AMT Atmospheric Measurement Techniques AMT Atmos. Meas. Tech. 1867-8548 Copernicus Publications Göttingen, Germany 10.5194/amt-4-445-2011 Characterization of aerosol photooxidation flow reactors: heterogeneous oxidation, secondary organic aerosol formation and cloud condensation nuclei activity measurements Lambe A. T. 1 2 Ahern A. T. 1 2 Williams L. R. 2 Slowik J. G. 3 Wong J. P. S. 3 Abbatt J. P. D. 3 Brune W. H. 4 Ng N. L. 2 Wright J. P. 1 Croasdale D. R. 1 Worsnop D. R. 2 Davidovits P. 1 Onasch T. B. 1 2 Chemistry Department, Boston College, Chestnut Hill, MA, USA Aerodyne Research Inc., Billerica, MA, USA Department of Chemistry, University of Toronto, Toronto, ON, Canada Department of Meteorology and Atmospheric Sciences, The Pennsylvania State University, State College, PA, USA 04 03 2011 4 3 445 461 Copyright: © 2011 A. T. Lambe et al. 2011 This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/ This article is available from https://amt.copernicus.org/articles/4/445/2011/amt-4-445-2011.html The full text article is available as a PDF file from https://amt.copernicus.org/articles/4/445/2011/amt-4-445-2011.pdf

Motivated by the need to develop instrumental techniques for characterizing organic aerosol aging, we report on the performance of the Toronto Photo-Oxidation Tube (TPOT) and Potential Aerosol Mass (PAM) flow tube reactors under a variety of experimental conditions. The PAM system was designed with lower surface-area-to-volume (SA/V) ratio to minimize wall effects; the TPOT reactor was designed to study heterogeneous aerosol chemistry where wall loss can be independently measured. The following studies were performed: (1) transmission efficiency measurements for CO<sub>2</sub>, SO<sub>2</sub>, and bis(2-ethylhexyl) sebacate (BES) particles, (2) H<sub>2</sub>SO<sub>4</sub> yield measurements from the oxidation of SO<sub>2</sub>, (3) residence time distribution (RTD) measurements for CO<sub>2</sub>, SO<sub>2</sub>, and BES particles, (4) aerosol mass spectra, O/C and H/C ratios, and cloud condensation nuclei (CCN) activity measurements of BES particles exposed to OH radicals, and (5) aerosol mass spectra, O/C and H/C ratios, CCN activity, and yield measurements of secondary organic aerosol (SOA) generated from gas-phase OH oxidation of <i>m</i>-xylene and α-pinene. OH exposures ranged from (2.0 &plusmn; 1.0) × 10<sup>10</sup> to (1.8 ± 0.3) × 10<sup>12</sup> molec cm<sup>−3</sup> s. Where applicable, data from the flow tube reactors are compared with published results from the Caltech smog chamber. The TPOT yielded narrower RTDs. However, its transmission efficiency for SO<sub>2</sub> was lower than that for the PAM. Transmission efficiency for BES and H<sub>2</sub>SO<sub>4</sub> particles was size-dependent and was similar for the two flow tube designs. Oxidized BES particles had similar O/C and H/C ratios and CCN activity at OH exposures greater than 10<sup>11</sup> molec cm<sup>−3</sup> s, but different CCN activity at lower OH exposures. The O/C ratio, H/C ratio, and yield of <i>m</i>-xylene and α-pinene SOA was strongly affected by reactor design and operating conditions, with wall interactions seemingly having the strongest influence on SOA yield. At comparable OH exposures, flow tube SOA was more oxidized than smog chamber SOA, possibly because of faster gas-phase oxidation relative to particle nucleation. SOA yields were lower in the TPOT than in the PAM, but CCN activity of flow-tube-generated SOA particles was similar. For comparable OH exposures, α-pinene SOA yields were similar in the PAM and Caltech chambers, but <i>m</i>-xylene SOA yields were much lower in the PAM compared to the Caltech chamber.

 References Aiken,&nbsp;A.&nbsp;C., DeCarlo,&nbsp;P.&nbsp;F., and Jimenez,&nbsp;J.&nbsp;L.: Elemental analysis of organic species with electron ionization high-resolution mass spectrometry, Anal. Chem., 79(21), 8350–8358, 2007. Aiken,&nbsp;A.&nbsp;C., Decarlo,&nbsp;P.&nbsp;F., Kroll,&nbsp;J.&nbsp;H., Worsnop,&nbsp;D.&nbsp;R., Huffman,&nbsp;J.&nbsp;A., Docherty,&nbsp;K.&nbsp;S., Ulbrich,&nbsp;I.&nbsp;M., Mohr,&nbsp;C., Kimmel,&nbsp;J.&nbsp;R., Sueper,&nbsp;D., Sun,&nbsp;Y., Zhang,&nbsp;Q., Trimborn,&nbsp;A., Northway,&nbsp;M., Ziemann,&nbsp;P.&nbsp;J., Canagaratna,&nbsp;M.&nbsp;R., Onasch,&nbsp;T.&nbsp;B., Alfarra,&nbsp;M.&nbsp;R., Prevot,&nbsp;A.&nbsp;S.&nbsp;H., Dommen,&nbsp;J., Duplissy,&nbsp;J., Metzger,&nbsp;A., Baltensperger,&nbsp;U., and Jimenez,&nbsp;J.&nbsp;L.: O/C and OM/OC ratios of primary, secondary, and ambient organic aerosols with high-resolution time-of-flight aerosol mass spectrometry, Environ. Sci. Technol., 42, 4478–4485, <a href="http://dx.doi.org/10.1021/es703009q">https://doi.org/10.1021/es703009q</a>, 2008. Atkinson,&nbsp;R.: Kinetics and mechanisms of the gas-phase reactions of the hydroxyl radical with organic compounds under atmospheric conditions, Chem. Rev., 86(1), 69–201, 1986. Bertram,&nbsp;A.&nbsp;K., Ivanov,&nbsp;A.&nbsp;V., Hunter,&nbsp;M., Molina,&nbsp;L.&nbsp;T., and Molina,&nbsp;M.&nbsp;J.: The reaction probability of OH on organic surfaces of tropospheric interest, J. Phys. Chem.&nbsp;A, 105, 9415–9421, 2001. Cooper,&nbsp;P.&nbsp;L. and Abbatt,&nbsp;J.&nbsp;P.&nbsp;D.: Heterogeneous interactions of OH and HO<sub>2</sub> radicals with surfaces characteristic of atmospheric particulate matter, J. Phys. Chem., 100, 2249–2254, 1996. Davis,&nbsp;D.&nbsp;D., Ravishankara,&nbsp;A.&nbsp;R., and Fischer,&nbsp;S.: SO<sub>2</sub> Oxidation via the Hydroxyl Radical: Atmospheric Fate of HSO<sub>x</sub> Radicals, Geophys. Res. Lett., 6, 113–116, 1979. de Gouw,&nbsp;J.&nbsp;A. and Lovejoy,&nbsp;E.&nbsp;R.: Reactive uptake of ozone by liquid organic compounds, Geophys. Res. Lett., 25, 931–934, 1998. DeCarlo,&nbsp;P.&nbsp;F., Kimmel,&nbsp;J.&nbsp;R., Trimborn,&nbsp;A., Northway,&nbsp;M.&nbsp;J., Jayne,&nbsp;J.&nbsp;T., Aiken,&nbsp;A.&nbsp;C., Gonin,&nbsp;M., Fuhrer,&nbsp;K., Horvath,&nbsp;T., Docherty,&nbsp;K.&nbsp;S., Worsnop,&nbsp;D.&nbsp;R., and Jimenez,&nbsp;J.&nbsp;L.: Field-deployable, high-resolution, time-of-flight aerosol mass spectrometer, Anal. Chem., 78, 8281–8289, <a href="http://dx.doi.org/10.1021/ac061249n">https://doi.org/10.1021/ac061249n</a>, 2006. Donahue,&nbsp;N.&nbsp;M., Robinson,&nbsp;A.&nbsp;L., Stanier,&nbsp;C.&nbsp;O., and Pandis,&nbsp;S.&nbsp;N.: Coupled partitioning, dilution, and chemical aging of semivolatile organics, Environ. Sci. Technol., 40, 2635–2643, 2006. Drewnick,&nbsp;F., Hings,&nbsp;S.&nbsp;S., DeCarlo,&nbsp;P., Jayne,&nbsp;J.&nbsp;T., Gonin,&nbsp;M., Fuhrer,&nbsp;K., Weimer,&nbsp;S., Jimenez,&nbsp;J.&nbsp;L., Demerjian,&nbsp;K.&nbsp;L., Borrmann,&nbsp;S., and Worsnop,&nbsp;D.&nbsp;R.: A&nbsp;new time-of-flight aerosol mass spectrometer (ToF-AMS) – instrument description and first field deployment, Aerosol Sci. Tech., 39, 637–658, <a href="http://dx.doi.org/10.1080/02786820500182040">https://doi.org/10.1080/02786820500182040</a>, 2005. George, I. J., Vlasenko, A., Slowik, J. G., Broekhuizen, K., and Abbatt, J. P. D.: Heterogeneous oxidation of saturated organic aerosols by hydroxyl radicals: uptake kinetics, condensed-phase products, and particle size change, Atmos. Chem. Phys., 7, 4187–4201, <a href="http://dx.doi.org/10.5194/acp-7-4187-2007">https://doi.org/10.5194/acp-7-4187-2007</a>, 2007. George,&nbsp;I.&nbsp;J., Chang,&nbsp;R.&nbsp;Y.&nbsp;W., Danov,&nbsp;V., Vlasenko,&nbsp;A., and Abbatt,&nbsp;J.&nbsp;P.&nbsp;D.: Modification of cloud condensation nucleus activity of organic aerosols by hydroxyl radical heterogeneous oxidation, Atmos. Environ., 43, 5038–5045, <a href="http://dx.doi.org/10.1016/j.atmosenv.2009.06.043">https://doi.org/10.1016/j.atmosenv.2009.06.043</a>, 2009. Hallquist, M., Wenger, J. C., Baltensperger, U., Rudich, Y., Simpson, D., Claeys, M., Dommen, J., Donahue, N. M., George, C., Goldstein, A. H., Hamilton, J. F., Herrmann, H., Hoffmann, T., Iinuma, Y., Jang, M., Jenkin, M. E., Jimenez, J. L., Kiendler-Scharr, A., Maenhaut, W., McFiggans, G., Mentel, Th. F., Monod, A., Prévôt, A. S. H., Seinfeld, J. H., Surratt, J. D., Szmigielski, R., and Wildt, J.: The formation, properties and impact of secondary organic aerosol: current and emerging issues, Atmos. Chem. Phys., 9, 5155–5236, <a href="http://dx.doi.org/10.5194/acp-9-5155-2009">https://doi.org/10.5194/acp-9-5155-2009</a>, 2009. Hanson,&nbsp;D.&nbsp;R. and Lovejoy,&nbsp;E.&nbsp;R.: The reaction of ClONO<sub>2</sub> with submicrometer sulfuric-acid aerosol, Science, 267, 1326–1328, 1995. Heald,&nbsp;C.&nbsp;L., Kroll,&nbsp;J.&nbsp;H., Jimenez,&nbsp;J.&nbsp;L., Docherty,&nbsp;K.&nbsp;S., DeCarlo,&nbsp;P.&nbsp;F., Aiken,&nbsp;A.&nbsp;C., Chen,&nbsp;Q., Martin,&nbsp;S.&nbsp;T., Farmer,&nbsp;D.&nbsp;K., and Artaxo,&nbsp;P.: A simplified description of the evolution of organic aerosol composition in the atmosphere, Geophys. Res. Lett., 37, L08803, <a href="http://dx.doi.org/10.1029/2010GL042737">https://doi.org/10.1029/2010GL042737</a>, 2010. Hearn,&nbsp;J.&nbsp;D. and Smith,&nbsp;G.&nbsp;D.: A mixed-phase relative rates technique for measuring aerosol reaction kinetics, Geophys. Res. Lett., 33, L17805, <a href="http://dx.doi.org/10.1029/2006GL026963">https://doi.org/10.1029/2006GL026963</a>, 2006. Hill Jr.,&nbsp;C.&nbsp;G.: An Introduction to Chemical Engineering Kinetics and Reactor Design, John Wiley and Sons, New York, 1977. Hinds,&nbsp;W.&nbsp;C.: Aerosol Technology: Properties, Behavior, and Measurement of Airborne Particles, Wiley-Interscience, New York, 1999. Joshi,&nbsp;S.&nbsp;B., Dodge,&nbsp;M.&nbsp;C., and Bufalini,&nbsp;J.&nbsp;J.: Reactivities of selected organic-compounds and contamination effects, Atmos. Environ., 16, 1301–1310, 1982. Kang, E., Root, M. J., Toohey, D. W., and Brune, W. H.: Introducing the concept of Potential Aerosol Mass&nbsp;(PAM), Atmos. Chem. Phys., 7, 5727–5744, <a href="http://dx.doi.org/10.5194/acp-7-5727-2007">https://doi.org/10.5194/acp-7-5727-2007</a>, 2007. Katrib,&nbsp;Y., Bishos,&nbsp;G., Buseck,&nbsp;P.&nbsp;R., Davidovits,&nbsp;P., Jayne,&nbsp;J.&nbsp;T., Mochida,&nbsp;M., Wise,&nbsp;M.&nbsp;E., Worsnop,&nbsp;D.&nbsp;R., and Martin,&nbsp;S.&nbsp;T.: Ozonolysis of mixed oleic acid/stearic acid particles: reaction kinetics and chemical morphology, J. Phys. Chem.&nbsp;A, 109, 10910–10919, 2005. Kroll,&nbsp;J.&nbsp;H. and Seinfeld,&nbsp;J.&nbsp;H.: Chemistry of secondary organic aerosol: formation and evolution of low-volatility organics in the atmosphere, Atmos. Environ., 42, 3593–3624, <a href="http://dx.doi.org/10.1016/j.atmosenv.2008.01.003">https://doi.org/10.1016/j.atmosenv.2008.01.003</a>, 2008. Kroll,&nbsp;J.&nbsp;H., Chan,&nbsp;A.&nbsp;W.&nbsp;H., Ng,&nbsp;N.&nbsp;L., Flagan,&nbsp;R.&nbsp;C., and Seinfeld,&nbsp;J.&nbsp;H.: Reactions of semivolatile organics and their effects on secondary organic aerosol formation, Environ. Sci. Technol., 41(10), 3545–3550, 2007. Kroll,&nbsp;J.&nbsp;H., Smith,&nbsp;J.&nbsp;D., Che,&nbsp;D.&nbsp;L., Kessler,&nbsp;S.&nbsp;H., Worsnop,&nbsp;D.&nbsp;R., and Wilson,&nbsp;K.&nbsp;R.: Measurement of fragmentation and functionalization pathways in the heterogeneous oxidation of oxidized organic aerosol, Phys. Chem. Chem. Phys., 11, 8005–8014, <a href="http://dx.doi.org/10.1039/b905289e">https://doi.org/10.1039/b905289e</a>, 2009. Lambe,&nbsp;A.&nbsp;T., Miracolo,&nbsp;M.&nbsp;M., Hennigan,&nbsp;C.&nbsp;J., Robinson,&nbsp;A.&nbsp;L., and Donahue,&nbsp;N.&nbsp;M.: Effective rate constants and uptake coefficients for the reactions of organic molecular markers (n-alkanes, hopanes and steranes) in motor oil and diesel primary organic aerosols with hydroxyl radicals, Environ. Sci. Technol., 43, 23, 8794–8800, 2009. Levenspiel,&nbsp;O. and Smith,&nbsp;W.&nbsp;K.: Notes on the diffusion-type model for the longitudinal mixing of fluids in flow, Chem. Eng. Sci., 6, 227–233, 1957. Lonneman,&nbsp;W.&nbsp;A., Bufalini,&nbsp;J.&nbsp;J., Kuntz,&nbsp;R.&nbsp;L., and Meeks,&nbsp;S.&nbsp;A.: Contamination from fluorocarbon films, Environ. Sci. Technol., 15, 99–103, 1981. Mao, J., Ren, X., Brune, W. H., Olson, J. R., Crawford, J. H., Fried, A., Huey, L. G., Cohen, R. C., Heikes, B., Singh, H. B., Blake, D. R., Sachse, G. W., Diskin, G. S., Hall, S. R., and Shetter, R. E.: Airborne measurement of OH reactivity during INTEX-B, Atmos. Chem. Phys., 9, 163–173, <a href="http://dx.doi.org/10.5194/acp-9-163-2009">https://doi.org/10.5194/acp-9-163-2009</a>, 2009. Massoli,&nbsp;P., Lambe,&nbsp;A.&nbsp;T., Ahern,&nbsp;A.&nbsp;T., Williams,&nbsp;L.&nbsp;R., Ehn,&nbsp;M., Mikkilä,&nbsp;J., Canagaratna,&nbsp;M.&nbsp;R., Brune,&nbsp;W.&nbsp;H., Onasch,&nbsp;T.&nbsp;B., Jayne,&nbsp;J.&nbsp;T., Petäjä,&nbsp;T., Kulmala,&nbsp;M., Laaksonen,&nbsp;A., Kolb,&nbsp;C.&nbsp;E., Davidovits,&nbsp;P., and Worsnop,&nbsp;D.&nbsp;R.: Relationship between aerosol oxidation level and hygroscopic properties of laboratory generated secondary organic aerosol&nbsp;(SOA) particles, Geophys. Res. Lett., 37, L24801, <a href="http://dx.doi.org/10.1029/2010GL045258">https://doi.org/10.1029/2010GL045258</a>, 2010. Matsunaga, A. and Ziemann, P. J.: Gas-wall partitioning of organic compounds in a teflon film chamber and potential effects on reaction product and aerosol yield measurements, Aerosol Sci. Tech., 44(10), 881–892, 2010. McMurry,&nbsp;P.&nbsp;H. and Grosjean,&nbsp;D.: Gas and aerosol wall losses in teflon film smog chambers, Environ. Sci. Technol., 19, 1176–1182, 1985. McMurry,&nbsp;P.&nbsp;H. and Rader,&nbsp;D.&nbsp;J.: Aerosol wall losses in electrically charged chambers, Aerosol Sci. Tech., 4, 249–268, 1985. McNeill, V. F., Yatavelli, R. L. N., Thornton, J. A., Stipe, C. B., and Landgrebe, O.: Heterogeneous OH oxidation of palmitic acid in single component and internally mixed aerosol particles: vaporization and the role of particle phase, Atmos. Chem. Phys., 8, 5465–5476, <a href="http://dx.doi.org/10.5194/acp-8-5465-2008">https://doi.org/10.5194/acp-8-5465-2008</a>, 2008. Mentel,&nbsp;T.&nbsp;F., Bleilebens,&nbsp;D., and Wahner,&nbsp;A.: A&nbsp;study of nighttime nitrogen oxide oxidation in a large reaction chamber – the fate of NO<sub>2</sub>, N<sub>2</sub>O<sub>5</sub>, HNO<sub>3</sub>, and NO<sub>3</sub><sup>-</sup> at different humidities, Atmos. Environ., 30, 4007–4020, 1996. Morris,&nbsp;J.&nbsp;W., Davidovits,&nbsp;P., Jayne,&nbsp;J.&nbsp;T., Jimenez,&nbsp;J.&nbsp;L., Shi,&nbsp;Q., Kolb,&nbsp;C.&nbsp;E., Worsnop,&nbsp;D.&nbsp;R., Barney,&nbsp;W.&nbsp;S., and Cass,&nbsp;G.: Kinetics of submicron oleic acid aerosols with ozone: a novel aerosol mass spectrometric technique, Geophys. Res. Lett., 29, 1357, <a href="http://dx.doi.org/10.1029/2002GL014692">https://doi.org/10.1029/2002GL014692</a>, 2002. Ng, N. L., Chhabra, P. S., Chan, A. W. H., Surratt, J. D., Kroll, J. H., Kwan, A. J., McCabe, D. C., Wennberg, P. O., Sorooshian, A., Murphy, S. M., Dalleska, N. F., Flagan, R. C., and Seinfeld, J. H.: Effect of NO<sub>x</sub> level on secondary organic aerosol&nbsp;(SOA) formation from the photooxidation of terpenes, Atmos. Chem. Phys., 7, 5159–5174, <a href="http://dx.doi.org/10.5194/acp-7-5159-2007">https://doi.org/10.5194/acp-7-5159-2007</a>, 2007a. Ng, N. L., Kroll, J. H., Chan, A. W. H., Chhabra, P. S., Flagan, R. C., and Seinfeld, J. H.: Secondary organic aerosol formation from <i>m</i>-xylene, toluene, and benzene, Atmos. Chem. Phys., 7, 3909–3922, <a href="http://dx.doi.org/10.5194/acp-7-3909-2007">https://doi.org/10.5194/acp-7-3909-2007</a>, 2007b. Odum,&nbsp;J.&nbsp;R., Hoffman,&nbsp;T., Bowman,&nbsp;F., Collins,&nbsp;D., Flagan,&nbsp;R.&nbsp;C., and Seinfeld,&nbsp;J.&nbsp;H.: Gas/particle partitioning and secondary organic aerosol yields, Environ. Sci. Technol., 30, 2580–2585, 1996. Petters,&nbsp;M.&nbsp;D., Prenni,&nbsp;A.&nbsp;J., Kreidenweis,&nbsp;S.&nbsp;M., DeMott,&nbsp;P.&nbsp;J., Matsunaga,&nbsp;A., Lim,&nbsp;Y.&nbsp;B., and Ziemann,&nbsp;P.&nbsp;J.: Chemical aging and the hydrophobic-to-hydrophilic conversion of carbonaceous aerosol, Geophys. Res. Lett., 33, L24806, <a href="http://dx.doi.org/10.1029/2006gl027249">https://doi.org/10.1029/2006gl027249</a>, 2006. Petters, M. D. and Kreidenweis, S. M.: A single parameter representation of hygroscopic growth and cloud condensation nucleus activity, Atmos. Chem. Phys., 7, 1961–1971, <a href="http://dx.doi.org/10.5194/acp-7-1961-2007">https://doi.org/10.5194/acp-7-1961-2007</a>, 2007. Pierce,&nbsp;J.&nbsp;R., Engelhart,&nbsp;G.&nbsp;J., Hildebrandt,&nbsp;L., Weitkamp,&nbsp;E.&nbsp;A., Pathak,&nbsp;R.&nbsp;K., Donahue,&nbsp;N.&nbsp;M., Robinson,&nbsp;A.&nbsp;L., Adams,&nbsp;P.&nbsp;J., and Pandis,&nbsp;S.&nbsp;N.: Constraining particle evolution from wall losses, coagulation, and condensation-evaporation in smog-chamber experiments: optimal estimation based on size distribution measurements, Aerosol Sci. Tech., 42, 1001–1015, <a href="http://dx.doi.org/10.1080/02786820802389251">https://doi.org/10.1080/02786820802389251</a>, 2008. Presto,&nbsp;A.&nbsp;A., Hartz,&nbsp;K.&nbsp;E.&nbsp;H., and Donahue,&nbsp;N.&nbsp;M.: Secondary organic aerosol production from terpene ozonolysis, 1.&nbsp;Effect of UV radiation, Environ. Sci. Technol., 39, 7036–7045, <a href="http://dx.doi.org/10.1021/es050174m">https://doi.org/10.1021/es050174m</a>, 2005. Qi, L., Nakao, S., Tang, P., and Cocker&nbsp;III, D. R.: Temperature effect on physical and chemical properties of secondary organic aerosol from <i>m</i>-xylene photooxidation, Atmos. Chem. Phys., 10, 3847–3854, <a href="http://dx.doi.org/10.5194/acp-10-3847-2010">https://doi.org/10.5194/acp-10-3847-2010</a>, 2010. Robbins,&nbsp;R.&nbsp;C. and Cadle,&nbsp;R.&nbsp;D.: Kinetics of the reaction between gaseous ammonia and sulfuric acid droplets in an aerosol, J. Phys. Chem., 62, 469–471, 1958. Roberts,&nbsp;G.&nbsp;C. and Nenes,&nbsp;A.: A&nbsp;continuous-flow streamwise thermal-gradient CCN chamber for atmospheric measurements, Aerosol Sci. Tech., 39, 206–221, 2005. Rudich,&nbsp;Y., Donahue,&nbsp;N.&nbsp;M., and Mentel,&nbsp;T.&nbsp;F.: Aging of organic aerosol: bridging the gap between laboratory and field studies, Annu. Rev. Phys. Chem., 58, 321–352, 2007. Seinfeld,&nbsp;J.&nbsp;H. and Pandis,&nbsp;S.&nbsp;N.: Atmospheric Chemistry and Physics: From Air Pollution to Climate Change, John Wiley and Sons, Inc., New York, 2006. Smith, J. D., Kroll, J. H., Cappa, C. D., Che, D. L., Liu, C. L., Ahmed, M., Leone, S. R., Worsnop, D. R., and Wilson, K. R.: The heterogeneous reaction of hydroxyl radicals with sub-micron squalane particles: a model system for understanding the oxidative aging of ambient aerosols, Atmos. Chem. Phys., 9, 3209–3222, <a href="http://dx.doi.org/10.5194/acp-9-3209-2009">https://doi.org/10.5194/acp-9-3209-2009</a>, 2009. Stanier,&nbsp;C.&nbsp;O., Pathak,&nbsp;R.&nbsp;K., and Pandis,&nbsp;S.&nbsp;N.: Measurements of the volatility of aerosols from alpha-pinene ozonolysis, Environ. Sci. Technol., 41, 2756–2763, <a href="http://dx.doi.org/10.1021/es0519280">https://doi.org/10.1021/es0519280</a>, 2007. Taylor,&nbsp;G.&nbsp;I.: Dispersion of soluble matter in solvent flowing slowly through a tube, P. Roy. Soc. Lond.&nbsp;A, 219, 186–203, 1953. Turpin,&nbsp;B.&nbsp;J., Saxena,&nbsp;P., and Andrews,&nbsp;E.: Measuring and simulating particulate organics in the atmosphere: problems and prospects, Atmos. Environ., 34, 2983–3013, 2000.