8 Pages, 3 Figures, 2 Tables. Table S1: The reagents used for this study, their CAS registry numbers, their sources, and their stated purity levels.

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1 Suleentary Material for The Feaibility of Photoenitized Reaction with Secondary Organic Aerool Particle in the Preence of Volatile Organic Coound Kurti T. Malecha and Sergey A. Nizkorodov* * nizkorod@uci.edu Ph: Fax: Deartent of Cheitry, Univerity of California, Irvine Content Reagent Ued for Thi Study... 1 PTR-ToF-MS Calibration... Derivation of Equation Ued in Thi Work... Utake Coefficient... Lo Rate for Lionene Under Tyical Abient Condition... 5 Sectral Flux Denitie of LED and Sun Coared... 7 Reference... 8 Reagent Ued for Thi Study 8 Page, Figure, Table Table S1: The reagent ued for thi tudy, their CAS regitry nuber, their ource, and their tated urity level. Reagent Nae Hydrogen Peroxide Solution (0 wt%, water balance) 5086 Nitric Oxide in Nitrogen CAS Regitry Manufacturer Nuber Fiher Praxair Stated Purity Nahthalene Fiher 98% Dichloroethane Fiher 99.9% d-lionene ((R)-1- Methyl--(1- ethylethenyl)- cyclohexene Siga Aldrich 97% Iorene (- Methybuta-1,- diene) Guaiacol (- ethoxyhenol) Siga Aldrich 99% Sectru 99% S1

2 PTR-ToF-MS Calibration The PTR-ToF-MS wa calibrated for four VOC analyzed for thi tudy (acetaldehyde, acetone, acetic acid, and lionene) by evaorating a known aount of a given VOC into the cleaned 5 chaber and onitoring the [M+1] eak, correonding to the rotonated VOC. The VOC wa added to the chaber in all increent, and the correonding PTR-ToF-MS ignal wa eaured after each ucceive addition. The inlet line through which the VOC wa injected into the chaber wa heated throughout the exerient to 60 C, and the PTR-ToF-MS inlet line wa alo heated to the ae teerature to revent loe of VOC on the teel urface of the inlet. (However, we could not account for loe haening on the urface of the Teflon chaber.) We created a calibration lot for each VOC coaring the actual aount of VOC in the chaber (auing no wall loe) with that reorted by the PTR-ToF-MS intruent (Figure S1). The reulting calibration factor, rereenting the ratio of eaured to actual VOC ixing ratio, ranged fro 1. to 6.. Confidence interval were calculated at the 95% level baed on the uncertainty in the injection, the PTR-ToF-MS trace, and the reulting linear regreion. Thee value are reorted in Table S. Figure S1. The PTR-ToF-MS calibration lot for (A) acetaldehyde, (B) acetone, (C) acetic acid, and (D) d-lionene. The horizontal axi i the PTR-ToF-MS eaured ixing ratio and the vertical axi i the known aount that wa injected into the chaber. Each data oint ha vertical and horizontal error bar correonding to 95% confidence interval of the aount of VOC reent and eaured, reectively. The vertical error bar increae with the VOC aount becaue of the accuulation of error in the ucceive injection of the VOC in the chaber. S

3 Table S: The reulting calibration factor for each VOC. For the SOA hotodegradation exerient, we ultilied the ixing ratio eaured by the PTR-ToF-MS by thi factor for each VOC in the ain text analyi. The ubcrit how the firt digit that i not ignificant. VOC Calibration Factor 95% Confidence Interval Acetaldehyde Acetone Acetic Acid Lionene Derivation of Equation Ued in Thi Work Utake Coefficient Figure S. Scheatic diagra of the flow cell. The geoetry of the exerient i cheatically hown in Figure S. The flow of air containing 00 bv lionene goe through a cylindrical tube with ID =1.5 at a volue flow rate of F = 00. The SOA ale i located on a CaF window at the botto of a cylindrical ide tube with length L = and inner diaeter ID =1.5. The PTR-ToF-MS eaure the concentration of lionene exiting fro the cell, C. For the ixing ratio of 00 bv ued in thee 1 exerient, C =.9 olec. When the UV-LED i on, the reduction in the eaured concentration i only a few ercent, o the inlet and outlet concentration of lionene can be regarded a aroxiately the ae. A all aount of lionene i lot onto the SOA coated window etablihing a gradient of concentration along the ide tube. The concentration in the S

4 iediate vicinity of the urface i C. The tranfer of lionene to the SOA coated window i not urely diffuive - we verified thi by dratically changing the flow geoetry and getting the ae final reult for the utake coefficient. Neverthele, we attet to odel the diffuion through the ide tube with noral diffuion equation below. The nuber of olecule delivered by the air flow er econd, Source, can be related to the volue flow rate et by the a flow controller, F, and the lionene concentration in the inlet flow a follow: Source = F C Under the teady tate condition, the net flux of lionene olecule through the flow, J, and the abolute lo rate due to the urface reaction, (1) Lo, can be calculated a follow: Lo γeff υ C γcorrected υ C J = = = () Area In thi equation, γ eff i the effective utake coefficient eaured in the exerient, γ corrected i the actual utake coefficient, Area[ ] i the area of the ale that i irradiated (about 1 ), and υ i the average eed of lionene (MW i the olecular weight of lionene, R i the ga contant, T i the abolute teerature): 8RT υ = =.15 π MW Equation () how that the effective and true utake coefficient are related γ corrected C = γeff C () () The fractional reduction in the lionene that we oberve in the flow with the PTR-ToF-MS i: IonUVoff IonUVon Lo γeff u Area = = Ion Source F UVoff (5) We can rearrange and ubtitute eaured value of PTR-ToF-MS ion current into Eq. (5) to calculate γ eff. We how an exale of thi calculation for the GUA/OH SOA yte below, in which the lionene ignal droed by 1.% during the irradiation: γ eff Ion. UVoff Ion UVon F = = 0.01 = 7. IonUVoff υ Area (6) S

5 Thi utake coefficient i reaonably large, o the diffuion gradient ay be ubtantial (if the lionene tranfer to the SOA ubtrate i controlled by diffuion). If we aue that the concentration gradient in the tube i linear, the diffuion flux can be aroxiated a: J = D ( ) C C L D 0. i the etiated diffuion coefficient of lionene at abient teerature and reure. 1 Fro thi, the concentration near the SOA urface can be etiated a follow: J L γ C = C = C 1 D eff υ L D And the corrected utake coefficient becoe γ corrected = γeff γ 1 eff 1 υ L D For the GUA/OH SOA exale, the corrected utake coefficient i γ corrected 1 = 7. = ( ) The correction i quite large even for thi allet oberved utake coefficient. For the ret of the SOA yte tudied in thi work the effective utake coefficient becoe too large for aking the diffuion correction reliably (the linear gradient aroxiation break down). Therefore, the effective utake coefficient lited in Table hould be interreted a the lower liit for the actual utake coefficient. Neverthele, a we dicu in the text, the actual value of the utake coefficient are not likely to be uch higher than the effective value lited in Table. Therefore, the ain concluion of the aer (that thee utake coefficient are too all to lay a role in controlling lo rate of VOC on SOA article) i not likely to be affected by the diffuion liitation in oe of our exerient. (7) (8) (9) () Lo Rate for Lionene Under Tyical Abient Condition We now derive the lifetie of lionene with reect to deoition on atoheric article under tyical atoheric condition (with aued effective abient utake coefficient γ abient = -6 ). Our calculation aue onodiere article with article diaeter, d = -7, a article aterial denity, r = 100 kg/, and the article a concentration in air, C a = 15 g/. The area to volue ratio (A/V) for uch article i 7-1. Poible diffuion liitation for the utake are neglected in thi etiation. The cobined volue of articulate atter er volue of air i ( air i the unit for the volue of air and i the unit for the volue of a article): S5

6 C volue g kg g kg C a air g air g = = = kg air kg 100 air r The cobined area of articulate atter er volue of air i (where A/V i the area to volue ratio for one article, er aution above): (11) C C A 1 7 area = volue = = air air V air air We can alo define the lo rate er unit volue air: υ C area = γ air olec CVOC air air Lo The effective firt order rate contant for lionene i then: υ Lo Carea air CVOC air air = = γ k (1) (1) (1) Uing the effective abient γ = -6, we get: air 8 k = =. (15) Thi correond to lifetie of lionene with reect to the deoition on SOA article of: 1 1 = = =. > 1yr k. [ ] 7 τ 8 If we coare thi lifetie to that of lionene reacting with OH and lionene reacting with O in the ga hae, we arrive at the following. We aue that the tyical [OH] i 6 olecule/ and the tyical [O ] i ~.8 x 11 olecule/. Rate contant are fro Atkinon. (16) olec k k OH olec 6 OH = OH + LIM [ ] = 1.7 = = = = 5.9 = 98 in [ ] τ OH k 1.7 OH olec k k O olec O = [ O+ LIM ] =.0.8 = 9.6 (17) (18) (19) S6

7 [ ] 1 1 = = = = τ O 5 k 9.5 O in Finally, we conider the lifetie of lionene with reect to utake onto urban urface. In thi cae, the firt ter in Eq. 1 i the ratio of the actual urface area to the geoetric urface area over 1 of ground (we et it to 50 a er the axiu dicued by Aner et al. ) and the econd ter i the height of the boundary layer where ecie ix freely (we et it to 500 ). The urface concentration i now coniderably larger than it wa etiated for the article: C urface S 1 1 = actual =0.1 [ ] area air Sgeoetric hboundary If we ubtitute the reult fro Eq. (1) into Eq. (1), we arrive at the rate of lionene lo and lifetie of lionene a: urface air 5 k = = 1.1 () 1 1 = = = 9. = 6hr k 1.1 [ ] τ 5 Thi lifetie i coniderably horter but till not hort enough to be coetitive with the oxidation of lionene by OH or ozone in the ga hae. (0) (1) () Sectral Flux Denitie of LED and Sun Coared We ued the following araeter fro the Quick TUV calculator entioned in the ain text: Latitude/Longitude ( /-118 ), Overhead Ozone (00 du), Surface Albedo (0.1), Ground and Meaured Altitude (0 k), Cloud Otical Deth/Bae/To (0.00/.00/5.00), Aerool Otical Deth/S-S Albedo/Alha (0.5/0.990/1.000), Sunlight Direct Bea/Diffue Down/Diffue U (1.0/1.0/0.0) and trea tranfer odel. Figure S how a coarion of the ectral flux denitie for the un and the la in the near-uv region (00-00 n). Each flux denity i integrated over thi wavelength range, and the reulting fluxe are coared in the ain text. S7

8 Figure S. The ectral flux denitie over the near-uv range of the electroagnetic ectru of the LED (in blue) and the un (in red) on the uer oltice in Lo Angele, California. The left axi correond to the LED, and the right axi rereent the un flux denity. Reference 1. Etiated Diffuion Coefficient in Air and Water - Extended Verion. htt:// (acceed June 7, 017).. Atkinon, R. Ga-Phae Trooheric Cheitry of Volatile Organic Coound: 1. Alkane and Alkene. J. Phy. Che. Ref. Data 1997, 6, Aner, G. P.; Scurlock, J. M. O.; Hicke, J. A. Global Synthei of Leaf Area Index Obervation: Ilication for Ecological and Reote Sening Studie. Global. Ecol. Biogeogr. 00, 1, S8