Partitioning of Semivolatile Organic Compounds in the Presence of a Secondary Organic Aerosol in a Controlled Atmosphere

The gas-particle partitioning of select semivolatile organic compounds (SOCs) was studied by injecting the SOCs into a 190 m3 Teflon film chamber containing a secondary organic aerosol (SOA) generated by volatilizing liquid -pinene into an ozone-concentrated atmosphere. The concentration of total suspended particulates (TSP) and gas and particle-phase SOCs was measured over the course of three experiments spanning a temperature range of 268–297 K and a relative humidity range of 55–100%. An equilibrium partition coefficient, Kp, was calculated for each sampling event. Empirical relationships were then developed to predict the partitioning of the SOCs on the SOA particle source as a function of temperature. Partitioning in this SOA system was compared to that of a SOA generated by the photochemical reaction of NOx with m-xylene. The results indicate that partitioning is similar between the two SOA systems. The effects of multiple particle sources on partitioning was also examined, revealing that a weighted average of predicted Kp values for individual sources can be used to predict partitioning in aerosol mixtures.     

Gaseous and Particulate Oxidation Products Analysis of a Mixture of α-pinene + β-pinene/O3/Air in the Absence of Light and α-pinene + β-pinene/NOx/Air in the Presence of Natural Sunlight

The gas and particle phase reaction products of a mixture of the atmospherically important terpenes -pinene and -pinene with the atmospheric oxidants O₃ and OH/NO_x were investigated using both gas chromatography-mass spectrometry (GC-MS) and high performance liquid chromatography (HPLC) for identification and quantification of reaction products. The nighttime oxidation of a mixture of -pinene and -pinene in the presence of O₃/air, and the daytime oxidation of a mixture of -pinene + -pinene with NO_x air in the presence of natural sunlight were carried out in the University of North Carolina's large outdoor smog chamber (190 m³) located in Chatham County, North Carolina. Mass balances for gaseous and aerosol reaction products are reported over the course of the reaction. More than twenty-nine products were identified and/or quantified in this study. On average, measured gas and particle phase products accounted for 74 to 80% of the reacted -pinen/-pinene mixture carbon. Measurements show that a number of reaction products were found in both O₃ and NO_x system [pinonaldehyde, pinic acid, pinonic acid, pinalic-3-acid, 4-hydroxypinalic-3-acid, 4-oxonopinone, 1-hydroxy-nopinone, 3-hydroxy-nopinone, and nopinone]. Pinonic acid, pinic acid, pinalic-3-acid, 4-hydroxypinalic-3-acid, and 10-hydroxypinonic acid were observed in the early stage in the aerosol phase and may play an important role in the early formation of secondary aerosols.     

Mass Balance of Gaseous and Particulate Products from β-Pinene/O3/Air in the Absence of Light and β-Pinene/NOx/Air in the Presence of Natural Sunlight

The gas and particle phase products from the reaction of -pinene with the atmospheric oxidants O₃ and OH radicals in the presence of NO_x were investigated using both gas chromatography-mass spectrometry (GC-MS) and high performance liquid chromatography (HPLC) for identification and quantification of reaction products. The nighttime oxidation of -pinene in the presence of O₃/air and the daytime oxidation of -pinene in the presence of NO_x/air and natural sunlight were carried out in the University of North Carolina large outdoor smog chamber (190 m³) located in Chatham County, North Carolina. A Scanning Mobility Particle Sizer system (3936, TSI) and a Condensation Particle Counter (3025A, TSI) were used to study the secondary organic aerosol (SOA) formation, and a filter pack/denuder sampling system was used for simultaneously collecting gas and particle phase products for analysis. A gas chromatograph coupled to a mass spectrometer (GC-EIMS or GC-CIMS) was used for the identification and quantification of gas and aerosol products. A HPLC method was used for the measurement of small carbonyl compounds (aldehydes and ketones) as their 2,4-dinitrophenylhydrazones (DNPH) derivatives. Mass balances for gaseous and aerosol reaction products were reported over the course of the reaction. More than sixteen products were identified and/or quantified in this study. On average, measured gas and particle phase products accounted for 57 to 71% of the reacted -pinene carbon. Measurements showed that a number of reaction products were found in both O₃ and NO_x systems (pinic acid, pinalic-3-acid, 4-hydroxypinalic-3-acid, 4-oxonopinone, 1-hydroxynopinone, 3-hydroxynopinone, and nopinone). Pinic acid, pinalic-3-acid, and 4-hydroxypinalic-3-acid were observed in the early stage in the aerosol phase and may play an important role in the early formation of secondary aerosols. Detailed reaction schemes are presented to account for most of the observed reaction products.