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<p class="MsoNormal" style="background:white"><span style="font-family:"Calibri",sans-serif;color:#464646;mso-ligatures:none">Xu, N., Le, C., Cocker, D. R., Chen, K., Lin, Y.-H., and Collins, D. R.: An oxidation flow reactor for simulating and accelerating
secondary aerosol formation in aerosol liquid water and cloud droplets, Atmos. Meas. Tech., 17, 4227–4243,
<a href="https://doi.org/10.5194/amt-17-4227-2024">https://doi.org/10.5194/amt-17-4227-2024</a>, 2024.<o:p></o:p></span></p>
<p class="MsoNormal" style="background:white"><span style="font-family:"Calibri",sans-serif;color:#464646;mso-ligatures:none"><o:p> </o:p></span></p>
<p style="margin-top:0in;background:white"><b><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#464646">Abstract.
</span></b><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#464646">Liquid water in cloud droplets and aqueous aerosols serves as an important reaction medium for the formation of secondary aerosol through aqueous-phase reactions (aqSA).
Large uncertainties remain in estimates of the production and chemical evolution of aqSA in the dilute solutions found in cloud droplets and the concentrated solutions found in aerosol liquid water, which is partly due to the lack of available measurement
tools and techniques. A new oxidation flow reactor (OFR), the Accelerated Production and Processing of Aerosols (APPA) reactor, was developed to measure secondary aerosol formed through gas- and aqueous-phase reactions, both for laboratory gas mixtures containing
one or more precursors and for ambient air. For simulating in-cloud processes, </span><span class="inline-formula"><span style="font-size:11.0pt;font-family:"Cambria Math",serif;color:#464646">∼</span></span><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#464646"> 3.3 </span><span class="inline-formula"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#464646">µ</span></span><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#464646">m
diameter droplets formed on monodisperse seed particles are introduced into the top of the reactor, and the relative humidity (RH) inside it is controlled to 100 %. Similar measurements made with the RH in the reactor </span><span class="inline-formula"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#464646"><</span></span><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#464646"> 100 %
provide contrasts for aerosol formation with no liquid water and with varying amounts of aerosol liquid water.<o:p></o:p></span></p>
<p style="margin-top:0in;background:white;box-sizing: border-box;border-radius: 0px;margin-bottom:1rem;font-variant-ligatures: normal;font-variant-caps: normal;orphans: 2;widows: 2;-webkit-text-stroke-width: 0px;text-decoration-thickness: initial;text-decoration-style: initial;text-decoration-color: initial;word-spacing:0px" id="d1e166">
<span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#464646">The reactor was characterized through a series of experiments and used to form secondary aerosol from known concentrations of an organic precursor and from ambient air. The residence
time distributions of both gases and particles are narrow relative to other OFRs and lack the tails at long residence time expected with laminar flow. Initial cloud processing experiments focused on the well-studied oxidation of dissolved SO</span><span class="inline-formula"><sub><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#464646">2</span></sub></span><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#464646"> by
O</span><span class="inline-formula"><sub><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#464646">3</span></sub></span><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#464646">, with the observed growth of seed particles
resulting from the added sulfuric acid agreeing well with estimates based on the relevant set of aqueous-phase reactions. The OH exposure (OH</span><span class="inline-formula"><sub><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#464646">exp</span></sub></span><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#464646">)
for low RH, high RH, and in-cloud conditions was determined experimentally from the loss of SO</span><span class="inline-formula"><sub><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#464646">2</span></sub></span><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#464646"> and
benzene and simulated from the KinSim chemical kinetics solver with inputs of the measured 254 nm UV intensity profile through the reactor and loss of O</span><span class="inline-formula"><sub><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#464646">3</span></sub></span><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#464646"> due
to photolysis. The aerosol yield for toluene at high OH</span><span class="inline-formula"><sub><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#464646">exp</span></sub></span><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#464646"> ranged
from 21.4 % at low RH with dry seed particles present in the reactor to 78.1 % with cloud droplets present. Measurement of the composition of the secondary aerosol formed from ambient air using an aerosol mass spectrometer showed that the oxygen-to-carbon
ratio (O : C) of the organic component increased with increasing RH (and liquid water content).<o:p></o:p></span></p>
<p class="MsoNormal"><a href="https://sites.google.com/site/pamwiki/publications-using-other-oxidation-flow-reactors">PAM Wiki - Publications Using Other Oxidation Flow Reactors (google.com)</a><o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><span style="mso-ligatures:none">Andrew Lambe<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-ligatures:none">Principal Scientist<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-ligatures:none">Aerodyne Research, Inc. <o:p>
</o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
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