B. Graham

Max Planck Institute for Biogeochemistry Jena, Jena, Thuringia, Germany

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Publications (18)58.15 Total impact

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    ABSTRACT: In the present study, we have tentatively identified the structures of three oxygenated derivatives of isoprene in Amazonian rain forest aerosols as the C(5) alkene triols, 2-methyl-1,3,4-trihydroxy-1-butene (cis and trans) and 3-methyl-2,3,4-trihydroxy-1-butene. The formation of these oxygenated derivatives of isoprene can be explained by acid-catalyzed ring opening of epoxydiol derivatives of isoprene, namely, 1,2-epoxy-2-methyl-3,4-dihydroxybutane and 1,2-dihydroxy-2-methyl-3,4-epoxybutane. The structural proposals of the C(5) alkene triols were based on chemical derivatization reactions and detailed interpretation of electron and chemical ionization mass spectral data, including data obtained from first-order mass spectra, deuterium labeling of the trimethylsilyl methyl groups, and MS(2) ion trap experiments. The characterization of 2-methyl-1,3,4-trihydroxy-1-butene (cis and trans) and 3-methyl-2,3,4-trihydroxy-1-butene in forest aerosols is important from an atmospheric chemistry viewpoint in that these compounds hint at the formation of intermediate isomeric epoxydiol derivatives of isoprene and as such provide mechanistic insights into the formation of the previously reported 2-methyltetrols through photooxidation of isoprene.
    Rapid Communications in Mass Spectrometry 02/2005; 19(10):1343-51. · 2.64 Impact Factor
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    ABSTRACT: Detailed organic analysis of natural aerosols from the Amazonian rain forest showed considerable quantities of previously unobserved polar organic compounds, which were identified as a mixture of two diastereoisomeric 2-methyltetrols: 2-methylthreitol and 2-methylerythritol. These polyols, which have the isoprene skeleton, can be explained by OH radical-initiated photooxidation of isoprene. They have low vapor pressure, allowing them to condense onto preexisting particles. It is estimated that photooxidation of isoprene results in an annual global production of about 2 teragrams of the polyols, a substantial fraction of the Intergovernmental Panel on Climate Change estimate of between 8 and 40 teragrams per year of secondary organic aerosol from biogenic sources.
    Science 03/2004; 303(5661):1173-6. · 31.48 Impact Factor
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    ABSTRACT: Size-fractionated ambient aerosol samples were collected at a pasture site and a primary rainforest site in the Brazilian Amazon Basin during two field campaigns (April–May and September–October 1999), as part of the European contribution to the Large-Scale Biosphere-Atmosphere Experiment in Amazonia (LBA-EUSTACH). The samples were analyzed for up to 19 trace elements by particle-induced X-ray emission analysis (PIXE), for equivalent black carbon (BCe) by a light reflectance technique and for mass concentration by gravimetric analysis. Additionally, we made continuous measurements of absorption and light scattering by aerosol particles. The vertical chemical composition gradients at the forest site have been discussed in a companion article (Journal of Geophysical Research-Atmospheres 108 (D18), 4591 (doi:4510.1029/2003JD003465)). In this article, we present the results of a source identification and quantitative apportionment study of the wet and dry season aerosols, including an apportionment of the measured scattering and absorption properties of the total aerosol in terms of the identified aerosol sources. Source apportionments (obtained from absolute principal component analysis) revealed that the wet and dry season aerosols contained the same three main components, but in different (absolute and relative) amounts: the wet season aerosol consisted mainly of a natural biogenic component, whereas pyrogenic aerosols dominated the dry season aerosol mass. The third component identified was soil dust, which was often internally mixed with the biomass-burning aerosol. All three components contributed significantly to light extinction during both seasons. At the pasture site, up to 47% of the light absorption was attributed to biogenic particles during the wet season, and up to 35% at the tower site during the wet-to-dry transition period. The results from the present study suggest that, in addition to pyrogenic particles, biogenic and soil dust aerosols must be taken into account when modeling the physical and optical properties of aerosols in forested regions such the Amazon Basin.
    Atmospheric Environment 03/2004; · 3.06 Impact Factor
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    ABSTRACT: Changes in aerosol composition associated with a cold front passage were examined during a field experiment in Tel Aviv, Israel (2–15 Dec, 2000). In addition to monitoring aerosol scattering and optical thickness, aerosol samples were collected for detailed chemical analyses. Data were compared to simultaneous measurements made at Sde Boker, a semi-remote site in the Negev Desert, to help determine what changes were due to local pollution as opposed to regional phenomena. During the pre-frontal period (2–7 Dec) both sites were influenced by air masses containing a relatively high content of sulphate and dust, originating from neighbouring regions of the Middle East. A steady build-up of local pollution was then observed in Tel Aviv due to vehicular emissions/industrial activities, as indicated by increasing concentrations of black carbon, organic carbon, V, Cu, Ni, Zn, Br, Pb, NO3− and PAHs. Identification of a number of organic biomass burning tracers (e.g., levoglucosan) indicates that smoke also contributed to the pollution build-up in Tel Aviv, while a range of sugars/sugar alcohols point to a microbial/bioaerosol component. Locally emitted pollutants tended to exhibit higher nighttime concentrations due to trapping of pollution under a nocturnal inversion. Fine aerosol iodine was the only element exhibiting higher daytime concentrations, hinting at a photochemical source. Post-frontal measurements (12–15 Dec) revealed a significant decrease in all pollutants due to dispersal of the haze by the cold front (8–9 Dec), with the air initially being dominated by marine aerosol. Concentrations of pollutants then began to increase, with backward trajectories indicating a possible contribution from Eastern Europe. Overall, the study identified a range of useful tracers for monitoring the contribution of different sources to the aerosol over Israel.
    Atmospheric Environment 01/2004; · 3.06 Impact Factor
  • Science, v.303, 1173-1176 (2004). 01/2004;
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    ABSTRACT: As part of the Large-Scale Biosphere-Atmosphere Experiment in Amazonia (LBA)-Cooperative LBA Airborne Regional Experiment (CLAIRE) 2001 campaign in July 2001, separate day and nighttime aerosol samples were collected at a ground-based site in Amazonia, Brazil, in order to examine the composition and temporal variability of the natural “background” aerosol. We used a high-volume sampler to separate the aerosol into fine (aerodynamic diameter, AD 2.5 μm) size fractions and quantified a range of organic compounds in methanolic extracts of the samples by a gas chromatographic-mass spectrometric technique. The carbon fraction of the compounds could account for an average of 7% of the organic carbon (OC) in both the fine and coarse aerosol fractions. We observed the highest concentrations of sugars, sugar alcohols, and fatty acids in the coarse aerosol samples, which suggests that these compounds are associated with primary biological aerosol particles (PBAP) observed in the forest atmosphere. Of these, trehalose, mannitol, arabitol, and the fatty acids were found to be more prevalent at night, coinciding with a nocturnal increase in PBAP in the 2–10 μm size range (predominantly yeasts and other small fungal spores). In contrast, glucose, fructose, and sucrose showed persistently higher daytime concentrations, coinciding with a daytime increase in large fungal spores, fern spores, pollen grains, and, to a lesser extent, plant fragments (generally >20 μm in diameter), probably driven by lowered relative humidity and enhanced wind speeds/convective activity during the day. For the fine aerosol samples a series of dicarboxylic and hydroxyacids were detected with persistently higher daytime concentrations, suggesting that photochemical production of a secondary organic aerosol from biogenic volatile organic compounds may have made a significant contribution to the fine aerosol. Anhydrosugars (levoglucosan, mannosan, galactosan), which are specific tracers for biomass burning, were detected only at low levels in the fine aerosol samples. On the basis of the levoglucosan-to-OC emission ratio measured for biomass burning aerosol, we estimate that an average of ∼16% of the OC in the fine aerosol was due to biomass burning during CLAIRE 2001, indicating that the major fraction was associated with biogenic particles.
    Journal of Geophysical Research, v.108 (2003). 12/2003;
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    ABSTRACT: 1] As part of the Large-Scale Biosphere-Atmosphere Experiment in Amazonia (LBA)-Cooperative LBA Airborne Regional Experiment (CLAIRE) 2001 campaign, separate day and nighttime aerosol samples were collected in July 2001 at a ground-based site in Amazonia, Brazil, in order to examine the composition and temporal variability of the natural ''background'' aerosol. A combination of analytical techniques was used to characterize the elemental and ionic composition of the aerosol. Major particle types larger than $0.5 mm were identified by electron and light microscopy. Both the coarse and fine aerosol were found to consist primarily of organic matter ($70 and 80% by mass, respectively), with the coarse fraction containing small amounts of soil dust and sea-salt particles and the fine fraction containing some non-sea-salt sulfate. Coarse particulate mass concentrations (CPM % PM 10 À PM 2) were found to be highest at night (average = 3.9 ± 1.4 mg m À3 , mean night-to-day ratio = 1.9 ± 0.4), while fine particulate mass concentrations (FPM % PM 2) increased during the daytime (average = 2.6 ± 0.8 mg m À3 , mean night-to-day ratio = 0.7 ± 0.1). The nocturnal increase in CPM coincided with an increase in primary biological particles in this size range (predominantly yeasts and other fungal spores), resulting from the trapping of surface-derived forest aerosol under a shallow nocturnal boundary layer and a lake-land breeze effect at the site, although active nocturnal sporulation may have also contributed. Associated with this, we observed elevated nighttime concentrations of biogenic elements and ions (P, S, K, Cu, Zn, NH 4 +) in the CPM fraction. For the FPM fraction a persistently higher daytime concentration of organic carbon was found, which indicates that photochemical production of secondary organic aerosol from biogenic volatile organic compounds may have made a significant contribution to the fine aerosol. Dust and sea-salt-associated elements/ions in the CPM fraction, and non-sea-salt sulfate in the FPM fraction, showed higher daytime concentrations, most likely due to enhanced convective downward mixing of long-range transported aerosol.
    Journal of Geophysical Research Atmospheres 12/2003; 108. · 3.44 Impact Factor
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    ABSTRACT: Optical properties of aerosol particles were characterized during two field campaigns at a remote rainforest site in Rondônia, Brazil, as part of the project European Studies on Trace Gases and Atmospheric Chemistry, a contribution to the Large-Scale Biosphere-Atmosphere Experiment in Amazonia (LBA-EUSTACH). The measurements included background (wet season), biomass burning (dry season), and transition period conditions. Optical measurements of light scattering and absorption were combined with data on number/size distributions in a new iterative method, which retrieves the effective imaginary refractive index of the particles at a wavelength of . For ambient relative humidities lower than 80%, background aerosols exhibited an average refractive index of 1.42−0.006i. Biomass burning aerosols displayed a much larger imaginary part, with an average refractive index of 1.41−0.013i. Other climate-relevant parameters were estimated from Mie calculations. These include single-scattering albedos of 0.93±0.03 and 0.90±0.03 (at ambient humidity), asymmetry parameters of 0.63±0.02 and 0.70±0.03, and backscatter ratios of 0.12±0.01 and 0.08±0.01 for background and biomass burning aerosols, respectively.
    Journal of Aerosol Science 07/2003; · 2.71 Impact Factor
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    ABSTRACT: The term "elemental carbon" (EC) is used to describe the most polymerized and refractory fraction of combustion-produced atmospheric carbonaceous aerosols, having chemical properties similar to graphitic carbon (disordered graphite lattice, mostly with carbon, but also with some oxygen and hydrogen atoms, and highly resistant to thermal degradation and oxidation). This species is insoluble either in water or organic solvents. In evolved gas analysis (EGA), it is usually represented by the peak evolving above ca. 400 ^oC in the thermograms. EGA analyses before and after water extraction have shown that in samples from biomass burning aerosols ca. 50% of the material evolving above 400 ^oC was removed by extraction with water and therefore was not true EC. These results suggest that this apparent EC (EC_a) is high-molecular weight organic material with thermal and oxidative properties similar to EC. This EC_a material also absorbs light, therefore, we have adopted the term of "brown carbon" (Cbrown) to refer to it. Here we will present a detailed chemical characterization of EC_a and Cbrown using EGA, optical transmission, thermo-optical analysis and pyrolysis GC/MS. This last technique will provide, for the first time, molecular characterization of Cbrown. The results of these analytical techniques will improve our understanding of the chemical, thermal and oxidative properties of true EC, EC_a and Cbrown from biomass burning aerosols. Brown carbon can be formed both during thermal decomposition of organic matter (charring) and through low-temperature microbial and abiotic reactions (humic/fulvic acids).
    04/2003;
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    ABSTRACT: As part of the European contribution to the Large-Scale Biosphere-Atmosphere Experiment in Amazonia (LBA-EUSTACH), size-fractionated aerosol samples were collected at a primary rainforest site in the Brazilian Amazon during the wet and dry seasons. Daytime-nighttime segregated sampling was carried out at three different heights (above, within and below canopy level) on a 54 m meteorological tower. The samples were analyzed for up to 19 trace elements, equivalent black carbon (BCe) and mass concentrations. Additionally, measurements of scattering and absorption coefficients were performed. Absolute principal component analysis revealed that the wet and dry season aerosols contained the same three main aerosol components, namely a natural biogenic, a pyrogenic, and a soil dust component, but that these were present in different (absolute and relative) amounts. The elements related to biomass burning and soil dust generally exhibited highest concentrations above the canopy and during daytime, whilst forest-derived aerosol was more concentrated underneath the canopy and during nighttime. These variations can be largely attributed to daytime convective mixing and the formation of a shallow nocturnal boundary layer, along with the possibility of enhanced nighttime release of biogenic aerosol particles. All three components contributed significantly to light extinction, suggesting that, in addition to pyrogenic particles, biogenic and soil dust aerosols must be taken into account when modeling the physical and optical properties of aerosols in forested regions such the Amazon Basin.
    03/2003; -1:9280.
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    ABSTRACT: We investigated the size distribution, scattering and absorption properties of Amazonian aerosols and the optical thickness of the aerosol layer under the pristine background conditions typical of the wet season, as well as during the biomass-burning-influenced dry season. The measurements were made during two campaigns in 1999 as part of the European contribution to the Large-Scale Biosphere-Atmosphere Experiment in Amazonia (LBA-EUSTACH). In moving from the wet to the dry season, median particle numbers were observed to increase from values comparable to those of the remote marine boundary layer (~400 cm<sup>-3</sup>) to values more commonly associated with urban smog (~4000 cm<sup>-3</sup>), due to a massive injection of submicron smoke particles. Aerosol optical depths at 500 nm increased from 0.05 to 0.8 on average, reaching a value of 2 during the dry season. Scattering and absorption coefficients, measured at 550 nm, showed a concomitant increase from average values of 6.8 and 0.4 Mm<sup>-1</sup> to values of 91 and 10 Mm<sup>-1</sup>, respectively, corresponding to an estimated decrease in single-scattering albedo from ca. 0.97 to 0.91. The roughly tenfold increase in many of the measured parameters attests to the dramatic effect that extensive seasonal biomass burning (deforestation, pasture cleaning) is having on the composition and properties of aerosols over Amazonia. The potential exists for these changes to impact on regional and global climate through changes to the extinction of solar radiation as well as the alteration of cloud properties.
    Atmospheric Chemistry and Physics 01/2003; · 4.88 Impact Factor
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    ABSTRACT: Fine (
    Journal of Analytical and Applied Pyrolysis, v.68-69, 351-369 (2003). 01/2003;
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    ABSTRACT: As part of the Large-Scale Biosphere-Atmosphere Experiment in Amazonia-European Studies on Trace Gases and Atmospheric Chemistry (LBA-EUSTACH), size-fractionated aerosol samples were collected at a primary rain forest in the Brazilian Amazon during two field campaigns in April–May and September–October 1999. These two periods encompassed parts of the wet and dry seasons, respectively. Daytime-nighttime-segregated sampling was carried out at three different heights (above, within, and below canopy level) on a 54-m meteorological tower at the forest site in order to better characterize the aerosol sources. The samples were analyzed for up to 19 trace elements by particle-induced X-ray emission analysis and for carbonaceous components by thermal-optical analysis. Equivalent black carbon (BCe) and gravimetric analyses were also performed. The average mass concentrations for particles
    Journal of Geophysical Research Atmospheres 01/2003; · 3.44 Impact Factor
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    ABSTRACT: We investigated nucleation scavenging of aerosols by cloud drops during the passage of a shallow cold front at a mountain station in northern Israel. The chemical composition and size of the aerosols were measured during and following the passage of the front. Analysis of the air mass trajectories show that, prior to the frontal passage, the air originated from the north, bringing with it pollution particles from sources in Eastern Europe. Following the frontal passage, the air originated from the east, bringing with it some mineral dust particles. The results show that sulfate, nitrate, and ammonium were the dominant compounds in the particles. Of the total sulfate-containing particles, 65% nucleated cloud drops. We found nucleation scavenging of aerosols to be correlated with the size of the aerosols. Aerosols smaller than 0.14 μm were not significantly affected by nucleation scavenging, while the number concentration of particles larger than 0.14 μm decreased in correspondence to the increase in droplet concentrations. During the time that the cloud covered the measuring site, 80% of the particles in the size range 0.3–1 μm were scavenged. The concentrations of the particles with diameter smaller than 1 μm returned to their original values after the cloud dissipated.
    Journal of Geophysical Research Atmospheres 01/2003; · 3.44 Impact Factor
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    ABSTRACT: Biogenic emissions dominate the aerosol population over the Amazon Basin under unpolluted conditions, which still exist over much of the basin during the wet season. Aerosol number concentrations and CCN concentrations are low, in the range typical of remote marine locations. A large fraction of particles is of primary biogenic origin, and consist of spores, pollen-related material, microbes, plant debris, etc. Secondary biogenic materials, including organics from VOC oxidation and biogenic sulfate account for much of the rest. Under these low-CCN conditions, cloud droplets can grow rapidly to the size where precipitation occurs and rain production by warm clouds is an important process. During the dry season, large-scale burning due to deforestation and clearing leads to a dramatic increase of aerosol and CCN concentrations. These smoke aerosols consist mostly of organic matter, include light-absorbing organic and near-elemental carbon species, and are efficient CCN. The result of the increased CCN abundance is a major shift towards clouds with high droplet number concentration, and thus increased colloidal stability of the cloud and a lower probability of rainfall from warm clouds. This favors rainfall mechanisms involving ice particles, which has substantial effects for the redistribution of energy and chemical species in the tropical atmosphere. First results from a campaign to study these relationships, using a combination of in-situ measurements, remote sensing, and modeling will be presented.
    AGU Fall Meeting Abstracts. 12/2002;
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    ABSTRACT: [1] As part of the European contribution to the Large-Scale Atmosphere-Biosphere Experiment in Amazonia (LBA-EUSTACH), aerosols were sampled at representative pasture and primary rainforest sites in Rondonia, Brazil, during the 1999 "burning season" and dry-to-wet season transition (September-October). Water-soluble organic compounds (WSOCs) within the samples were characterized using a combination of H-1 Nuclear Magnetic Resonance (NMR) spectroscopy for chemical functional group analysis, and Gas Chromatography-Mass Spectrometry (GC-MS) for identification and quantification of individual low-molecular- weight compounds. The H-1 NMR analysis indicates that WSOCs are predominantly aliphatic or oxygenated aliphatic compounds (alcohols, carboxylic acids, etc.), with a minor content of aromatic rings carrying carboxylic and phenolic groups. Levoglucosan (1,6-anhydro-beta-D-glucose), a well-known cellulose combustion product, was the most abundant individual compound identified by GC-MS (0.04-6.90 mug m(-3)), accounting for 1-6% of the total carbon (TC) and 2-8% of the water-soluble organic carbon (WSOC). Other anhydrosugars, produced by hemicellulose breakdown, were detected in much smaller amounts, in addition to series of acids, hydroxyacids, oxoacids, and polyalcohols (altogether 2-5% of TC, 3-6% of WSOC). Most correlated well with organic carbon, black carbon, and potassium, indicating biomass burning to be the major source. A series of sugar alcohols (mannitol, arabitol, erythritol) and sugars (glucose, fructose, mannose, galactose, sucrose, trehalose) were identified as part of the natural background aerosol and are probably derived from airborne microbes and other biogenic material. The bulk of the WSOCs (86-91% WSOC) eluded analysis by GC-MS and may be predominantly high- molecular weight in nature.
    Journal of Geophysical Research, v.107 (2002). 01/2002;
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    ABSTRACT: Chemical characterization was performed on carbonaceous aerosols from Rondonia in the Brazilian Amazon region as part of the European contribution to the Large-Scale Biosphere- Atmosphere Experiment in Amazonia (LBA-EUSTACH). The sampling period (October 1999) included the peak of the burning season as well as the dry-to-wet season transition. Characterization of the carbonaceous material was performed by using a thermal combustion method. This enabled determination of aerosol total carbon (TC), black carbon (BC), and organic carbon (OC). A significant fraction of the BC material (on average about 50%) seemed to be highly refractory organic material soluble in water. A more detailed analysis of the water-soluble organic carbon (WSOC) fraction of the TC was undertaken, involving measurements of WSOC content, high-performance liquid chromatography (HPLC) separation (with UV detection) of the water-soluble components, and characterization of individual components by gas chromatography/mass spectrometry (GC/MS). The WSOC fraction accounted for 45-75% of the OC. This high WSOC fraction suggests an aerosol derived mainly from smoldering combustion. Using GC/MS, many different compounds, containing hydroxy, carboxylate, and carbonyl groups, were detected. The fraction of the WSOC identified by GC/MS was about 10%. Three classes of compounds were separated by HPLC/UV: neutral compounds (N), monocarboxylic and dicarboxylic acids (MDA), and polycarboxylic acids (PA). The sum of these three groups accounted for about 70% of the WSOC, with MDA and PA being most abundant (about 50%). Good correlations (r(2) between 0.84 and 0.99) of BCwater (BC after water extraction) and levoglucosan (both indicators of biomass combustion) with the water-soluble species (i.e., WSOC, N, MDA, and PA), and their increase in concentrations during the burning period provided strong evidence that biomass burning is a major source of the WSOC. Particularly interesting is that PA and therefore, probably, humic-like substances (due to their polyacidic nature) are generated in significant amounts during biomass burning. These substances, due to their water solubility and surface tension- lowering effects, may play an important role in determining the overall cloud condensation nuclei activity of biomass burning aerosols and, consequently, could be important in cloud processes and climate forcing.
    Journal of Geophysical Research, v.107 (2002). 01/2002;
  • Rapid Communications in Mass Spectrometry, v.19, 1343-1351 (2005).