Publications by authors named "David O De Haan"

25 Publications

  • Page 1 of 1

Elucidating an Atmospheric Brown Carbon Species-Toward Supplanting Chemical Intuition with Exhaustive Enumeration and Machine Learning.

Environ Sci Technol 2021 06 3;55(12):8447-8457. Epub 2021 Jun 3.

Faculty of Physics, University of Vienna, Kolingasse 14-16, AT-1090 Wien, Austria.

Brown carbon (BrC) is involved in atmospheric light absorption and climate forcing and can cause adverse health effects. Understanding the formation mechanisms and molecular structure of BrC is of key importance in developing strategies to control its environment and health impact. Structure determination of BrC is challenging, due to the lack of experiments providing molecular fingerprints and the sheer number of molecular candidates with identical mass. Suggestions based on chemical intuition are prone to errors due to the inherent bias. We present an unbiased algorithm, using graph-based molecule generation and machine learning, which can identify all molecular structures of compounds involved in biomass burning and the composition of BrC. We apply this algorithm to CHO, a light-absorbing "test case" molecule identified in chamber experiments on the aqueous photo-oxidation of syringol, a prevalent marker in wood smoke. Of the 260 million molecular graphs, the algorithm leaves only 36,518 (0.01%) as viable candidates matching the spectrum. Although no unique molecular structure is obtained from only a chemical formula and a UV/vis absorption spectrum, we discuss further reduction strategies and their efficacy. With additional data, the method can potentially more rapidly identify isomers extracted from lab and field aerosol particles without introducing human bias.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/acs.est.1c00885DOI Listing
June 2021

Brown Carbon Production by Aqueous-Phase Interactions of Glyoxal and SO.

Environ Sci Technol 2020 04 9;54(8):4781-4789. Epub 2020 Apr 9.

Cooperative Institute for Research in Environmental Sciences and Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado 80309, United States.

Oxalic acid and sulfate salts are major components of aerosol particles. Here, we explore the potential for their respective precursor species, glyoxal and SO, to form atmospheric brown carbon via aqueous-phase reactions in a series of bulk aqueous and flow chamber aerosol experiments. In bulk aqueous solutions, UV- and visible-light-absorbing products are observed at pH 3-4 and 5-6, respectively, with small but detectable yields of hydroxyquinone and polyketone products formed, especially at pH 6. Hydroxymethanesulfonate (HMS), C, and C sulfonates are major products detected by electrospray ionization mass spectrometry (ESI-MS) at pH 5. Past studies have assumed that the reaction of formaldehyde and sulfite was the only atmospheric source of HMS. In flow chamber experiments involving sulfite aerosol and gas-phase glyoxal with only 1 min residence times, significant aerosol growth is observed. Rapid brown carbon formation is seen with aqueous aerosol particles at >80% relative humidity (RH). Brown carbon formation slows at 50-60% RH and when the aerosol particles are acidified with sulfuric acid but stops entirely only under dry conditions. This chemistry may therefore contribute to brown carbon production in cloud-processed pollution plumes as oxidizing volatile organic compounds (VOCs) interact with SO and water.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/acs.est.9b07852DOI Listing
April 2020

Methylglyoxal Uptake Coefficients on Aqueous Aerosol Surfaces.

J Phys Chem A 2018 May 18;122(21):4854-4860. Epub 2018 May 18.

Laboratoire Interuniversitaire des Systèmes Atmosphériques (LISA), UMR CNRS 7583, Institut Pierre Simon Laplace (IPSL) , Université Paris-Est Créteil (UPEC) et Université Paris Diderot (UPD) , Créteil , France.

In order to predict the amount of secondary organic aerosol formed by heterogeneous processing of methylglyoxal, uptake coefficients (γ) and estimates of uptake reversibility are needed. Here, uptake coefficients are extracted from chamber studies involving ammonium sulfate and glycine seed aerosol at high relative humidity (RH ≥ 72%). Methylglyoxal uptake coefficients on prereacted glycine aerosol particles had a strong dependence on RH, increasing from γ = 0.4 × 10 to 5.7 × 10 between 72 and 99% RH. Continuous methylglyoxal losses were also observed in the presence of aqueous ammonium sulfate at 95% RH (γ = 3.7 ± 0.8 × 10). Methylglyoxal uptake coefficients measured at ≥95% RH are larger than those reported for glyoxal on nonacidified, aqueous aerosol surfaces at 90% RH. Slight curvature in first-order uptake plots suggests that methylglyoxal uptake onto aqueous aerosol surfaces is not entirely irreversible after 20 min. Methylglyoxal uptake by cloud droplets was rapid and largely reversible, approaching equilibrium within the 1 min mixing time of the chamber. PTR-MS measurements showed that each cloud event extracted 3 to 8% of aerosol-phase methylglyoxal and returned it to the gas phase, likely by an oligomer hydrolysis mechanism.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/acs.jpca.8b00533DOI Listing
May 2018

Nitrogen-Containing, Light-Absorbing Oligomers Produced in Aerosol Particles Exposed to Methylglyoxal, Photolysis, and Cloud Cycling.

Environ Sci Technol 2018 04 13;52(7):4061-4071. Epub 2018 Mar 13.

Laboratoire Interuniversitaire des Systèmes Atmosphériques (LISA), UMR7583, CNRS , Université Paris-Est-Créteil (UPEC) et Université Paris Diderot (UPD), Institut Pierre Simon Laplace (IPSL) , 94010 Créteil , France.

Aqueous methylglyoxal chemistry has often been implicated as an important source of oligomers in atmospheric aerosol. Here we report on chemical analysis of brown carbon aerosol particles collected from cloud cycling/photolysis chamber experiments, where gaseous methylglyoxal and methylamine interacted with glycine, ammonium, or methylammonium sulfate seed particles. Eighteen N-containing oligomers were identified in the particulate phase by liquid chromatography/diode array detection/electrospray ionization high-resolution quadrupole time-of-flight mass spectrometry. Chemical formulas were determined and, for 6 major oligomer products, MS fragmentation spectra were used to propose tentative structures and mechanisms. Electronic absorption spectra were calculated for six tentative product structures by an ab initio second order algebraic-diagrammatic-construction/density functional theory approach. For five structures, matching calculated and measured absorption spectra suggest that they are dominant light-absorbing species at their chromatographic retention times. Detected oligomers incorporated methylglyoxal and amines, as expected, but also pyruvic acid, hydroxyacetone, and significant quantities of acetaldehyde. The finding that ∼80% (by mass) of detected oligomers contained acetaldehyde, a methylglyoxal photolysis product, suggests that daytime methylglyoxal oligomer formation is dominated by radical addition mechanisms involving CHCO*. These mechanisms are evidently responsible for enhanced browning observed during photolytic cloud events.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/acs.est.7b06105DOI Listing
April 2018

Brown Carbon Production in Ammonium- or Amine-Containing Aerosol Particles by Reactive Uptake of Methylglyoxal and Photolytic Cloud Cycling.

Environ Sci Technol 2017 Jul 14;51(13):7458-7466. Epub 2017 Jun 14.

Laboratoire Interuniversitaire des Systèmes Atmosphériques (LISA), UMR7583, CNRS, Université Paris-Est-Créteil (UPEC) et Université Paris Diderot (UPD), Institut Pierre Simon Laplace (IPSL), 94010 Créteil, France.

The effects of methylglyoxal uptake on the physical and optical properties of aerosol containing amines or ammonium sulfate were determined before and after cloud processing in a temperature- and RH-controlled chamber. The formation of brown carbon was observed upon methylglyoxal addition, detected as an increase in water-soluble organic carbon mass absorption coefficients below 370 nm and as a drop in single-scattering albedo at 450 nm. The imaginary refractive index component k reached a maximum value of 0.03 ± 0.009 with aqueous glycine aerosol particles. Browning of solid particles occurred at rates limited by chamber mixing (<1 min), and in liquid particles occurred more gradually, but in all cases occurred much more rapidly than in bulk aqueous studies. Further browning in AS and methylammonium sulfate seeds was triggered by cloud events with chamber lights on, suggesting photosensitized brown carbon formation. Despite these changes in optical aerosol characteristics, increases in dried aerosol mass were rarely observed (<1 μg/m in all cases), consistent with previous experiments on methylglyoxal. Under dry, particle-free conditions, methylglyoxal reacted (presumably on chamber walls) with methylamine with a rate constant k = (9 ± 2) × 10 cm molecule s at 294 K and activation energy E = 64 ± 37 kJ/mol.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/acs.est.7b00159DOI Listing
July 2017

Maillard Chemistry in Clouds and Aqueous Aerosol As a Source of Atmospheric Humic-Like Substances.

Environ Sci Technol 2016 07 30;50(14):7443-52. Epub 2016 Jun 30.

Department of Chemistry and Biochemistry, University of San Diego , 5998 Alcala Park, San Diego California 92110, United States.

The reported optical, physical, and chemical properties of aqueous Maillard reaction mixtures of small aldehydes (glyoxal, methylglyoxal, and glycolaldehyde) with ammonium sulfate and amines are compared with those of aqueous extracts of ambient aerosol (water-soluble organic carbon, WSOC) and the humic-like substances (HULIS) fraction of WSOC. Using a combination of new and previously published measurements, we examine fluorescence, X-ray absorbance, UV/vis, and IR spectra, complex refractive indices, (1)H and (13)C NMR spectra, thermograms, aerosol and electrospray ionization mass spectra, surface activity, and hygroscopicity. Atmospheric WSOC and HULIS encompass a range of properties, but in almost every case aqueous aldehyde-amine reaction mixtures are squarely within this range. Notable exceptions are the higher UV/visible absorbance wavelength dependence (Angström coefficients) observed for methylglyoxal reaction mixtures, the lack of surface activity of glyoxal reaction mixtures, and the higher N/C ratios of aldehyde-amine reaction products relative to atmospheric WSOC and HULIS extracts. The overall optical, physical, and chemical similarities are consistent with, but not demonstrative of, Maillard chemistry being a significant secondary source of atmospheric HULIS. However, the higher N/C ratios of aldehyde-amine reaction products limits the source strength to ≤50% of atmospheric HULIS, assuming that other sources of HULIS incorporate only negligible quantities of nitrogen.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/acs.est.6b00909DOI Listing
July 2016

Free energy map for the co-oligomerization of formaldehyde and ammonia.

J Phys Chem A 2015 Mar 27;119(10):2122-31. Epub 2015 Feb 27.

Department of Chemistry and Biochemistry, University of San Diego , 5998 Alcala Park, San Diego, California 92110, United States.

Density functional theory calculations, including Poisson-Boltzmann implicit solvent and free energy corrections, are applied to construct a free energy map of formaldehyde and ammonia co-oligomerization in aqueous solution at pH 7. The stepwise route to forming hexamethylenetetramine (HMTA), the one clearly identified major product in a complex mixture, involves a series of addition reactions of formaldehyde and ammonia coupled with dehydration and cyclization reactions at key steps in the pathway. The free energy map also allows us to propose the possible identity of some major peaks observed by mass spectroscopy in the reaction mixture being the result of stable species not along the pathway to HMTA, in particular those formed by intramolecular condensation of hydroxyl groups to form six-membered rings with ether linkages. Our study complements a baseline free energy map previously worked out for the self-oligomerization of formaldehyde in solution at pH 7 using the same computational protocol and published in this journal (J. Phys. Chem. A 2013, 117, 12658).
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/jp512396dDOI Listing
March 2015

Secondary organic aerosol formation during evaporation of droplets containing atmospheric aldehydes, amines, and ammonium sulfate.

Environ Sci Technol 2014 Dec 3;48(24):14417-25. Epub 2014 Dec 3.

Department of Chemistry and Biochemistry, University of San Diego , 5998 Alcalá Park, San Diego California 92110, United States.

Reactions of carbonyl compounds in cloudwater produce organic aerosol mass through in-cloud oxidation and during postcloud evaporation. In this work, postcloud evaporation was simulated in laboratory experiments on evaporating droplets that contain mixtures of common atmospheric aldehydes with ammonium sulfate (AS), methylamine, or glycine. Aerosol diameters were measured during monodisperse droplet drying experiments and during polydisperse droplet equilibration experiments at 75% relative humidity, and condensed-phase mass was measured in bulk thermogravimetric experiments. The evaporation of water from a droplet was found to trigger aldehyde reactions that increased residual particle volumes by a similar extent in room-temperature experiments, regardless of whether AS, methylamine, or glycine was present. The production of organic aerosol volume was highest from droplets containing glyoxal, followed by similar production from methylglyoxal or hydroxyacetone. Significant organic aerosol production was observed for glycolaldehyde, acetaldehyde, and formaldehyde only at elevated temperatures in thermogravimetric experiments. In many experiments, the amount of aerosol produced was greater than the sum of all solutes plus nonvolatile solvent impurities, indicating the additional presence of trapped water, likely caused by increasing aerosol-phase viscosity due to oligomer formation.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/es5044479DOI Listing
December 2014

Formation of semisolid, oligomerized aqueous SOA: lab simulations of cloud processing.

Environ Sci Technol 2014 Feb 28;48(4):2273-80. Epub 2014 Jan 28.

Department of Chemistry, Harvey Mudd College , 301 Platt Boulevard, Claremont, California 91711.

Glyoxal, methylglyoxal, glycolaldehyde, and hydroxyacetone form N-containing and oligomeric compounds during simulated cloud processing with small amines. Using a novel hygroscopicity tandem differential mobility analysis (HTDMA) system that allows varied humidification times, the hygroscopic growth (HG) of each of the resulting products of simulated cloud processing was measured. Continuous water uptake (gradual deliquescence) was observed beginning at ∼ 40% RH for all aldehyde-methylamine products. Particles containing ionic reaction products of either glyoxal or glycine were most hygroscopic, with HG between 1.16 and 1.20 at 80% RH. Longer humidification times (up to 20 min) produced an increase in growth factors for glyoxal-methylamine (19% by vol) and methylglyoxal-methylamine (8% by vol) aerosol, indicating that unusually long equilibration times can be required for HTDMA measurements of such particles. Glyoxal- and methylglyoxal-methylamine aerosol particles shattered in Raman microscopy impact-flow experiments, revealing that the particles were semisolid. Similar experiments on glycolaldehyde- and hydroxyacetone-methylamine aerosol found that the aerosol particles were liquid when dried for <1 h, but semisolid when dried for 20 h under ambient conditions. The RH required for flow (liquification) during humidification experiments followed the order methylglyoxal > glyoxal > glycolaldehyde = hydroxyacetone, likely caused by the speed of oligomer formation in each system.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/es4049626DOI Listing
February 2014

Heterogeneous ice nucleation on simulated secondary organic aerosol.

Environ Sci Technol 2014 27;48(3):1675-82. Epub 2014 Jan 27.

Cooperative Institute for Research in Environmental Sciences and Department of Chemistry and Biochemistry, University of Colorado , Boulder, Colorado 80309, United States.

In this study, we have explored the phase behavior and the ice nucleation properties of secondary organic aerosol made from aqueous processing (aqSOA). AqSOA was made from the dark reactions of methylglyoxal with methylamine in simulated evaporated cloud droplets. The resulting particles were probed from 215 to 250 K using Raman spectroscopy coupled to an environmental cell. We find these particles are in a semisolid or glassy state based upon their behavior when exposed to mechanical pressure as well as their flow behavior. Further, we find that these aqSOA particles are poor depositional ice nuclei, in contrast to previous studies on simple mixtures of glassy organics. Additionally, we have studied the effect of ammonium sulfate on the phase, morphology, and ice nucleation behavior of the aqSOA. We find that the plasticizing effect of ammonium sulfate lowers the viscosity of the aqSOA, allowing the ammonium sulfate to effloresce within the aqSOA matrix. Upon humidification, the aqSOA matrix liquefies before it can depositionally nucleate ice, and the effloresced ammonium sulfate can act as an immersion mode ice nucleus. This change in the mode of nucleation is accompanied by an increase in the overall ice nucleation efficiency of the aqSOA particles.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/es4046428DOI Listing
October 2015

Brown carbon formation by aqueous-phase carbonyl compound reactions with amines and ammonium sulfate.

Environ Sci Technol 2014 Jan 31;48(2):985-93. Epub 2013 Dec 31.

Department of Chemistry and Biochemistry, University of San Diego , 5998 Alcala Park, San Diego California 92110.

Reactions between small water-soluble carbonyl compounds, ammonium sulfate (AS), and/or amines were evaluated for their ability to form light-absorbing species in aqueous aerosol. Aerosol chemistry was simulated with bulk phase reactions at pH 4, 275 K, initial concentrations of 0.05 to 0.25 M, and UV-vis and fluorescence spectroscopy monitoring. Glycolaldehyde-glycine mixtures produced the most intense absorbance. In carbonyl compound reactions with AS, methylamine, or AS/glycine mixtures, product absorbance followed the order methylglyoxal > glyoxal > glycolaldehyde > hydroxyacetone. Absorbance extended into the visible, with a wavelength dependence fit by absorption Ångstrom coefficients (Å(abs)) of 2 to 11, overlapping the Å(abs) range of atmospheric, water-soluble brown carbon. Many reaction products absorbing between 300 and 400 nm were strongly fluorescent. On a per mole basis, amines are much more effective than AS at producing brown carbon. In addition, methylglyoxal and glyoxal produced more light-absorbing products in reactions with a 5:1 AS-glycine mixture than with AS or glycine alone, illustrating the importance of both organic and inorganic nitrogen in brown carbon formation. Through comparison to biomass burning aerosol, we place an upper limit on the contribution of these aqueous carbonyl-AS-amine reactions of ≤ 10% of global light absorption by brown carbon.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/es4038325DOI Listing
January 2014

Glycolaldehyde monomer and oligomer equilibria in aqueous solution: comparing computational chemistry and NMR data.

J Phys Chem A 2013 Apr 29;117(14):2997-3008. Epub 2013 Mar 29.

Department of Chemistry and Biochemistry, University of San Diego, 5998 Alcala Park, San Diego, California 92110, USA.

A computational protocol utilizing density functional theory calculations, including Poisson-Boltzmann implicit solvent and free energy corrections, is applied to study the thermodynamic and kinetic energy landscape of glycolaldehyde in solution. Comparison is made to NMR measurements of dissolved glycolaldehyde, where the initial dimeric ring structure interconverts among several species before reaching equilibrium where the hydrated monomer is dominant. There is good agreement between computation and experiment for the concentrations of all species in solution at equilibrium, that is, the calculated relative free energies represent the system well. There is also relatively good agreement between the calculated activation barriers and the estimated rate constants for the hydration reaction. The computational approach also predicted that two of the trimers would have a small but appreciable equilibrium concentration (>0.005 M), and this was confirmed by NMR measurements. Our results suggest that while our computational protocol is reasonable and may be applied to quickly map the energy landscape of more complex reactions, knowledge of the caveats and potential errors in this approach need to be taken into account.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/jp312202jDOI Listing
April 2013

Optical properties of the products of α-dicarbonyl and amine reactions in simulated cloud droplets.

Environ Sci Technol 2012 May 19;46(9):4845-51. Epub 2012 Apr 19.

Department of Chemistry and Biochemistry, University of Colorado at Boulder, Boulder, Colorado 80309-0216, USA.

Secondary organic aerosol makes up a significant fraction of the total aerosol mass, and a growing body of evidence indicates that reactions in the atmospheric aqueous phase are important contributors to aerosol formation and can help explain observations that cannot be accounted for using traditional gas-phase chemistry. In particular, aqueous phase reactions between small organic molecules have been proposed as a source of light absorbing compounds that have been observed in numerous locations. Past work has established that reactions between α-dicarbonyls and amines in evaporating water droplets produces particle-phase products that are brown in color. In the present study, the complex refractive indices of model secondary organic aerosol formed by aqueous phase reactions between the α-dicarbonyls glyoxal and methylglyoxal and the primary amines glycine and methylamine have been determined. The reaction products exhibit significant absorption in the visible, and refractive indices are similar to those for light absorbing species isolated from urban aerosol. However, the optical properties are different from the values used in models for secondary organic aerosol, which typically assume little to no absorption of visible light. As a result, the climatic cooling effect of such aerosols in models may be overestimated.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/es2040152DOI Listing
May 2012

Thermodynamics and kinetics of imidazole formation from glyoxal, methylamine, and formaldehyde: a computational study.

J Phys Chem A 2011 Mar 15;115(9):1667-75. Epub 2011 Feb 15.

Department of Chemistry, University of San Diego, San Diego, California 92110, USA.

Density functional theory calculations, including Poisson-Boltzmann implicit solvent and free energy corrections, are applied to study the mechanism of experimentally observed imidazole formation from the reaction of glyoxal and methylamine in solution. Our calculations suggest that a diimine species is an important intermediate in the reaction. Under acidic conditions, we find that the diimine acts as a nucleophile in attacking the carbonyl group of either formaldehyde or glyoxal to first generate an acyclic enol intermediate, which then goes on to close the ring and form imidazoles. Our results confirm that formaldehyde and, by extension, other small aldehydes are likely to be incorporated into imidazole ions in the presence of glyoxal and primary amines in clouds and aqueous aerosol. This is a new mechanism of aerosol formation by formaldehyde, the most abundant aldehyde in the atmosphere. The amount of aerosol formed will depend on the amounts of glyoxal and amines present.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/jp111527xDOI Listing
March 2011

Formation of nitrogen-containing oligomers by methylglyoxal and amines in simulated evaporating cloud droplets.

Environ Sci Technol 2011 Feb 20;45(3):984-91. Epub 2010 Dec 20.

Department of Chemistry and Biochemistry, University of San Diego, San Diego, California 92110, United States.

Reactions of methylglyoxal with amino acids, methylamine, and ammonium sulfate can take place in aqueous aerosol and evaporating cloud droplets. These processes are simulated by drying droplets and bulk solutions of these compounds (at low millimolar and 1 M concentrations, respectively) and analyzing the residuals by scanning mobility particle sizing, nuclear magnetic resonance, aerosol mass spectrometry (AMS), and electrospray ionization MS. The results are consistent with imine (but not diimine) formation on a time scale of seconds, followed by the formation of nitrogen-containing oligomers, methylimidazole, and dimethylimidazole products on a time scale of minutes to hours. Measured elemental ratios are consistent with imidazoles and oligomers being major reaction products, while effective aerosol densities suggest extensive reactions take place within minutes. These reactions may be a source of the light-absorbing, nitrogen-containing oligomers observed in urban and biomass-burning aerosol particles.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/es102933xDOI Listing
February 2011

Gas-phase water-mediated equilibrium between methylglyoxal and its geminal diol.

Proc Natl Acad Sci U S A 2010 Apr 8;107(15):6687-92. Epub 2010 Feb 8.

Department of Chemistry and Biochemistry, and Cooperative Institute for Research in Environmental Sciences, Campus Box 215, University of Colorado, Boulder, CO 80309, USA.

In aqueous solution, aldehydes, and to a lesser extent ketones, hydrate to form geminal diols. We investigate the hydration of methylglyoxal (MG) in the gas phase, a process not previously considered to occur in water-restricted environments. In this study, we spectroscopically identified methylglyoxal diol (MGD) and obtained the gas-phase partial pressures of MG and MGD. These results, in conjunction with the relative humidity, were used to obtain the equilibrium constant, K(P), for the water-mediated hydration of MG in the gas phase. The Gibbs free energy for this process, DeltaG(o), obtained as a result, suggests a larger than expected gas-phase diol concentration. This may have significant implications for understanding the role of organics in atmospheric chemistry.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1073/pnas.0912121107DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2872392PMC
April 2010

Secondary organic aerosol formation by self-reactions of methylglyoxal and glyoxal in evaporating droplets.

Environ Sci Technol 2009 Nov;43(21):8184-90

Department of Chemistry and Biochemistry, University of San Diego, USA.

Glyoxal and methylglyoxal are scavenged by clouds, where a fraction of these compounds are oxidized during the lifetime of the droplet. As a cloud droplet evaporates, the remaining glyoxal and methylglyoxal must either form low-volatility compounds such as oligomers and remain in the aerosol phase, or transfer back to the gas phase. A series of experiments on evaporating aqueous aerosol droplets indicates that over the atmospherically relevant concentration range for clouds and fog (4-1000 microM), 33 +/- 11% of glyoxal and 19 +/- 13% of methylglyoxal remains in the aerosol phase while the remainder evaporates. Measurements of aerosol density and time-dependent AMS signal changes are consistent with the formation of oligomers by each compound during the drying process. Unlike glyoxal, which forms acetal oligomers, exact mass AMS data indicates that the majority of methylglyoxal oligomers are formed by aldol condensation reactions, likely catalyzed by pyruvic acid, formed from methylglyoxal disproportionation. Our measurements of evaporation fractions can be used to estimate the global aerosol formation potential of glyoxal and methylglyoxal via self-reactions at 1 and 1.6 Tg C yr(-1), respectively. This is a factor of 4 less than the SOA formed by these compounds if their uptake is assumed to be irreversible. However, these estimates are likely lower limits for their total aerosol formation potential because oxidants and amines will also react with glyoxal and methylglyoxal to form additional low-volatility products.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/es902152tDOI Listing
November 2009

Thermodynamics and kinetics of methylglyoxal dimer formation: a computational study.

J Phys Chem A 2009 Jun;113(25):6994-7001

Department of Chemistry, University of San Diego, 5998 Alcala Park, San Diego, California 92110, USA.

Density functional theory (B3LYP//6-311+G*) calculations, including Poisson-Boltzmann implicit solvent and free energy corrections, are applied to study the hydration of methylglyoxal and the subsequent formation of dimeric species in solution. Our calculations show that, unlike glyoxal, fully hydrated species are not thermodynamically favored over their less hydrated counterparts, nor are dioxolane ring species the thermodynamic sink, which is in agreement with experimental data. Instead, we find that aldol condensations are the most favored oligomerization reactions for methylglyoxal. These results differ from those of glyoxal, which, lacking the methyl group, cannot access the enol structure leading to aldol condensation. For methylglyoxal, the product from nucleophilic attack at the aldehyde rather than the ketone was favored. Our results help explain some of the observed differences between methylglyoxal and glyoxal, in particular the different array of oligomers formed.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/jp903213kDOI Listing
June 2009

Secondary organic aerosol-forming reactions of glyoxal with amino acids.

Environ Sci Technol 2009 Apr;43(8):2818-24

Department of Chemistry and Biochemistry, University of San Diego, 5998 Alcala Park, San Diego California 92110, USA.

Glyoxal, the simplest and most abundant alpha-dicarbonyl compound in the atmosphere, is scavenged by clouds and aerosol, where it reacts with nucleophiles to form low-volatility products. Here we examine the reactions of glyoxal with five amino acids common in clouds. When glyoxal and glycine, serine, aspartic acid or ornithine are present at concentrations as low as 30/microM in evaporating aqueous droplets or bulk solutions, 1,3-disubstituted imidazoles are formed in irreversible second-order reactions detected by nuclear magnetic resonance (NMR), aerosol mass spectrometry (AMS) and electrospray ionization mass spectrometry (ESI-MS). In contrast, glyoxal reacts with arginine preferentially at side chain amino groups, forming nonaromatic five-membered rings. All reactions were accompanied by browning. The uptake of 45 ppb glyoxal by solid-phase glycine aerosol at 50% RH was also studied and found to cause particle growth and the production of imidazole measured by scanning mobility particle sizing and AMS, respectively, with a glyoxal uptake coefficient alpha = 0.0004. Comparison of reaction kinetics in bulk and in drying droplets shows that conversion of glyoxal dihydrate to monohydrate accelerates the reaction by over 3 orders of magnitude, allowing these reactions to occur at atmospheric conditions.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/es803534fDOI Listing
April 2009

Uptake of glyoxal by organic and Inorganic aerosol.

Environ Sci Technol 2008 Jun;42(12):4428-33

Department of Chemistry, University of San Diego, 5998 Alcala Park, San Diego California 92110, USA.

The uptake of glyoxal by a variety of organic and inorganic aerosol types was examined in a Teflon chamber. Rapid glyoxal uptake was observed for all liquid-phase aerosols at all relative humidity levels tested (< 5 to 50% RH). Even for aerosol with known water content, Henry's Law cannot predict glyoxal uptake: H* > (3 +/- 1.5) x 10(8) mol kg(-1) atm(-1) for l-tartaric acid, H* > (1 +/- 0.5) x 10(8) for dl-malic acid and H* = (2 +/- 1) x 10(7) for malonic acid aerosol. Other liquid-phase aerosol particles containing amine functional groups (arginine, aspartic acid, and glutamic acid) took up even more glyoxal (H* > 3 x 10(8)). The trend of higher glyoxal uptake onto aerosol containing more nucleophilic organic compounds suggests that glyoxal is reacting with organic compounds in the aerosol phase. Solid-phase aerosol showed RH-dependent glyoxal uptake, likely due to the existence of surface water layers. However, particle growth rates were the highestfor sodium sulfate aerosol. For organic aerosol, growth rates correlated with the acidity of the carboxylic acid groups of the aerosol material, suggesting that glyoxal uptake is enhanced by mildly acidic conditions.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/es7032394DOI Listing
June 2008

Thermodynamics and kinetics of glyoxal dimer formation: a computational study.

J Phys Chem A 2008 Jan 8;112(1):66-72. Epub 2007 Dec 8.

Department of Chemistry, University of San Diego, 5998 Alcala Park, San Diego, California 92110, USA.

Density functional theory (B3LYP//6-311+G) calculations including Poisson-Boltzmann implicit solvent were used to study the hydration of glyoxal and subsequent formation of dimeric species in solution. Our calculations show that the dioxolane ring dimer is the thermodynamic sink among all monomers and dimers with varying degrees of hydration. Although fully hydrated species are thermodynamically favored over their less hydrated counterparts, we find that a preliminary dehydration step precedes dimerization and ring closure. Ring closure of the open dimer monohydrate to the dioxolane ring dimer is kinetically favored over both hydration to the open dimer dihydrate and ring closure to form the dioxane ring dimer. The kinetic barriers for different geometric approaches for dimerization suggest an explanation why oligomerization stops after the formation of a dioxolane ring trimer as observed experimentally.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/jp076573gDOI Listing
January 2008

Oligomer formation in evaporating aqueous glyoxal and methyl glyoxal solutions.

Environ Sci Technol 2006 Oct;40(20):6318-23

Chemistry Department, University of San Diego, 5998 Alcala Park, San Diego, California 92110, USA.

Glyoxal and methyl glyoxal are common secondary atmospheric pollutants, formed from aromatic and terpene precursors. Both compounds are extremely water-soluble due to dihydrate formation and partition into cloudwater. In this work, FTIR-ATR and mass measurements indicate that both compounds remain primarily in the condensed phase due to oligomer formation when aqueous solution droplets are evaporated, regardless of concentration (> or = 1 mM) or, for glyoxal, droplet evaporation rate. FTIR spectral analyses suggestthat oligomer formation is triggered by conversion from dihydrate to monohydrate forms, which are still nonvolatile but contain reactive carbonyl groups. Methyl glyoxal hemiacetal formation is observed by changes in the C-0/C=0 stretch peak area ratio. The formation of glyoxal oligomers is detected by a dramatic shift of the C-0 stretching peak toward low frequencies. Glyoxal oligomer peaks at 1070 cm(-1), 950 cm(-1), and 980 cm(-1) are assigned to free C-OH stretch, dioxolane-linked C-OC asymmetric stretch, and tentativelyto non-dioxolane-linked C-OC stretches, respectively. Acids have little effect on glyoxal oligomer formation; however, base interrupts oligomer formation by catalyzing glyoxal hydration and disproportionation to glycolic acid. Since glyoxal and methyl glyoxal are commonly found in cloudwater and are expected to remain largely in the aerosol phase when cloud droplets evaporate, this process may be a source of secondary organic aerosol by cloud processing.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/es060810wDOI Listing
October 2006

Secondary organic aerosol formation by glyoxal hydration and oligomer formation: humidity effects and equilibrium shifts during analysis.

Environ Sci Technol 2005 Nov;39(22):8728-35

Chemistry Department, University of San Diego, 5998 Alcala Park, San Diego, California 92110, USA.

Glyoxal is a significant atmospheric aldehyde formed from both anthropogenic aromatic compounds and biogenic isoprene emissions. The chemical behavior of glyoxal relevant to secondary organic aerosol (SOA) formation and analysis is examined in GC-MS, electrospray ionization (ESI)-MS, and particle chamber experiments. Glyoxal oligomers are shown to rapidly decompose to glyoxal in GC injection ports at temperatures > or = 120 degrees C. Glyoxal dihydrate monomer is dehydrated at temperatures > or = 140 degrees C during GC analysis but shows only oligomers (n < or = 7) upon ESI-MS analysis. Thus both of these analytical techniques will cause artifacts in speciation of glyoxal in SOA. In particle chamber experiments, glyoxal (at -0.1 Torr) condensed via particle-phase reactions when relative humidity levels exceeded a threshold of -26%. Both the threshold humidity and particle growth rates (-0.1 nm/min) are consistent with a recent study performed at glyoxal concentrations 4 orders of magnitude below those used here. This consistency suggests a mechanism where the surface water layer of solid-phase aerosol becomes saturated with glyoxal dihydrate monomer, triggering polymerization and the establishment of an organic phase.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/es050446lDOI Listing
November 2005

Formation of secondary organic aerosol by reactive condensation of furandiones, aldehydes, and water vapor onto inorganic aerosol seed particles.

Environ Sci Technol 2004 Oct;38(19):5064-72

Department of Chemistry, University of San Diego, San Diego, California 92110, USA.

Volatile furandiones and aldehydes are significant atmospheric oxidation products of aromatic compounds. The mechanism of secondary organic aerosol formation by these compounds was probed using particle chamber observations and macroscale simulations of condensed phases. Growth of inorganic seed aerosol was monitored in the presence of humidity and high concentrations of 2,5-furandione (maleic anhydride), 3-methyl-2,5-furandione (citraconic anhydride), benzaldehyde, and trans-cinnamaldehyde. Particle growth commenced when the gas-phase saturation level of each organic compound and water vapor (relative to its pure liquid), when summed together, reached a threshold near one, implying the formation of a nearly ideal mixed organic/aqueous phase. However, these organics are immiscible with water at the high mole fractions that would be expected in such a phase. Highly acidic dicarboxylic acids produced by the reactions between furandiones and water were shown to rapidly acidify an aqueous phase, resulting in greatly increased benzaldehyde solubility. Thus, the uptake of these organics onto particles in the presence of humidity appears to be reaction-dependent. Finally, it is shown that dicarboxylic acids produced in these reactions recyclize back to furandiones when subjected to normal GC injector temperatures, which could cause large artifacts in gas/particle phase distribution measurements.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/es034672bDOI Listing
October 2004

Simulating secondary organic aerosol activation by condensation of multiple organics on seed particles.

Environ Sci Technol 2003 Oct;37(20):4672-7

Department of Chemistry, University of San Diego, 5998 Alcala Park, San Diego, California 92110, USA.

The conditions under which semivolatile organic gases condense were studied in a Teflon particle chamber by scanning mobility particle sizing (SMPS) of the resultant particles. Benzaldehyde, maleic and citraconic anhydrides, n-decane, trans-cinnamaldehyde, and citral were introduced in various combinations into a particle chamber containing either particle-free nitrogen or nitrogen with dry seed particles made out of sodium chloride, D-tartartic acid, ammonium sulfate, or 1,10-decanediol. No organic gas was allowed to reach its saturation point relative to the vapor pressure of its pure liquid in any experiment. In the absence of seed particles, organic aerosol particles formed by ternary nucleation when the sum of the individual organic saturation levels reached a threshold between 1.17 and 1.86. With seed particles present, particle sizes began to increase when the sum of organic saturation levels reached 1.0. This size increase corresponds to the establishment and activation of ternary organic layers on the "clean" seed particles, as predicted by absorption partitioning theory. The observed increases in particle volume depended on initial seed particle volume, indicating that either gas diffusion rates or chemical reactions were controlling the rate of uptake.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/es034110sDOI Listing
October 2003