Chemistry of Particle Inception and Growth during α-Pinene Ozonolysis

Abstract

A flow-tube reactor was used to study the formation of particles from alpha-pinene ozonation. Particle phase products formed within the first 3-22 s of reaction were analyzed online using a scanning mobility particle sizer and two particle mass spectrometers. The first, a photoionization aerosol mass spectrometer (PIAMS), was used to determine the molecular composition of nascent particles between 30 and 50 nm in diameter. The second, a nano-aerosol mass spectrometer (NAMS), was used to determine the elemental composition of individual particles from 50 nm to below 10 nm in diameter. Molecular composition measurements with PIAMS confirm that both the stabilized Criegee intermediate and hydroperoxide channels of alpha-pinene ozonolysis are operative. However, these channels alone cannot explain the high oxygen content of the particles measured with NAMS. The carbon-to-oxygen mole ratios of suspected nucleating agents are in the range of 2.25-4.0, while the measured ratios are from 1.9 for 9 nm particles to 2.5 and 2.7 for 30 and 50 nm particles, respectively. The large oxygen content may arise by cocondensation of small oxygenated molecules such as water or multistep reactions with ozone, water, or other species that produce highly oxygenated macromolecules. In either case, the increasing ratio with increasing particle size suggests that the aerosol becomes less polar with time.

Relating hygroscopicity and optical properties to chemical composition and structure of secondary organic aerosol particles generated from the ozonolysis of α-pinene

“…Additional reactions in the particle phase can take place after the SOA formation, and can for example lead to the formation of oligomers (Kalberer et al, 2004;Gao et al, 2004a, b;Tolocka et al, 2004;Yasmeen et al, 2012;Reinhardt et al, 2007;Rudich et al, 2007), Table 4. The bulk O : C retrieved in our study are in agreement with Shilling et al (2008), , Reinhardt et al (2007) and Tolocka et al (2006). Values at the beginning of the reaction are, however, higher than those obtained by Aiken et al (2007) and Qi et al (2012) who used AMS to retrieve the O : C. Limited information is given by Aiken et al (2007) about their experimental conditions.…”

Oligomer Content of α-Pinene Secondary Organic Aerosol

“…Aerosol mass concentration measurements were made sequentially with SMPS and OCEC by switching the valve back and forth. For some OCEC measurements, a flow-tube reactor (FTR), described elsewhere (Heaton et al 2007;Heaton et al 2009;Tolocka et al 2006), was placed after the three-way valve to simulate the sample stream dilution in the SMPS (0.3 LPM sample flow and 1.0 LPM sheath flow). Five L/min of clean, dry air was introduced to the FTR as a sheath (dilution) flow where it mixed with 1.5 L/min of aerosol flow from the bag.…”

Identification of Organic Hydroperoxides and Peroxy Acids Using Atmospheric Pressure Chemical Ionization – Tandem Mass Spectrometry (APCI-MS/MS): Application to Secondary Organic Aerosol

“…Several mechanisms for oligomer product formation in SOA arising from VOC oxidation have been proposed: i) self-and cross-reactions of the peroxy radicals (RO 2 ) (Zhang et al, 2016), ii) reaction of ozonolysis products in the condensed-phase, such as aldol condensation, esterification, hemiacetal and peroxyhemiacetal formation (Ziemann, 2003;Tolocka et al, 2004;Kristensen et al, 2014;Docherty et al, 2005;Muller et al, 2009;Yasmeen et al, 2010;Hall and Johnston, 2012;Witkowski and Gierczak, 2012;DePalma et al, 2013;Lim and Turpin, 2015), iii) dimer cluster formation from carboxylic acids 15 (Hoffmann et al, 1998;Tobias and Ziemann, 2000;Claeys et al, 2009;Camredon et al, 2010;DePalma et al, 2013), iv) reactions of Criegee intermediates (CIs) with VOCs oxidation products (Bonn et al, 2002;Lee and Kamens, 2005;Tolocka et al, 2006;Heaton et al, 2007;Witkowski and Gierczak, 2012;Kristensen et al, 2016;Wang et al, 2016), and vi) reactions of RO 2 radicals with Cis (Sadezky et al, 2008;Zhao et al, 2015). Among them, the reactions of CIs with protic substances (water, alcohols, acids and hydroperoxides) can form ROOH.…”