A New Aerosol Flow System for Photochemical and Thermal Studies of Tropospheric Aerosols

Abstract

For studying the formation and photochemical/thermal reactions of aerosols relevant to the troposphere, a unique, high-volume, slow-flow, stainless steel aerosol flow system equipped with UV lamps has been constructed and characterized experimentally. The total flow system length is 8.5 m and includes a 1.2 m section used for mixing, a 6.1 m reaction section and a 1.2 m transition cone at the end. The 45.7 cm diameter results in a smaller surface to volume ratio than is found in many other flow systems and thus reduces the potential contribution from wall reactions. The latter are also reduced by frequent cleaning of the flow tube walls which is made feasible by the ease of disassembly. The flow tube is equipped with ultraviolet lamps for photolysis. This flow system allows continuous sampling under stable conditions, thus increasing the amount Received 3 November 2009; accepted 10 January 2010. We are grateful to the U.S. Department of Energy (Grant # DE-FG02-05ER64000) for support of this work. Additional support was provided by the AirUCI Environmental Molecular Science Institute funded by the National Science Foundation (Grant # CHE-0431312). E.A.B. acknowledges financial support from a National Science Foundation graduate student fellowship. This research was in part in collaboration with the Environmental Molecular Sciences Laboratory, a national scientific user facility sponsored by the U.S. Address correspondence to Barbara J. Finlayson-Pitts, Department of Chemistry, University of California Irvine, Irvine, CA 92697-2025, USA. E-mail: bjfinlay@uci.edu of sample available for analysis and permitting a wide variety of analytical techniques to be applied simultaneously. The residence time is of the order of an hour, and sampling ports located along the length of the flow tube allow for time-resolved measurements of aerosol and gas-phase products. The system was characterized using both an "inert" gas (CO 2 ) and particles (atomized NaNO 3 ). Instruments interfaced directly to this flow system include a NO x analyzer, an ozone analyzer, relative humidity and temperature probes, a scanning mobility particle sizer spectrometer, an aerodynamic particle sizer spectrometer, a gas chromatograph-mass spectrometer, an integrating nephelometer, and a Fourier transform infrared spectrophotometer equipped with a long path (64 m) cell. Particles collected with impactors and filters at the various sampling ports can be analyzed subsequently by a variety of techniques. Formation of secondary organic aerosol from α-pinene reactions (NO x photooxidation and ozonolysis) are used to demonstrate the capabilities of this new system.

Simplified mechanism for new particle formation from methanesulfonic acid, amines, and water via experiments and ab initio calculations

“…Experiments were performed in an aerosol flow reactor (42) at atmospheric pressure and 25°C where measured gas-phase MSA, water, and trimethylamine (TMA) or DMA were mixed, and number concentrations of the new particles were determined using a scanning mobility particle sizer (SMPS) whose lower detection limit of 3 nm defined what was measured as a particle and what was modeled using the kinetics scheme discussed below. (Potential effects of particle coagulation and wall losses, discussed in SI Text, are shown not to alter the conclusions.)…”

The Caltech Photooxidation Flow Tube reactor: design, fluid dynamics and characterization

“…A transition cone at the end of the reactor concentrates the reactants into a common sampling line that can be split among multiple instruments; thus, samples extracted at the end of the reactor represent the so-called cupmixed average of the entire reactor cross section. This design is similar to the exit cone of the UC Irvine flow tube reactor (Ezell et al, 2010). The Pyrex glass exit cone gradually reduces the diameter of the reactor from 15 to 0.72 cm at an angle of 15 • .…”

“…For example, the PAM reactor described by Kang et al (2007) is constructed of Teflon, which is transparent to UV radiation; consequently, the UV lamps that drive the photochemistry can be positioned outside the reactor itself. By contrast, another class of flow reactors is constructed of aluminum, for which the UV lamps must be positioned inside the reactor itself Ezell et al, 2010). Characterization of the behavior of the flow tube reactor requires ideally a combination of flow and residence time modeling and experiment, chemical kinetic modeling and experiment, and modeling and experimental measurement of interactions of vapor molecules and particles with reactor walls.…”

“…Such reactors comprise both chambers and flow reactors. The flow tube reactor has emerged as a widely used platform (Bruns et al, 2015;Chen et al, 2013;Ezell et al, 2010;Kang et al, 2007Kang et al, , 2011Karjalainen et al, 2016;Keller and Burtscher, 2012;Khalizov et al, 2006;Lambe et al, 2011aLambe et al, , b, 2012Lambe et al, , 2015Li et al, 2015;Ortega et al, 2013Ortega et al, , 2016Palm et al, 2016;Peng et al, 2015Peng et al, , 2016Simonen et al, 2016;Tkacik et al, 2014). The flow tube reactor is generally operated under steadystate conditions.…”

Assessing the degree of plug flow in oxidation flow reactors (OFRs): a study on a potential aerosol mass (PAM) reactor

“…Unfortunately, low levels of conversion and high wall losses seen in these large reactors did not allow simulated exposures that exceeded a day at most, which is just a short glimpse into the average 2-week lifespan of an atmospheric aerosol (Seinfeld and Pandis, 2006). Due to such limitations, oxidation flow reactors (OFRs) with short spacetimes (ratio of reactor volume to the volumetric flow rate) are being developed (Cazorla and Brune, 2010;Ezell et al, 2010;George et al, 2007;Huang et al, 2017;Kang et al, 2007).…”