Assessment of upper tropospheric HO sources over the tropical Pacific based on NASA GTE/PEM data:

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1 JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 104, NO. DI3, PAGES 16,255-16,273, JULY 20, 1999 Assessment of upper tropospheri HO soures over the tropil Pifi bse on NASA GTE/PEM t: Net effet on HO n other photohemil prmeters J. Crwfor, 1 D. Dvis, 2 J. Olson, 1 G. Chen, 2 S. Liu 2, G. Gregory, 1 J. Brrik, G. Shse, 1 S. Snholm, 2 B. Heikes, 3 H. Singh, 4 n D. Blke 5 Abstrt. Dt for the tropil upper troposphere (8-12 km, 20øN-20øS) ollete uring NASA's Pifi Explortory Missions hve been use to rry out etile exmintion of the photohemil proesses ontrolling HOx (OH+HO2). Of prtiulr signifine is the vilbility of mesurements of nonmethne hyrorbons, oxygente hyrorbons (i.e., etone, methnol, n ethnol) n peroxies (i.e., H202 n CH3OOH). These observtions hve provie onstrints moel lultions permitting n ssessment of the potentil impt of these speies on the levels of HOx, CH302, CH20, s well s ozone buget prmeters. Sensitivity lultions using time-epenent photohemil box moel show tht when onstrine by mesure vlues of the bove oxygente speies, moel estimte HOx levels re elevte reltive to unonstrine lultions. The impt of onstrining these speies ws foun to inrese with ltitue, refleting the systemti roll-off in wter vpor mixing rtios with ltitue. At km, overll inreses HOx pprohe ftor of 2 with somewht lrger inreses being foun for gross n net photohemil proution of ozone. While signifint, the impt on HO ue to peroxies ppers to be less thn previously estimte. In prtiulr, observtions of elevte H202 levels my be more influene by lol photohemistry thn by onvetive trnsport. Issues relte to the unertinty high-ltitue wter vpor levels n the possibility of other ontributing soures of HOx re isusse. Finlly, it is note ththe unertinties gs kineti rte oeffiients t the low tempertures of the upper troposphere n s well s OH sensor librtions shoul be res of ontinue investigtion. 1. Introution mnusript, 1999]. Still f'ml ftor reltes to the inherent unertinties ssoite with the gs kineti rte oeffiients use Knowlege of upper tropospheri photohemistry ritil in moeling exerises. For the low tempertures involve t to unerstning the globl buget of tropospheri ozone n is upper tropospheri ltitues, mny of these oeffiients hve prtiulrly importnt in efining the role of ozone in limte signifintly higher unertinties. Tken overll, these onerns hnge [e.g., Fishmn et l., 1979; Wng et l., 1986; Lis et lerly suggestht the photohemil piture of the upper l., 1990; Roeloj et l., 1997]. There is lso gret interest in the troposphere is one tht is likely to ontinue to evolve. potentil impt of irrft emissions on upper tropospheri In the lst few yers, mny ttempts to verify the key fetures ozone [Brssur et l., 1996; Stevenson et l., 1997]. Our of upper tropospheri fst photohemistry hve involve the use urrent unerstning of upper tropospheri photohenfistry, of photohemil moels onstrine by irborne observtions. however, ontinues to be limite for severl resons. Most These exerises hve been lrgely limite to moel versus notble is the lk of omprehensive upper tropospheri observtionl omprisons for the speies NO2, H202, n tbse. Aitionlly, the role of fst vertil trnsport in CH3OOH [e.g., Crwfor et l., 1996; Dvis et l., 1993, 1996; ltering the omposition of the upper troposphere, while Job et l., 1996; Shultz etk, 1999; Brshw et l., 1999]. ppreite, is still iffiult to quntify [e.g., ChtfieM n These omprisons provie importnt ignostis for iniretly Crutzen, 1984; Dikerson et l., 1987; Pikering et l., 1992; ssessing moel estimtes for the fst photohemistry of HOx Dvis et l., 1996; Cohn et l., 1999; $. Liu et l., unpublishe (OH+HO2). More reently, iret observtions of rio 2 n OH in the upper troposphere n lower strtosphere hve beome vilble (e.g., Strtospheri Trers of Atmospheri Trnsport (STRAT), [Wennberg et l., 1998] n Subsoni Airrft: NASA Lngely Reserh Center, Hmpton, Virgini. Contril n Clou Effets Speil Stuy (SUCCESS),[Brune et 2Shool of Erth n Atmospheri Sienes, Georgi Institute of Tehnology, Atlnt. l., 1998]). These observtions hve offere n opportunity for 3Center for Atmospheri Chemistry Stuies, University of Rhoe Isln, more iret tests of HOx photohemil theory in the upper Nrrgnsett. troposphere. 4NASA Ames Reserh Center, Moffett Fiel, Cliforni. With the vilbility of these new HOx mesurements hs 5Deprtment of Chemistry, University of Cliforni, Irvine. ome the reliztion tht the photohemistry of the upper troposphere my be more omplex thn previously thought. For Copyright 1999 by the Amerin Geophysil Union exmple, moel lultions of upper tropospheri HO 2 n OH Pper number 1999JD levels uring both the STRAT n SUCCESS mpigns hve /99/1999JD revele tht moel estimte vlues often fll well below those 16,255

2 16,256 CRAWFORD ET AL.: ASSESSMENT OF UPPER TROPOSPHERIC HOx SOURCES mesure [Wennberg et l., 1998; Jegl et L, 1997, 1998; MKeen et l., 1997; Brune et 1.,1998]. This isgreement hs le to the suggestion tht there my be gps in our unerstning sine it is reltively insoluble [O'Sullivn et l., 1996] s ompre to H202. Although the STRAT n SUCCESS progrms hve opene of the hemistry in this region of the tmosphere. Suh problems oul exist with urrent mehnisms being use to moel tmospherihemistry. Alterntively, the tbses being use to rry out the moeling my be inequte either from the point of view of their being sttistilly non-representtive of the environment being exmine or in terms of their not proviing the neessry onstrints on moel lultions. The bove ite HOx investigtions fouse on evluting potentil soures of HOx previously unounte for in photohemil moels. Soures ientifie in these stuies tht might explin the isrepnies were etone n peroxies. The importne of etone s soure of HOx in the upper up new oppommities for testing HOx photohemil theory, both progrms hve lke the supporting mesurements of etone n peroxies neessry for more onlusive results. The STRAT n SUCCESS stuies hve relie hevily on observtions from NASA's reent Pifi Explortory Missions (PEM) to infer possible levels of etone n peroxies. This investigtion exmines the photohemil onsequenes of onstrining moel lultions with mesurements of etone, methnol/ethnol, n peroxies, s well s other ritil photohemil prmeters reore uring NASA's PEM missions. Of speifi interest will be the upper tropospheri tropil t. troposphere ws first ientifie by Singh et l. [1995] bse on mesurements tken uring NASA' s Pifi Explortory Mission (PEM)-West B. The photolysis of etone proues the ril 2. Observtionl Dtbse speies CH3CO 3 n CH302 whih, upon further retion, n The t use in this nlysis were reore in the upper yiel up to 3.2 HOx rils, given high NOx-tO-HOx troposphere (8-12 km) over the tropil North n South Pifi environment. Aitionl oxygente hyrorbons mesure by Singh et l. [1995] uring PEM-West B were methnol n ethnol. These ompouns re lost primrily through retion Oens. This region ws visite on three seprte osions uring NASA's Pifi Explortory Missions: PEM-West A (PWA), September-Otober 1991; PEM-West B (PWB), with OH, n similr to mny other nonmethne hyrorbons, Februry-Mrh 1994; n PEM-Tropis A (PTA), Augustthey n potentilly serve s net soure of HOx vi further egrtion of the primry ril speies. Soures of oxygente hyrorbons re not well quntifie, but inlue primry nthropogeni n biogeni emissions s well s seonry hemil soures from hyrorbon oxition [Singh Otober Figure 1 shows the geogrphi overge of these mpigns. The PWA n PWB missions overlppe in the North Pifi, wheres PTA primrily smple in the South Pifi. With some minor exeptions, the suite of mesurements vilble to onstrin the moel lultions ws the sme for et l., 1994, n referenes therein]. Reent stuies hve eh flight mpign [Hoell et l., 1996, 1997, 1999]. Eqully provie eviene of prtiulrly strong biogeni soures importnt is the ft tht the investigtors n mesurement [Goln, et l., 1995; Kirstine et l., 1998]. Peroxie ompouns (e.g., H202 n CH3OOH ) hve lso been ientifie s potentil soure of HOx in the upper tehniques were nerly the sme for ll three mpigns. In ition to the stnr photohemil moeling prmeters (e.g., 03, CO, NO, ew/frost point, NMHCs), observtions were troposphere. The ie tht peroxies might represent soure of lso reporte for the entrlly importnt lbile oxygente HOx ws first propose by Chtfiel n Crutzen [1984], but speies H202, CH3OOH, etone, methnol, n ethnol, the more reently hs been further explore by Prther n Job [1997] n Jegl et l. [1997,1998] in light of the new upper ltter three speies being mesure only in PWB. Moeling results for PWA, PWB, n PTA hve been bse tropospheri HOx mesurements. Peroxies represent rther on merget sets proue by S. Snholm t the Georgi unique soure of HOx in tht there re no iret emissions of Institute of Tehnology. These merges re vilble by these speies. Being prouts of photohemistry, they hve not nonymous FTP from ftp://lif. gtri.gteh. eu/pub. Sin eh of tritionlly been viewe s HOx soures. By invoking fst these merges hs ifferent time bse (3 min, PWA; 30 s, PWB; onvetive trnsport, however, peroxie-rih bounry lyer n 60 s, PTA), justments hve been me to provie (BL) ir n be move to the upper free troposphere. In this se, uniform sttistil tbse spnning ll three mpigns. The peroxie speies oul be enhne bove wht might be pproh tken involve weighting the t suh tht the 30 s expete if their only soure were lol photohemistry. One n PWB t were ounte one, the 60 s PTA t were ounte rgue tht this onition shoul be more likely for CH3OOH twie, n the 3 min PWA t were ounte six times. This 20 N 1ON ON 10S 20 S 110 E 130 E 150 E 170 E 170 W 150 W 130 W Figure 1. Geogrphi istribution of tropil upper tropospheri (8-12 km) t for PWA, PWB, n PTA.

3 CRAWFORD ET AL.: ASSESSMENT OF UPPER TROPOSPHERIC HOx SOURCES 16,257 Tble 1. Distribution of Fli,ht Dt Altitue Flight Durtion 8-9 km 9 hours, 20 rnin 8 hours, 56 min 6 hours, 18 min km 2 hours, 16 min proeure ensure tht mein sttistis for the tbse were representtive of the tul smpling times involve. Tble 1 gives the size of the PEM tbse between 8-12 km. For this nlysis, the t hve been groupe into four ltitue rnges of 1 km thikness. The bsi hemil input prmeters 03, CO, NO, n H20 were vilble for ll moel lultions. Distributions for these onstituents re shown in Figure 2. Conurrent NMHC observtions were vilble for only 50% of the t. Gps in these observtions were trete s previously esribe by Dvis et l. [1996] n Crwfor et l. [1996, 1997b]. Interpolte vlues were use for 43% of the t with the remining 7% being ssigne regionl mein vlues for speifi ltitue bns Wter Vpor Wter vpor mesurements were vilble from three ifferent instruments. For PWA, high-ltitue wter vpor t were those mesure by Lymn-0 fluoresene. For PWB, the t from ryogenilly oole, hille-mirror hygrometer [Busen n Buk, 1995] ws use. During PTA, ryogeni hygrometer mesurements were gin vilble, but ioe lser mesurements of wter vpor [Vy et l., 1998] were lso reore. The ioe lser mesurements whih were vilble for ~60% of the high-ltitue t provie n opportunity to exmine the potentil rnge of unertinty wter vpor mesurements. As note by Shultz et l. [1999], greement between the two sensors ws quite goo for mixing rtios bove 100 ppmv (e.g., +30%). Below 100 ppmv, however, the ioe lser ws onsistently higher thn the ryogeni hygrometer by n verge ifferene of 28 ppmv, with over 70% of the t iffering by ppmv. Given the low wter vpor t km (see Figure 2), the ioe lser mesure wter vpor exeee tht reporte by the ryogeni hygrometer by ftors rnging from 2.5 to 4.7. Sine both of these systems hve previously emonstrte the pbility for mesuring wter vpor t tens ofppmv, this work oes not ttempto resolve the isrepny. Inste, t from km 8-9 km O3 (ppbv) CO (ppbv) NO (pptv) H20 (pprnv) km 8-9 km Aetone (pptv) H202 (pptv) CH3OOH (pptv) Figure 2. Distributions for key tmospheri onstituents. The enter line enotes the mein vlue, boxes enompss the inner qurtiles, n whiskers enompss to 5 th n 95 th perentiles.

4 16,258 CRAWFORD ET AL.: ASSESSMENT OF UPPER TROPOSPHERIC HOx SOURCES the ryogeni hygrometer hve been use sine this system ws retions, n heterogeneous loss for soluble speies. A etile operteuring both PTA n PWB n lso provie lrger listing of retions n rte oeffiients re ontine in the tbse. However, lultions bse on the ioe lser wter ppenix. The NMHC hemistry is bse on the onense vpor re isusse lter in the text. The wter vpor istribution mehnism of Lurrnnn et l. [1986] with moifitions tht shown in Figure 2 is tht ef'me by the ryogeni hygrometer for inlue ppropritely upte rte oeffiients, itionl PWB n PTA n tht reore by the Lymn-e fluoresene retions for remote low-nox environments (e.g., formtion of instrument uring PWA. orgni peroxies), n expliit hemistry for some speies 2.2. Oxygente Hyrorbons previously "lumpe" into fmilies (e.g., etone, propne, n benzene). Photolysis rte oeffiients re bse on DISORT 4- Oxygente hyrorbon mesurements were vilble only strem implementtion of the NCAR Tropospheri Ultrvioletfor PWB [Singh et l., 1995]. These mesurements suggeste, Visible (TUV) ritive trnsfer oe (S. Mronih, privte however, tht etone, methnol, n ethnol re ubiquitous in ommunition). A more etileesription of the photolysis the tropil upper troposphere. As result, they hve been use rte oeffiient lultions is given by Crwfor et l. [1999]. to infer etone onentrtions in number of other stuies Moel lultions re onstrine by observtions of 03, [MKeen et l., 1997; Jegl et l., 1997, 1998]. For purposes CO, NO, NMHCs, temperture, ew point, n pressure. When of this stuy, etone for PWA n PTA hs lso been inferre mesurements re vilble, moel lultions n lso be to llow mximum usge of the PEM tbse. Aetone vlues onstrine by the following speies: H202, CH3OOH, HNO3, were inferre oring to the nlysis of MKeen et l. [1997] PAN, etone, CH3OH, C2H5OH, HCOOH, n CH3COOH. whih revele strong orreltion between etone n CO in With the exeption of NO, onstrining prmeters re ssume the upper tropospheri PWB t. In this stuy, inferre etone to be onstnt over the iurnl yle. NO is llowe to vry vlues were use for 83% of the t nlyze. The istribution imlly; however, totl short-live nitrogen (NO+NO2+NO 3 of etone use in these lultions is shown in Figure 2. +2N2Os+HONO+HO2NO2) is hel onstnt. The mount of short Methnol n ethnol were lso inferre oring to the -live nitrogen is etermine suh tht the NO onentrtion PWB observtions. These observtions showe methnol mthes the mesurement t the pproprite time of y. exeeing etone in ll ses with n verge methnol-to- Photohemistry ittes the prtitioning of short-live nitrogen etone rtio of 1.5. Thus, in those ses where etone ws mong the onstituent speies. inferre, the mixing rtio for methnol ws tken to be ftor Moel-lulte speies re ssume to be t stey stte, of 1.5 times lrger. While ethnol ws lso shown to hve mening tht onentrtions were integrte in time until their mesurble onentrtions in the upper troposphere uring PWB, iurnl yles no longer vrie fxom y to y. Results onentrtions were onsierbly more vrible, n its short presente here re bse on iurnl verge vlues for lulte lifetime in the upper troposphere (- 5 ys) reners it fr less speies n photohemil rtes. preitble thn either etone or methnol. For this reson, onstnt mixing rtio of 30 pptv ws use when mesurement 4. Approh of ethnol ws not vilble. This vlue is on the onservtive sie given tht more thn 85% of the high-ltitue ethnol Assessing the impt of iniviul HOx soures in the upper mesurements exeee this level. troposphere is omplite by the fththe system is highly nonliner. One pproh tken in erlier stuies hs involve 2.3. Peroxies looking t primry soure strengths for iniviul pthwys The peroxie speies H202 n CH3OOH were mesure in [Wennberg et l., 1998; Jegl et l., 1997]. While this oes ll three mpigns [Heikes et l., 1996; O'Sullivn et l., 1999]. provie n inition of the reltive importne of vrious HO Unlike the oxygente hyrorbons, peroxie speies oul not soures, it oes not fully ress the most pivotl question be esily inferre for gps in the t; thus, the t use in this onerning the finl impt on HO onentrtions. In the upper nlysis were limite to those time perios for whih troposphere, HO tens to be regulte not by primry soures, mesurements were vilble. The istribution of peroxies is but by seonrt formtion through the oxition of CH4 n given in Figure 2. This inlues those perios when peroxies other NMHCs [Liu et l., 1980]. Aitionlly, some of the most were t or below the limit of etetion (LOD). LOD vlues for importnt sink proesses for HO re qurti losses (HO2+HO2, H202 n CH3OOH were 15 n 25 pptv, respetively. While the HO2+OH); thus, bsolute HOx onentrtions re not very sensiunertinty these mesurements vries with onentrtion, the tive to hnges in primrt proution rtes. This n be most typil unertinty for the t use here is +30%. Note, while lerly emonstrte with n exmple bse on tul PEM H202 ws mesure t LOD vlues for less thn 2% of the t, flight t. A speifi t smple fxom PTA flight 17 ws LOD vlues for CH3OOH omprise 12% of the t. Further- hosen with the following onitions: 8.7 kin, 38 ppbv 03, 80 more, 42% of the CH3OOH t t km were LOD. ppbv CO, 100 pptv NO, 93 ppmv tt20, n 363 pptv etone. Bse on these input onitions, three lultions were 3. Moel Desription onute. The first onsiere only the impt of primry proution of HO fxom wter vpor. The seon inlue only Dt nlysis for this stuy involve the use of time primrt proution fxom etone. The preite HO for these epenent photohemil box moel similr to tht use for two lultions ws ientil (i.e., 2.45xl 07 moleules/m3). In previous PEM relte work [Dvis et l., 1993, 1996; Crwfor thir lultion whih inlue both primry soures, the et l., 1996, 1997, b]. The moel mehnism hs been upte preite HOx inrese to 2.92xl 07 moleules/m 3. Thus, when to reflethe most urrent retions n rte oeffiient ombine, these two HO soures resulte in only 20% more HOx reommentions [DeMore et l., 1997; Atkinson et l., 1992] thn eh otfi proue by itself in isoltion. This result n n inlues bsi HOx-NOx-CH 4 gs phse hemistry, only be unerstoo when the importne of seonry HOx nonmethne hyrorbon (N C) hemistry, photolysis formtion is exmine.

5 CRAWFORD ET AL.' ASSESSMENT OF UPPER TROPOSPHE C HOx SOURCES 16,259 Seonry formtion of HOx is initite by the oxition of totl formtion rte of HOx in the thir lultion is only bout CH4 (or some other hyrorbon speies) by OH to form orgni 35% greter thn tht for the first two lultions espite peroxy rils, e.g.' oubling in primry proution. (R1) CH 4 + OH -. CH3 + H20 For purposes of this stuy, n ppro hs been tken tht oes not ttempto evlute the reltive importne of iniviul (R2) CH ' CH302 primry soures. Rther, series of sensitivity lultions hs been onute to evlute how preitions of lion n relte In the presene of NO, these orgni peroxy rils n ret to form HO 2 n formlehye (CH20), e.g.' photohemil prmeters hnge for suessive egrees of moel onstrint. This sensitivity nlysis exmines the inrementl hnge in moel lultions bse on PEM t by (R4) CH302 + NO -. CH30 + NO 2 CH ' CH20 + HO2 onstrining the moel oring to the following progression: (1) wter vpor, (2) NMHCs, (3) etone, (4) methnol/ethnol, (5) CH3OOH, n (6) H202. As emonstrte bove, the orer Through photolysis, formlehye n yiel itionl HO2: in whih these onstrints re invoke nnot be onstrue s ny (R5) CH20 + hv -' CHO + H inition of their reltive importne in terms of primry proution of HOx; however, there re other proeurl resons (R6) CHO q- 02 -' HO 2 q- GO for hoosing this orer. (R7) H ' HO 2 Wter vpor is onsiere first. Through O( D)+H20, it represents the most bsi HOx preursor tht is universlly For the first smple lultion isusse bove, the iurnl verge primry HOx soure from wter vpor (i.e., O(1D)+H2 ) onsiere in ll moels; thus, ny hnges to our urrent unerstning of upper tropospheri HOx hemistry shoul be ws pproximtely 8x103 moleules m '3 s 'l. The seonry referene to how these moifitions lter this bsi hemistry. formtion rte resulting from the ombintion of (R3) n (R5) NMHCs re onsiere next sine they lso represent n input to totle 4.5x 104 moleules m '3 s 'l. Thus, primry proution moels tht hs been well reognize. They sometimes re onstitute only bout 15% of the totl HOn formtion rte. In neglete in the upper troposphere ue to low onentrtions, but the se of the seon lultion, CH302 n CH20 resulting they still represent bsi omponent of most photohemil from etone photolysis versus methne oxition h to be ifferentite, but the sme result (i.e., 8x 103 versus 4.5x 104 moleules m '3 s 'l) ws etermine. In the thir lultion, the ombintion of primry soures oubles primry formtion, but the inrese in seonry formtion epens on the inrese in OH whih is smll given the qurti loss of HOn. Thus, the moels. Aetone represents more reently reognize ition to the bsi photohemistry of the upper troposphere. Sine the work ofsingh et l. [ 1995], the impt of etone hs been onsiere in severl photohemil nlyses of NASA GTE t [Dvis et L, 1996; Job et l., 1996; Crwfor et l., 1997, b; Shultz km km 8-9 km 8-9 km 7-8 km 7..8 km 6-7 km 6-7 km 5-6 km 5-6 km 4-5 km 4-5 km 3.4 km 3.4 km 2-3 km 2-3 km 1-2 km 1-2 km 0-1 km, r--i, ) 0-1 km - I - b) I I I I I I I I I I I H202(mesll) CH3OOH(mesll) Figure 3. Box-whisker plot of () H202(mes/l ) n (b) CH3OOH(mes/l). See Figure 2 for box-whisker ef'mition.

6 16,260 CRAWFORD ET AL.' ASSESSMENT OF UPPER TROPOSPHERIC HOx SOURCES km km II 8-9 km I I I I " 1 I I J I I I I I Cse FIA '" Cse E/A D Cse DIA r-i Cse CIA 13 Cse BIA '2 OH rtio 8-9 km ), I I I I i i i i i I 1 I I I Cse FIA D Cse EIA D Cse DIA I Cse CIA I-'! Cse BIA b) I I I I I I I I HO 2 rtio Figure 4. Box-whisker plots of moel sensitivity lultions normlize to the "stnr" se (se A) for () OH n (b) HO 2. See Figure 2 for box-whisker efinition. et l., 1999]. Given its ubiquitous nture n orreltion with onstrine only by mesure vlues of 03, CO, NO, n H20 CO, resonble mixing rtios n be inorporte into moel (se A). Subsequent moeling runs, referre to s ses B-F, lultions with little effort. Similrly, methnol n ethnol representhe sequentil ition of NMHCs (se B), etone re e to more ompletely evlute the impt from (se C), methnol n ethnol (se D), CH3OOH (se E), n oxygente hyrorbons. H202 (Cse F). This llows for n exmintion of the Peroxies re onsiere lst ue to their trnsient nture. inrementl hnges in preite HOx levels n relte Sine they re short-live, it is expete tht their enhnements prmeters s the number of onstrint speies is progressively in the upper troposphere re limite in spe n time by the inrese. For ses A-D, CH3OOH n H202 hve been stohsti nture of onvetive events. Unlike the other lulte to be in photohemil equilibrium. For ll LOD onstrining speies, peroxies n be estimte from moel bse on photohemil equilibrium onsiertions in the bsene of mesurements. Constrining the moel with peroxies must therefore be viewe s evition from photohemil equilibrium s efine by observtions. Suh n peroxie vlues, these speies ontinue to be lulte bse on photohemil equilibrium onitions for ses E n F. The mein lulte CH3OOH n H202 vlues for LOD mesurements were 30 n 95 pptv, respetively. Figures 4-6 show how the suessive ition of onstrints justment oul tke the form of either n inrese or erese influene lulte levels of HO n relte photohemil in peroxie mixing rtios. To emonstrte this, Figure 3 shows prmeters. These hnges re represente by the rtio for eh box-whisker plots of mesure-to-lulte peroxie rtios for ll tropil PEM t. In this se, the lulte vlues re se reltive to se A. Tble 2 gives the overll mein n men hnge for eh speies or prmeter (i.e., se F/se A). bse on moel runs tht hve been onstrine by ll mesure To ompny the isussion of results, Tble 3 outlines the most vribles other thn the peroxies. Sine this evlution is in the relevnt retions ssoite with eh HOx soure. form of rtio, only those mesurement perios where peroxie levels were bove the LOD re shown. These results show tht Ox (O11 n 1tO2) H202 is resonbly well preite, i.e., the mein rtio is ner Figures 4 n 4b illustrte tht inreses HOx ue to unity. Furthermore, there ppers to be no signifintren in hnges in moel onstrints ten to be gretest t higher the rtio with inresing ltitue, the exeption being the t t ltitues. This tren is onsistent with the erese in wter km. By ontrst, vlues for the CH3OOH rtio exhibit vpor with inresing ltitue, n thus, reution in the strong ltitue tren, espeilly bove 8 _km. Potentil ontribution from the O(ID)+H20 soure. Although OH n HO 2 explntions for these trens in H202 n CH3OOH will be re in rpi photohemil equilibrium, Figures 4 n 4b revel explore lter in the isussion of results. tht their respetive responses to hnging moel onstrints re 5. Results The moeling results tht follow re presente s series of not ientil. Tble 2 lso shows tht below 10 km mein inreses HO 2 re nerly 3 times greter thn those for OH. Only t km o hnges in OH pproh those lulte ses beginning with the "stnr" se of bsi photohemistry for HO 2.

7 11-12 km CRAWFORD ET AL.: ASSESSMENT OF UPPER TROPOSPHERIC HOx SOURCES 16,261 I I I...I. I I I km :' I Cse FIA -- [] Cse EIA D Cse DIA r Cse CIA 8-9 km i ' r-i Cse BIA 8-9 km!! I Cse FIA [] Cse EIA Cse DIA r-i Cse CIA r-i Cse BIA I I I I I i i CH302 rtio CH20 rtio Figure 5. Box-whisker plots of moel sensitivity lultions normlize to the "stnr" se (se A) for () CH302 n (b) CH20. See Figure 2 for box-whisker efinition. The mute response of OH ppers to be relte to ombintion of ftors. Most obvious is the itionl buren on OH presente by the onstrints ssoite with ses B-F. This is prtiulrly true for NMHCs, methnol, n ethnol whih re priniplly lost through retion with OH. Aetone n CH3OOH ret with OH s well, but they lso hve importnt losses through photolysis. Another ftor reltes to the potentil for HOx yling. Unlike O(ID)+H20 n H202+h¾ whih introue HOx in the form of OH, the other HOx soures initilly form HO 2. Thus, for thosenvironments where mbient HOx n NOx levels re omprble, it beomes more likely tht HO 2 will be lost to either self-retion or retion with other orgni peroxy rils before being yle into OH vi retion with NO. Below 11 km, the lrgest hnges in HOx levels re ssoite with etone n CH3OOH. NMHCs, methnol, n ethnol pper to exert miniml influene both on HO 2 n OH. H202 lso shows little impt below 11 km; however, the rnge of vlues is broene. Above 11 km, H202 hs greter impthn CH3OOH, n etone ontinues to be strong influene. Sine H202 introues HOx in the form of OH, it lso helps explin why inreses OH pproh those for HO 2 t this ltitue CH302 n CH20 CH302 n CH20 represen two importnt intermeite prouts in the formtion of HOx from the oxition of NMHCs, etone, methnol, ethnol, n CH3OOH. Figures 5 n 5b show tht shifts in the rtio for these speies re signifintly lrger thn those for OH n HO 2. The lrger response for these speies is expete sine the follow-on hemistry for eh oes not utomtilly le to HO 2 formtion. This is prtiulrly true for the ril speies CH302 when the environment is NOx poor. Formlehye lso hs lternte egrtion pthwys tht o not proue HO 2 (see Tble 3). The lrgest shifts in the rtio for CH302 n CH20 re ssoite with etone n CH3OOH; however, for CH20, methnol n ethnol lso mke signifint ontribution. H202 hs reltively little impt on CH302 n CH20, even t km. As ws observe for OH n HO2, the overll hnges for both CH302 n CH20 inrese with ltitue. Of the two, CH20 is lerly the most sensifive speies, mking it n iel nite in testing for the presene of itionl HOx soures Ozone Buget Impts on the ozone buget re epite in Figure 6. Shifts in the ozone buget re ouple iretly to hnges in HOx levels. Ozone formtion, F(O3), whih is riven by the retion of NO with peroxy rils is strongly epenent upon HO 2 n, to lesser egree, CH302 n other orgni peroxy rils. This is reflete in Tble 2 whih shows tht mein inreses in F(O3) exee enhnements in HO 2 but re less thn those for CH302. On the other hn, D(O3) epens only prtilly on HO2 n OH; thus,.inreses in its mein vlue re smller thn those for HO 2. In the upper free troposphere, F(O3) typilly exees D(O3); therefore, the net ozone teneny, P(O3), tens to be positive n to trk F(O3). Mein inreses in P(O3) re similr to, but slightly lrger thn, those for F(O3). 6. Disussion Similr to previous stuies, these results lerly emonstrte tht moel-lulte vlues of HOx for the upper troposphere bse solely on the H20+O( D) soure will le to n unerestimte of HOx levels. Furthermore, these unerestimtes my be even lrger for relte quntities suh s gross n net

8 , 16,262 CRAWFORD ET AL.' ASSESSMENT OF UPPER TROPOSPHERIC HOx SOURCES km km I I I I I I I I I I I I ß ----[! km D I Cse F/A Cse EIA -- * D Cse DIA, :. :!-1 Cse'CIA i-i Cse BIA ) I I I I I I I I I I! I I I I I km I Cse FIA _ D Cse E/A D Cse DIA /.. Cse CIA!-] Cse BIA b) I I I I I I I I I I I ; F(O3) rtio D(O3) rtio i i i i q i i i km 8-9 km I Cse FIA -- Cse E/A r Cse DIA,, :,, : ' I-I i-i Cse CIA BIA -D-- ) i i i i i I I P(O3) rtio Figure 6. Box-whisker plots of moel sensitivity lultions normlize to the "stnr" se (se A) for () F(O3), (b) D(O3), n () P(O3). See Figure 2 for box-whisker efmition. ozone proution. Even so, the inreses lulte HOx for the PEM t, espeilly inreses ue to peroxies, pper to be signifintly less thn wht might be expete bse on reent HOx mesurements [Wennberg et l., 1998; Brune et l., 1998; Jegl et l., 1997, 1998]. Thus, the urrent moel restfits rise severl key questions: (1) While wter vpor lone n sustin most of the lulte HOx, how well oes one nee to know the mesure wter vpor level? (2) If peroxies re influening upper tropospheri HOx through onvetion, why oes H202 rther thn CH3OOH hve the greter influene?, n (3) Wht

9 CRAWFORD ET AL.: ASSESSMENT OF UPPER TROPOSPHERIC HOx SOURCES 16,263 Tble 2. Overll Chnl es in Tropil Upper Tropospheri Photohemil Prmeters (se F/se A) OH HO CH30 CH O F(O3) D(O3) P(O3) 8-9kin Mein Men Mein Men Mein Men km Mein Men other HOx soures might ply role in upper tropospheri An initil set of lultions ws bse on hemistry hemistry? Below, we explore eh of these questions in the onsiering only the ioe lser wter observtions (i.e., se A). ontext of the GTE-PEM observtions n moeling restfits. Reltive to "se A" lultions for the ryogeni hygrometer, 6.1. Wter Vpor OH n HO 2 vlues were bout 30% lrger. This represents smll hnge given tht inreses primry proution of HOx Erlier isussion of wter vpor observtions from PTA were ftors of 3 to 5. These results further highlighthe erlier revele tht mesurements hve very high unertinty below 100 ppmv (e.g., ftors of 3-5). This onlusion ws bse on pointht HO x tens to be firly insensitive to hnges in primry omprison of ryogeni hygrometer n ioe lser observproution t these ltitues. These lultions lso mke the tions. The issue of wter levels beomes espeilly importnt strong point tht reltively smll errors in the mesurement of with respet to lultions t ltitues of km where HOx levels n le to the onlusion tht there is nee for sensitivity lultion showe moel onstrints to hve their lrge hnge in primry proution. gretest impt. Aitionl ltfitions for the PTA t t 11- Clultions were lso rrie out bse on the ioe lser 12 km were onute bse on ioe lser wter vpor to wter mesurements together with ll other moel onstrints exmine the impt of this unertinty. (i.e., se F). Reltive to lultions bse on the ryogeni Tble 3. Soures of lion n Competinl Retions Soures of HOx Ozone Photolysis O3+h¾- O(1D)+O2 O('D)+H20-2OH Nonmethne Hyrorbon Oxition RH+OH- ø2-.ro2+h20 RO2+NO- h-.rcho+ho2+no2 RCHO+hv- ø2- RO2+HO2+CO Aetone Photolysis CH3C ( O)CH3+hv- 0,.., CH3C O3+CH302 CH3CO3+NO- h- CH302+NO2+CO CH302+NO- h-.ch20+ho2+no2 CH O hv- ø'-.2ho2+co Methnol/Ethnol Oxition' CH30H+OH- ø'- CH20+HO2+H20 C2HsOH+OH- h-'ch3cho+ho2+h20 CH3CHO+hv-'CH302+H02+CO CH3OOH Photolysis b CH OOH+h v- oh_. CH20+H O2+OH CH3OOH+OH-' CH20+OH+H20 H202 Photolysis H202+hv-'2OH Competing Retions O('D)+M- O(3p)+M RO2+HO2-'ROOH+O2 RCHO+OH- h_ RCO3+H20 CH3C O3+HO2-.ROOH+O2/Aeti Ai+O 3 CH3CO3+NO2- PAN CH302+HO2-.CH3OOH CH20+h¾-. CO+H 2 CH20+OH- O, HO2+CO+H20 H202+OH-.HO2+H20 'see etone for subsequent retions of CH CO, CH O2, n CH20 bsee etone for subsequent retions of CH O2 n CH20 CH3CHO+OH-. CH3CO3+H20 CH300H+OH-' CH3 O2+H20

10 - _ 16,264 CRAWFORD ET AL.: ASSESSMENT OF UPPER TROPOSPI- C HO x SOURCES hygrometer mesurements, OH n HO 2 vlues inrese by only 5% on verge. Thus, HOx levels re inite to be reltively insensitive to the bsolute wter level in the upper troposphere (11-12 km), refleting the ominne of seonry proution s well s the ft tht wter is less importnt s primry soure thn etone. looo Peroxies Unerstning the role tht peroxies ply in upper tropospheri photohemistry omplite by the fththese 300 speies re erive not only from lol photohemistry but lso 200 from trnsport. Thus, observtions of these speies in the upper troposphere must be viewe s the net result from some loo ombintion of both soures. Box moels n only ssess the levels of peroxies expete from lol photohemistry. Thus, ny impt ue to trnsport (e.g., eep onvetion) must be inferre through omprisons of mesure n lulte peroxie levels. Convetive trnsport of peroxies nnot be relistilly ientifie by only ompring ifferenes in the mesure peroxie mixing rtios between two ir msses. This is emonstrte by lose exmintion of the PWB t for the o loo tropil upper troposphere. This t hs been use in reent stuies to infer onvetive trnsport of peroxies [Jegl et l., = ; Folkins et l., 1998]. For exmple, Jegl et l. ompre -r lo o PWB peroxies for onvete n bkgroun ir using imethyl ' 5 sulfie s onvetive trer. When levels were bove 3 pptv, the ir mss ws ssume to be one whih h been strongly influene by eep onvetion. Folkins et l. me similr omprison of PWB peroxie levels but bse their ssessment o.15 on NO levels. For ir msses with NO below 25 pptv, it ws ssume tht the ir mss h been signifintly influene by -r reent mrine onvetion. Both pprohes le to the onlusion 0.05 tht onvetion h enhne both H202 n CH3OOH by ill,, tj, ftors of 2-3 n 5-6, respetively. Not reognize, however, ws the ifferene in wter vpor for the two ir mss types Crwforet l., [ 1997] isusse in some etil the tropil Time (ys) PWB t use by Jegle et l., n Folkins et l., iviing it into wht were lbele "high NOx" n "low NOx" regimes. Figure 7. Time evolution of onvetively perturbe peroxies Crwfor et l. rgue tht both regimes resulte from reent n CH20 for mein onitions observe in the low NOx regime onvetion, one of ontinentl origin (high NO0 n the other of of PEM-West B. Perturbtions onsist of typil mrine mrine origin (low NO0. Among the importnt ifferenes ite bounry lyer vlues for CH OOH (1 ppbv) n CH20 (200 ws the lrge ifferene in wter vpor between these regimes. pptv). Soli lines represent the ssumption of totl svenging of The t in Tble 4 show tht muh of the ifferene in peroxie H202. Dotte lines ssme H202 to be 75% svenge (250 pptv). Horizontl lines represent the stey-stte solution. levels for these two regimes n be expline by ifferenes in the lol hemil environment rther thn trnsport of peroxies from the mrine bounry lyer. The mein vlues for the rtio of mesure-to-lulte H202 for both regimes suggest ththe lol photohemil environment oul esily sustin the Tble 4). The higher H202 levels in the low NOx regime pper observe H202 mixing rtios without invoking trnsport (see to be the result of bot higher wter vpor leing to inrese HOx levels n lower NO leing to less HOx yling, n hene, inrese formtion of H202. This interprettion of the t Tble 4. Mein Vlues for H20, NO, H202, CH3OOH, woul seem to be in better or with the known high solubility H202(mes/l), n CH3OOH(mes/l ) for 8-12 km, of H202 n woul rgue ginst H202 being effetively 20 øn- 10 o S During PEM-West B trnsporte to the upper troposphere by eep onvetion. High NOx Low NOx By ontrst, Tble 4 shows tht mein vlues for the rtio of H20, ppmv mesure-to-lulte CH3OOH re greter thn unity for both NO, pptv regimes. This suggests tht in the se of CH3OOH there oul H202, pptv be role for onvetive trnsport. The low NO regime is shown CH3OOH, pptv to hve the higher mein rtio (i.e., 2.16 vs 1.57); however, this H202(mes/l) ifferene in rtios flls fr short of explining the ftor of 5 CH3OOH(mes/l) ifferene in mein levels of CH3OOH whih gin pper to be lrgely ttributble to ifferenes in lol photohemistry

11 CRAWFORD ET AL.' ASSESSMENT OF LIPPER TROPOSPHERIC HOx SOURCES 16,265 Although the bove ite moeling results point towr the nee to ritilly exmine lol photohemil trens in the peroxies, it must be note tht moel preition suh s those These lultions show how rpily photohemil equilibrium for peroxies n be reestblishe in high wter vpor environment suh s the PWB low NO regime. It lso in Tble 4 lso hve shortomings in tht they ssume shows tht one might expet reently onvete ir to exhibit photohemil equilibrium. In relity, it is quite likely tht muh enhne CH3OOH ompnie by eplete H202. Figure 8 of the tropil upper troposphere is perturbe with frequeny exmines the peroxie observtions for the PWB low NO regime tht prelues rehing lol stey stte [Prther n Job, in terms of this expettion. While it is not relisti to expethe 1997]. Thus, evluting the time evolution of peroxies fiel t to losely mth these simultions, it is interesting to following onvetivevent s they move towr photohemil see tht when observtions of CH3OOH re elevte bove their equilibrium vlues n prove useful. This type of pprohs been implemente in stuies by Jegl et l. [1997] n Cohn et l. [ 1999]. Here, simultions re bse on mein onitions for the PWB low NOx regime for two ses. In the first, CH3OOH n CH20 re ssume to be trnsporte from the mrine bounry lyer unilute (e.g., 1 ppbv n 200 pptv, respetively) n H202 is ssume to be totlly svenge. The seon se is ifferent in tht H202 is ssume to be 75% svenge (e.g., 250 pptv). Results re shown in Figure 7. The time evolution of these speies is somewht rtifiil in tht no ilution ue to mixing is ssume, but the results still give some inition of how peroxie levels might evolve ue to lol lulte stey-stte vlues in this t, H202 observtions ten to be eplete below their lulte stey-stte vlues. Thus, there is some onsisteny in the mesure-to-lulte peroxie rtios with the rgument tht they hve been influene by onvetion. Relling the sensitivity lultions, peroxies were estimte to hve their gretest impt on HO levels t km (--- 30%). One of the more interesting spets of these results ws fining tht t this ltitue the lrgest HO inrese is relte to the onstrint of H202, not CH3OOH. This ws foun to be true even though Figure 3 lerly shows tht the rtio of mesure-tolulte vlues for CH3OOH exhibithe lrgest inrese bove photohemistry. In both ses, enhnements in CH3OOH bove 8 kin. This is suggestive of fst vertil trnsport, but it is lso stey stte erese from ftor of 5 to ftor of 2 t the en of 2 ys. Atter 3 ys, H202 is slightly bove or below its stey-stte vlue epen'rg on the se ssume. CH20 behves muh s CH OOH. HO 2 is initilly elevte by 35%. possible tht this tren my be somewht overestimte, espeilly for kin, owing to the lrge perentge of the CH3OOH t t LOD vlues (i.e., 42%). In this ontext, the question n be rise whether the enhne vlue ofthe rtio for Over the first y, iurnl verge HO 2 is elevte by 21% bove H202 t km is, in ft, unerstoo. For exmple, if the stey stte with the lrgest enhnement (45%) ourring t observe H202 enhnement is to be ttribute to onvetion, one sunrise. -By the seony, the iurnl vergenhnement oul rgue tht there shoul be some orresponene with the rpily iminishes to less thn 15%, lthough sunrisenhne- enhnement in CH3OOH. Looking speifilly t the CH3OOH ment of 32% is still present. OH is initilly epresse by 20% with reovery to within 10% of stey stte within the first y. observtions km tht were t or below LOD, it woul seem iffiult to rgue tht these CH3OOH levels were signifintly influene by onvetion. Yet for this subset of t, the mein rtio of mesure-to-lulte H202 remins signifintly greter thn one (i.e., 3.6). This woul seem to 1.8 suggest tht the enhnement in the H202 rtio t km is not ue to onvetion but rther to other ftors suh s lol 1.6 photohemistry. Similr to the PWB low NOx regime, Figure 9 exmines the time evolution of onvetively perturbe peroxies bse on mein onitions for ll tropil PEM t t km. The two perturbtion senrios use here re the sme s those use for the PWB low NOx regime moel rims. The most signifint ifferene between these two t sets is the wter vpor mix'rg 1 rtio. The km t hs mein vlue of 15 ppmv; wheres, the PWB low NO regime hs mein of 600 ppmv. 0.8 As shown in Figure 9, the time evolution profiles bse on the km t show some signifint ifferenes, espeilly with respeto H202. Both CH3OOH n CH20 ey rpily over the first 2-3 ys, lthough, CH3OOH is still signifintly bove its stey-stte vlue even tter 3 ys. H202 in this low H20 environment is enhne bove the stey-stte vlue by s muh s 2-5 times, epening on the senrio. In greement with the 0.2 I I I I I I I I lultions of Jegl et l. [1997] n Cohn et l. [1999], the enhnement in H202 persists longer thn tht for CH3OOH. CH3OOH (mesll) Lrge initil enhnements in HO 2 n OH re lso observe in these lultions. These enhnements relx to iurnl verge Figure 8. vlues tht re bout 20% bove finl stey stte tter 3 ys. Stterplot of H202(mes/l) versus These lultions emonstrte two importnt points: (1) in low CH OOH(mes/l) for the low NOx regime of PEM-West B. wter vpor environment, H202 n CH3OOH enhnements ue Soli n otte l'mes represent the evitions from stey stte to onvetion re not simultneous n (2) enhne H202 n preite in Figure 7. Numbers long eh line represent the number of ys from the initil perturbtion. ontinue to influene HO well tter the perturbtion in CH3OOH levels hs issipte.

12 _ 16,266 CRAWFORD ET AL.' ASSESSMENT OF UPPER TROPOSPHERIC HOx SOURCES looo while t other times they exeee preitions by ftors of [Brune et l., 1998]. In both stuies, the possibility tht 600 onvete peroxies might onstitute n importnt itionl soure of HOx ws propose. The results from the PEM t suggest tht peroxies oul hve resulte in inreses HOx, -r but even t km the inrese is typilly no more thn 30% n never more thn ftor of 2. While the mein inrese of % oes pproh the men inrese of 1.5 ite for the STRAT - _ 200 t, rell tht the itionl 20% ifferene requires nontrivil inreses primry HOx proution In ll likelihoo, ifferenes between these mpigns re '" 50 most likely expline by the ft tht onitions observeuring I I I I I I I I I - the PEM missions were simply ifferent from those enountere uring STRAT n SUCCESS. In STRAT, for instne, the ER- 2 smple between ltitues of 8 km n the tropopuse ( km), while the DC-8 ws limite to eiling of 12 km uring the 100 5O - PEMmissions. It is lso noteworthy, however, tht isrepnies between mesure n lulte HOx uring STRAT were gretest for the lower ltitues (i.e, km) with higher wter 2O I I I I I I I I vpor (i.e., ppmv), while the rier ir msses t higher ltitues ppere to be explinble in terms of wter vpor n etone only [MKeen et l., 1997]. STRAT t highlighte by Jegl et l. [1997] ws lso preominntly in the km ltitue rnge. Regrless of the similrities n ifferenes 0 ',' 5 between these mpigns, it is worthwhile to explore the 0.5 possibility tht other still unientifie impts on HOx my exist. One possibility for itionl HOx oul ome from the 0.4 extension of known NMHC soures to inlue the presene of 0.3 more omplex, but nlogous oxygente hyrorbons [S. Liu et l., unpublishe mnusript, 1999]. For instne, etone -r oul be extene to inlue ll ketones. While higher-orer 0.1 ketones re expete to hve muh less bunne, they lso I I I I might provie greter yiel of HOx. The sme n be si for 0 I orgni peroxies, lohols, n lehyes. Although mesuring ll of these speies is urrently imprtil, some inition of Time (ys) the importne of these soures oul be gine through Figure 9. Time evolution of onvetively perturbe peroxies mesurements of CH20. Rell, lultionshowe CH20 to be n CH20 for mein onitions observe t kin. fr more sensitive thn either HOx or CH302. Thus, mesure- Perturbtions onsist of typil mrine bounry lyer vlues for ments of this speies in the upper troposphere oul prove to be CH3OOH (1 ppbv) n CH20 (200 pptv). Soli lines represent useful initor of the integrte impt from NMHC soures. the ssumption of totl svenging of H202. Dotte lines ssume Another possible HOx soure propose by Tourni [1993] lso H202 to be 75% svenge (250 pptv). Horizontlines emns new ttention in light of the reent HOx observtions. represent the stey-stte solution. Toumi propose tht OH my be proue in the tmosphere by retion of eletronilly exite oxygen with hyrogen (i.e., O2(bZ g) + H 2 -' 2Olt). While O2(bl g) is expete to be ollisionlly quenhe, Toumi showe tht even if only 1% of the While onvetion of peroxies is inrgubly n importnt ollisions result in retion, the resulting primry proution of onsiertion in unerstning upper tropospheri HOx, it is OH woul exee tht for O( D)+H2 in the upper troposphere. importnto reognize tht the lose reltionship between HOx In Toumi's stuy the potentil importne of this retion ws n H202 possesses ertin level of mbiguity. Elevte H202 mximize in the upper troposphere both ue to the inresing will le to elevte HOx, but the reverse is lso true. Is it bunne of O2(bZ g) n ue to the eresing mount of wter possible tht the elevte H202 t 11-12kmissimplyrefietion vpor. In follow-up stuy by Siskin et l. [1993], it ws of elevte HOx levels ue to soure whih is unounte for pointe out tht fter orreting for n overestimte by Toumi for by ny of the onstrints onsiere here? Suh possibilities re the bunne of O2(b g), 4% of the ollisions were require to exmine below. be retive to be equivlento the originl proposl by Toumi. Siskin et l. lso note tht the resulting impt woul inrese 6.3. Other Possible HOx Influenes? the iuml-verge OH bunne by up to ftor of 2 t n During the STRAT mpign, HO 2 observtions were foun ltitue of 15 km. to exee wht might be expete from wter vpor n etone Subsequent to these theoretil stuies, no lbortory stuies by ftor of 1.5 on verge with instnes of ifferenes s high were initite to support or refute the possible importne of this s ftor of 5 [Jegl et l., 1997]. During SUCCESS, HOx retion. Reently, however, lbortory stuy hs been mesurements were sometimes in greement with preitions, onute whih shows this retion to hve n OH yiel of less

13 CRAWFORD ET AL.' ASSESS1V NT OF UPPER TROPOSPHERIC HOx SOURCES 16,267 Tble A1. Chemil Mehnism for the Photohemil Box Moel Retion Bsi HOx-NOx-CH4 Retions Gs Phse Retions k, O('D)+N -O( P) k O('D)+O -.O( P) k O('D)+H O-.2OH k40('d)+ch4-ch +OH k O('D)+CH4-CH O+H k O('D)+H -H+OH k? OH+CO-CO +H k H+O +M-.HO k HO +NO-.NO +OH k,o HO +O -.OH+20 kll HO2-I-HO2--'H202 k12 OH+HO2--'H20-I-O2 k,3 HO2+NO2+M-'HO2NO2 k,4 HO2NO2+M-'HO2+NO2 k 5 HO2+NO3-' OH+NO2+O2 k 6 H202+OH-+HO2+H2 kl? CH4+OH-'CH3+H20 k 8 CH3+O2+M-'CH302 k 9 CH302+NO-'CH30+NO2 k20 CH302+HO2-'CH3OOH+O2 k21 CH302+CH302-'2CH30+O2 k22 CH302+CH302-' CH20+CH3 OH k23 CH302+NO2+M-' CH302NO2 k24 CH302NO2+M-' CH302+NO2 k25 CH3OOH+OH-'CH302+H2 k26 CH3OOH+OH-' CH20+OH+H20 k27 CH20+OH-'CHO+H20 k28 CH20+NO3-'HNO3+CHO k29 CH30+O2-'CH20+HO2 k30 CHO+O2-'HO2 +CO k3 OH+CH3OH- CH2OH+H20 k32 CH2OH+O2-'CH20+HO2 k33 OH+H2-'H20+H k34 O3+OH-'HO2+O2 k3 O3+NO-'NO2+O2 k36 O3+NO2-'NO3+O2 k37 OH+NO+M-'HONO k38 OH+NO2+M-'HNO3 k39 OH+NO3-'HO2+NO2 k02 OH+HNO3-'H20+NO3 k41 OH+HONO-'NO2+H2 k42 OH+HO2NO2-'NO2+H20+O2 k43 NO3+M-'NO+O2 k44 NO+NO3-'2NO2 k4 NO3+CO-'NO2+CO2 k46 NO2+NO3+M-'N20 k47 N20 +M-'NO2+NO3 k48 N2Os+H20-'2HNO3 Rinout/Wshout n Deposition R 1 H202,CH3OOH,CH20,CH3OH,HNO3, HONO,HO2NO2-. Rinout/Wshout D, H202,CH20,CH3OH,HNO3,HONO, HO2NO2-.Surfe Deposition D 2 CH3OOH-'Surfe Deposition Al NO3,N2Os-.Aerosol Photolyri Retions Jl O3+h¾-'O(ID) J2 H202+hv-'2OH J3 CH3OOH+hv--CH30+OH J4 CH20+hv-.CHO+H Js CH20+h¾-' CO+H2 J6 NO2 +hv-'no+o J? NO3+hv-*NO2+O Rte Coeffiient 1.8x 10'llexp(110/T) 3.2x 10'l'exp(70/T) 2.2x10 'lø 1.35x10 'lø 1.Sx x10 4ø 1.Sx 1043(1 +0.6P, ) 1 øø=5.7 x 10 '32, n=l.6, øø=7.5 x 10 'll, m=0 3.5 x 1042exp(250/T) 1.1 x 10'14exp(-500/T) [2.3 x 10'13exp(600/T)+ 1.7 x 10'33 [M] exp(1000/t)] *[ x 10'21 [H20] exp(2200/t)] 4.8x 104 lexp(250ff) 1 øø= 1.8x 10 '31, n=3.2, øø=4.7 x 1042, m=l.4 k,3/(2.1 x 10-27exp(10900/T)) 3.5x x 10'12exp( - 160/T) 2.8 x 1044exp( /T)*T ø'6 7 1 øø=4.5 x 10 '31, n=3, oo= 1.8x 1042, m=l.7 3.0x 10'12exp(280FF) 3.8x 10'13exp(800/T) 0.4'2.5x 1043exp(190/T) 0.6'2.5 x 10'13exp(190/T) k3ooo=1.5 x 10-3ø, n=4, øø=6.5 x 1042, m=2 k23/(1.3x 10'28exp(11200/T)) 0.7'3.8 x 1042exp(200/T) 0.3'3.8 x 10'12exp(200/T) 1.0x x10 '16 3.9x 1044exp(-900/T) 3.5x 1042exp(140/T) 6.7x 10'12exp(-600/T) 9.1x x 1042exp(-2000/T) 1.6x 1042exp(-940/T) 2.0x 10'12exp( /T) 1.2x 10'13exp(-2450/T) 1 øø=7.0 x 10 '31, n=2.6, øø=3.6 x 10 'li, m=0.1 1 øø=2.5 x 10 '3ø, n=4.4, øø=l.6x 10 'li, m=l.7 2.2x10-11 see note q 1.Sx 10'l exp(-390/t) 1.3 x 1042exp(3 80/T) 2.5x 10%xp(-6100/T) 1.5x 10'lexp(170/T) 4.0x øø=2.2 x 10 '3ø, n=3.9, øø=1.5 x 10 '12, m=0.7 k4(2.7 x 10'27exp(11000/T)) 2.0x km, 2.31x10 '6 > 4 km (z in km), 2.31 x 10'6exp( z) 0-1 km, 1.0x 10'5; > 1 km, 0.0 0=1 km, 3.0x 10'6; > 1 km, 0.0 y= x10 '5 7.4x 10 '6 5.4x x10 '5 4.8x10 '5 9.0xlO x10 4 Notes,p,p,p,p,p,p g,p,k,o,o,o,o,o,o b,o

14 16,268 CRAWFORD ET AL.: ASSESSMENT OF UPPER TROPOSPHERIC HOx SOURCES Tble A1. (ontinue) Retion Rte Coeffiient Notes Js N2Os+hv-.NO2+NO3 J9 HNO3+h¾-. OH+NO2 Jlo HO2NO2+hv-.HO2+NO2 Jll HO2NO2+hv-. OH+NO3 Jl2 HONO+hv-'OH+NO Nonmethne Hyrorbon Retions Ketones kk 1 CH3COCH3+OH-. CH3COCH202+H20 kk 2 MEK+OH-.KO2+H20 kk3 CH3COCH3+hv-.CH3CO3+CH302 kk 4 MEK+hv-.CH3C03+C2H O2 kk5 MEK+NO3-.KO2+HNO3 kk6 CH3COCH202+NO RAN2+0.96(NO2+MGLY+HO2 ) kk KO2+NO-.0.07RAN (NO2+ALD2+CH3CO0 kk8 CH3COCH202+HO2-. CH3CO3+CH302+H20 kk9 KO2+HO2-.MGLY+CH302+H20 Alknes ka 1 C2H6+OH-. C2H5 O2+H20 ka 2 C2H502+NO-.ALD2+HO2 +NO2 ka3 C2H O2+HO2-.C2H OOH+O2 ka 4 C2H O2+C2H O ALD2+l.2HO2 ka C3Hs+OH-. n-c3h?o2+h20 C3Hs+OH-. i-c3h?o2+h20 ka? n-c3h?o2+no-. ALD2+NO2+HO2 ka8 i-c3h?o2+no-. CH3COCH3+NO2+HO 2 ka9 n-c3h?o2+h02-.n-c3h?ooh+o2 kalo i- C3H?O2+H 02-. i- C3H? OH+O2 kall n-c3h?o2+n-c3h?o ALD2+0.5n-C3H?OH+HO2 ka12 i-c3h?o2+i-c3h?o CH3COCH3+0.5i-C3H?OH+HO2 ka13 ALKA+OH-.RAO2+H20 ka14 ALKA+NO3-.RAO2+HNO3 RAO2+NO-. BiNO2+B2NO+B3RAN2+BqALD2+BsMEK+ B6C2H O2+B?CH302+BsHO2+B C3H?O2+0.06RA02 ka16 RAO2+HO2-.RAP+O2 kal? RAN2+OH-.RANi+H20 ka18 RANi+NO-.NO2+HCHO+RANO2 ka19 RAN l/rano 2+H O 2-. RANP/RANP 2 ka2o RANO2+NO-.2NO2+2ALD 2 Alkenes kg 1 C2H4+OH-.HOC2H302 C2H4+O3-.HCHO+0.4CH HO2+0.42CO+0.06CH4 HOC2H302+NO-.NO2+2HCHO+HO2 HOC2H 302+H02-.HOC2H 3OOH+O 2 ke HOC2H302+HOC2H HCHO+ 1.2HO2+0.4ALD2 ke6 ALKE+OH-.PO2 ke7 ALKE+O HCHO+0.5ALD2+0.2(CHO2+CRO2)+ 0.23HO CH OH+0.33CO ke 8 ALKE+NO3-.PRN l PO2+NO-.NO2+ALD2+HCHO+HO2 kglo PO2+HO2-.PP+O2 kgll PO2+PO2-.2.2ALD2+ 1.2HO 2 kg12 PRNl+NO2-.PRN2 kgl3 PRNl+HO2-.PRPN+O2 kgl4 PRN l+no-.2no2+hcho+ald2 kg15 CHO2+NO-.HCHO+NO2 kgl6 CHO2+NO2-. HCHO+NO3 kgl7 CHO2+H20-.HCOOH kg18 CHO2+SO2-.HCHO+SO4 kg19 CHO2+HCHO-.OZID kg2o CHO2+ALD2-. OZID kg21 CRO2+NO-.ALD2+NO 2 kg22 CRO2+NO2-.ALD2+NO3 kg23 CRO2+H20-. CH3COOH kg24 CRO2+SO2-.ALD2+SO4 kg25 CRO2+HCHO-. OZID ke26 CRO2+ALD2-. OZID 5.0x10 ' 7.5x10 '7 3.1x x 10 '6 1.9x10 '3 2.2x 10'12exp(-6gS/T) 1.8x 10'1 lexp(-g90/t) 6.9x x 10'4J(NO2) 7.0x x 10' 2exp(365/T) 7.5x 10'13exp(700FF) 8.7x 10'12exp( /T) 7.5x 1043exp(700/T) 6.8x10 ' x 10' 2exp( /T) 6.3 x 10' 2exp(-580/T) 8.7x10 '12 8.5x10 '12 3.0x x 10'12exp(-2200/T) 2.0x 10'llexp(-500/T) 4.0x10 -l? 2.0x10 '12 2.6x 10'2exp(365FF) 2.6x 10' 2exp(365/T) k øø=l.0x 10 '28, n=0.8 k øø=8.8 x 10 '12, m=0 1.2x 10'14exp(-263 3FF) 2.6x 10'13exp(365/T) 7.5x 10' 3exp(700/T) 5.0x x 10-12exp(537/T) 7.8x 10'14exp(-2105/T) 1.26x10 '13 2.6x 10'13exp(365/T) 7.5x 10-13exp(700/T) 5.0x10 '14 6.8x10 ' 2 7.5x 10' 3exp(700/T) 2.6x 10'13exp(365/T) 7.0x x x10-7.0x10 ' x x10 '14 7.0x x10 '13 4.0x10 '18 7.0x10 ' x10 ' x10 ' 4,o,o,o,o,o b e e f f b b f f b b e, 13,p

15 CRAWFORD ET AL.: ASSESSMENT OF LIPPER TROPOSPHERIC HOx SOURCES 16,269 Tble A1. (ontinue) Retion Isoprene kil ISOP+OH- RIO2 ki2 ISOP+O- 0.5HCHO+0.2MVK+0.3MACR+0.2CHO HO2+0.2MVKO+0.3MAOO ki ISOP+NO- INO2 ki 4 RIO2+NO-.0.9(NO2+HO2+HCHO)+0.45 (MVK+MACR) l 5 RIO2+HO2--.XAP 1+O2 ki6 INO2 +NO- 2NO2+HCHO+0.5(MVK+MACR) ki7 INO2+NO2 IPN4 ki8 INO2+HO2 - PROD kio MVK+OH- VRO2 kilo MVK+O3 0.5(MGGY+HCHO)+0.2(CHO2+CRO2) HO2+0.15ALD2+0.15CH3CO3 kill MVK+NO3- MVN2 ki12 VRO2+NO' 0.9NO2+0.6(CH3CO3+ALD2)+ 0.3(HO2+HCHO+MGLY) ki13 VRO2+HO2--'RP+O2 ki14 MVN2+NO-'2NO2+HCHO+0.5(CH3CO3+MGGY+HO2) kil5 MVN2+HO2 - PROD ki16 MACR+OH- MAO3 kil? MACR+OH- MRO2 ki18 MACR+O3-0'65HCHO+0' 5MGGY+0' 36HO (CHO2+CRO2)+0.15(NO2-NO) kilo MACR+NO3- MAO3+HNO3 ki2o MACR+NO3- MAN2 ki21 MAO3+NO2 ' MPAN ki22 MPAN'-'MAO3+NO2 ki23 MAO3+NO'-'NO2+PO2+C O2 ki24 MAO3+HO2-'DAP+O2 ki25 MRO2+NO- 0.9(NO2+HO2 +CO+HACO) ki26 MRO2+HO2--'XAP2+O2 ki2? MAN2+NO 2NO2+HCHO+MGGY ki28 MAN2+HO2 - PROD ki20 MVKO+NO- MVK+NO2 kilo MVKO+NO2 - MVK+NO ki l MVKO+H20- PROD ki 2 MVKO+HO2 - PROD ki33 MVKO+SO2' MVK+SO4 ki 4 MAOO+NO-'MACR+NO2 ki35 MAOO+NO2-'MACR+NO3 ki36 MAOO+H20-'PROD ki 7 MAOO+HO2-'PROD ki38 MAOO+SO2--'MACR+SO4 kilo MGGY+hv- CH CO+HO2 ki4o MGGY+OH- CH CO3 Aromtis km C6I-I6+OH- C6H6(OH)OO km2 C6H6(OH)OO+NO- NO2+HO2 +GLYX+DIAL km AROM+OH 0.84TO2+0.16CRES+0.16HO2 km4 TO2+NO- NO2+HO2+0.72MGLY+0-18GLYX+DIAL km 5 TO2+HO2--'TP+O2 km 6 CRES+OH- B12HO2+0.9(ZO2+TCO3-OH)+B13NO2 km? CRES+NO3- HNO3+BloNO2+B11OH km8 MGLY+hv- CH3CO3+HO2 +CO kmo MGLY+OH- CH3CO3+H20+CO kmlo GLYX+hv - PROD kmll GLYX+OH- HO2+2CO+H20 km12 DIAL+hr-0.98HO2+0.02CH3CO3+TCO3 km13 DIAL+OH- TCO3+H20 km14 ZO2+NO'-'NO2 kml5 ZO2+HO2- ZP 4-02 km16 TCO3+NO-'NO2+0.92HO GLYX+0.11MGLY CH3C O C O+0.79CO2+2ZO2 km17 TCO3+HO2-'TCP+O2 km18 TCO3+NO2- TPAN kml9 TPAN' TCO3+NO2 Rte Coeffiient 4.0x 10'løexp(-410/T) 7.0x 10'lSexp( /T) 3.23x10 '13 0.1kP6 7.5x 10'l exp(700/t) 0.2 kp 1 4.0x 10'lSexp(-2000/T) 6.0x10 ' x10 -ll 3.86x 10'12exp(500/T) 4.4x 10'15exp(-2500/T) 3.3x x x x 1016exp(-13543/T) 0. lkp29 3.4x10 '18 7.5x 10-13exp(700/T) 7.0x10 '14 2.6x 10-12exp(365/T) 0. lkp34 3.4x10 '18 7.0x J($O2) 1.7x10 -ll 1.2x10 '12 2.6x 10'13exp(365/T) 1.52x10 -ll 2.6x 10'13exp(365/T) 4.0x x10 -ll 1.0x10 -ll J(NO2) 1.73x10 'll J(NO2) 1.15x10 ' J(NO2) 2.8x10 -ll 2.6x 10'lexp(365/T) 1.0x x 10'lexp(365/T) 4.0x x x 1016exp(-13543/T) Notes e, n f e, n f e f f f e e, 13,[3 e e

16 16,270 CRAWFORD ET AL.' ASSESSMENT OF UPPER TROPOSPI-IE C HOx SOURCES Tble A1. (ontinue) Retion Rte Coeffiient Alehyes kd 1 ALD2+OH CH3CO3+H20 5.6x 10'12exp(270/T) kd2 ALD2+NO3 CH3CO3+HNO3 1.4x 10'12exp( /T) kd 3 ALD2+h¾ CH302+HO2+CO 5.6x 10-6 kd 4 ALD2+h¾ CH4+CO 6.0x 10 '11 kd5 CH3CO3+NO-*CH302+NO2+CO2 5.3 x 10'12exp(360/T) kd 6 CH3CO +HO2 0.33(CH3C(O)OOH+O2)+0.67(CH3COOH+O ) 4.5x 10'l exp(1000/t) kd 7 CH3CO3+NO2-*PAN ko øø=9.7x 10-29, n=5.6,1 øø=9.3 x 10-12, m=l.5 kd 8 PAN CH3CO3+NO2 kd7/(9.0x 10'29exp(14000/T)) kd9 CH3CO3+CH302 CH3C(O)OH+CH20+O2 1.3 x 10'12exp(640/T)(1 +2.2x 10%xp(-3 820/T)) kdlo CH3CO3+CH302-'CH302+CH20+HO2+CO2 1.3 x 10'12exp(640/T)(1 + 1/(2.2 x 106exp(-3 820/T))) kdll PAN+OH--0.5 NO2+prouts 4.0x kd12 PAN+hv-'CH3CO3+NO 2 8.6x 10 '7 Orgni Ais n Alohols kc1 HCOOH+0H-'HO2+CO2+H20 4.0x 10 '13 kc 2 CH3COOH+OH-,CH302+CO2+H20 4.0x 10'13exp(200/T) kc3 C2H5OH+OH-'ALD2+HO2+H20 7.0x 10'12exp(-235/T) kc 4 HCOOH, CH3COOH,C2H OH--Rinout/Wshout 0-4 km, 2.31 x 10-6 > 4 km (z in km), 2.31 x 10'%xp( z) Orgni Peroxie Loss n Reyling kp 1 C2H OOH+OH-,0.5(C2H O2+ALD2+OH)+H20 1.0x 10 '11 kp 2 C2H OOH+h¾ OH+HO2+ALD 2 5.0x 10'4J(NO2) kp 3 (n/i)c3h7ooh+oh 0.5(n/i-C3H702+ALD2+OH)+H20 1.0x 10 '11 kp 4 (n/i)c3h7ooh+hv-,oh+ho2+ald2 5.0x 10'4j(NO2) kp 5 RAP+OH--'0.5(RAO2+ALD2+OH)+H20 1.0x 10 '11 kp 6 RAP+h¾- OH+HO2+ALD2 5.0x 10'4J(NO2) kp 7 CH3C(O)OOH+OH 0.5(CH CO3+HCHO+OH)+H20 1.0x 10 '11 kp 8 CH3C(O)OOH+hv-,OH+HO2+HCHO 5.0x 10'4j(NO2) kp 9 HOC2H3OOH+OH 0.5(HOC2H302+2HCHO+OH)+H20 1.0x 10 -ll kp10 HOC2H3OOH+hwOH+HO2+2HCHO 5.0x 10'4j(NO2) kpll PP+OH-.0.5(PO2+ALD2+OH)+H20 1.0x 10 'll kpl2 PP+h¾ OH+HO2+ALD2 5.0x 10'4J(NO2) kp13 TP+OH- TO2+H20 1.0x 10 'll kp14 TCP+OH-'TCO +H20 1.0x 10 'll kp s ZP+OH-'ZO2+H20 1.0x 10 '11 kpl6 XAPi+OH-,0.5(RIO2+ALD2+OH)+H20 1.0x 10 'll kp17 XAPl+hv OH+HO2+ALD2 1.0x 10'3J(NO2) kp18 RP+OH-'0.5(VRO2+ALD2+OH)+H20 1.0x 10 'll kpl9 RP+h¾ OH+HO2+ALD 2 5.0x 10'4J(NO2) kp20 DAP+OH 0.5(MAO3+ALD2+OH)+H20 1.0x 10 -ll kp21 DAP+hv-.OH+HO2+ALD2 1.0x 10'3J(NO2) kp22 XAP2+OH 0.5(MRO2+ALD2+OH)+H20 1.0x 10 '11 kp23 XAP2+h¾-*OH+HO2+ALD 2 1.0x 10'3J(NO2) kp24 HACO+NO2 IPAN 4.7x 10 '12 kp2s IPAN- HACO+NO2 1.95x 101%xp(-13543/T) kp26 HACO+NO--NO2+HO2+HCHO kp27 HACO+HO2-,HEP 3.0x 10 '12 kp28 HEP+OH 0.5(HACO+2HCHO+OH)+H20 1.0x 10 'll kp29 HEP+hwOH+HO2+2HCHO 5.0x 10'4J(NO2) kp 0 C2HsOOH,(n/i)C H7OOH,CH3C(O)OOH, 0-4 km, 2.31 x 10-6 HOC2H OOH,DAP,HEP,PP,RAP,RP,TCP, > 4 km (z in km), 2.31 x 10-6exp( z) TP XAP XAP? ZP Rinout/Wshout Notes b,o b,o,p 'DeMore et l. [ 1997]. Mtkinson et l. [1992]. CConense hemil retion mehnism [Lurmnn et/., 1986]. ridetile hemil retion mehnism [Lurmnn et l., 1986]. eassumes rte for C2H502 + NO. fassumes rte for C2H502 + HO 2. g lohnston et l. [ 1986]. hlogn et l. [ 1981 ]. 'Estimte. JDentener n Crutzen [ 1993]. ktemperture epenene of rossetion from Molin n Molm [ 1986] n quntum yiels from Tlukr et l. [ 1998]. ICrossetions from Hynes et l. [ 1992] n quntum yiels from MKeen et l. [ 1997]. mpulson et l. [ 1992]. nprouts bse on Pulson et l. [1992].

17 CRAWFORD ET AL.: ASSESSMENT OF UPPER TROPOSPt{ERIC HO x SOURCES 16,271 oj vlues shown re lulte for the surfe t 30 ø solr zenith ngle, T = 298K, n n 03 olumn ensity of 250 Dobson Units. PTermoleulr k vlues given by k=( kø(t)[m] /0.6 [1 +(1øg ø(kø(t)[mfk'(t))):]- 1 +(ko(t)[m]/k..(t)) ] where, ko(t)= øø(t/300) 'n n (T)= øø(t/300)'m qrte is given by k=k + k3[m] o 1 +k3[m]/k 2 where, 1q,=7.2 x 10'l exp(785/t), k2=4.1 x 10'l%xp(1440/T), n k3 = 1.9x 10'33exp(725/T) ødetils on the lultion of [I oeffiients re foun in Lurmnn et l. [ 1986]. thn 0.1% (R. K. Tlukr n A. R. Rvishnkr, privte 7. Summry ommunition, 1999). This restfit inites tht this retion hs no signifint impt on iurnl verge HOx onentrtions. Dt reore in the tropil upper troposphere (8-12 kin, Furthermore, this yiel is too smll to even expet ny signifint 20 øn-20 øs) uring NASA' s Pifi Explortory Missions (PEMontribution t high solr zenith ngles. West A, PEM-West B, n PEM-Tropis A) hve been use to Finlly, errors in kineti rte oeffiients n in OH exmine HOx photohemistry in this region. The vilbility of librtion soures must be reognize s potentil ontributors mesurements of oxygente hyrorbons n peroxies from to the isrepny between observe n lulte HOx levels. these flight mpigns hve me it possible to quntittively Errors in kineti rte oeffiients hve been investigte ssess the potentil impt from these speies on HO x levels s previously through Monte Crlo lultions [Thompson n well s on other relte photohemil prmeters. Sensitivity Stewrt, 1991; Thompson et l., 1997; Dvis et l., 1993; lultions using time epenent photohemil box moel Crwfor et l., 1997b; Crwfor, 1997]. In the upper were rrie out in whih moel rims were sequentilly troposphere, where tempertures re olest, the unertinties onstrine by observtions of wter vpor, NMHCs, etone, lulte OH n HO 2 Cll beome quite lrge (e.g., 30-50%). methnol/ethnol, CH OOH, n H202. The bsolute librtion of OH instnments must lso ontinue to The impt ue to onstrining speies ws foun to inrese be investigte for possible soures of systemti error. A mjor with ltitue, refleting the systemti roll-off in wter vpor. evelopement on this from woul involve rigorous (e.g., ouble Reltive to wter vpor hemistry whih eftne the bse blin) interomprison of urrent irborne instnments. At lultion, the lrgest inreses below 11 km were ssoite present there pper to be t lestwo OH insmunents (e.g., LIF with etone n CH OOH. At km, H202 ontribute n CIMS), bse on totlly ifferent operting priniples, tht more to HOx inreses thn CH OOH. The overll mein oul be interompre. inrese HO x from ll onstrints pprohe ftor of 2 t Tble A2. Speies Abbrevitions Use in Nonmethne Hyrorbon Retions. Abbr. Definition Abbr. Definition ALD2 > C2 lehyes MVN2 ALKA lumpe > C4 lknes OZID ALKE > C3 lkenes PAN AROM romtis PO 2 CHO 2 Criegee biril (CH202) PP CRES Cresol PRN1 CRO 2 Criegee biril (CH3CHO2) PRN 2 DAP CH2=C(CH )C(O)OOH PROD DIAL unsturteirbonyl PRPN GLYX (CHO)2(glyoxl) RAN l HACO HOCH2C(O)OO RAN 2 HEP HOCH2C(O)OOH RANO2 INO2 isoprene-no3-o2 ut RANP [PAN HOCH2C(O)OONO 2 RANP 2 IPN INO2+NO 2 prout RAO2 ISOP isoprene (CsHlo) RAP KO2 methyl ethyl ketone RO2 RIO2 MACR methrolein RP MAN, MACR+NO3 ril prout TCO3 MAO CH =C(CH3)C(O)OO TCP MAOO Criegee biril (CH =C(CH3)CHOO) TO _ MEK methyl ethyl ketone (CH COCH2CH ) TP MGGY e -irbonyl TPAN MGLY CH3COCHO (methylglyoxl) VRO2 IV[PAN CH C(CH )C(O)OONO _ XAP 1 MRO 2 MACR RO 2 XAP 2 MVK methyl vinyl ketone ZO2 MVKO Criegee biril (CH?=CHC(OO)CH0 ZP MVK+NO 3 ril prout ozonie or rerrngement prout CH3CO3NO 2 > C lkene RO2 > C3 lkene ROOH > C3 lkene+no ril PRN +NO ril Unefine prouts PRNi+HO prout > C lkne RNO 2 C lkne RONO RANi+NO prout RAN1 ROOH RANO2 ROOH > C lkne RO 2 2 C lkne ROOH isoprene RO 2 RC(O)OOH (R=2) CHOCH=CHCO CHOCH=CHC(O)OOH romti RO 2 romti ROOH- CHOCH=CHCO3NO2 MVK RO2 ISOP ROOH MACR ROOH romti RO 2 romti ROOH

18 16,272 CRAWFORD ET AL.: ASSESSMENT OF UPPER TROPOSPHERIC HOx SOURCES km. Mein inreses CH302 n CH20 t km Referenes exeee ftor of 3, n inreses in gross n net photohemil proution of ozon exeee ftor of 2. Atkinson, R., D. L. Bulh, R. A. Cox, R. F. Hmpson Jr., J. A. Kerr, n An exmintion of the unertinty in high-ltitue wter J. Troe, Evlute kineti n photohemil t for tmospheri hemistry, Supplement IV, IUPAC subommittee on gs kineti t vporevele tht lultions were firly insensitive to lrge evlution for tmospheri hemistry,. Phys. Chem. Ref Dt, 21, hnges in wter vpor (e.g., ftors of 3-5) when bsolute wter , vpor ws below 100 ppmv. For fully onstrine lultions Brshw, J., et l., Photofrgmenttion two-photon lser-inue (se F), the bove ite ifferenes in wter vporesulte in fluoresene etetion of NO2 n NO: Comprison of mesurements only 5% hnge in HOx levels. This result suggests tht with moel results bse on irborne observtions uring PEM-Tropis A, Geophys. Res. Lett., 26, , mesurements of etone n peroxieshoul be regre s Brsseur, (3. P., J.-F. M/lller, n C. Grnier, Atmospheri impt of NOx more ritil thn the ury of wter vpor when the ltter hs emissions by subsoni irrft: A three-imensionl moel stuy,. mixing rtios below 100 ppmv. This lk of sensitivity to wter Geophys. Res., 101, , below 100 ppmv is ue both to the ft tht wter is no longer the Brune, W. H., et l., Airborne in situ OH n HO2 observtions in the louominnt primry HOx soure n tht seonry HOx formtion free troposphere n strtosphere uring SUCCESS, Geophys. Res. exees primry formtion. Lett., 25, , Peroxie observtions were evlute for eviene of Busen, R., n A. L. Buk, A high-performne hygrometer for irrft use: Desription, instlltion, n flight t,. Atmos. Oeni Tehnol., onvetive impts. For high wter vpor environmentsuh s 12, 73-84, the PWB 10WNOx regime, lultions inite tht onvetively Chtfiel, R. B., n P. J. Crutzen, Sulfur ioxie in remote oeni ir: perturbe peroxies rpily return to expete stey-stte Clou trnsport of retive preursors,. Geophys. Res., 89, vlues. The peroxie observtions lso supporthe ontention 7132, tht H202 is eplete reltive to preite stey-stte vlues Cohn, D. S., M. G. Shultz, D. J. Job, B. G. Heikes, n D. R. Blke, while CH3OOH is elevte. In ontrst, lultions bse on Convetive injetion n photohemil ey of peroxies in the upper troposphere,. Geophys. Res., 106, , the low wter vpor environment t km show tht Crwfor, J. H., An nlysis of the photohemil environment over the perturbtions to CH3OOH n le to elevte H202 levels whih western, North Pifi bse on irborne fiel observtions, Ph.D. n remin bove the expete stey-stte level for severl ys isserttion, G. Inst. of Tehnol., Atlnt, fter CH3OOH hs issipte. This potentilly serves to explin Crwfor, J., et l., Photosttionry stte nlysis of the NO2-NO system why H202 n hve vlues elevte bove stey stte by ftors bse on irborne observtions from the western n entrl North Pifi,. Geophys. Res., 101, , of 3 even when CH3OOH is mesure t or below its LOD..Crwfor, J., et l., Implitions of lrge sle shifts in tropospheri NOx The possibility tht itionl HOx soures might be present levels in the remote tropil Pifi,. Geophys. Res., 102, 28,447- in the upper troposphere ws lso explore. One suggestion 28,468, hypothesize potentilly lrge integrte soure of HOx from Crwfor, J. H., et l., An ssessment of ozone photohemistry in the the egrtion of ll orgni peroxies/ketones/lohols/l- extrtropil western North Pifi: Impt of ontinentl outflow ehyes/et. A seon possibility relting to the retion of uring the lte winter/erlier spring,. Geophys. Res., 102, 28,469-28,487, 1997b. O2(bl ]g) with H 2 ppers to be unimportnt bse on reent Crwfor, J., D. Dvis, G. Chen, R. Shetter, M. Mtiller, J. Brrik, n J. lbortory stuy. Still other res requiring ontinue Olson, An ssessment of lou effets on photolysis rte oeffiients: investigtion inlue further stuies of temperture epenenies Comprison of experimentl n theoretil vlues, 3'. Geophys. Res., for gs kineti rte oeffiients t the low tempertures of the 104, , upper troposphere n timher librtion exerises involving OH Dvis, D. D., et l., Photosttionry stte nlysis of the NO2-NO system sensors. Both of these res must be knowlege s potentil bse on irborne observtions from the subtropil/tropil North n ontributors to future isgreements between moel lultions South Atlnti,. Geophys. Res., 98, 23,501-23,523, [)vis, D. D., et l., Assessment of the ozone photohemistry teneny in the n observtions. western North Pifi s inferre from PEM-West A observtions Finlly, it is reognize tht s itionl HOx mesurements uring the fll of 1991,. Geophys. Res., 101, , re me in the upper troposphere, onurrent mesurements of DeMore, W. B., S. P. Sner, D. M. Golen, R. F. Hmpson, M. J. Kurylo, etone n peroxies will be ritil to estblishing whether C. J. Howr, A. R. Rvishnkr, C. E. Kolb, n M. J. Molin, they lone re suffiiento explin the HOx observtions. In this Chemil kinetis n photohemil t for use in strtospheri moeling, JPL Publ., 97-4, ontext, mesurements of CH20 woul lso be of gret vlue s Dentener, F. J., n P. J. Crutzen, Retion of N20 on tropospheri further initor for soures of HOx from wie rnge of erosols: Impt on the globl istributions of NO, 03, n OH,. oxygente hyrorbon speies. Geophys. Res., 98, , Dikerson, R. R., et l., Thunerstorms: An importnt mehnism in the Appenix trnsport of ir pollutnts, Siene, 235, , Fishmn, J., S. Solomon, n P. Crutzen, Observtionl n theoretil Tble A1 provies etile list of the photohemil box eviene in support of signifint in-situ photohemil soure of moel mehnism use in this stuy. Tble A2 provies tropospheri ozone, Tellus, 31, , ef'mitions for the numerous bbrevitions use for NMHC- Folkins, I., R. Chtfiel, H. Singh, Y. Chen, n B. Heikes, Ozone relte speies. Most of these bbrevitions re in keeping with proution effiienies of etone n peroxies in the upper those estblishe by Lurmnn et l. [1986]. troposphere, Geophys. Res. Lett., 25, , Goln, P. D., W. C. Kuster, F. C. Fehsenfel, n S. A. Montzk, Hyrorbon mesurements n the southestern Unite Sttes: The rurl Aknowlegments. This work ws supporte by funs fromnasa oxints in the southern environment (ROSE) progrm 1990, J. s prt of the PEM-Tropis progrm. We woul like to espeilly Geophys. Res., 100, 25,945-25,963, thnk A. R. Rvishnkr for his oopertion n timely lbortory Heikes, B. G., et l., Hyrogen peroxie n methylhyroperoxie results. We lso thnk two nonymous reviewers for their helpful istributions relte to ozone n o hyrogen over the North Pifi omments. in the fll of 1991,. Geophys. Res., 101, , 1996.

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