10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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A High Volume Laminar Flow Reactor to Investigate the Influence of Photochemical Aging on the Health-related Properties of Combustion Emission: Method Characterization and Utilization to Investigate Wood Combustion Emissions
OLLI SIPPULA, Petri Tiitta, Mika Ihalainen, Pasi Yli-Pirilä, Anni Hartikainen, Tuukka Ihantola, Pasi Jalava, Ari Leskinen, Jarkko Tissari, Miika Kortelainen, Heikki Suhonen, Ralf Zimmermann, Maija-Riitta Hirvonen, Jorma Jokiniemi, University of Eastern Finland, Kuopio, Finland
Abstract Number: 1124 Working Group: Oxidation Flow Reactor: Development, Characterization, and Application to Aerosols
Abstract One of the main challenges for the assessment of the environmental effects of combustion emissions is their constant transformation in the atmosphere, due to photochemical aging, which may change the health-related toxicological, chemical and physical properties of the emission particles. The devices used to simulate aerosol photo-oxidation include smog chambers and different flow tube reactors. The modern air-liquid cell exposure devices used in toxicological studies, with combined physico-chemical characterizations of aerosol emissions, require relatively high amounts of aerosol sample. To provide sufficient sample flow rates of aged aerosols for these studies, a High-Volume Photochemical Emission Aging Reactor (PEAR), capable of photo-oxidizing high emission concentrations and volumes, was designed and constructed. First, the PEAR was characterized and validated with common precursors for inorganic and organic secondary aerosols. Next, the PEAR-method was compared to a smog chamber using emissions of a logwood-fired stove as a reference. Finally, the device was utilized in connection with air-liquid interface exposure systems, providing information on how aging of combustion emissions influences the biological responses of the exposed lung cells.
The reactor is constructed from stainless steel tube which has 254 nm UV lamps assembled at the inner walls. Ozone and water vapor are added into the reactor to produce OH radicals via photolytical decomposition of O3. The inlet of the reactor consists of flow diffuser, which is designed to achieve a nearly optimal laminar flow profile in the reactor, when used with the designed flow rates (50-200 lpm). The flow dynamics of the reactor were simulated with the aid of computational fluid dynamics software (ANSYS 15.0, Fluent) to optimize the reactor dimensions and other boundary conditions. According to the gas residence times, measured with CO2 marker gas, almost fully developed laminar flow profile was achieved at a flow rate of 100 lpm. Consequently wall losses of particles < 50 nm in diameter were very low, below 10%.
In the wood stove experiments diluted exhaust from two different spruce log fired stoves were introduced both into the PEAR and in a 29 m3 smog chamber (Tiitta et al., 2016). The composition and concentrations of gaseous and particulate species were measured online using HR-PTR-ToF (Ionicon) and SP-AMS (Aerodyne), respectively. Aging in flow tube increased the organic aerosol (OA) mass fraction by 2.1–2.7 times the initial OA mass with OH exposures between 0.8–5.8× 1011 molec. cm-3s. OA enhancement ratios were at highest with low OH exposures, which corresponded to 1-2 days of equivalent atmospheric aging at typical boundary-layer OH concentrations. In the smog chamber, the wall-loss corrected OA enhancement ratios were 1.8-2.1, with similar OH exposures, indicating slightly more efficient SOA formation in the PEAR. The AMS mass spectra and calculated oxidation state of OA was similar in PEAR and the smog chamber at similar OH exposures. Furthermore, an intermediate slope of Van Krevelen diagram between -0.6 and -0.7 in ambient oxidation levels indicated similar oxidation reactions (e.g. fragmentation and functionalization) in PEAR and in the smog chamber.
To investigate the role of aging on potential health effects of the emissions, A549 cells were exposed to fresh and aged wood combustion aerosol using an air-liquid interface, in which the particle deposition on the cell surfaces occurs via controlled thermophoretic force. Comparison of fresh and aged aerosol indicated higher inflammation (IL-8), and genotoxic (Comet assay) responses for the aged aerosol, while the cell viability and production of reactive oxygen species (ROS) remained at a similar level. Thus, photochemical aging induced clear changes also in the toxicological properties of the emissions.
This work was funded by the Academy of Finland.
References: Tiitta, P., Leskinen, A. et al. (2016) Atmospheric Chemistry & Physics 16, 13251-13269.