skip to main content
US FlagAn official website of the United States government
dot gov icon
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
https lock icon
Secure .gov websites use HTTPS
A lock ( lock ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


  • NSF Public Access
  • Search Results
  • Technical note: Improved synthetic routes to cis - and trans -(2-methyloxirane-2,3-diyl)dimethanol ( cis - and trans - β -isoprene epoxydiol)
Title: Technical note: Improved synthetic routes to cis - and trans -(2-methyloxirane-2,3-diyl)dimethanol ( cis - and trans - β -isoprene epoxydiol)
Abstract. We report improved synthetic routes to the isomericisoprene-derived β-epoxydiols (β-IEPOX) in high yield(57 %–69 %) from inexpensive, readily available starting compounds. Thesyntheses do not require the protection/deprotection steps or time-consumingpurification of intermediates and can readily be scaled up to yield thetarget IEPOX isomers in gram quantities. Emissions of isoprene(2-methyl-1,3-butadiene, C5H8), primarily from deciduousvegetation, constitute the largest source of nonmethane atmospherichydrocarbons. In the gas phase under low-nitric-oxide (NO) conditions,addition of the atmospheric hydroxyl radical (OH) followed by rapid addition ofO2 yields isoprene-derived hydroxyperoxyl radicals. The major sink(>90 %) for the peroxyl radicals is a sequential reaction withthe hydroperoxyl radical (HO2), OH, and O2, which is then followed bythe elimination of OH to yield a ∼2:1 mixture ofcis- and trans-(2-methyloxirane-2,3-diyl)dimethanol (cis- and trans-β-IEPOX). The IEPOXisomers account for about 80 % of closed-shell hydroxyperoxylproducts and are rapidly taken up into acidic aerosols to form secondaryorganic aerosol (SOA). IEPOX-derived SOA makes a significant masscontribution to fine particulate matter (PM2.5), which is known to be amajor factor in climate forcing as well as adversely affecting respiratory andcardiovascular systems of exposed populations. Prediction of ambientPM2.5 composition and distribution, both in regional- and global-scaleatmospheric chemistry models, crucially depends on the accuracy ofidentification and quantitation of uptake product formation. Accessibilityof authentic cis- and trans-β-IEPOX in high purity and in large quantity forlaboratory studies underpins progress in developing models as well asidentification and quantitation of PM2.5 components.  more » « less
Award ID(s):
2001027 2304669
PAR ID:
10486753
Author(s) / Creator(s):
; ; ;
Publisher / Repository:
EGU
Date Published:
Journal Name:
Atmospheric Chemistry and Physics
Volume:
23
Issue:
14
ISSN:
1680-7324
Page Range / eLocation ID:
7859 to 7866
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; (, Atmospheric Chemistry and Physics)
    Abstract. Atmospheric oxidation of isoprene, the most abundantly emitted non-methane hydrocarbon, affects the abundances of ozone (O3), the hydroxyl radical (OH), nitrogen oxide radicals (NOx), carbon monoxide (CO), oxygenated and nitrated organic compounds, and secondary organic aerosol (SOA). We analyze these effects in box models and in the global GEOS-Chem chemical transport model using the new reduced Caltech isoprene mechanism (RCIM) condensed from a recently developed explicit isoprene oxidation mechanism. We find many similarities with previous global models of isoprene chemistry along with a number of important differences. Proper accounting of the isomer distribution of peroxy radicals following the addition of OH and O2 to isoprene influences the subsequent distribution of products, decreasing in particular the yield of methacrolein and increasing the capacity of intramolecular hydrogen shifts to promptly regenerate OH. Hydrogen shift reactions throughout the mechanism lead to increased OH recycling, resulting in less depletion of OH under low-NO conditions than in previous mechanisms. Higher organonitrate yields and faster tertiary nitrate hydrolysis lead to more efficient NOx removal by isoprene and conversion to inorganic nitrate. Only 20 % of isoprene-derived organonitrates (excluding peroxyacyl nitrates) are chemically recycled to NOx. The global yield of formaldehyde from isoprene is 22 % per carbon and less sensitive to NO than in previous mechanisms. The global molar yield of glyoxal is 2 %, much lower than in previous mechanisms because of deposition and aerosol uptake of glyoxal precursors. Global production of isoprene SOA is about one-third from each of the following: isoprene epoxydiols (IEPOX), organonitrates, and tetrafunctional compounds. We find a SOA yield from isoprene of 13 % per carbon, much higher than commonly assumed in models and likely offset by SOA chemical loss. We use the results of our simulations to further condense RCIM into a mini Caltech isoprene mechanism (Mini-CIM) for less expensive implementation in atmospheric models, with a total size (108 species, 345 reactions) comparable to currently used mechanisms. 
    more » « less
  2. ; ; ; ; ; ; ; ; ; (, AAAR 40th Annual Conference)
    Acid-driven multiphase chemistry of isoprene epoxydiols (IEPOX) with inorganic sulfate aerosols contributes substantially to formation of secondary organic aerosol (SOA), which constitutes a large mass fraction of atmospheric fine particulate matter (PM2.5). However, atmospheric chemical sinks of freshly generated IEPOX-SOA particles remain unclear. We examined the role of heterogeneous oxidation of freshly-generated IEPOX-SOA particles by gas-phase hydroxyl radical (•OH) under dark conditions as one potential atmospheric sink. After 4 h of gas-phase •OH exposure (~3x108 molecules cm-3), chemical changes in smog chamber-generated IEPOX-SOA particles were assessed by hydrophilic interaction liquid chromatography coupled with electrospray ionization high-resolution quadrupole time-of-flight mass spectrometry (HILIC/ESI-HR-QTOFMS). Comparison of molecular-level compositional changes in IEPOX-SOA particles during aging with or without •OH revealed that decomposition of oligomers by heterogeneous •OH oxidation acts as a sink for •OH and maintains a reservoir of low-volatility compounds including monomeric sulfate esters and oligomer fragments. We propose tentative structures and formation mechanisms for previously uncharacterized SOA constituents in PM2.5. Our results suggest that this •OH-driven renewal of low-volatility products may extend atmospheric lifetimes of IEPOX-SOA particles by slowing production of low-molecular weight, high-volatility organic fragments, and likely contributes to large quantities of 2-methyltetrols and methyltetrol sulfates reported in PM2.5. 
    more » « less
  3. ; ; ; ; ; ; (, ACS Earth and Space Chemistry)
    Blum, Joel (Ed.)
    Atmospheric oxidation of isoprene yields large quantities of highly water-soluble isoprene epoxydiols (IEPOX) that partition into fogs, clouds, and wet aerosols. In aqueous aerosols, the acid-catalyzed ring-opening of IEPOX followed by nucleophilic addition of inorganic sulfate or water forms organosulfates and 2-methyltetrols, respectively, contributing substantially to secondary organic aerosol (SOA). However, the fate of IEPOX in clouds, fogs, and evaporating hydrometeors is not well understood. Here we investigate the rates, product branching ratios, and stereochemistry of organosulfates from reactions of dilute IEPOX (5–10 mM) under a range of sulfate concentrations (0.3–50 mM) and pH values (1.83–3.38) in order to better understand the fate of IEPOX in clouds and fogs. From these aqueous dark reactions of β-IEPOX isomers (trans- and cis-2-methyl-2,3-epoxybutane-1,4-diols), which are the predominant IEPOX isomers, products were identified and quantified using hydrophilic interaction liquid chromatography coupled to an electrospray ionization high-resolution quadrupole time-of-flight mass spectrometer operated in negative ion mode (HILIC/(−)ESI-HR-QTOFMS). We found that the regiochemistry and stereochemistry were affected by pH, and the tertiary methyltetrol sulfate (C5H12O7S) was promoted by increasing solution acidity. Furthermore, the rate constants for the reaction of IEPOX under cloud-relevant conditions are up to 1 order of magnitude lower than reported in the literature for aerosol-relevant conditions due to a markedly different solution activities. Nevertheless, the contribution of cloud and fog water reactions to IEPOX SOA may be significant in cases of lower aqueous-phase pH (model estimate) or during droplet evaporation (not studied). 
    more » « less
  4. ; ; ; ; ; ; ; ; ; ; et al (, The Journal of Physical Chemistry A)
    ABSTRACT: At fixed aerosol acidity, we recently demonstrated that dimers in isoprene epoxydiol-derived secondary organic aerosol (IEPOX-SOA) can heterogeneously react with hydroxyl radical (·OH) at faster rates than monomers. Aerosol acidity influences this aging process by enhancing the formation of oligomers in freshly generated IEPOX-SOA. Therefore, we systematically examined the role of aerosol acidity on kinetics and products resulting from heterogeneous ·OH oxidation of freshly generated IEPOX-SOA. IEPOX reacted with inorganic sulfate aerosol of varying initial pH (0.5, 1.5, and 2.5) in a steady state smog chamber to yield a constant source of freshly generated IEPOX-SOA, which was aged in an oxidation flow reactor for 0−22 equiv days of atmospheric ·OH exposure. Molecular-level chemical analyses revealed that the most acidic sulfate aerosol (pH 0.5) formed the largest oligomeric mass fraction, causing the slowest IEPOX-SOA mass decay with aging. Reactive uptake coefficients of ·OH (γOH) were 0.24 ± 0.06, 0.40 ± 0.05, and 0.49 ± 0.20 for IEPOX-SOA generated at pH 0.5, 1.5, and 2.5, respectively. IEPOXSOA became more liquid-like for pH 1.5 and 2.5, while exhibiting an irregular pattern for pH 0.5 with aging. Using kinetic and physicochemical data derived for a single aerosol pH in atmospheric models could inaccurately predict the fate of the IEPOX-SOA. 
    more » « less
  5. ; ; ; ; ; ; ; ; (, 2021 AAAR 39th Annual Conference)
    In isoprene‐rich regions, acid‐catalyzed multiphase reactions of isoprene epoxydiols (IEPOX) with inorganic sulfate (Sulfinorg) particles form secondary organic aerosol (IEPOX‐SOA), extensively converting Sulfinorg to lowervolatility particulate organosulfates (OSs), including 2‐ methyltetrol sulfates (2‐MTSs) and their dimers. Recently, we showed that heterogeneous hydroxyl radical (OH) oxidation of particulate 2‐MTSs generated multifunctional OS products. However, atmospheric models assume that OS‐rich IEPOX‐SOA particles remain unreactive towards heterogeneous OH oxidation, and limited laboratory studies have been conducted to examine the heterogeneous OH oxidation kinetics of full IEPOX‐SOA mixtures. Hence, this study investigated the kinetics and products resulting from heterogeneous OH oxidation of freshly‐generated IEPOXSOA in order to help derive model‐ready parameterizations. First, gas‐phase IEPOX was reacted with acidic Sulfinorg particles under dark conditions in order to form fresh IEPOX‐SOA particles. These particles were then subsequently aged at RH of 56% in an oxidation flow reactor at OH exposures ranging from 0~15 days of equivalent atmospheric exposure. Aged IEPOX‐SOA particles were sampled by an online aerosol chemical speciation monitor (ACSM) and collected onto Teflon filters for off‐line molecular‐level chemical analyses by hydrophilic liquid interaction chromatography method interfaced to electrospray ionization high‐resolution quadrupole time‐offlight mass spectrometry (HILIC/ESI‐HR‐QTOFMS). Our results show that heterogeneous OH oxidation only caused a 7% decay of IEPOX‐SOA by 10 days exposure, likely owing to the inhibition of reactive uptake of OH as fresh IEPOXSOA particles have an inorganic core‐organic shell morphology. A significantly higher fraction of IEPOX‐SOA (~37%) decayed by 15 days exposure, likely due to the increasing reactive uptake of OH as IEPOX‐SOA become more liquid‐like with aging. Freshly‐generated IEPOX‐SOA constituents exhibited varying degrees of aging with 2‐MTSdimers being the most reactive, followed by 2‐MTSs and 2‐ methyltetrols (2‐MTs), respectively. Notably, extensive amounts of previously characterized particle‐phase products in ambient fine aerosols were detected in our laboratory‐aged IEPOX‐SOA samples. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email