Assessing the degree of plug flow in oxidation flow reactors (OFRs): a study on a Potential Aerosol Mass (PAM) reactor

Abstract

24 25Oxidation flow reactors (OFRs) have been developed to achieve high degrees of oxidant exposures 26 over relatively short space times (defined as the ratio of reactor volume to the volumetric flowrate). 27While, due to their increased use, attention has been paid to their ability to replicate realistic 28 tropospheric reactions by modeling the chemistry inside the reactor, there is a desire to customize 29 flow patterns. This work demonstrates the importance of decoupling tracer signal of the reactor 30 from that of the tubing when experimentally obtaining these flow patterns. We modeled the 31 residence time distributions (RTDs) inside the Washington University Potential Aerosol Mass 32 (WU-PAM) reactor, an OFR, for a simple set of configurations by applying the tank-in-series (TIS) 33 model, a one parameter model, to a deconvolution algorithm. The value of the parameter, , is 34 close to unity for every case except one having the highest space time. Combined, the results 35 suggest that volumetric flowrate affects mixing patterns more than use of our internals. We 36 selected results from the simplest case, at 78s space time with one inlet and one outlet, absent of 37 baffles and spargers, and compared the experimental F-Curve to that of a computational fluid 38 dynamics (CFD) simulation. The F-Curves, which represents the cumulative time spent in the 39 reactor by flowing material, match reasonably well. We value that the use of a small aspect ratio 40 reactor such as the WU-PAM reduces wall interactions, and suggest applying the methodology of 41 tracer testing described in this work to investigate RTDs in OFRs and modify inlets, outlets, and 42 use of internals prior to applications (e.g., field deployment vs. laboratory study). 43 44 1 Introduction 45

Response to Reviewer 2 Comments

“…To minimize noise, AMS data are plotted only for points where sufficient total organic concentrations were achieved, around the peak of the concentration profile. The triangles formed by the blue dotted lines provide visual guidelines for the evolution of OA chemical composition across f 44 vs. f 43 space; the apex of the triangle indicates the direction of OA photochemical oxidation (Ng et al, 2010).…”

“…Our observations demonstrate the importance of chemically speciated data in fully understanding bulk aerosol measurements provided by the AMS in both laboratory and field studies. 2200 C. F. Fortenberry et al: Bulk and molecular characterization of BBOA from oak fuels (PM 1 ) and may consist of thousands of distinct organic compounds (Goldstein and Galbally, 2007;Ng et al, 2010;Zhang et al, 2007). Given the multitude of organic compounds in the atmosphere and the numerous chemical reactions they can experience during atmospheric processing (e.g., Goldstein and Galbally, 2007;Kroll et al, 2009), laboratory studies are needed to fully understand the chemical composition and oxidative evolution of source-specific primary OA (POA, aerosol emitted directly into the atmosphere) and secondary OA (SOA, formed from gas-phase material that partition into the particle phase following photooxidation).…”

“…2 ) and m/z 44 (CO + 2 ) signals to quantify primary and aged emissions, respectively (e.g., Cubison et al, 2011;Ng et al, 2010Ng et al, , 2011a. Levoglucosan, a cellulose decomposition product often used as a molecular tracer for freshly emitted BBOA (e.g., Simoneit et al, 1999Simoneit et al, , 2004, is frequently considered to be a primary contributor to m/z 60 in AMS laboratory and field studies (e.g., Lee et al, 2010;Ng et al, 2011b).…”

Response to Reviewer 3 Comments

“…(PM 1 ) and may consist of thousands of distinct organic compounds (Goldstein and Galbally, 2007;Ng et al, 2010;Zhang et al, 2007). Given the multitude of organic compounds in the atmosphere and the numerous chemical reactions they can experience during atmospheric processing (e.g., Goldstein and Galbally, 2007;Kroll et al, 2009), laboratory studies are needed to fully understand the chemical composition and oxidative evolution of source-specific primary OA (POA, aerosol emitted directly into the atmosphere) and secondary OA (SOA, formed from gas-phase material that partition into the particle phase following photooxidation).…”

“…Although the AMS provides real-time measurements of ensemble-averaged properties for submicron nonrefractory aerosol, it does not achieve molecular speciation and thus cannot be used to identify individual compounds present in OA. Typical AMS BBOA studies use m/z 60 (C 2 H 4 O + 2 ) and m/z 44 (CO + 2 ) signals to quantify primary and aged emissions, respectively (e.g., Cubison et al, 2011;Ng et al, 2010Ng et al, , 2011a. Levoglucosan, a cellulose decomposition product often used as a molecular tracer for freshly emitted BBOA (e.g., Simoneit et al, 1999Simoneit et al, , 2004, is frequently considered to be a primary contributor to m/z 60 in AMS laboratory and field studies (e.g., Lee et al, 2010;Ng et al, 2011b).…”