Abstract
Abstract. The gas-phase oxidation of α-pinene produces a large amount of secondary organic aerosol (SOA) in the atmosphere. A number of carboxylic acids, organosulfates and nitrooxy organosulfates associated with α-pinene have been found in field samples and some are used as tracers of α-pinene oxidation. α-pinene reacts readily with OH and O3 in the atmosphere followed by reactions with both HO2 and NO. Due to the large number of potential reaction pathways, it can be difficult to determine what conditions lead to SOA. To better understand the SOA yield and chemical composition from low- and high-NOx OH oxidation of α-pinene, studies were conducted in the Caltech atmospheric chamber under controlled chemical conditions. Experiments used low O3 concentrations to ensure that OH was the main oxidant and low α-pinene concentrations such that the peroxy radical (RO2) reacted primarily with either HO2 under low-NOx conditions or NO under high-NOx conditions. SOA yield was suppressed under conditions of high-NOx. SOA yield under high-NOx conditions was greater when ammonium sulfate/sulfuric acid seed particles (highly acidic) were present prior to the onset of growth than when ammonium sulfate seed particles (mildly acidic) were present; this dependence was not observed under low-NOx conditions. When aerosol seed particles were introduced after OH oxidation, allowing for later generation species to be exposed to fresh inorganic seed particles, a number of low-NOx products partitioned to the highly acidic aerosol. This indicates that the effect of seed acidity and SOA yield might be under-estimated in traditional experiments where aerosol seed particles are introduced prior to oxidation. We also identify the presence of a number of carboxylic acids that are used as tracer compounds of α-pinene oxidation in the field as well as the formation of organosulfates and nitrooxy organosulfates. A number of the carboxylic acids were observed under all conditions, however, pinic and pinonic acid were only observed under low-NOx conditions. Evidence is provided for particle-phase sulfate esterification of multi-functional alcohols.
Highlights
Emitted monoterpenes are important to atmospheric organic aerosol concentration and composition due to their large emission rates and high secondary organic aerosol (SOA) yields (Guenther et al, 1995; Hoffmann et al, 1997; Chung and Seinfeld, 2002; Pye et al, 2010)
The SOA density used to calculate SOA mass and SOA yield were taken from previous results: 1.32 g cm−3 under low-NOx conditions and 1.33 g cm−3 under high-NOx conditions (Ng et al, 2007a)
The OH concentration through the experiments was determined by comparing the loss of α-pinene to a kinetic model of α-pinene OH oxidation under low- or highNOx conditions
Summary
Emitted monoterpenes are important to atmospheric organic aerosol concentration and composition due to their large emission rates and high secondary organic aerosol (SOA) yields (Guenther et al, 1995; Hoffmann et al, 1997; Chung and Seinfeld, 2002; Pye et al, 2010). It was determined that pinonaldehyde is an important oxidation product under both low- and high-NOx conditions. It is of interest to understand how the different gas-phase reaction mechanisms influence the particle-phase composition and concentration This understanding will improve the ability to accurately simulate the amount of aerosol produced in the oxidation of α-pinene. Under low-NOx conditions, photolysis of hydrogen peroxide (H2O2) was the OH source, while for the highNOx experiments the photolysis of nitrous acid (HONO) or methyl nitrite (CH3ONO) produced OH. Once the aerosol seed was added and stable, α-pinene was added to the chamber by transferring a known amount of αpinene from a small glass bulb to achieve a concentration of 20–50 ppb. Filter sample extracts were analyzed by ultra-performance liquid chromatography/electrospray ionization-time-of-flight mass spectrometry (UPLC/ESITOFMS) operated in negative ion mode. Wmode data were analyzed using the high-resolution spectra toolbox, PIKA, to determine the chemical formulas contributing to distinct m/z (DeCarlo et al, 2006)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
