[Show abstract][Hide abstract] ABSTRACT: An oxygenated MW 188 compound is commonly observed in substantial abundance in atmospheric aerosol samples and was proposed in previous studies as an α-pinene-related marker compound which is associated with ageing processes. Owing to difficulties to produce this compound in sufficient amounts in laboratory studies and the occurrence of isobaric isomers, a complete assignment for individual MW 188 compounds could not be achieved in these studies. Results from a comprehensive mass spectrometric analysis are presented here to corroborate the proposed structure of the most abundant MW 188 compound as a 2-hydroxyterpenylic acid diastereoisomer with 2R,3R configuration. The application of collision-induced dissociation with liquid chromatography/electrospray ionization - ion trap mass spectrometry in both negative and positive ion modes, as well as chemical derivatization to methyl ester derivatives and analysis by the latter technique and gas chromatography/electron ionization mass spectrometry, enabled a comprehensive characterization of MW 188 isomers, including a detailed study of the fragmentation behavior using both mass spectrometric techniques. Furthermore, a MW 188 positional isomer, 4-hydroxyterpenylic acid, was tentatively identified, which is also of atmospheric relevance as it could be detected in ambient fine aerosol. Quantum chemical calculations were performed to support the diastereoisomeric assignment of the 2-hydroxyterpenylic acid isomers. Results from a time-resolved α-pinene photooxidation experiment show that the 2-hydroxyterpenylic acid 2R,3R diastereoisomer has a time profile distinctly different from 3-methyl-1,2,3-butanetricarboxylic acid, a marker for oxygenated (aged) secondary organic aerosol. This study presents a comprehensive chemical data set for a more complete structural characterization of hydroxyterpenylic acids in ambient fine aerosol, which sets the foundation to better understand the atmospheric fate of α-pinene in future studies.
[Show abstract][Hide abstract] ABSTRACT: A decoction of the leaves and stems of Desmodium adscendens (Fabaceae), a herb occurring in Africa and South America, is used in traditional medicine. Previous phytochemical research revealed that flavonoids, soyasaponins, β-phenylethylamines, and an indol-3-alkylamine were present. Our investigations have led to the identification of D-pinitol, a carbohydrate with antihyperglycemic, hepatoprotective and anti-inflammatory effects, as a potentially active compound. In order to prepare a quantified extract to be used in in vivo experiments, an analytical method was developed and validated.A gas chromatographic method was developed. Two different derivatization methods, i.e. acetylation and trimethylsilylation, were evaluated. Trimethylsilylation yielded repeatable results and was selected. Five different sugar alcohols were evaluated in order to find a suitable internal standard. Xylitol was chosen since it did not co-elute and its structure closely resembled D-pinitol. Sonication and reflux extraction were investigated in order to obtain a quantitative extraction. This was achieved through reflux extraction during 0.5 h.The method was validated according to the ICH guidelines. The calibration model appeared to be linear, ranging from 5.13 μL/mL to 25.65 μL/mL. The method was precise with an inter-day precision lower than 1.3%. The accuracy ranged from 103.38% to 105.84%. The validated method was used for quantification of D-pinitol in lyophilized decoctions from D. adscendens administered in in vivo experiments. Typically, a D-pinitol level about 5% was measured. Additionally, different food supplements available on the market were screened. The amount D-pinitol found in these supplements ranged from 1.8 mg/capsule to 30 mg/capsule and was 2.0 mg/mL solution.
[Show abstract][Hide abstract] ABSTRACT: Nitro-organic compounds were determined in a one-year set of atmospheric
PM10 filter samples that were collected at a rural background
site in Hamme, Belgium. In an earlier study, it was found that the site
was substantially impacted by wood burning, making the filter samples
appropriate for further investigations on wood burning indicators. In
total, four groups of nitro-aromatic compounds (with molecular weights
(MWs) of 139, 155, 169, and 183), α-pinene-related
nitrooxy-organosulfates (MW 295), and the resin acid dehydroabietic acid
(DHAA, MW 300) were quantified using liquid chromatography combined with
negative ion electrospray ionization mass spectrometry. The annual mean
concentrations were 0.94, 6.0, 7.7, 4.8, 7.8, and
1.76 ng m-3 for the sum of the nitrophenols
(MW 139), 4-nitrocatechol (MW 155), the sums of the
methyl-nitrocatechols (MW 169), of the dimethyl-nitrocatechols (MW 183),
and of the α-pinene-related nitrooxy-organosulfates (MW 295), and
DHAA (MW 300), respectively. 4-nitrocatechol, the sum of the
methyl-nitrocatechols, and the sum of the dimethyl-nitrocatechols were
substantially correlated with levoglucosan (r-values of 0.71, 0.66, and
0.65, respectively), consistent with their proposed origin from biomass
burning. The nitro-aromatic compounds were also observed during the
summer months, indicating a non-negligible usage of wood burning for
domestic purposes at the site. The α-pinene-related
nitrooxy-organosulfates (MW 295) were detected in high concentrations
during the winter period, but they were poorly correlated with the
biomass burning tracers. All of the targeted species showed a clear
seasonal variation with highest concentrations in winter, followed by
autumn, spring, and summer. Based on the DHAA measurements, it is
suggested that burning of softwood is likely an important source for the
formation of all the nitro-organic compounds measured.
[Show abstract][Hide abstract] ABSTRACT: In the present work, we have evaluated whether isomeric C5-alkene diols (1,2-dihydroxy-2-methyl-3-butene, 1,2-dihydroxy-3-methyl-3-butene, and 1,4-dihydroxy-2-methyl-2-butene (cis + trans)), which have first been detected upon photooxidation of isoprene in the absence of NO and are known to be formed in the ambient atmosphere, can serve as precursors for the 2-methyltetrols, C5-alkene triols, and 2-methylglyceric acid under low-NO(x) conditions. The C5-alkene diols were prepared following published synthesis procedures. It is shown that under the applied chamber conditions the isomeric C5-alkene diols give rise to 2-methyltetrols with different threo/erythro abundance ratios and that certain diols produce 2-methylglyceric acid, but that they do not form C5-alkene triols. Furthermore, it is shown that the photooxidation of isoprene under the applied chamber conditions employing photolysis of H2O2 under dry conditions yields relatively small amounts of C5-alkene triols compared to those of the 2-methyltetrols, unlike under ambient conditions. It is argued that the chamber conditions are not optimal for the formation of C5-epoxydiols, which serve as gas-phase precursors for the C5-alkene triols, and likely as in some previous studies favor the formation of C5-alkene diols as a result of RO2 + RO2 reactions.
[Show abstract][Hide abstract] ABSTRACT: Nitrogen-containing organic compounds in the atmosphere have drawn attention owing to their impact on aerosol chemistry and physics and their potential adverse effects on the biosphere. Among them, nitrocatechols and their homologs have recently been associated with biomass burning. In the present study, nitrocatechols, nitrophenols, nitroguaiacols and nitrosalicylic acids (NSAs) were simultaneously quantified for the first time by using a new analytical method based on liquid chromatography/tandem mass spectrometry, which was systematically optimized and validated. Several analyte specific issues regarding the sample preparation and chromatographic analysis were addressed in order to ensure method sensitivity, precision, and accuracy. Sample matrix effects were thoroughly investigated in order to ensure method specificity. The method was found to be sensitive with limits of detection ranging from 0.1 to 1.0μgL(-1), and with accuracy generally between 90 and 104%. The relative standard deviations for repeatability and intermediate precision were better than 4% and 9%, respectively. The method was applied to the analysis of winter and summer PM(10) samples from the city of Ljubljana, Slovenia. Aerosol concentrations as high as 152 and 134ngm(-3) were obtained for the major aerosol nitro-aromatics: 4-nitrocatechol (4NC) and methyl-nitrocatechols (MNCs), respectively. Up to 500-times higher concentrations of 4NC and MNCs were found in winter compared to summer aerosols. The correlation analysis for winter samples showed that 4NC, MNCs, and NSAs are strongly inter-correlated (R(2)=0.84-0.96). Significant correlations between these analytes and anhydrosugars support their proposed origin from biomass burning. The studied nitro-aromatics were found to constitute a non-negligible fraction (around 1%) of the organic carbon.
Journal of Chromatography A 10/2012; · 4.61 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: From February 2010 to February 2011 PM10 aerosol samples were simultaneously taken every 4th day at 7 monitoring sites in Flanders, Belgium. Two of the sites (i.e., Borgerhout and Gent) were urban background sites; one (i.e., Mechelen) a suburban background site, and the other four (i.e., Hamme, Lier, Retie, and Houtem) rural background sites, whereby Hamme and Lier were expected to be particularly impacted by biomass burning. The samplings were done for 24h and 47-mm diameter Pallflex® Tissuquartz™ 2500 QAT-UP filters were used. After sampling the PM10 mass concentration was determined by weighing; organic and elemental carbon (OC and EC) were measured by thermal-optical transmission analysis and the wood burning tracers levoglucosan, mannosan, and galactosan were determined by means of gas chromatography/mass spectrometry. The atmospheric concentrations of levoglucosan and the other two monosaccharide anhydrides showed a very clear seasonal variation at each site, with highest levels in winter, followed by autumn, spring, and summer. The levoglucosan levels for 5 of our 7 sites (i.e., Retie, Lier, Mechelen, Borgerhout, and Gent) were very highly correlated with each other (all between site correlation coefficients r>0.9, except for one value of 0.86) and the levels in the parallel samples of these 5 sites were similar, indicating that wood burning at these 5 sites was a regional phenomenon and that it was taking place in many individual houses on similar occasions (e.g., on cold days, weekends or holidays). The levoglucosan levels at Houtem and the correlation coefficients of the 5 sites with Houtem were lower, which is explained by the fact that the latter site is at less than 20km from the North Sea so that the air there is often diluted by rather clean westerly maritime air. A peculiar behavior was seen for Hamme, with on many occasions very high levoglucosan levels, which was attributed to the fact that there is wood burning going on in several houses nearby this site. From our levoglucosan/mannosan ratios we derived the relative contributions of softwood and hardwood burning, thereby following the same approach as used by Schmidl et al. (Atmos Environ 2008;38:126-41). It was found that softwood burning accounted, on average, for about 70%, and there was little variation in this percentage with site or with season. The levoglucosan data were used to assess the contribution of wood burning to the OC and to the PM10 mass, again following the approach of Schmidl et al. (2008). The annual average contributions of wood burning OC to the PM10 OC were in the range of 20-25% for 6 of our 7 sites and 36% for Hamme; the averages for summer were 2.0-3.9% for the 6 sites and 14.5% for Hamme; the corresponding data for winter were 36-43% and 60%. As to the contribution from wood burning to the PM10 mass, the annual averages were in the range of 4.8-6.3% for 6 of our 7 sites and 13.3% at Hamme; the averages for summer were 0.51-1.14% for the 6 sites and 5.0% for Hamme; the corresponding data for winter were 8.6-11.3% and 22%. Our finding that wood burning is an important contributor to the OC and the PM10 mass, especially in winter, is in line with published data from various other sites in other European countries.
Science of The Total Environment 08/2012; 437:226-36. · 3.26 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Measurements of organic marker compounds and inorganic species were
performed on PM2.5 aerosols from a Belgian forest site that
is severely impacted by urban pollution ("De Inslag", Brasschaat,
Belgium) during a 2007 summer period within the framework of the
"Formation mechanisms, marker compounds, and source apportionment for
biogenic atmospheric aerosols (BIOSOL)" project. The measured organic
species included (i) low-molecular weight (MW) dicarboxylic acids (LMW
DCAs), (ii) methanesulfonate (MSA), (iii) terpenoic acids originating
from the oxidation of α-pinene, β-pinene, d-limonene and
Δ3-carene, and (iv) organosulfates related to secondary
organic aerosol from the oxidation of isoprene and α-pinene. The
organic tracers explained, on average, 5.3 % of the organic carbon (OC),
of which 0.7 % was due to MSA, 3.4 % to LMW DCAs, 0.6 % to
organosulfates, and 0.6 % to terpenoic acids. The highest atmospheric
concentrations of most species were observed during the first five days
of the campaign, which were characterised by maximum day-time
temperatures >22 °C. Most of the terpenoic acids and the
organosulfates peaked during day-time, consistent with their local
photochemical origin. High concentrations of
3-methyl-1,2,3-butanetricarboxylic acid (MBTCA) and low concentrations
of cis-pinonic acid were noted during the first five days of the
campaign, indicative of an aged biogenic aerosol. Several correlations
between organic species were very high (r>0.85), high
(0.7<r<0.85), or substantial (0.5<r<0.7), suggesting that
they are generated through similar formation pathways. Substantial
correlations with temperature were found for OC, water-soluble OC,
MBTCA, and several other organic species. MBTCA and terebic acid were
highly correlated with the temperature (r>0.7) and showed an
Arrhenius-type relationship, consistent with their formation through OH
ATMOSPHERIC CHEMISTRY AND PHYSICS 01/2012; 12(1):125-138. · 5.51 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In this study, we present liquid chromatographic and mass spectral data for predominant terpenoic acids formed through oxidation of α-pinene, β-pinene, d-limonene, and Δ(3)-carene that occur in fine forest aerosol from K-puszta, Hungary, a rural site with coniferous vegetation. Characterization of these secondary organic aerosol tracers in fine ambient aerosol is important because it allows one to gain information on monoterpene precursors and source processes such as oxidation and aging processes. The mass spectral data were obtained using electrospray ionization in the negative ion mode, accurate mass measurements, and linear ion trap tandem mass spectrometric experiments. Emphasis is given to the mass spectrometric differentiation of isobaric terpenoic acids, such as, e.g. the molecular weight (MW) 186 terpenoic acids, cis-pinic, cis-caric, homoterpenylic, ketolimononic, and limonic acids. Other targeted isobaric terpenoic acids are the MW 184 terpenoic acids, cis-pinonic and cis-caronic acids, and the MW 204 tricarboxylic acids, 3-methyl-1,2,3-butanetricarboxylic and 3-carboxyheptanedioic acids. Fragmentation pathways are proposed to provide a rational explanation for the observed isomeric differences and/or to support the suggested tentative structures. For the completeness of the data set, data obtained for recently reported lactone-containing terpenoic acids (i.e. terpenylic and terebic acids), related or isobaric compounds (i.e. norpinic acid, diaterpenylic acid acetate, and unknown MW 188 compounds) are also included, the rationale being that other groups working on this topic could use this data compilation as a reference.
Biological Mass Spectrometry 04/2011; 46(4):425-42. · 3.41 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Measurements of organic marker compounds and inorganic species were performed on PM2.5 aerosols from a Belgian forest site that is severely impacted by urban pollution ("De Inslag", Brasschaat, Belgium) during a 2007 summer period within the framework of the "Formation mechanisms, marker compounds, and source apportionment for biogenic atmospheric aerosols (BIOSOL)" project. The objectives of this study were to determine sources, source processes, time series, and diel variations of the organic species, and to explore the relationships between their concentrations and those of trace gases (O3, NO2, SO2, and CO2) or meteorological parameters (temperature, relative humidity, wind speed, and rain fall). The measured organic species included (i) low-molecular weight (MW) dicarboxylic acids (LMW DCAs), (ii) methanesulfonate (MSA), and (iii) terpenoic acids originating from the oxidation of alpha-pinene, beta-pinene, d-limonene and Delta3-carene, and (iv) organosulfates related to secondary organic aerosol (SOA) from the oxidation of isoprene and alpha-pinene. The measurements of MSA, the LMW DCAs and selected inorganic species were done with ion chromatography (IC), while those of the terpenoic acids and organosulfates were performed using liquid chromatography with negative ion electrospray ionisation mass spectrometry [LC/(-)ESI-MS]. The organic tracers explained, on average, 5.3 % of the organic carbon (OC), of which 0.7 % was due to MSA, 3.4 % to LMW DCAs, and 1.2 % to organosulfates and terpenoic acids. The highest atmospheric concentrations of most species were observed during the first five days of the campaign, which were characterised by maximum day-time temperatures >22 °C. Most of the terpenoic acids and the organosulfates peaked during day-time, consistent with their photochemical origin, except the MW 295 alpha-pinene-related nitrooxy organosulfates and the terpenoic acids, cis-pinic, caric, and limonic acid. High concentrations of 3-methyl-1,2,3-butanetricarboxylic acid (MBTCA) and low concentrations of cis-pinonic acid were noted during the first five days of the campaign, indicative of an aged biogenic aerosol. Several correlations between organic species were very high (r>0.85), high (0.7
Atmospheric Chemistry and Physics 01/2011; 11:23541-23572. · 4.88 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Measurements of polar organic marker compounds were performed on
aerosols that were collected at a pasture site in the Amazon basin
(Rondônia, Brazil) using a high-volume dichotomous sampler (HVDS)
and a Micro-Orifice Uniform Deposit Impactor (MOUDI) within the
framework of the 2002 LBA-SMOCC (Large-Scale Biosphere Atmosphere
Experiment in Amazônia - Smoke Aerosols, Clouds, Rainfall,
and Climate: Aerosols From Biomass Burning Perturb Global and Regional
Climate) campaign. The campaign spanned the late dry season (biomass
burning), a transition period, and the onset of the wet season (clean
conditions). In the present study a more detailed discussion is
presented compared to previous reports on the behavior of selected polar
marker compounds, including levoglucosan, malic acid, isoprene secondary
organic aerosol (SOA) tracers and tracers for fungal spores. The tracer
data are discussed taking into account new insights that recently became
available into their stability and/or aerosol formation processes.
During all three periods, levoglucosan was the most dominant identified
organic species in the PM2.5 size fraction of the HVDS
samples. In the dry period levoglucosan reached concentrations of up to
7.5 μg m-3 and exhibited diel variations with a
nighttime prevalence. It was closely associated with the PM mass in the
size-segregated samples and was mainly present in the fine mode, except
during the wet period where it peaked in the coarse mode. Isoprene SOA
tracers showed an average concentration of 250 ng m-3
during the dry period versus 157 ng m-3 during the
transition period and 52 ng m-3 during the wet period.
Malic acid and the 2-methyltetrols exhibited a different size
distribution pattern, which is consistent with different aerosol
formation processes (i.e., gas-to-particle partitioning in the case of
malic acid and heterogeneous formation from gas-phase precursors in the
case of the 2-methyltetrols). The 2-methyltetrols were mainly associated
with the fine mode during all periods, while malic acid was prevalent in
the fine mode only during the dry and transition periods, and dominant
in the coarse mode during the wet period. The sum of the fungal spore
tracers arabitol, mannitol, and erythritol in the PM2.5
fraction of the HVDS samples during the dry, transition, and wet periods
was, on average, 54 ng m-3, 34 ng m-3,
and 27 ng m-3, respectively, and revealed minor
day/night variation. The mass size distributions of arabitol and
mannitol during all periods showed similar patterns and an association
with the coarse mode, consistent with their primary origin. The results
show that even under the heavy smoke conditions of the dry period a
natural background with contributions from bioaerosols and isoprene SOA
can be revealed. The enhancement in isoprene SOA in the dry season is
mainly attributed to an increased acidity of the aerosols, increased
NOx concentrations and a decreased wet deposition.
ATMOSPHERIC CHEMISTRY AND PHYSICS 10/2010; · 5.51 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In the present study, we have characterized the structure of a higher-molecular weight (MW) 358 α- and β-pinene dimeric secondary organic aerosol (SOA) product that received ample attention in previous molecular characterization studies and has been elusive. Based on mass spectrometric evidence for deprotonated molecules formed by electrospray ionization in the negative ion mode and chemical considerations, it is suggested that diaterpenylic acid is a key monomeric intermediate for dimers of the ester type. It is proposed that cis-pinic acid is esterified with the hydroxyl-containing diaterpenylic acid, which can be explained through acid-catalyzed hydrolysis of the recently elucidated lactone-containing terpenylic acid and/or diaterpenylic acid acetate, both first-generation oxidation products. To a minor extent, higher-MW 358 and 344 diester products are formed containing other terpenoic acids as monomeric units, i.e., diaterpenylic acid instead of cis-pinic acid, and diaterebic acid instead of diaterpenylic acid. It is shown that the MW 358 diester and related MW 344 compounds, which can be regarded as processed SOA products, also occur in ambient fine (PM2.5) rural aerosol collected at night during the warm period of the 2006 summer field campaign conducted at K-puszta, Hungary, a rural site with coniferous vegetation. This indicates that, under ambient conditions, the higher-MW diesters are formed in the particle phase over a longer time-scale than that required for gas-to-particle partitioning of their monomeric precursors in laboratory α-/β-pinene ozonolysis experiments.
ATMOSPHERIC CHEMISTRY AND PHYSICS 01/2010; · 5.51 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The objectives of this study were to obtain insights into acid effects in the formation of secondary organic aerosol and 2-methyltetrols from the photooxidation of isoprene in the presence of NOx. A photooxidation experiment was performed with isoprene in the presence of NOx where the gaseous reaction mixture was passed over a sulfuric acid-treated and non-treated quartz fibre filter. Consistent with previous laboratory data, the organic carbon and 2-methyltetrol amounts on the sulfuric acid-treated filter were significantly enhanced. In addition, oxygenated isoprene products related to the 2-methyltetrols and formed on the sulfuric acid-treated filter were structurally characterized as enol tautomers of 4-hydroxy-1,3-dioxo-2-methylbutane. No evidence could be found for the formation of C5-epoxydiols in the gas phase but very small amounts, about two orders of magnitude lower than those of the 2-methyltetrols, were generated on the sulfuric acid-treated filter. The formation of the 2-methyltetrols and enol tautomers of 4-hydroxy-1,3-dioxo-2-methylbutane is explained by acid-catalyzed reactions of gas-phase nitrooxypolyols. Implications for the measurement of the 2-methyltetrols using gas chromatography/mass spectrometry (GC/MS) with prior trimethylsilylation are discussed.
Atmospheric Research 01/2010; 98(2):183-189. · 2.20 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Atmospheric aerosols were collected in separate fine (<2.5 μm) and coarse (>2.5 μm) size fractions in the period December 2006–March 2007 at Amsterdam Island in the southern Indian Ocean. A major objective of the study was to assess biogenic impact on the marine aerosol. The samples were analysed for organic carbon, water-soluble organic carbon, major inorganic ionic species, and organic species, including methanesulphonate (MSA), dicarboxylic acids, and organosulphates. The concentrations of sea salt, non-sea-salt sulphate, and water-soluble and water-insoluble organic matter (WSOM and WIOM) were estimated. Sea salt dominated the composition of the aerosol and accounted for 83% and 91% of the sum of the mass of the four aerosol types in the fine and coarse size fractions, respectively. WSOM, which can serve as a proxy for biogenic secondary organic aerosol (SOA), accounted for only 2.8% of the sum of the mass of the four aerosol types in the fine size fraction. MSA was the dominating organic compound with a median concentration of 47 ng m−3. The organosulphates were characterised as sulphate esters of hydroxyl acids and a dihydroxylaldehyde, which may originate from the oxidation of algal/bacterial unsaturated fatty acid residues. No evidence was found for isoprene SOA.
[Show abstract][Hide abstract] ABSTRACT: Blue haze is a natural phenomenon that is observed in forested regions worldwide and is due to the formation of secondary organic aerosol (SOA) particles. While evidence exists for organic molecular clusters in the size range of < 2 nm, the chemical structures of the nucleating particles have remained unresolved. In the present study, novel SOA products from the monoterpene alpha-pinene with unique dimer-forming properties have been identified as lactone-containing terpenoic acids, i.e., terpenylic (molecular weight (MW) 172), terebic (MW 158) and 2-hydroxyterpenylic acid (MW 188), and diaterpenylic acid acetate (MW 232). The structural characterizations were based on synthesis of reference compounds and detailed interpretation of negative ion electrospray ionization mass spectral [(-)ESI-MS] data, including accurate mass and MSn ion trap measurements. Terpenylic acid and diaterpenylic acid acetate are early oxidation products formed upon both photooxidation and ozonolysis, and are abundant SOA tracers in ambient fine aerosol from coniferous forest sites (e.g., K-puszta, Hungary). Terebic and 2-hydroxyterpenylic acid can be explained by further oxidation of terpenylic acid, and are also prominent tracers in ambient fine aerosol. Quantum chemical calculations support that non-covalent dimer formation involving double hydrogen bonding interactions between carboxyl groups of the monomers is energetically favorable. Lactone-containing terpenoic acids also form through photooxidation from monoterpenes other than alpha-pinene, i.e., terebic acid from Delta3-carene, and terpenylic, homoterpenylic (MW 186), and terebic acid from beta-pinene. A distinct feature of terpenylic acid and related lactone-containing acids is that they can be selectively detected in positive ion (+)ESI-MS, unlike isobaric dicarboxylic terpenoic acids such as norpinic (MW 172) and pinic acid (MW 186). Interestingly, terpenylic, terebic and homoterpenylic acid were already reported in the early German literature as condensed-phase oxidation products of terpenoids. In addition, evidence was found that terpenylic and terebic acid serve together with cis-pinic acid as precursors for covalent dimers of the ester type. The molecular properties of the lactone-containing terpenoic acids allow us to explain initial particle formation and growth in laboratory chamber experiments and are suggested to play a role in new particle formation and growth above forests, a natural phenomenon that has fascinated scientists for more than a century.
[Show abstract][Hide abstract] ABSTRACT: Novel secondary organic aerosol (SOA) products from the monoterpene alpha-pinene with unique dimer-forming properties have been identified as lactone-containing terpenoic acids, i.e., terpenylic and 2-hydroxyterpenylic acid, and diaterpenylic acid acetate. The structural characterizations were based on the synthesis of reference compounds and detailed interpretation of mass spectral data. Terpenylic acid and diaterpenylic acid acetate are early oxidation products generated upon both photooxidation and ozonolysis, while 2-hydroxyterpenylic acid is an abundant SOA tracer in ambient fine aerosol that can be explained by further oxidation of terpenylic acid. Quantum chemical calculations support that noncovalent dimer formation involving double hydrogen bonding interactions between carboxyl groups of the monomers is energetically favorable. The molecular properties allow us to explain initial particle formation in laboratory chamber experiments and are suggested to play a role in new particle formation and growth above forests, a natural phenomenon that has fascinated scientists for more than a century.
Environmental Science and Technology 09/2009; 43(18):6976-82. · 5.26 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Organosulfates of isoprene, alpha-pinene, and beta-pinene have recently been identified in both laboratory-generated and ambient secondary organic aerosol (SOA). In this study, the mechanism and ubiquity of organosulfate formation in biogenic SOA is investigated by a comprehensive series of laboratory photooxidation (i.e., OH-initiated oxidation) and nighttime oxidation (i.e., NO3-initiated oxidation under dark conditions) experiments using nine monoterpenes (alpha-pinene, beta-pinene, d-limonene, l-limonene, alpha-terpinene, gamma-terpinene, terpinolene, Delta(3)-carene, and beta-phellandrene) and three monoterpenes (alpha-pinene, d-limonene, and l-limonene), respectively. Organosulfates were characterized using liquid chromatographic techniques coupled to electrospray ionization combined with both linear ion trap and high-resolution time-of-flight mass spectrometry. Organosulfates are formed only when monoterpenes are oxidized in the presence of acidified sulfate seed aerosol, a result consistent with prior work. Archived laboratory-generated isoprene SOA and ambient filter samples collected from the southeastern U.S. were reexamined for organosulfates. By comparing the tandem mass spectrometric and accurate mass measurements collected for both the laboratory-generated and ambient aerosol, previously uncharacterized ambient organic aerosol components are found to be organosulfates of isoprene, alpha-pinene, beta-pinene, and limonene-like monoterpenes (e.g., myrcene), demonstrating the ubiquity of organosulfate formation in ambient SOA. Several of the organosulfates of isoprene and of the monoterpenes characterized in this study are ambient tracer compounds for the occurrence of biogenic SOA formation under acidic conditions. Furthermore, the nighttime oxidation experiments conducted under highly acidic conditions reveal a viable mechanism for the formation of previously identified nitrooxy organosulfates found in ambient nighttime aerosol samples. We estimate that the organosulfate contribution to the total organic mass fraction of ambient aerosol collected from K-puszta, Hungary, a field site with a similar organosulfate composition as that found in the present study for the southeastern U.S., can be as high as 30%.
The Journal of Physical Chemistry A 10/2008; 112(36):8345-78. · 2.77 Impact Factor