NO CE 0.95) cavity thought which thesides sample of gas the flows centre (Buhr, section 2007). are On 1 two of the opposing units were also supplied by AQD. rate of 1 standard L min a propriety Teflon-like material block is housed which serves as a highly UV reflective ( for the sample gas. wavelength band, thus providing a more selective NO (photonscm Sadanaga et al., 2010) with variationssults. implementation, Experiments though with similar operation either and NO and re- pressure; 20 The rate constant of photolysisNO of beyond that NO in the original sample is given in Eq. (3). j In Eq. (3) 5 5 25 20 10 20 15 15 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | (R9) PNs, (R10) (R11) P , 2 C, to thermally ◦ (Day et al., 2002). 2 , which is typically ap- 2 determination to compare (Di Carlo et al., 2013). To 2 2 measurement, as opposed to 2 cells, respectively (Di Carlo et al., 2013). 3 after conversion into NO • 3 3 28709 28710 2 CH respectively into NO 2 being MFC controlled. The time resolution of the + 3 NO from a cylinder (NIST traceable) diluted in zero air 2 • 2 NO + 2 2 concentrations directly (Dari-Salisburgo et al., 2009; • 2 ANs, and HNO C(O)O 3 C(O)O P C(O)O 3 ANs), and HNO 3 CH P , and the last three heated at 200, 400 and 550 CH 2 CH → ANs, and HNO PNs, → converters is desirable in order to properly know the source of any . A detailed description of the TD-LIF instrument can be found in P P → 2 hv 3 , 2 2 + signal. NO 2 NO 2 PNs, O + + . The common inlet system is split in four channels: one at ambient temper- reacts stoichiometrically with the acyl radical to form PAN. In practice, an • 2 • 2 P + 1 − 2 2) for NO CO 2 ) = C(O)O C(O)O 3 3 3 PNs), alkyl nitrates ( The Thermal Dissociation Laser Induced Fluorescence (TD-LIF) system is a cus- ANs, and HNO P 2.4 PAN preparation In order to testit the was sensitivity prepared by of theet the photolysis al., instrument in 1987) to air and peroxy-acetyl ofactions later acetone nitrate (R9)–(R11) and by interferences describe NO (Warneckphotolysis. as the and described mechanism Zerbach, by by 1992; (Meyrahn Zellweger which et PAN is al.,(CH 2000). formed Re- from acetone – the flow of both zero air and NO sitivity of the TD-LIF,fluorescence each lifetime cell and is facilitates the keptduce time-gating the at background of (Dari-Salisburgo low the et pressure photomultiplier al.,background 2009). to (3–4 by The Torr). an further TD-LIF This over-flow re- is of increases routinely zeroaddition air checked the for in of the known detection cells; amount and of calibrated by NO standard measurements is 10 Hz and theS/N detection limits are: 9.8, 18.4, 28.1, and 49.7 pptv (1 s, CH Matsumoto and Kajii, 2003;pled Matsumoto with et a al., thermal 2001;( dissociation Thornton inlet et system, al., 2000) allows and, measurement cou- of peroxy nitrates tom instrument developed for aircraft and ground-based observations of NO chemiluminescence with conversion. A direct methodwith of NO the BLC NO “artefact” NO P Di Carlo et al.orescence (2013), (LIF) with to a detect short NO description given here. It uses laser induced flu- The TD-LIF comprises fourthe main inlet parts: system the and(Spectra-Physics, laser model the source, Navigator pumps. the I) The that detectiona emits laser cells repetition light source system, at rate is 532prises of nm a with four 15 Nd:YAG kHz a identical pulse power cells, and doubledsurements. of one Each 20 laser 3.8 ns for W, cell each is pulse-width. formed compoundthrough The by class, the a detection sample to cube air allow cells and flowand two simultaneous system in arms mea- air the com- where centre flow) the of laser therepass the beam cell. is filters passes Perpendicular the to to both detector optimizelight (laser that that the beam reaches is fluorescence the a detector detection,pump (Di gated system minimizing Carlo includes photomultiplier et a the with al., roots non-fluorescence of blower 2013; lens 6 coupled Dari-Salisburgo Lmin to and et a al., long rotary 2009).ature vane The to pump to measure maintain NO a flow CH 2.3 TD-LIF analyser Laser induced fluorescence (LIF) provides a direct NO minimize quenching due to atmospheric molecules, and therefore increase the sen- dissociate Here NO excess of acetone isfound used to in ensure the that photolysis NO of reacts acetone completely. A is minor methyl product nitrate, also MeONO proximately 1 % of thenitrate total yield is (Mills shown et in al.,sphere 2007). Reactions through The (R12)–(R16). oceanic proposed emission origin Methylthermal of (Moore nitrate decomposition the and of is methyl PAN Blough, (Fischer also and 2002)1992; found Nwankwoala, Warneck and 1995; and in Zerbach, as Roumelis 1992). the and a Reactions Glavas, 1995) (R15), atmo- product (R17) show of (Fischer that and the Nwankwoala, the formation of nitro-methane and HONO is also possible from PAN 5 5 15 10 10 15 20 25 25 20 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | C ◦ (R12) (R13) (R14) (R16) LIF analyser. 2 C) molybdenum catalyst (Thermo , Sigma Aldrich) to ensure a con- ◦ × C dew point) compressed air by subsequent ◦ 28712 28711 . The counts recorded are therefore the sum of • 2 1 40 − − CO 3 , thus a 4–4.5 cps improvement in zero background 1 − content of the zero air sources a direct measurement CH 2 and volatile organic compounds (VOC) which may be 2 produced directly in the PAN generator with the results + O x fluorescence was observed. Typical sensitivity of the LIF • 2 + HONO) (R17) 2 2 O • 2 3 + C; and a Pyrex glass photolysis cell illuminated by UV light ) (R15) ◦ 2 CO 2 CH ONO 3 of zero air. The dark counts of the PMT in the absence of laser 180 cpsppb 3 NO 1 → CO 3 ∼ − HCHO • 2 CH + 2CH • 3 CH . Table 1 shows the photomultiplier counts per second whilst sampling → → 2 → 2 2 content of any zero air used is critical (more so than NO) in this study. → • 2 CH C(O)O 2 2 NO 3 → fluorescence and scattered laser light. It is clear that the Sofnofil/Carbon filter NO was required in order to avoid biasing the experimental procedure. The LIF + • 2 2 NO + • CH erence in the counts of the NO analyser was observed between the two sources 2 • C(O)O + ff channel was O + 3 CO O • 3 3 2 3 • 3 3 The NO Zero air from both PAG 003 and filter stack was sampled by the NO All flow rates within the PAN generator were calibrated using a Gilian Gilibrator-2 Air sistent humidity throughout all experiments and was regenerated by heating to 250 filtering through a cartridge of molecular sieve (13 for 24 h when necessary. Apacked second with filter cartridge Sofnofil placed (Molecular afterorder the Products) to molecular and sieve remove was activated ozone, charcoal NO (Sigma Aldrich) in No di of zero air. Thuscomparably low. the NO content of both sources of zero airof was NO considered toinstrument described be in Sect. 2.2.3 was used to compare the zeroAdditionally, air sources high (Table 1). grade bottled zeroalyzed for air NO (BTCA 178, BOC Specialty Gasses) was an- present in the compressedcartridges air. system Zero and air zero generated(the air from industry the from standard) compressed an were air Eco both and Physics filter AG sampled PAG by 003 the pure NO air chemiluminescence generator analyser. 2.5 Zero air Zero air was generated from dried ( In order to determine the NO 1.5 standard L min light are typically less than 3 countss equates to 22–25 pptsand improvement PAN generation in utilized the accuracy. Sofnofil/Carbon Consequently, filter all system. dilution, zeroing, system has an advantagethat over a both lower the signal PAG 003 for and NO BTCA 178 zero air sources in any NO NO synthesis by acetone photolysis. 2CH CH CH (CH CH (CH meation oven consisting ofwith a a silicone reservoir permeation of tubeall placed HPLC thermo-stated in grade the at headspace acetone 30 through (ACS which grade, zero air Acros) flows, et al., 2007). Flow Calibrator (Sensidyne). The PAN0.1–20.0 generator ppbv PAN. is Linearity and capable mixing of ratioGC continuously of equipped the producing PAN with output an was confirmed ECDcomplete by detector PAN- reduction as back described to by NO Whalley using et a al. heated (2004), (325 and also by A dedicated “PAN generator”, asduce used a by consistent Whalley source et ofthe al. PAN. NO (2004), The standard was generator gas, employed consists to the of: pro- acetone flow flow, control and elements the for zero air diluent flow; an acetone per- centred at 285 nm (Pen-Raylengths mercury below lamp, 290 nm UVP). within The the Pyrex photolysis functions cell to thus filter minimizing wave- PAN photolysis (Mills Environmental). A Laser Inducedwas Fluorescence used instrument, to described findpresented in if in Sect. Sect. any 2.4.1. 2.2.3, NO 5 5 10 15 20 25 20 10 15 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | , 2 i.e. ff analyser analyser was em- x 2 x is the number analyser. Next, n signal observed x 2 ciency and sampling ffi where analyser was then shut analyser was allowed to /n x x analyser as acetone does directly (i.e. rather than as x 2 analyser from sampling ambient signal was recorded once stable. 2 x analyser is reduced by high humidity x ), a direct measurement of NO 2 28714 28713 into the PAN generator, the acetone flow was channel when sampling various mixing ratios of 1 2 − NO mixture was illuminated by the photolysis lamp. / and the diluent flow of zero air adjusted to achieve the 1 measurement cycle was observed in either case, photol- − 2 analyser was sampling zero air from the PAN generator. Note that 10 mLmin x ∼ at 1000 ppt PAN (0.1 %) is produced by the PAN generator. This is less 2 analysers were first calibrated for sensitivity/converter e analyser with excess flow vented to the atmosphere. The system was then 0 ppbv after the acetone x x ∼ measurement cycle was observed during these experiments at any mixing ratio. 2 so that the NO It was therefore determined that only PAN could be an interfering species in the To investigate any interference from unreacted peroxy radicals left over from photol- To test whether the PAN generator produced any NO In order to investigate any interference from unreacted acetone, the NO ff while sampling PAN from the generatorment. lies within In the this noise case of the eachment. zero point With signal represents an measure- a averaging time 10be min of less average 10 min as than the 0.1 does pptv theoretical the10 – limit min) zero taking of the measure- a detection precision 10 is improves Hz estimated by LOD a to of factor 9.8 of pptv, approximately and 1 averaging 6000 points (i.e. ysed acetone with or withoutdoes nitric not oxide interfere addition. Thus, withinbroadband it the was photolysis BLC concluded cell and that of acetone that thetone peroxy PAN does generator. radicals It cause do should an not be increase noted exist in that outside the sampling of zero ace- the count of the NO PAN from the generator as shown in Fig. 1. It is evident that the NO react with ozone; thisand chemiluminescence is interference accounted is for known in (Dunlea the et measurements. al., 2007) a consequence of conversion ofployed using PAN to the NO TD-LIF describedzero in air Sect. was 2.2.3. measured The in measured the signal relative LIF to NO pure BOC specialty gases) of 0.5 mLmin in the sample. This means that switching the NO (humid) air toof zero the air reaction causes cell the to sensitivity decrease. to Afterthen rise establishing adjusted slowly an to and NO flow the (4.78 humidity ppm inside NO in N BLC from the PANproduced generator. is The discounted small dueally, percentage the to percentage of it interference methyl being observed nitrate is less significantly which thermally greater may than labile any be that expected PAN or itself. Addition- of points averaged (Lee etthan al., 1 ppt 2009). NO It isthan therefore previously conservatively estimated estimated that (Millslower less et residence times al., within 2007), the acetone albeit photolysis at cell higher with the PAN same mixing generator. ratios and sample acetone that had beenNO. photolysed NO within was the added PANzero generator downstream air in of during the the the absence NO photolysis or of cell NO also. No additional signal over ysis of excess acetone, produced in Reaction (R6), the NO 2.6 Experimental procedure The NO zero air by overflowing theleast inlet 2 h. from This the is internallow because source dew the prior point PAN to from and the the experiment the generator for sensitivity is at in of zero the air NO which has a very desired output mixing ratio.o The internal zero air of the NO the total flow fromthe the NO PAN generator always exceeded the sample requirements of allowed to stabilize until a stable NO value was recorded on the NO the acetone photolysis lampwas of photolysed in the the PAN presencewas generator indicated of was by NO the switched to fact on that form in so PAN. all Complete that cases NO the acetone conversion NO to signal measured PAN by the NO a flow of acetone andNO NO gas. No additional signal relative to zero air during the NO or fell to was allowed to sample the output of the PAN generator with the photolysis lamp o The diluent flow from theof PAN between generator 0.2 was then to varied 1.3This ppbv. to procedure The achieve was PAN corresponding mixing repeated NO ratios analyser for operation various modes. combinations of BLC lamps/assemblies and 5 5 20 25 15 10 10 15 25 20 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | x ect ff ects in ff ect are addressed in ff ; an average of 5.8 %. 2 signal from PAN to be negligible and subsequently NO within the 2 2 is on average highest at the lowest con- 2 analyser in switching mode analyser in constant mode x x 28716 28715 analyser, equipped with a BLC as described in analyser channels (which share a common inlet). x x were 8–25 % of the initial PAN mixing ratio. 2 ects signal is proportional to increasing PAN mixing ratios. The ff measurements 2 produced obscured any trend, however it is clear that there 2 signal resulting from the same three BLC units operated in 2 2 ciency and signal are not as clearly evident here as for constant mode ffi ciency and vice versa. Potential reasons for this e instruments. In Sect. 3.1 and 3.2 we explore the interference in the laboratory ffi 2 The percentage conversion of PAN to NO Table 2 demonstrates that the residence time of PAN within the inlet does not a Sect. 3.6. 3.2 Standard BLC and laboratory NO Figure 3 shows theswitching mode NO (40 % duty cycle). Theall percentage cases PAN conversion than observed in is the lowertemperature in corresponding as constant mode. a This result isconversion of likely e due operating to only the 40operation lower % lamp (Fig. of 2). the It time.the is The lower possible amounts relationship that of between NO the greater variation in the measurement due to the signal arising from PAN decompositioncontribution in from our the system. inlet This to rules PAN out decomposition. any The significant inlet in this case consists of ca. is still a significant proportion of PAN measured as NO It is not clearthe BLC from exclusively either or Fig.(Fehsenfeld within et 2 the al., inlet 1987). or Previous of 3 studiesSadanaga the (Fehsenfeld et whether et al., system, 2010) al., the as have 1990; also has PAN Ridleyverters, reported et decomposition been while a al., small claimed some occurs 1988; PAN found interference previously within with the photolytic contribution con- to the NO 3.3 Inlet residence time e (Ryerson et al., 2000). Othersan interference (Val and Martin estimate et a small al.,designs (2 2008) in to acknowledge 4 the pptv) the aforementioned positive possibility bias. studieshave The for the vary photolytic same greatly converter ubiquity in as their BLCs2011). used implementation here, and i.e. do within the not GAW network (Penkett et al., verter e reported methyl nitrate yieldet from al., PAN synthesis 2007). by Inthermal acetone the dissociation photolysis following of i.e. discussion PAN 1 or % we methyl (Mills address nitrate the to NO possibility of photolytic and photolytic convertor. 2.7 Residence time The residence time of PAN inanalyser the was varied 2.7 m by PFA varying inletflows the linking through flow the the rate. PAN each This generator was of to achieved the the by NO NO altering the sample 3 Impact of PAN on NO two NO In this section we discuss experiments investigating the potential impact of PAN on the instrument with a range of BLC convertors, eliminating any possibility for inlet e measured mixing ratios of NO Sect. 2.2.1, diluted inratio zero recorded by air the through analyserFigure was a 2 recorded range shows and that of is the presented mixing NO in ratios. the following The sections. resulting mixing Sect. 3.3, and in Sect.has 3.4 an we active explore cooling thedecomposition of interference of the in PAN the convertor. could aircraft In leadwhether instrument Sect. thermal to which decomposition 3.5 the could we interferences be investigate and the whether in source. photolytic Sect.3.1 3.6 we investigate Standard BLC and laboratory NO PAN was introduced to the NO 5 5 10 25 15 20 10 20 15 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ciency of measured ffi 2 ect of cooling the ff quartz collector. The π conversion e C. In other applications, signal is observed when ◦ 2 absorption band and the 2 2 converter 2 ciency considerably. ciency is strongly dictated by the ffi ffi erent BLC UV-LED units. These units ff cient. It is also shown that there in min- ffi ciency by half, but by a much smaller per- ffi 28717 28718 signal between the cooled and uncooled high 2 NO. → 2 erence in NO ff quantum yield (Gardner, 1987; Koepke et al., 2010). It can be dis- 2 concentrations measured whilst sampling a range of PAN mixing ratios 2 ect of actively cooling the BLC lamps is significant as apparent in the much 4 inch PFA tubing shielded from light and held at 20 ff / quantum yield and is therefore photon e 2 ciency has dropped below 30 % with new lamps will not lead to a recovery of the ciency was 93 % for NO Figure 5 shows the spectral emission of six di Figure 6 depicts the absorption cross sections of atmospheric nitrogen compounds From these experiments it is evident that a significant NO The e ffi ffi cerned that the UV-LED output overlaps fully with the NO spectrometer and collector optics were(OL calibrated FEL-A, using an Gooch NIST and traceableHousego). Housego) light The and source ultra-linear light power sourcelamp supply is with (OL a spectral 83A, irradiance 1000 Gooch W standard(125 and V), quartz-halogen F-1128. with The tungsten the lamp coiled-coil lamp-collector was filament distance operated at fixed at 8 Amps 50 DC cm. Calibration was carried out in a light sealed chamber. Spectralight-proof of the chamber BLC with UV-LED the lamps same were distance taken between within the the lamp same and collector. shown is the NO NO against the measured spectralused in output lamp-type of PCL UG5 opticsspectral e.g. UV-passing output Eco filter Physics of PCL glass six 762, (Schott, and individual 1997) the BLC averaged measured UV-LED arrays of varying running hours. Also UV-LEDs which acts to mitigate any signal arising from3.5 PAN. Possible photolytic interferences of BLCs Spectral radiograms of thean UV-LED Ocean elements Optics of QE65000 standard spectral BLCs radiometer were coupled obtained to using a 2 ranged in age fromficiency new of to nearing the the wholeage, end BLC the of relative unit their intensity had servicedue of to fallen life dimming their i.e. below of outputs the acceptable theby conversion declines, overall limits. visual output, ef- this As or inspection decrease failure the during ofintensity in operation. LED individual of intensity array It the units elements can UV-LEDs should determined is be be not directly pointed proportional out to however, the that NO the light centage. Additionally, replacing the UV-LED elementse of a converter whose conversion of the surface will however recover the conversion e imal overlap with HONOshown and (Carbajo no and overlap Orr-Ewing, ineither 2010; the with Talukdar spectrum methyl, et at ethyl al.,PAN all or synthesis. 1997) with isopropyl There that nitrate is PAN. It only – theremethyl very has methyl is ethyl, minor been nitrate no overlap and being in overlap isopropyl a the nitrate. PCL minor There optics impurity is spectrum in a with great PAN, deal of overlap with HONO which conversion. Scrupulous cleaning of the reflective cavity with solvent and mild abrasion sampling PAN diluted in zerothe air. PAN supplied The which signal represents seen adecomposition corresponds significant within to interference. the The around inlet possibility 5 was of to ruled thermal out. 25 % of 3.4 High powered and actively cooledFigure photolytic 4 NO shows the di (Fig. 4). It is therefore plainly evident that there is a significant e condition of the reflective Teflon-like cavity. Forin example, disabling a one BLC of does the not two reduce lamps the conversion e for example if the inletquite is possible heated, that contaminated, significant or PAN has decomposition a occurs. very long residence time, it is powered BLC described in Sect. 2.2.2. In all of the cooled cases the NO lower NO the complete whole BLC. Rather, the conversion e 2.7 m 1 was significantly lower than infact the (the uncooled signal case; recorded this when accounts samplinge for zero any air) increased in arte- the uncooled case. The conversion 5 5 25 20 20 25 15 15 10 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 3 2 ; Re- 0.43) (R18) 2 occurs C) the = ◦ 2 2 produced ciency but R 2 ffi ciencies when ffi conversion cavity 2 C. ciency of PAN to NO ◦ ciency, the percentage ffi ffi er some overlap with NO ff 0.96) and indeed with output was found to be, on average, 2 = . However, as only the two UV- to NO conversion e ciencies (Table 3) suggests that NO convertor e 2 2 2 ffi R → 2 ciency as in Eq. (2) where converter concentration is derived, which is an ffi 2 28720 28719 2 . 2 NO erent convertor e ciency and vice versa. The fact that the convertor + ff ffi • C(O)OO 3 ciency and temperature. It is worth noting that the power con- , more so in the case of PCL optics than for UV-LEDs. ffi ciency. It is shown more clearly in the inset that an average tem- CH 2 ffi

2 C. At the maximum LED surface temperature recorded (80 C would cause a 4.6 % decomposition of PAN and account for the NO ◦ ◦ C. ◦ and attributed to atmospheric NO converter is significantly above ambient. In fact, the entire NO C(O)OONO 2 x 3 ciency (Fig. 2) lies in the way that the NO ciency is expressed fractionally. If in fact the conversion e The model output indicates that measureable PAN decomposition to NO Table 3 details the power draw and surface temperature of three BLC UV-LED lamp It is known that the major product from thermal decomposition of PAN is NO In Sect. 3.1 the percentage conversion of PAN to NO ffi ffi in Facsimile using rate constants2006). from IUPAC Evaluated Kinetic Data (Atkinson et al., above ca. 50 a proxy – the temperaturesame was conversion lower e in switching mode than in constant mode for the LED lamps are atent/heating such rate an within elevated the temperaturegas BLC we over the so can 0.96 that expect s residence a themode is with temperature average somewhat only temperature lower. gradi- Also, 40 seen % it duty isalso. by expected cycle the This that of sample in the is a lamps, borne switching their surface out temperature when would be using lower the external surfaceperature of temperature 60 of the BLC as radicals and BrONO 3.6 Possible thermal interferences in BLCs The thermal and electronic characteristics ofin the standard bench BLC tests lamps were and ascertained bench are whilst summarized recording in the Tableelement. 3. surface The Each temperature lamp surface and was temperaturereached power run and was draw maintained constantly recorded of for on at once themode. the least The light 10 a min ambient emitting stable – temperature representative maximum during of the using had experiments a been was BLC 20 in constant assembled as a complete BLC.late The positively surface temperature with of the the power individual drawn lamps by corre- each lamp ( model predicts ca. 30 % decomposition of PAN to NO measured during experiments withspectral measurements the reported standard in BLCs.of Sect. the Therefore, 3.5, artefact signal together it is seems with throughmodelled direct highly in the photolysis unlikely Fig. of that PAN, 7 leaving the the thermal remaining decomposition source explanation. highest at the lowesttemperatures converter are e very similar at di inverse function of the assumed conversion e the UV-LEDs do not possess however. Both systems su pairs measured during tests, along with their NO the percentage of PANthe thermally inverse dissociated relationship between in percentagee each conversion of case PAN is to NO similar. and Explanation conversion for in the convertor was not related to the measured NO intensity (Fig. 2), but with each lamp pair there is only weak correlation ( e sumption is a combination of thefan. light It output, is heat clear dissipation, however andNO that power the to the temperature cooling experienced by the sample gas within the between converter e is heated by the lamps leadingand to 45 external temperatures of the converter of between 34 action (R18) (Roumelis and Glavas, 1992; Tuazon et al., 1991). The NO instead a constant value, then thewould apparent relationship disappear. between This CE and explanationconversion % percentage is conversion in consistent Fig. with 2 is the normalized fact to that conversion e when the average thermally within the converter may thenNO be photolysed to NO and thus beCH measured as A model of the thermalBLC decomposition with of a PAN residence over time a of range 0.96 of s temperatures is within shown the in Fig. 7. The model run was conducted 5 5 10 15 10 20 25 15 20 25 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | , y 2 (4) C in ◦ NO 2 O from the 3 2 ) is derived), ; CH t 5 ( T O 2 , is calculated as species. Whereas τ ;N y 2 ciency and PAN “arte- ffi C and a 1 s residence time. ciency of a BLC, the greater ◦ ; ClONO at the operating temperatures ffi 2 formed in Reaction (R18) may 2 2 resolution, plus updates described ◦ of 5 to 20 % of the PAN supplied. The 2 ; BrONO 2.5 2 × ◦ C, the NO ◦ 28721 28722 NO and thus does not include the extra signal NO conversion e s) for temperature from the ambient temperature → → τ 2 2 is then more readily photolysed to NO within the BLC NO with converters where conversion is less than unity  ∗ 2 )[PAN] (5) t τ )), and the parameterized temperature within the instru- )) as it passes through the instrument. This can be param- t ) as in Eq. (4). → t ( measurements by NO chemiluminescence using BLCs has − ( k ∗ 2 2  T when PAN is present. BLC B/T − species within a BLC photolytic converter. The species used T 2 − . The discussion above suggests that a similar proportion of the = y 2 )exp 0 T exp( A − )[PAN] = ciency of 100 % NO T C) of the instrument, a number of more thermally labile compounds exist ) ( ffi BLC ◦ T T k ( ( − k )), the fraction of the compounds that will have decomposed can be found by + . Thermal decomposition information are taken from IUPAC evaluated kinetic t = ( 2 0 T T C ambient temperature, a BLC temperature of 75 ◦ evolved from thermal dissociation of PAN is converted to NO within the BLC lead- NO = t 2 2 ) ) to that of the BLC ( 5 % at 60 d Figure 9 uses output from the GEOS-Chem model (version 9.3, http://www. Given a 1st order loss of the PAN like compound and a temperature profile within in Above a threshold temperature of 25 The degree of thermal decomposition within the instrument will depend upon the The positive bias in NO t 0 ( T ∼ d[PAN] geos-chem.org, Bey et al.,in 2001) Sherwen run et al. atdecomposition (2015), 2 of to NO provide an estimate of the interference on NO ment ( for this analysis are: PAN; MPAN; PPN; IONO Given the laboratory observations of(typically the temperature dependence of the rate constant numerical integration. The rate at which thermal equilibriumat is 20 reached within the cell, ( data (Atkinson et al.,of 2003, a 2006, one 2007). year simulation Interferences andconversion are the e calculated maximum value for shown. each The month estimate assumes a BLC This allows a calculation of the potential interference from other thermally labilethe instrument NO as described in 4 we have 5: 0.42 s from the observed PAN decomposition of 4.6 % (fromcompounds. which HO from the photolysis of NO T – in this case a multiplying factor exists. only a small fraction of PAN is found to convert to NO ( which become more important at higher latitudes and altitudes. thermal profile of the aireterized ( as a relaxation timescale ( implications for datashows in the both thermal remote decomposition background profiles sites of and many polluted common areas. NO Figure 8 for the three BLCs isof remarkably 4.6 similar % (Table 4) needed with to the produce average the PAN spurious decomposition signal observed. normal operation with theand surface output temperature intensity. correlating positively with power draw be excited through the(Mazely et dissipating al., of 1995), internal this energy NO from the parent PAN molecule fact”. Consequently, the lower NO the positive error in NO than ground state NO 4 Atmospheric implications We have shown thatnormal a operating significant conditions proportionleading of of to a a PAN spurious can BLC increase be equipped in measured decomposed NO NO under chemiluminescence the instrument UV-LED light source employed by was found to reach a temperature of 56 to 80 NO ing to the apparent inverse correlation between conversion e 5 5 15 10 20 25 20 25 15 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | , 2 y x x S 2 ◦ , RO x measure- . 2 2 C. Our results concentrations ◦ is much greater : NO ratio which x 2 2 C, however does not ◦ ciency less than unity. ffi or mystery oxidant. converter (Droplet Mea- bias we have shown ex- of 0.42 s and a residency 2 and it is not surprising that 2 X τ ciency of 100 %, whereas in x ffi may be over-reported by many ” or, (b) theoretical mechanisms 2 data and ancilarry measurments. X 2 ), i.e. measured NO , BrO and IO. The model value is in conversion e 2 x 2 converter e HO 2 , RO + 2 C (described by 2 ◦ 28723 28724 RO + (Bauguitte et al., 2012; Cantrell et al., 2003; Frey , T, HO 3 2 ciency was 59 % thus, a multiplying factor may apply (RO ffi ,O x 2 1.7. over-reporting closes the oxidative balance implied by their ∼ ect of having an NO NO environments. This has led to either hypothesizing (a) an un- 2 , RO j ff x 2 converters which operate above ambient temperature. This is , 2 2 channel from the instrumental decomposition of a range of BLC 2 are in high concentrations compared to NO bias shown in Fig. 9 impacts the modelled Leighton ratio. In Fig. 10 the 2 7 ppt) due to the low ambient temperature range of 3 to 11 , CO, OH, HO 2 ciency is 59 % the actual temperature would not necessarily be so high as 3 < NO ffi 2 bias cause by a BLC with a lamp temperature of around 90 C. Eliminating this NO 2 ◦ The results presented by Hosaynali Beygi et al. (2011) show an NO As a practical example with an analogous system to that used in this study, the NO Presented in Fig. 4 of Hosaynali Beygis’ paper on page 8503 (Hosaynali Beygi et al., The NO Figure 9 shows that in extreme circumstances NO As shown in Fig. 10 the Leighton ratio can be extremely perturbed from what would The authors estimate a minimal photolytic interference from atmospheric nitrates us- et al., 2013, 2015; Hosaynali Beygi et al., 2011). observations of Hosaynali Beygi“OOMPH” et project al. (Ocean (2011) Organicsas taken Modifying a in Particles case the in study. South both During Atlantic Hemispheres) this during serve cruise the a BLC photolytic NO 2011) is the Leighton ratio calculated from their NO exceeding what the authors are able to explain given their measurments of HO include any multiplying e model is sampled every daylight hourThe for calculation every surface shown grid box incentrations for red the of month is of NO, the March. NO Leighton ratio calculated from the modelled con- by which NO is converted to NO to any PAN interference of The ratio in the pristine background appears to be significantly biased towards NO concentrations could be as high as 150 pptv. known, unmeasured, selective oxidant “compound than the Leighton relationship wouldby predict. the author This to apparent an Leighton “unknown ratio oxidant” is which attributed selectively converts NO to NO thermal decomposition can have an impact. Upper tropospheric over estimates of NO general close to 1. In theferences blue on the the same NO calculation islamp performed temperatures but between including the 60 inter- time and of 105 1 s). Here there are significant interferences. be predicted by allists available with measurements photolytic NO givenespecially the true in NO low NO surement Technologies, Colorado, USA),in with this a study residence –the time coupled French to of research an 1 s, vessel NO Marion as chemiluminescence described Dufresne analyser was II. deployed The aboard cruise track covered the South ing their BLC, consistent with ourtion analysis within (Sect. the 3.5 inlet and line Fig.minimal is 6). ( considered Only as PAN decomposi- a potentialhave interference, shown but is that estimated thermal,species to with be rather the than converter itself photolyticments is made decomposition the with major of source BLCs. atmospheric of Indeed,in over-reporting the our NO in region model NO of study thethe predicts cruise, OOMPH interference assuming observations of an the NO 50 e to 100 % and OH. Theirwhen values an fit instrumental well biasNO is within included the however. This modelled is Leighton suggestive ratios of an shownAs instrumental in the e Fig. 10 90 other data and removes the need to invoke any compound Atlantic Ocean from Cape Town, South Africa to Punta Arenas, Chile, reaching 60 during March 2007. is a factor c.a. 7tions greater of than O can be explained given the available supporting observa- hundreds of percent. These are in regions that typically have low NO and are cold (polar),and HO and in the upper troposphere. Here, compounds such as PAN 5 5 20 20 10 15 25 10 15 25 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | x x M NO + 2 ects of → to NO ff 2 y C(O)O 3 determination. CH 2 ⇔ in the summer marine M species, Atmos. Chem. x x + 2 ect of having lower con- ff NO + and SO 2 x mixing ratio by the dissociation 2 ” which selectively oxidizes NO to , NO X x C(O)O 3 environments. Thermal decomposition x , HO x , E. W., and Plane, J. M. C.: Summertime NO ff has been shown to lead to apparent gaps in ciency is now achievable thanks to advance- 2 28725 28726 ffi observations. converter produces spuriously high readings; this is 2 2 in ambient air using a solid-state photolytic converter, in: Sym- 2 collected using photolytic converters and chemiluminescence 2 The authors would like to express their gratitude to Stephane Bauguitte ciency, i.e. unity, to mitigate the multiplying e ffi ciencies. High conversion e ffi species within the NO 95 % for example. Additionally, actively cooling the UV emitting elements or y > , however this is likely anomalous and simply due to error in the NO 2 In order to mitigate this overestimation of the NO tropospheric ozone on netRev. Plant primary Biol., productivity 63, and 637–661,, doi:10.1146/annurev-arplant-042110-103829 implications 2012. for climate change, Annu. ron., 28, 949–964,, doi:10.1111/j.1365-3040.2005.01341.x 2005. M. E., Rossi, M.chemistry: J., Volume and I – Troe, J.: gas phase Evaluated reactions kinetic of and O photochemical data for atmospheric measurements during the CHABLISserved campaign: diurnal can cycles?, source Atmos.2012. and Chem. sink Phys., 12, estimates 989–1002, unravel, doi:10.5194/acp-12-989-2012 ob- Kinetic and theoretical studies ofbetween the 248 reactions CH anddoi:10.1021/j100162a031, 393 K 1991. and between 30 andLerner, 760 B. torr, M., Jakoubek, J. R.,Kuster, Phys. Middlebrook, W. A. Chem., M., C., DeGouw, 95, Angevine, J.Fehsenfeld, 3594–3600, A., W. F. C., Warneke, M., and C., Ravishankara, Goldan, Sueper, A. P.boundary D., R.: D. layer, Nighttime T., Geophys. removal Res. Quinn, of Lett., NO P. 31, K., L07108, Bates, doi:10.1029/2004GL019412, 2004. T.posium S., on Meagher, Air Quality J. Measurement F., 171, Methods Cary, and NC, Technology USA, 2004, 20–22 2004. April 2004, 165– July 2007. Phys., 4, 1461–1738, doi:10.5194/acp-4-1461-2004, 2004. Jenkin, M. E., Rossi, M.chemical J., data Troe, for J., atmospheric and chemistry: IUPAC Volume Subcommittee:Atmos. II – Evaluated Chem. gas kinetic Phys., phase and 6, reactions photo- 3625–4055, of organic, doi:10.5194/acp-6-3625-2006 species, 2006. M. E., Rossi, M.chemistry: J., Volume and III Troe, J.: – Evaluated gas981–1191, kinetic phase, doi:10.5194/acp-7-981-2007 and 2007. reactions photochemical of data inorganic for halogens, atmospheric Atmos. Chem. Phys.,Lee, J. 7, D., Saiz-Lopez, A., Roscoe, H. K., Wol Bridier, I., Caralp, F., Loirat, H., Lesclaux, R., Veyret, B., Becker, K. H., Reimer, A., and Zabel, F.: Brown, S. S., Dibb, J. E., Stark, H., Aldener, M., Vozella, M., Whitlow, S.,Buhr, Williams, M.: Measurement E. of J., NO Buhr, M.: Solid-State Light Source Photolytic Nitrogen Dioxide Converter, US 7238328 B2, 3 Atkinson, R., Baulch, D. L., Cox, R. A., Crowley, J. N., Hampson, R. F., Hynes, R. G., Bauguitte, S. J.-B., Bloss, W. J., Evans, M. J., Salmon, R. A., Anderson, P. S., Jones, A. E., ments in the power densitya of UV-LEDs CE currently available; new generation BLCs have Atkinson, R., Baulch, D. L., Cox, R. A., Crowley, J. N., Hampson, R. F., Hynes, R. G., Jenkin, version e Ashmore, M. R.: Assessing the future global impactsAtkinson, of R., ozone Baulch, on D. vegetation, L., Plant Cox, Cell R. Envi- A., Crowley, J. N., Hampson, R. F., Hynes, R. G., Jenkin, conversion e ratio may be high. Over-reporting of NO separating them from the gasnot stream contact is any essential surfacemay in which result order in is that spuriously the above high sample ambient NO gas temperature.Acknowledgements. should Failure to achieve this spectral radiometer/calibration equipment. Thetre financial for support Atmospheric of Science,supporting NCAS, and the the studentship of National of NERC, Chris Cen- the Reed is Natural gratefully Environmental acknowledged. Research Council for References Ainsworth, E. A., Yendrek, C. R., Sitch, S., Collins, W. J., and Emberson, L. D.: The e of FAAM for their scientific discussion, and Lisa Whalley of Leeds for the PAN generator and of NO especially true in pristine environments and at highoxidation elevations chemistry where which the cannot NO behas explained led with to any available theorization measurements. ofNO This an unknown “compound of PAN and other compounds it is desirable to have the highest possible NO 5 Conclusions Measurements of NO systems may be significantly biased in low NO 5 5 25 20 25 30 15 15 20 10 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | , per- ney, J. 2 ff c emissions, ffi on tropospheric aerosols: impact 5 O 2 emissions ratio from road tra , total peroxy nitrate, total alkyl nitrate, and 2 x measurement techniques, J. Geophys. Res., quantum yields from ultraviolet photodisso- y NO / 2 2 , and OH, J. Geophys. Res., 94, 7149–7163, 28727 28728 , J. Geophys. Res., 107, ACH 4-1–ACH 4-14, 3 3 in the chemistry of the troposphere and stratosphere, ,O 2 x , and NO x ey, M., Atlas, E., Stephens, S., Heikes, B. G., Snow, J., ff measurements: observations at a central Italy background site, 2 measurement techniques, J. Geophys. Res., 95, 3579–3597, 2 o, E., Busilacchio, M., Giammaria, F., Dari-Salisburgo, C., Biancofiore, F., Vis- ff , Atmos. Meas. Tech., 6, 971–980, doi:10.5194/amt-6-971-2013, 2013. 3 doi:10.1029/2001JD000779, 2002. oxy nitrates, alkyl nitrates, and HNO Atmos. Environ., 43, 970–977,, doi:10.1016/j.atmosenv.2008.10.037 2009. mal dissociation laser-induced fluorescence instrument for in situ detection of NO on thedoi:10.1029/92JD02979, global 1993. distributions of NO conti, G., Lee,Ouyang, J., B.: Moller, Aircraft S., based four-channelstrument Reeves, thermal for C. simultaneous dissociation E., measurements laser of Bauguitte, inducedHNO NO fluorescence S., in- Forster, G., Jones, R. L.,tropospheric and NO measurements, J.1985. Atmos. Chem., 2, 287–306,, doi:10.1007/BF00051078 Zahniser, M. S., Shorter,S., J. Marley, N. H., A., Wormhoudt,Villegas, Grutter, J. C. M., C., R., Marquez, Lamb,ide Kolb, C., B. chemiluminescence C. Blanco, K., monitors S., E., Allwine, in Cardenas, Molina,2691–2704, E. a B.,, doi:10.5194/acp-7-2691-2007 L. J., polluted 2007. Retama, T., urban Ga A., and environment, Ramos Atmos. Molina, Chem. M. Phys., J.:Curran, 7, C. Evaluation M., of Eubank, nitrogen C.based S., intercomparison diox- Fahey, of D. W., NO, Mindplay,92, NO P. C., 710–722, and doi:10.1029/JD092iD12p14710, 1987. Pickering, K. E.: A ground- Burr, M. P.,Heikes, Parrish, B. G., D. Kok, G.Intercomparison D., L., Shetier, of Hobler, J. G., D., NO doi:10.1029/JD095iD04p03579, Walega, 1990. J. Langford, G., A. Elsworth, C. O., M., and Calvert, Mohnen,oxyacetyl V. nitrate J. A.: (PAN), Atmos. G., Environ., 29,T, 3277–3280, Ridley, 1995. 10.1016/1352-2310(95)00252- doi: B. A., of nitric oxidepollutants, with Anal. ozone. Chem., Implications 42, 575–579, for, doi:10.1021/ac60288a034 continuous 1970. selective monitoring of gaseous air Blake, D. R., Blake,Seid, N., G., Katzenstein, and A., Lopez, Talbot,during R. TOPSE, J., J. Browell, W.: Geophys. E. Steady Res., 108, V., state 8361, Dibb, free doi:10.1029/2002JD002198 , J. 2003. radical E., budgets Scheuer, E., and ozone photochemistry Atmos. Environ., 39, 4793–4802,, doi:10.1016/j.atmosenv.2005.06.023 2005. cent reaction,doi:10.1039/TF9646000359 between 1964. nitric oxideAnnu. and Rev. ozone, Earth1979. Panetary Trans. Sci., Faraday 7, Soc., 443–472,, doi:10.1146/annurev.ea.07.050179.002303 60,distribution 359–370, 1990–2001 anddoi:10.1029/2006GL027295, 2006. its impact on methane,rescence instrument Geophys. for NO Res. Lett., 33, L23811, Brune, W. H., Stevens,deviations P. S., and and steady state Mather, calculations J.iment during H.: at the Peroxy Idaho Tropospheric radicals OH Hill, Photochemistry from1997. Colorado, Exper- photostationary 1993, state J. Geophys. Res., 102, 6369,, doi:10.1029/96JD01703 Hall, S., Campos, T.heimer, L., A. Ridley, B., J., Walega, Hannigan, J. J., G., Co Fried, A., Wert, B., Flocke, F. M., Wein- ciation of,doi:10.1039/c001425g methyl 2010. and isopropyl nitrate., Phys. Chem. Chem. Phys., 12, 6084–6091, Drummond, J. W., Volz, A., and Ehhalt, D. H.: An optimizedDunlea, chemiluminescence E. detector J., for Herndon, S. C., Nelson, D. D., Volkamer, R. M., San Martini, F., Sheehy, P. M., Fehsenfeld, F. C., Dickerson, R. R., Hobler, G., Luke, W. T., Nunnermacker, L. J., Roberts, J. M., Fehsenfeld, F. C., Drummond, J. W., Roychowdhury, U. K., Galvin, P. J., Williams, E.Fischer, G. and J., Nwankwoala, A. U.: A spectroscopic study of the thermal decomposition of per- Fontijn, A., Sabadell, A. J., and Ronco, R. J.: Homogeneous chemiluminescent measurement Dentener, F. J. and Crutzen, P. J.: Reaction of N Day, D. A., Wooldridge, P. J., Dillon, M. B., Thornton, J. A., and Cohen, R. C.: A ther- Di Carlo, P., Aru Carbajo, P. G. and Orr-Ewing, A. J.: NO Clyne, M. A. A., Thrush,Crutzen, B. P. J.: The A., role of NO and and NO Wayne, R.Dalsøren, P.: S. Kinetics B. and of Isaksen, the I. chemilumines- S.Dari-Salisburgo, C., A.: Di Carlo, CTM P., Giammaria, F., study Kajii, Y., of and D’Altorio, changes A.: Laser in induced fluo- tropospheric hydroxyl Cantrell, C. A., Shetter, R. E., Calvert, J. G., Eisele, F.Cantrell, L., C. Williams, A., Mauldin, E., L., Baumann, Zondlo, K., M., Eisele, F. L., Kosciuch, E., Shetter, R. E., Lefer, B., Carslaw, D. C.: Evidence of an increasing NO 5 5 30 30 10 15 20 25 10 15 20 25 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | , J. x in the 2 photodissocia- 2 over Brazil during TROCCI- x from photolysis of peroxyacetyl photolysis frequencies in street 2 2 ) at Dome C, East Antarctica, during 2 28730 28729 ) above the Antarctic Plateau driven by atmospheric stability and snow emissions, 2 , E. W., and Savarino, J.: The diurnal variability of atmospheric nitrogen oxides (NO , H. D., Brown, S. S., Ryerson, T. B., Fortin, T. J., Lerner, B. M., Williams, E. J., Petters- ff ff measurements of nitrogen oxideslayer, and J. ozone Geophys. in Res., 114, the D21302, tropical, doi:10.1029/2009JD011878 North 2009. Atlantic marineArbor, boundary Michigan, USA, 1961. in the self-cleansingdoi:10.5194/acp-4-2337-2004, 2004. capacity of the troposphere,doi:10.1016/0032-0633(72)90177-8, Atmos. 1972. Chem. Phys., 4, 2337–2344, rescence technique, Atmos. Environ., 37,2003. 4847–4851,, doi:10.1016/j.atmosenv.2003.08.023 nitrate, J. Phys. Chem., 99, 8162–8169, doi:10.1021/j100020a044, 1995. yacetyl nitrate:doi:10.1007/BF00113903, two 1987. convenient calibration techniques,Seasonal J. variation Atmos. of peroxyacetylnitrateinstrument Chem., (PAN) for in the coastal 5, detection of Antarctica7, sub-part 405–415, measured 4589–4599, per with trillion doi:10.5194/acp-7-4589-2007, mixing a 2007. ratios new of PAN, Atmos. Chem. Phys., 27-1–27-4,, doi:10.1029/2002GL014989 2002. marine atmosphere by laser-induced2814,, doi:10.1016/S1352-2310(01)00078-4 fluorescence 2001. technique, Atmos. Environ., 35, 2803– variability in ozone production, resultingron., 39, health 2851–2866, damages, doi:10.1016/j.atmosenv.2004.12.041 and 2005. economic costs, Atmos. Envi- son, A., Baynard, T., Dubé, W. P., Ciciora, S. J., and Ravishankara, A. R.: Measurement of Wol and NO Atmos. Chem. Phys., 13, 3045–3062,,10.5194/acp-13-3045-2013 doi: 2013. Preunkert, S.: Atmospheric nitrogen oxides (NOthe and OPALE NO campaign, Atmos. Chem. Phys., 15,2015. 7859–7875,, doi:10.5194/acp-15-7859-2015 tion, J. Geophys. Res., 92, 6642–6652,, doi:10.1029/JD092iD06p06642 1987. boundary contributions to ozone-induced cropgeosciences, yield 9, losses 271–292, in10.5194/bg-9-271-2012 , doi: the 2012. Northern Hemisphere, Bio- Brookes, D. M., Monks, P. S.,lantic and Lelieveld, boundary J.: layer: Oxidation unexpected photochemistryPhys., deviations in 11, the of 8497–8513, Southern photochemical, doi:10.5194/acp-11-8497-2011 At- steady 2011. state, Atmos. Chem. Schwierz, C., Richter, A., and Stohl, A.: Lightning-produced NO Geophys. Res., 86, 3153–3161, doi:10.1029/JC086iC04p03153, 1981. NOX: airborne measurements in tropicalof and mesoscale subtropical convective thunderstorms systems, and2987-2007, Atmos. the 2007. Chem. importance Phys., 7, 2987–3013, doi:10.5194/acp-7- ides ofdoi:10.1029/JC085iC12p07417, 1980. nitrogen and nitricRes. Chem. acid Intermed., 20, in 335–384, doi:10.1163/156856794X00379, 1994. clean air, J. Geophys.canyons, Res., Atmos. Chem. 85, Phys., 10, 7457–7466, 7417–7425, doi:10.5194/acp-10-7457-2010, 2010. Meyrahn, H., Helas, G., and Warneck, P.:Mills, Gas G. chromatographic P., Sturges, determination W. T., Salmon, of R. perox- A., Bauguitte, S. J.-B., Read, K. A., andMoore, Bandy, R. B. M. J.: and Blough, N. V.: A marine source of methyl nitrate, Geophys. Res. Lett., 29, Ostho Mauzerall, D. L., Sultan, B., Kim, N., and Bradford, D. F.: NO emissions from large point sources: Mazely, T. L., Friedl, R. R., and Sander, S. P.:Production of NO Gardner, E. P., Sperry, P. D., and Calvert, J. G.: Primary quantum yields of NO Hosaynali Beygi, Z., Fischer, H., Harder, H. D., Martinez,Huntrieser, H., M., Schlager, H., Sander, Roiger, A., R., Lichtenstern, M., Williams, Schumann, U., Kurz, J., C., Brunner, D., Koepke, P., Garhammer, M., Hess, M., and Roeth, E.-P.: NO Hollaway, M. J., Arnold, S. R., Challinor, A. J., and Emberson, L. D.: Intercontinental trans- Kelly, T. J., Stedman, D. H., Ritter, J. A., andKley, D., Harvey, Drummond, R. J. W., B.: McFarland, M., Measurements and Liu, of S. ox- C.: Tropospheric profiles of NO Kleindienst, T. E.: Recent developments in the chemistry and biology of peroxyacetyl nitrate, Lee, J. D., Moller, S. J., Read, K. A., Lewis, A. C., Mendes, L., andLeighton, Carpenter, P. L. A.: J.: Photochemistry Year-round of Air Pollution, AcademicLelieveld, Press, University J., of Dentener, Michigan, F. Ann J., Peters, W., and Krol,Levy M. C.: II, On H.: the Photochemistry role of ofMatsumoto, hydroxyl the J. radicals and lower Kajii, troposphere, Y.: Planet. Improved Space analyzer for Sci.,Matsumoto, nitrogen 20, J., dioxide 919–935, Hirokawa, by J., laser-induced Akimoto, fluo- H., and Kajii, Y.: Direct measurement of NO Frey, M. M., Brough, N., France, J. L., Anderson, P. S., Traulle, O., King, M. D.,Frey, Jones, M. A. M., Roscoe, E., H. K., Kukui, A., Savarino, J., France, J. L., King, M. D., Legrand, M., and 5 5 25 10 20 30 15 10 15 20 25 30 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | : in situ laser-induced cient photolysis sys- 2 ffi in the free troposphere us- y abatement: a review., Sci. Total over the temperature range 283– x 2 and NO converter for continuously measuring 2 2 on chemistry and nitrate aerosol forma- over the northwestern North Atlantic: mea- 5 O y 2 28732 28731 and NO x made during the NASA GTE/CITE 1 aircraft program, J. by photolysis – chemiluminescence, J. Atmos. Chem., 65, x 2 measurements, J. Geophys. Res., 105, 26447–26461, 2 by pulsed cavity ring-down spectroscopy, J. Geophys. Res., 111, D12305, ects of gases and particles and the influence of cause of death, age, and 2 ff behavior at urban roadside and background locations in Seoul, Korea, Atmos. x and NO, Monatsh. Chem., 123, 63–72, doi:10.1007/BF01045298, 1992. 2 in the atmosphere, Anal. Chem., 82, 9234–9239,, doi:10.1021/ac101703z 2010. 2 , NO 2 fluorescence detection at parts per trillion mixing ratios, Anal.and Chem., reactions 72, of 528–39, 2000. acetyl peroxy radicals with NO and NO Ravishankara, A. R.,Orkin, Kolb, V. C. L.: E., ChemicalEvaluation No. Molina, Kinetics 17, and M. JPL Photochemicalable Publication J., at: 10-6, Data Finlayson-Pitts,http://jpldataeval.jpl.nasa.gov Jet(last for B. Propulsion access: Use Laboratory, 22 J., Pasadena, October in USA, Huie, 2015), Atmospheric 2011. avail- R.materials_filters_schott_uvTransmitting_UG5.aspx Studies, (last E., access: 25 and July 2014), 1997. Volkamer, R., Saiz-Lopez, A., Prados-Roman,impact C., on Mahajan, tropospheric A. oxidants: S., a andDiscuss., global Ordóñez, 15, model C.: 20957–21023, study Iodine’s doi:10.5194/acpd-15-20957-2015, in 2015. GEOS-Chem, Atmos. Chem. Phys. ing quantum cascade laser spectroscopy, Atmos.6-927-2013, Meas. Tech., 2013. 6, 927–936, doi:10.5194/amt- ides in the centraldoi:10.1029/2007JD009688, 2008. North Atlantic lower free troposphere, J. Geophys. Res., 113, D17307, Environ., 408, 3976–3989,, doi:10.1016/j.scitotenv.2010.06.001 2010. and mortality: e season, J. Air Waste2002. Manag. Assoc., 52, 470–484,, doi:10.1080/10473289.2002.10470794 hankara, A. R.:sections Atmospheric and photodissociation fate quantum2805, of, doi:10.1039/A701781B yields, 1997. several J. Chem. alkyl Soc. nitrates Faraday Part Trans., 93, 2 2797– UV absorption cross- 313 K, J. Phys. Chem., 95, 2434–2437, doi:10.1021/j100159a059, 1991. Emmenegger, L.: Selective measurements of NO, NO surements and measurement,doi:10.1029/1998JD100088 1999. accuracy, J. Geophys. Res.for Atmos., detection of 104, atmospheric NO 111–125, 11695–11707, doi:10.1007/s10874-011-9184-3 , 2011. gory, G. L.: An intercomparison ofniques results from for ferrous measurements sulphate and of photolyticGeophys. converter NO Res., tech- 93, 15803–15811, doi:10.1029/JD093iD12p15803, 1988. pact of the heterogeneous hydrolysis of N NO atmospheric NO doi:10.1029/2000JD900389, 2000. ment of a selective light-emitting diode photolytic NO ,doi:10.1029/2005JD006942 2006. study of NO Environ., 42, 607–622,, doi:10.1016/j.atmosenv.2007.10.015 2008. Flocke, F. M., Gerwig, H.,Torseth, Lee, K., J. Wielgosz, D., R., Milton,Workshop Suda, M., on Roher, K., Global F., Long-term Akimoto, Ryerson,for Measurements H., T. GAW B., Nitrogen of and Steinbacher, Oxides Nitrogen Tarasova, M., Network, Oxides O.:TD Hohenpeissenberg, No. and A Germany, 1570, Recommendations 8–9 WMO/GAW 45 October pp., Expert 2009, February WMO 2011. tion in thedoi:10.1029/2002JD002436, lower 2003. troposphere under photosmog conditions, J.O Geophys. Res., 108, 1–21, tem for fast-response NO Pollack, I. B., Lerner, B. M., and Ryerson, T. B.: Evaluation ofRidley, B. ultraviolet A., light-emitting Carroll, diodes M. A., Torres, A. L., Condon, E. P., Sachse, G. W., Hill,Riemer, G. N., F., and Vogel, Gre- H., Vogel, B., Schell, B., Ackermann, I., Kessler, C., and Hass, H.: Im- Sadanaga, Y., Fukumori, Y., Kobashi, T., Nagata, M., Takenaka, N., and Bandow, H.: Develop- Penkett, S., Gilge, S., Plass-Duelmer, C., Galbally, I., Brough, N., Bottenheim, J.Peterson, C. W., and Honrath, R. E.: NO Roumelis, N. and Glavas, S.: Thermal decomposition of peroxyacetyl nitrateRyerson, in the presence T. of B., Williams, E. J., and Fehsenfeld, F. C.: An e Tuazon, E. C., Carter, W. P. L., and Atkinson, R.: Thermal decomposition of peroxyacetyl nitrate Sander, S. P., Golden, D. M., Kurylo, M. J., Moorgat, G. K., Keller-Rudek, H., Wine,Schott: P. H., Schott UG5 UV-passingSherwen, filter, T., Evans, datasheet, M. J., Carpenter, available L. J., at: Andrews, S. J.,http://www.uqgoptics.com/ Lidster, R. T., Dix, B., Koenig, T. K., Skalska, K., Miller, J. S., and Ledakowicz, S.: Trends in NO Val Martin, M., Honrath, R. E., Owen, R. C., and Li, Q. B.: Seasonal variation of nitrogen ox- Stieb, D. M., Judek, S., and Burnett, R. T.: Meta-analysis of time-series studies of air pollution Talukdar, R. K., Burkholder, J. B., Hunter, M., Gilles, M.Thornton, K., J. A., Roberts, Wooldridge, P. J. J., and M., Cohen, and R. C.: Ravis- Atmospheric NO Tuzson, B., Zeyer, K., Steinbacher, M., McManus, J. B., Nelson, D. D., Zahniser, M. S., and Pandey, S. K., Kim, K. H., Chung, S. Y., Cho, S. J., Kim, M. Y., and Shon, Z. H.: Long-term 5 5 10 30 15 20 25 15 20 30 10 25 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | molec- × mann, J.: Interferences of commer- ff speciation at the Jungfraujoch, 3580 m above sea 28734 28733 y PAG 003 BTCA 178 Sofnofil/Carbon signal observed from measurement of three zero air sources. 2 Signal (cps)Standard Deviation 1.64 88.10 1.56 88.66 1.81 83.95 instruments in the urban atmosphere and in a smog chamber, Atmos. Meas. Tech., 2 Comparison of the NO cial NO 5, 149–159,, doi:10.5194/amt-5-149-2012 2012. as a climate gas, Atmos. Res., 37, 247–256,, doi:10.1016/0169-8095(94)00080-W Environ. 1995. Sci. Technol., 26, 74–79,,10.1021/es00025a005 doi: 1992. weger, C., and Ridgeon,surement P.: of Two high-speed, non-methane portable hydrocarbonstude and GC Observatory, J. PAN: systems Environ. results designed Monit., from 6, for the 234–41, the Jungfraujoch doi:10.1039/b310022g, mea- 2004. Highand Alti- Baltensperger, U.: Summertime NO level, Switzerland, J. Geophys. Res., 105, 6655–6667, doi:10.1029/1999JD901126 , 2000. of reactive oxidized nitrogen, atdoi:10.1016/j.atmosenv.2008.06.034 2008. eight Canadian rural sites, Atmos. Environ., 42, 8065–8078, Wang, W.-C., Liang, X.-Z., Dudek, M. P., Pollard, D., and Thompson,Warneck, S. P. L.: and Atmospheric Zerbach, ozone T.: Synthesis ofWhalley, peroxyacetyl L. nitrate K., in Lewis, air A. by acetone C., photolysis, McQuaid, J. B., Purvis, R. M.,Zellweger, C., Lee, Ammann, J. M., D., Buchmann, B., Stemmler, Hofer, K., P., Lugauer, Zell- M., Streit, N., Weingartner, E., Zhang, L., Wiebe, A., Vet, R., Mihele, C., O’Brien, J. M., Iqbal, S., and Liang, Z.: Measurements Table 1. (Eco Physics AG PAG 003, BOC Specialty Gasses BTCA 178, and Sofnofil/Carbon/13 ular sieve filters) bysecond LIF. as The well average as of the ten standard 1 deviation min of averages those is averages. shown in raw PMT counts per Villena, G., Bejan, I., Kurtenbach, R., Wiesen, P., and Kle 5 15 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | C ◦ 0.0005 ) ± 1 − C) Draw (A) ◦ 0.05 ± 28736 28735 Inlet residence time (s 0.84 1.05 1.40 2.10 1 ± ciency Temperature ( (%) 5.4 5.4 5.2 5.3 (ppt) 60.2 61.3 60.6 61.5 (%) ffi 2 2 NO NO ciency, current, and surface temperature. LampNo. Converter BLC Lamp Surface e 1 Current 2345 416 35 22 79.8 75.3 0.969 77.6 0.953 74.0 0.933 76.2 0.931 56.4 0.916 0.567 ffi concentrations. 2 ect of varying the residence time of PAN (1.0 ppb) within a 2.7 m PFA inlet on ff E Peak surface temperature and current drawn by BLC lamps in a bench test at 20.0 measured NO showing converter e Table 3. Table 2. Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 1 ± measured, and normalized to the 2 Converter ciency (%) ffi 42 33 22 e 28738 28737 Measured %Normalized % 10.8 4.4 15.9 19.6 5.2 4.3 ciency of each BLC. ffi The average raw counts per second recorded by a LIF instrument when sampling The average percentage conversion of PAN to NO Figure 1. various mixing ratios of PANalso (in shown red) (dashed and black). The zerozero average air signal signal. (black). while The sampling variance PAN falls of within the the zero noise air of signal the is converter e Table 4. Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 41 % = 28740 28739 22 % CE. signal as a function of the supplied PAN mixing ratio = signal (left panel) of the supplied PAN mixing ratio, and 2 2 22 % CE. = 35 % CE, Blue = 35 % CE, Blue The measured absolute NO The measured absolute NO = 41 % CE, Red = (left panel), and as aGreen percentage (right panel), for three BLC units operating in switching mode. Figure 3. Figure 2. as a percentage (rightCE, panel), Red for three BLC units operating in constant mode. Green Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | quantum yield is shown in black. 2 ciency, and two which fall below acceptable limits 28742 28741 ffi signal as a function of the supplied PAN mixing ratio (left panel), 2 Shown is the spectral output vs. wavelength of two new, previously unused BLC The measured NO Figure 5. No. 5 (solid) and 6 (dashed) in blue. The NO lamps No. 1 (solid)in red; and still 2 within (dashed) acceptable in conversion e green, two used lamps No. 3 (solid) and 4 (dashed) Figure 4. and as a percentage (right panel), for the cooled (blue) and uncooled (red) high powered BLC. Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | (cir- 2 NO 2 , presented 2 radicals (green), 3 (squares), HO 5 O 2 C. ◦ with a residence time of 0.96 s at 2 (triangles), N 2 28744 28743 C. Inset is detail of 30 to 90 ◦ (lilac) which are overlapped significantly by the UG5 optics – com- 2 (diamonds) shown for reference. 3 Model of thermal decomposition of PAN to NO Absorption cross section (red) and quantum yield (dashed black) of NO temperatures between 0 to 150 Figure 7. Figure 6. with the spectral outputused of UG5 in optical this filtering study (purple) output and an (dark average blue). of the Shown six are BLC interfering lamps species; NO HONO (light blue), BrONO pletely in theBLC. case Also of shown HONO, issources. whilst Additional PAN non-interfering much (gold), species; which less ClONO cles), clearly overlap HNO is is not exhibited overlapped by by the either UV-LEDs UG5 of or the BLC light Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ; • (d) 2 is over NO and 2 (c) (c) ; HO I 2 . Calculated from H ; ClONO ; PPN .

2 N 2 NO 2 ; PAN  ; BrONO  2 ; MPAN  2 28745 28746 NO 2 O 2 C(O)CH 3 by altitude in any month of a 1 year simulation. Panels ; CH  (b) 2 NO is not shown but has the same profile as HO 2 2 O 5 NO H 2 2 GEOS-Chem model showing the monthly maximum percentage over-reporting of Thermal decomposition profiles of IONO O zonally and 3 ;C J (a) 5 2 O 2 IUPAC recommended kinetic dataNote CH using FACSIMILE software based on 1 s residence time. Figure 9. NO N show the same inthe maximum absolute range of pptv themonth, values. colour zonal Note; scale. values Surface are the values the are maximum areagrid over the boxes. reporting over maximum in over-reporting the any in month Amazon any and in in any plot of the longitudinal Figure 8. Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | concentration and the 2 0.42 s and a residence time of 1 s. = τ concentration. The instrument interference is 2 28747 C. ◦ Leighton ratio calculated for each model grid-box for each daylight hour for March erent lamp temperatures, 65 to 105 ff characterized by a numerical solution of Eq. (5) with by the model as a function ofRed the grid shows box the NO values calculated without the interference on the NO Figure 10. blue indicated the values calculateddi with the interference. The interferences are calculated for