10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
A New Computer Model for the Simulation of Secondary Organic Aerosol Formation from Stir-frying Additives Using Aspen Plus
MEHDI AMOUEI TORKMAHALLEH, Fariza Aldemkhan, Chemical and Aerosol Research Team, Nazarbayev University
Abstract Number: 673 Working Group: Indoor Aerosols
Abstract The formation of volatile organic compounds (VOCs) and particulate matter (PM) indoors as a result of cooking are becoming one of the major topics of interest in environmental engineering, due to their increasing hazardous effects on inhabitants. In this study, the simulation of stir-frying corn oil with food additives, namely, myrcia and salt, was developed using Aspen Plus. According to Amouei Torkmahalleh et al [1], this approach presents the results for the time instant at which the operating conditions are established. The scope of this investigation is to determine the chemical composition and physical properties of primary organic aerosol (POA) and secondary organic aerosol (SOA) produced from stir-frying myrcia. Since, the herbs are mainly composed of terpenes [2], it is expected to have significant SOA compounds produced from ozonolysis of terpenes. Furthermore, the effect of cooking temperature on the formation organic PM was investigated. Aspen Plus V9 was employed to simulate the cooking process. In order to estimate the phase equilibrium in vapor and liquid phases a Non-Random Two- Liquid (NRTL) model and Ideal Gas law were applied. Missing parameters were estimated via UNIFAC method, which considers the contribution of present functional groups on the properties of the compound of interest. Indoor VOC and major pollutants including sulfur dioxide, nitrogen dioxide and carbon dioxide were included to air to show their interaction with emissions from cooking. There are three reactors where hydrolysis of oil, oxidation of free fatty acids and ozonolysis of terpenes are simulated. Products of free fatty acids oxidation and terpene ozonolysis were inserted according to existing literature. The outputs from these reactors were mixed with air and cooled to represent rapid dilution and condensation of precursor gases leading to aerosol formation. Finally, Flash block was employed to separate formed aerosol from VOC.
The POA from high temperature frying with myrcia is dominated by terpenes, terpenoids and other aromatic compounds. There are other compounds emitted as well including aldehydes, alkanes and ketones; however they are present in significantly lower amounts. Due to high composition of ring structures, POA possesses relatively high viscosity of 0.0092Pa-sec. Density of the liquid mixture is governed by α-humulene, because it contributes to 93% of the total POA and equals 1.021g/ccm. After introducing excess ozone to cooking emissions, the composition of SOA from stir-frying myrcia was determined. It is governed by products of myrcene oxidation including Hydroxyacetone, 4-vinyl-4-pentanal, 4-oxopentanal and 2-vinyl-pentandial. It is followed by products of α-pinene ozonolysis: acetone, formaldehyde, pinonaldehyde and norpinic acid. Lastly, limonene oxidation yielded 4-acetyl-1-methylcyclohexane, 3-isopropenyl-6-oxo-heptanal, dihydrocarvone and limononic acid. As noted, SOA is comprised of linear structures, therefore its viscosity is significantly lower than that of POA and equals 0.00098Pa-sec. That is, POA was approximately 10 times more viscous than SOA, but the densities of POA and SOA are quite similar, such that density of SOA was estimated to be 1.028 g/ccm. In conclusion, mass percentage of the corresponding products from myrcene, limonene, and a-pinene were estimated to be 68%, 24.34% and 7.66% respectively. Myrcia appeared to increase the rate of particulate matter formation. Heating corn oil to 240 °C produced 10 times less POA than stir-frying myrcia in corn oil. Moreover, stir-frying of myrcia produced nearly 3 times more SOA that heating corn oil alone.