10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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Three-Stage Modelling of Indoor Aerosol Formation Caused by Reaction of Ozone with Volatile Organic Compounds Emitted from Air Fresheners
Thai Phuong Vu, SEUNG-BOK LEE, Gwi-Nam Bae, HoChiMinh University of Natural Resources and Environment
Abstract Number: 281 Working Group: Indoor Aerosols
Abstract A three-stage modelling of aerosol formation potential (AFP) was proposed to investigate secondary organic aerosols caused by ozone reaction of volatile organic compounds emitted from air fresheners. The AFP was defined as a function of formed aerosol mass per unit ozone reacted. The experimental system consisted of a reaction chamber, ozone and pure air generators and ozone and particle monitoring instruments. The volume of the cube-shaped reaction chamber made of 2-mil (about 51 μm) FEP Teflon film was 1 m3 (1× 1× 1 m). The chamber was installed in a wooden box equipped with a door in order to avoid any light disturbances from the outside. The ozone concentration was monitored every one minute using a U.V. photometric O3 analyzer (TEI 49i). The particle number size distribution was determined using a scanning mobility particle sizer (SMPS), which consisted of an electrostatic classifier (TSI 3081) and a condensation particle counter (CPC, TSI 3010). Total particle number concentration was also monitored using an ultrafine condensation particle counter (UCPC, TSI 3025) with a 1-sec response time. The air temperature and relative humidity in the Teflon chamber were maintained at 20oC and 20%, respectively. The total sampling flow rate for monitoring particles and ozone in the chamber was controlled to be similar to the flow rate of ozone injected into the chamber. A 0.5-mL test specimen of a liquid-type air freshener was contained in a 50-mL glass petri dish with a diameter of 65 mm that was then placed in the bottom of the chamber. Ozone injection started after the test specimen was set and occurred into the center of the chamber through the top surface using a photometric O3 calibrator (API 401). The ozone calibrator was operated at three different concentrations (50, 100 and 200 ppb) at a flow rate of 4.0 L/min. Each experiment lasted for 4 h. The aerosol formation process can be classified into three stages. The first stage of the AFP was determined at beginning time t0 (t0 = 0) to time t1 at which particle was not formed, AFP0 = 0. The second stage of the AFP began from t1 to time t2. There was a nucleation burst and conversion of formed particles to larger particles (size of 100 nm), AFP1 = a1ΔO3 – b1 (a1 = 0.4 – 1.9 and b1 = 0.6 – 4.3). The third stage of the AFP began from t2 to end experiment time t3. There was stable increase in particle concentration, AFP2 = a2ΔO3 – b2 (a1 = 0.7 – 3.0 and b2 = 15.0 – 27.0). Values of ai and bi were depended on concentration and quantity of biogenic volatile organic compounds in the air fresheners and ΔO3 was ozone quantity reacted. The three-stage modeling was easy to be applied for investigation of the secondary organic aerosol formation under other environmental conditions such as ozone concentration, temperature, air freshener quantity, and initial volatile organic compounds. The three-stage modelling was easily and effectively used to evaluate and control secondary aerosol sources for indoor pollution management.