Nontargeted Tandem Mass Spectrometry Analysis Reveals Diversity and Variability in Aerosol Functional Groups across Multiple Sites, Seasons, and Times of Day

Abstract

Organic aerosol (OA) is a complex mixture of compounds with diverse elemental and structural features, and its composition affects its health and environmental impacts. A detailed speciation of the functional group distribution in OA is important for constraining atmospheric reaction pathways and products, evaluating chemical mechanisms and models, and understanding OA impacts. We used high-resolution tandem mass spectrometry to perform a nontargeted analysis of OA functional groups from three diverse ambient sites across times of day and seasons. We observed a range of oxygen-, nitrogen-, and/or sulfur-containing functional groups, including oxygenates such as hydroxyls (29−69%) and carboxylic acids (19−59%), that dominated the functional group distribution and that may participate in hydrogen bonding and thus impact the chemical and physical properties of OA (percentages indicate average ion abundance contributions across campaigns). We also observed esters (7−39%) and ethers (13−42%) that suggest the importance of oligomerization. On average, organonitrates represented only 12% of identified nitrogen-containing groups and organosulfates represented 21% of identified sulfur-containing groups, while we observed many other nitrogen-and/or sulfurcontaining structures that were important contributors to OA composition (e.g., amines, imines, nitrophenols, and sulfides). Most compounds (81%) were multifunctional and likely multigenerational oxidation products, which typically contained two to five functional groups in total.

Atmospheric evolution of emissions from a boreal forest fire: the formation of highly functionalized oxygen-, nitrogen-, and sulfur-containing organic compounds

“…As such, we limited the following adsorbent tube data analysis to compounds in the C 10 -C 25 range to focus on intermediate-volatility and semivolatile compounds (I/SVOCs) present in the gas phase. In our analyses and interpretation, the compounds included in each of these volatility ranges are defined based on fixed values of saturation mass concentrations (e.g., Donahue et al, 2011;Murphy et al, 2014) at the observed 18-22 µg/m 3 OA loadings present during adsorbent tube sampling times.…”

“…Samples were analyzed via liquid chromatography (Agilent 1260 LC) with electrospray ionization (ESI) and the same Q-TOF. For filters, the ESI source was operated in both positive and negative ionization modes, and the Q-TOF was operated in both MS mode (i.e., TOF data collection, "LC-ESI-MS") and MS/MS mode (i.e., tandem mass spectral data collection, "LC-ESI-MS/MS") (Ditto et al, , 2020. Filter extracts were also analyzed using GC-APCI-MS in positive ionization mode.…”

Effects of Aerosol Size and Coating Thickness on the Molecular Detection using Extractive Electrospray Ionization

“…al., 1997;Kalberer et al, 2004;Berndt et al, 2005;Jimenez et al, 2009;Kirkby et al, 2011). Heterogeneous reactions may also further increase the complexity of ambient aerosol mixtures (George and Abbatt 2010;Ditto et al, 2020).…”

The Production and Hydrolysis of Organic Nitrates from OH Radical Oxidation of β-Ocimene

“…This implies that these values may be close to representative for a range of hydroxy nitrates. This rapid aqueous-phase hydrolysis can explain the difficulty to detect the presence of substantial aerosol phase organic nitrates under ambient conditions (Ditto et al, 2020). As hydroxy nitrate production can represent an important fate for daytime oxidation of isoprene and terpenes in forest-impact environments, the uptake of these compounds into acidic aerosol followed by hydrolysis can represent an important mechanism for conversion of NOx to HNO3, as discussed in Romer Present et al, 2019 andZare et al, 2018. While the fate of the resulting diol in solution is unclear, there is a range of possible processes in the aqueous phase, including OH radical attack and oligomerization.…”

“…These low volatility, water-soluble compounds are important precursors to and constituents of SOA due to their efficient partitioning with the condensed-phase (Biesenthal et al, 1997;Fry et al, 2009Fry et al, , 2014Perraud et al, 2012;Rollins et al, 2012). Ambient measurements have indicated that up to 23% of molecules in organic aerosol contain the RONO2 functional group, suggesting RONO2 represent a significant fraction of BVOC-derived oxidation products (Ditto et al, 2020;Rollins et al, 2013). However, the hydrolysis lifetime in the aerosol phase (~1-3 hours) is much shorter than the lifetime of the aerosol itself (~1 week), which suggests the contribution of organic nitrates to aerosol mass may have been underestimated from the observational data (Romer et al, 2016).…”