skip to main content

Explore Research Products in the NSF-PAR

Title: An omnipresent diversity and variability in the chemical composition of atmospheric functionalized organic aerosol
Abstract

The atmospheric evolution of organic compounds encompasses many thousands of compounds with varying volatility, polarity, and water solubility. The molecular-level chemical composition of this mixture plays a major, yet uncertain, role in its transformations and impacts. Here we perform a non-targeted molecular-level intercomparison of functionalized organic aerosol from three diverse field sites and a chamber. Despite similar bulk composition, we report large molecular-level variability between multi-hour organic aerosol samples at each site, with 66 ± 13% of functionalized compounds differing between consecutive samples. Single precursor environmental laboratory chamber experiments and fully chemically-explicit modeling confirm this variability is due to changes in emitted precursors, chemical age, and/or oxidation conditions. These molecular-level results demonstrate greater compositional variability than is typically observed in less-speciated measurements, such as bulk elemental composition, which tend to show less daily variability. These observations should inform future field and laboratory studies, including assessments of the effects of variability on aerosol properties and ultimately the development of strategic organic aerosol parameterizations for air quality and climate models.

  more » « less
NSF-PAR ID:
10154119
Author(s) / Creator(s):
; ; ; ; ; ; ; ; ; ; ; ; ;
Publisher / Repository:
Nature Publishing Group
Date Published:
Journal Name:
Communications Chemistry
Volume:
1
Issue:
1
ISSN:
2399-3669
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; ; ; ; ; ( , Atmospheric Chemistry and Physics)
    null (Ed.)
    Abstract. The chemical complexity of biomass burning organic aerosol (BBOA) greatlyincreases with photochemical aging in the atmosphere, necessitatingcontrolled laboratory studies to inform field observations. In theseexperiments, BBOA from American white oak (Quercus alba) leaf andheartwood samples was generated in a custom-built emissions and combustionchamber and photochemically aged in a potential aerosol mass (PAM) flowreactor. A thermal desorption aerosol gas chromatograph (TAG) was used inparallel with a high-resolution time-of-flight aerosol mass spectrometer(AMS) to analyze BBOA chemical composition at different levels ofphotochemical aging. Individual compounds were identified and integrated toobtain relative decay rates for key molecules. A recently developedchromatogram binning positive matrix factorization (PMF) technique was usedto obtain mass spectral profiles for factors in TAG BBOA chromatograms,improving analysis efficiency and providing a more complete determination ofunresolved complex mixture (UCM) components. Additionally, the recentlycharacterized TAG decomposition window was used to track molecular fragmentscreated by the decomposition of thermally labile BBOA during sampledesorption. We demonstrate that although most primary (freshly emitted) BBOAcompounds deplete with photochemical aging, certain components eluting withinthe TAG thermal decomposition window are instead enhanced. Specifically, theincreasing trend in the decomposition m∕z 44 signal (CO2+)indicates formation of secondary organic aerosol (SOA) in the PAM reactor.Sources of m∕z 60 (C2H4O2+), typically attributed tofreshly emitted BBOA in AMS field measurements, were also investigated. Fromthe TAG chemical speciation and decomposition window data, we observed adecrease in m∕z 60 with photochemical aging due to the decay ofanhydrosugars (including levoglucosan) and other compounds, as well as anincrease in m∕z 60 due to the formation of thermally labile organic acidswithin the PAM reactor, which decompose during TAG sample desorption. Whenaging both types of BBOA (leaf and heartwood), the AMS data exhibit acombination of these two contributing effects, causing limited change to theoverall m∕z 60 signal. Our observations demonstrate the importance ofchemically speciated data in fully understanding bulk aerosol measurementsprovided by the AMS in both laboratory and field studies. 
    more » « less
  2. ; ; ; ( , Atmospheric Chemistry and Physics)
    null (Ed.)
    Abstract. An accurate measurement of the optical properties of aerosol is critical for quantifying the effect of aerosol on climate. Uncertainties persist and results of measurements vary significantly. Biomass burning (BB) aerosol has been extensively studied through both field and laboratory environments for North American fuels to understand the changes in opticaland chemical properties as a function of aging. There is a need for a widersampling of fuels from different regions of the world for laboratory studies. This work represents the first such study of the optical andchemical properties of wood fuel samples commonly used for domestic purposes ineast Africa. In general, combustion temperature or modified combustionefficiency (MCE) plays a major role in the optical properties of the emitted aerosol. For fuels combusted with MCE of 0.974±0.015, which is referred to as flaming-dominated combustion, the single-scattering albedo (SSA) values were in the range of 0.287 to 0.439, while for fuels combusted with MCE of 0.878±0.008, which is referred to as smoldering-dominated combustion, the SSA values were in the range of 0.66 to 0.769. There is a clear but very small dependence of SSA on fuel type. A significant increase in the scattering and extinction cross section (with no significant change inabsorption cross section) was observed, indicating the occurrence of chemistry, even during dark aging for smoldering-dominated combustion. Thisfact cannot be explained by heterogeneous oxidation in the particle phase,and we hypothesize that secondary organic aerosol formation is potentiallyhappening during dark aging. After 12 h of photochemical aging, BB aerosolbecomes highly scattering with SSA values above 0.9, which can be attributedto oxidation in the chamber. Aging studies of aerosol from flaming-dominatedcombustion were inconclusive due to the very low aerosol number concentration. We also attempted to simulate polluted urban environments byinjecting volatile organic compounds (VOCs) and BB aerosol into the chamber, but no distinct difference was observed when compared to photochemical aging in the absence of VOCs. 
    more » « less
  3. ; ; ; ; ; ; ; ; ; ; et al ( , Journal of Geophysical Research: Atmospheres)
    Abstract

    After smoke from burning biomass is emitted into the atmosphere, chemical and physical processes change the composition and amount of organic aerosol present in the aged, diluted plume. During the fourth Fire Lab at Missoula Experiment, we performed smog‐chamber experiments to investigate formation of secondary organic aerosol (SOA) and multiphase oxidation of primary organic aerosol (POA). We simulated atmospheric aging of diluted smoke from a variety of biomass fuels while measuring particle composition using high‐resolution aerosol mass spectrometry. We quantified SOA formation using a tracer ion for low‐volatility POA as a reference standard (akin to a naturally occurring internal standard). These smoke aging experiments revealed variable organic aerosol (OA) enhancements, even for smoke from similar fuels and aging mechanisms. This variable OA enhancement correlated well with measured differences in the amounts of emitted volatile organic compounds (VOCs) that could subsequently be oxidized to form SOA. For some aging experiments, we were able to predict the SOA production to within a factor of 2 using a fuel‐specific VOC emission inventory that was scaled by burn‐specific toluene measurements. For fires of coniferous fuels that were dominated by needle burning, volatile biogenic compounds were the dominant precursor class. For wiregrass fires, furans were the dominant SOA precursors. We used a POA tracer ion to calculate the amount of mass lost due to gas‐phase oxidation and subsequent volatilization of semivolatile POA. Less than 5% of the POA mass was lost via multiphase oxidation‐driven evaporation during up to 2 hr of equivalent atmospheric oxidation.

     
    more » « less
  4. ; ; ; ; ; ( , Atmospheric Chemistry and Physics)
    null (Ed.)
    Abstract. There are many fuels used for domestic purposes in east Africa, producing a significant atmospheric burden of the resulting aerosols, which includes biomass burning particles. However, the aerosol physicochemical properties are poorly understood. Here, the combustion of eucalyptus, acacia, and olive fuels was performed at 500 and 800 ∘C in a tube furnace, followed by immediate filter collection for fresh samples or introduction into a photochemical chamber to simulate atmospheric photochemical aging under the influence of anthropogenic emissions. The aerosol generated in the latter experiment was collected onto filters after 12 h of photochemical aging. 500 and 800 ∘C were selected to simulate smoldering and flaming combustion, respectively, and to cover a range of combustion conditions. Methanol extracts from Teflon filters were analyzed by ultra-performance liquid chromatography interfaced to both a diode array detector and an electrospray ionization high-resolution quadrupole time-of-flight mass spectrometer (UPLC/DAD-ESI-HR-QTOFMS) to determine the light absorption properties of biomass burning organic aerosol constituents chemically characterized at the molecular level. Few chemical or UV–visible (UV: ultraviolet) differences were apparent between samples for the fuels when combusted at 800 ∘C. Differences in single-scattering albedo (SSA) between fresh samples at this temperature were attributed to compounds not captured in this analysis, with eucalyptol being one suspected missing component. For fresh combustion at 500 ∘C, many species were present; lignin pyrolysis and distillation products are more prevalent in eucalyptus, while pyrolysis products of cellulose and at least one nitro-aromatic species were more prevalent in acacia. SSA trends areconsistent with this, particularly if the absorption of those chromophoresextends to the 500–570 nm region. Upon aging, both show that resorcinolor catechol was removed to the highest degree, and both aerosol types weredominated by loss of pyrolysis and distillation products, though they differed in the specific compounds being consumed by the photochemical aging process. 
    more » « less
  5. ; ; ; ; ; ; ; ; ( , Atmospheric Chemistry and Physics)
    The effect of relative humidity (RH) on the chemical composition of secondary organic aerosol (SOA) formed from low-NOx toluene oxidation in the absence of seed particles was investigated. SOA samples were prepared in an aerosol smog chamber at < 2 % RH and 75 % RH, collected on Teflon filters, and analyzed with nanospray desorption electrospray ionization high-resolution mass spectrometry (nano-DESI–HRMS). Measurements revealed a significant reduction in the fraction of oligomers present in the SOA generated at 75 % RH compared to SOA generated under dry conditions. In a separate set of experiments, the particle mass concentrations were measured with a scanning mobility particle sizer (SMPS) at RHs ranging from < 2 to 90 %. It was found that the particle mass loading decreased by nearly an order of magnitude when RH increased from < 2 to 75–90 % for low-NOx toluene SOA. The volatility distributions of the SOA compounds, estimated from the distribution of molecular formulas using the molecular corridor approach, confirmed that low-NOx toluene SOA became more volatile on average under high-RH conditions. In contrast, the effect of RH on SOA mass loading was found to be much smaller for high-NOx toluene SOA. The observed increase in the oligomer fraction and particle mass loading under dry conditions were attributed to the enhancement of condensation reactions, which produce water and oligomers from smaller compounds in low-NOx toluene SOA. The reduction in the fraction of oligomeric compounds under humid conditions is predicted to partly counteract the previously observed enhancement in the toluene SOA yield driven by the aerosol liquid water chemistry in deliquesced inorganic seed particles. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email