Methyltetrol sulfates are unique tracers for secondary organic aerosols (SOA) formed from acid-driven multiphase chemistry of isoprene-derived epoxydiols. 2-Methyltetrol sulfate diastereomers (2-MTSs) are the dominant isomers and single most-abundant SOA tracers in atmospheric fine particulate matter (PM2.5), but their atmospheric sinks remain unknown. We investigated the oxidative aging of authentic 2-MTS aerosols by gas-phase hydroxyl radicals (•OH) at a relative humidity of 61 ± 1%. The effective rate constant for this heterogeneous reaction was determined as 4.9 ± 0.6 × 10–13 cm3 molecules–1 s–1, corresponding to an atmospheric lifetime of 16 ± 2 days (assuming an •OH concentration of 1.5 × 106 molecules cm–3). Chemical changes to 2-MTSs were monitored by hydrophilic interaction liquid chromatography interfaced to electrospray ionization high-resolution quadrupole time-of-flight mass spectrometry (HILIC/ESI-HR-QTOFMS). Plausible reaction mechanisms are proposed for previously unknown OSs detected in atmospheric PM2.5 at mass-to-charge ratios (m/z) of 139 (C2H3O5S–), 155 (C2H3O6S–), 169 (C3H5O6S–), 171 (C3H7O6S–), 185 (C3H5O7S–), 199 (C4H7O7S–), 211 (C5H7O7S–), 213 (C5H9O7S–), 227 (C5H7O8S–), 229 (C5H9O8S–), and 231 (C5H11O8S–). Heterogeneous •OH oxidation of 2-MTSs redistributes the particulate sulfur speciation into more oxygenated/functionalized OSs, likely modifying the aerosol physicochemical properties of SOA containing 2-MTSs.
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Seasonal Contribution of Isoprene‐Derived Organosulfates to Total Water‐Soluble Fine Particulate Organic Sulfur in the United States.
Organosulfates (OSs) are the most abundant class of
organosulfur compounds (OrgS) in atmospheric fine
particulate matter (PM2.5). Globally, isoprene‐derived
OSs (iOSs) are the most abundantly reported OSs. The
methyltetrol sulfates (MTSs), formed from multiphase
chemical reactions of isoprene‐derived epoxidiols
(IEPOX) with acidic sulfate aerosols, are the predominant
iOSs. A recent study revealed that the heterogeneous
hydroxyl radical (•OH) oxidation of fine particulate MTSs
yields several highly oxygenated and functionalized OSs
previously attributed to non‐IEPOX pathways. By using
hydrophilic interaction liquid chromatography interfaced
to electrospray ionization high‐resolution quadrupole
time‐of‐flight mass spectrometry (HILIC/ESI‐HRQTOFMS),
iOSs were quantitatively characterized in
PM2.5 collected from 20 ground sites within the
Interagency Monitoring of Protected Visual
Environments (IMPROVE) network during the 2016
summer and winter seasons. Total water‐soluble sulfur
(TWS‐S) and sulfur in the form of inorganic sulfate
(Sinorg) were determined by inductively coupled plasmaoptical
emission spectroscopy (ICP‐OES) and ion
chromatography (IC), respectively. The difference
between TWS‐S and Sinorg was used as an upper bound
estimate of water‐soluble OrgS concentration.
Significantly higher OrgS concentrations, coincident with
elevated iOS concentrations, were observed only in
summer. On average, iOSs (130 ± 60, up to 240 ng m‐3)
explained 29% (± 7%) of OrgS and 5% (± 2%) of organic
matter (OM = 1.8*OC) in summertime PM2.5 collected
from the eastern U.S. For the western U.S., iOSs (11 ± 6
ng m‐3) account for 6% (± 5%) of OrgS and 0.7% (± 0.4%)
of OM. This study provides critical insights into the
abundance, prevalence, spatial variability of iOSs across
the U.S.
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- Award ID(s):
- 2001027
- NSF-PAR ID:
- 10313552
- Date Published:
- Journal Name:
- 2021 AAAR 39th Annual Conference
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Acid-catalyzed multiphase chemistry of isoprene epoxydiols (IEPOX) on sulfate aerosol produces substantial amounts of water-soluble secondary organic aerosol (SOA) constituents, including 2-methyltetrols, methyltetrol sulfates, and oligomers thereof in atmospheric fine particulate matter (PM 2.5 ). These constituents have commonly been measured by gas chromatography interfaced to electron ionization mass spectrometry (GC/EI-MS) with prior derivatization or by reverse-phase liquid chromatography interfaced to electrospray ionization high-resolution mass spectrometry (RPLC/ESI-HR-MS). However, both techniques have limitations in explicitly resolving and quantifying polar SOA constituents due either to thermal degradation or poor separation. With authentic 2-methyltetrol and methyltetrol sulfate standards synthesized in-house, we developed a hydrophilic interaction liquid chromatography (HILIC)/ESI-HR-quadrupole time-of-flight mass spectrometry (QTOFMS) protocol that can chromatographically resolve and accurately measure the major IEPOX-derived SOA constituents in both laboratory-generated SOA and atmospheric PM 2.5 . 2-Methyltetrols were simultaneously resolved along with 4–6 diastereomers of methyltetrol sulfate, allowing efficient quantification of both major classes of SOA constituents by a single non-thermal analytical method. The sum of 2-methyltetrols and methyltetrol sulfates accounted for approximately 92%, 62%, and 21% of the laboratory-generated β-IEPOX aerosol mass, laboratory-generated δ-IEPOX aerosol mass, and organic aerosol mass in the southeastern U.S., respectively, where the mass concentration of methyltetrol sulfates was 171–271% the mass concentration of methyltetrol. Mass concentrations of methyltetrol sulfates were 0.39 and 2.33 μg m −3 in a PM 2.5 sample collected from central Amazonia and the southeastern U.S., respectively. The improved resolution clearly reveals isomeric patterns specific to methyltetrol sulfates from acid-catalyzed multiphase chemistry of β- and δ-IEPOX. We also demonstrate that conventional GC/EI-MS analyses overestimate 2-methyltetrols by up to 188%, resulting (in part) from the thermal degradation of methyltetrol sulfates. Lastly, C 5 -alkene triols and 3-methyltetrahydrofuran-3,4-diols are found to be largely GC/EI-MS artifacts formed from thermal degradation of 2-methyltetrol sulfates and 3-methyletrol sulfates, respectively, and are not detected with HILIC/ESI-HR-QTOFMS.more » « less
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