Real-Time Measurement of Oligomeric Species in Secondary Organic Aerosol with the Aerosol Time-of-Flight Mass Spectrometer

Abstract

Real-time detection of oligomers in secondary organic aerosols has been carried out with an aerosol time-of-flight mass spectrometer sampling particles generated in a smog chamber. The photooxidation products of 1,3,5-trimethylbenzene and NOx were studied over a range of initial 1,3,5-trimethylbenzene concentrations (137-1180 ppb), while keeping the 1,3,5-trimethylbenzene to NOx ratio nearly constant. The photooxidation products of a mixture of alpha-pinene (initial concentration 191 ppb), 1,3,5-trimethylbenzene (60 ppb), and NOx were also investigated. In both systems, ions were observed in the single-particle mass spectra up to 750 Da; the species observed differed in the two systems. These high-mass ions occur with characteristic spacing of 14 and 16 Da, indicative of oligomeric species. The results obtained agree well with off-line (matrix-assisted) laser desorption/ionization mass spectrometry results. The real-time capabilities of the aerosol time-of-flight mass spectrometer make it possible to investigate the temporal development of the oligomers with 5-min time resolution and also demonstrate that there are certain ions within the oligomer population that occur in nearly all of the particles and with relatively high signal intensity, suggesting that these ions have higher stability or that the species are formed preferentially.

Source apportionment of PM<sub>2.5</sub> in Cork Harbour, Ireland using a combination of single particle mass spectrometry and quantitative semi-continuous measurements

“…These ions are absent for the Oligomer class identified in this work, suggesting that these particles may be relatively fresh compared to those observed by Denkenberger et al (2007). The rate of formation of detectable oligomers in secondary organic aerosol simulation chamber studies is typically of the order of hours (Kalberer et al, 2004;Gross et al, 2006), although studies performed in the absence of seed aerosol are often characterised by long induction periods while oxidation products reach high enough concentrations to induce nucleation Gross et al, 2006;Healy et al, 2008). In the case of Denkenberger et al (2007), increased particle acidity was observed to accelerate oligomer formation.…”

“…13). ATOFMS particle mass spectra containing similar high mass negative ion signals have been identified as oligomer-containing, both in simulation chamber experiments and in ambient datasets (Gross et al, 2006;Denkenberger et al, 2007). In the latter study, several different aged particle types were found to contain oligomers, including vanadium-rich, amine-rich, organic carbon, and internally mixed organic/elemental carbon particles.…”

Real-time secondary aerosol formation during a fog event in London

“…In general, HULIS are considered refractory organic molecules that can only be thermally vaporised from 400-600 • C ( Andreae and Gelencser, 2006). Recent smog chamber experiments have shown that the ATOFMS can detect oligomeric species (Gross et al, 2006) whilst the AMS provides other very useful information but may not be able to detect oligomeric species well . Additionally, as the AMS is responding to aerosol mass, it will inevitably be of less sensitivity towards minor components of the aerosol.…”

Glyoxal uptake on ammonium sulphate seed aerosol: reaction products and reversibility of uptake under dark and irradiated conditions

“…Carbonyl containing species are known to participate in aldol, acetal, and esterification reactions, which form low volatility compounds that add to SOA mass. Field and laboratory studies have also yielded evidence for the formation of high molecular weight products within SOA (Gross et al, 2006;Reinhardt et al, 2007;Denkenberger et al, 2007) and it is well known that GL will polymerize in the presence of water (Whipple, 1970;Loeffler et al, 2006). These properties of GL, together with its production via oxidation of many VOCs, have inspired chamber investigations into GL partitioning onto a variety of seed particles (Jang et al, 2002;Liggio et al, 2005a,b;Kroll et al, 2005;Corrigan et al, 2008;Volkamer et al, 2009).…”