Brian Giebel - Academia.edu (original) (raw)

Papers by Brian Giebel

Science of The Total Environment, May 1, 2022

There is concern about the buildup of plastic waste in soil, their degradation into microplastics... more There is concern about the buildup of plastic waste in soil, their degradation into microplastics, and their potential to interfere with the natural processing of soil organic carbon and other nutrient cycling processes. Here we used scanning electron microscopy (SEM) and 13C isotope ratio mass spectrometry to determine if precut consumer plastics comprised of either high density polyethylene (HDPE), a blend of linear low density polyethylene and low density polyethylene (L/LDPE), or polyethylene terephthalate (PETE) would degrade or transform during a short-term, 32 day, exposure to soil or sludge in laboratory microcosms. SEM confirmed morphological changes occurred to all plastics, but the attachment of biofilm and presence of microorganisms mostly favored PETE and HDPE surfaces. These observations support the idea that abiotic and/or biotic processes may degrade plastics in soil; however distinguishable and significant changes in mean stable isotopic values (Dd 13C) of ~0.2-0.7‰ were only observed for exposed PETE and HDPE. This indicates that each plastic's degradation in soil may be dependent on their physical and chemical properties, with L/LDPE being more resistant and less prone to degradation compared to the others, and less dependent on the environmental conditions or properties of the soil or sludge. Our experiments were short-term and while the mechanisms of degradation are not clear, the results provide strong motivation for further studies of plastic fate and processing in soil systems. Direct mechanistic studies using stable isotopic approaches in combination with other characterizations and techniques are clearly warranted and may lead to a significant enhancement in our present understanding of the interactions and dynamics of plastics in the soil environment.

AGUFM, Dec 1, 2009

ABSTRACT Phytogenic methanol is the dominant source of methanol to the atmosphere, where it is th... more ABSTRACT Phytogenic methanol is the dominant source of methanol to the atmosphere, where it is the second most abundant organic compound. Beyond methanol’s role in atmospheric chemistry, it is an indicator of plant function and is linked to plant wound response. Methanol emissions are considered to be a by-product of cell wall expansion and, more specifically, the demethylation of pectin by pectin methylesterase (PME) in cell walls. Production of methanol was investigated in mature and immature tomato Lycopersicon esculentum via measurement of methanol flux, foliar PME activity, and methanol extraction from leaf, root, and stem tissues. δ13C values for mature and immature methanol emissions were also measured using a GC-IRMS system. Environmental control over methanol production and emission was studied by changing temperature and light while holding stomatal conductance constant. As seen previously, mature leaf methanol emissions were significantly less than immature emissions. Surprisingly, preliminary results suggest mature leaf methanol production to be similar to immature leaves, indicating an enhanced metabolic sink for methanol in mature leaves. These data enhance our understanding of methanol production, a term which is not well constrained in current methanol flux models.

Environmental Science & Technology, Jun 30, 2011

Analytical Chemistry, Jul 20, 2010

We present a new method for analyzing the delta(13)C isotopic composition of several oxygenated v... more We present a new method for analyzing the delta(13)C isotopic composition of several oxygenated volatile organic compounds (OVOCs) from direct sources and ambient atmospheric samples. Guided by the requirements for analysis of trace components in air, a gas chromatograph isotope ratio mass spectrometer (GC-IRMS) system was developed with the goal of increasing sensitivity, reducing dead-volume and peak band broadening, optimizing combustion and water removal, and decreasing the split ratio to the isotope ratio mass spectrometer (IRMS). The technique relies on a two-stage preconcentration system, a low-volume capillary reactor and water trap, and a balanced reference gas delivery system. The instrument's measurement precision is 0.6 to 2.9 per thousand (1sigma), and results indicate that negligible sample fractionation occurs during gas sampling. Measured delta(13)C values have a minor dependence on sample size; linearity for acetone was 0.06 per thousand ng C(-1) and was best over 1-10 ng C. Sensitivity is approximately 10 times greater than similar instrumentation designs, incorporates the use of a diluted working reference gas (0.1% CO(2)), and requires collection of >0.7 ng C to produce accurate and precise results. With this detection limit, a 1.0 L sample of ambient air provides sufficient carbon for isotopic analysis. Emissions from vegetation and vehicle exhaust are compared and show clear differences in isotopic signatures. Ambient samples collected in metropolitan Miami and the Everglades National Park can be differentiated and reflect multiple sources and sinks affecting a single sampling location. Vehicle exhaust emissions of ethanol, and those collected in metropolitan Miami, have anomalously enriched delta(13)C values ranging from -5.0 to -17.2 per thousand; we attribute this result to ethanol's origin from corn and use as an additive in automotive fuels.

AGU Spring Meeting Abstracts, May 1, 2007

AGUFM, Dec 1, 2008

Determining delta13C values for reduced hydrocarbons in atmospheric samples is emerging as an imp... more Determining delta13C values for reduced hydrocarbons in atmospheric samples is emerging as an important area of interest in isotopic analytical chemistry. The importance of stable isotopic data stems from its usefulness to differentiate between multiple sources and allows for an assessment of changing source structure and source strength in a constantly changing environment. Though much stable isotopic work is available on CH4 and other VOCs, particularly NMHCs, few studies have focused on oxygenated volatile organic compounds (OVOCs) such as methanol, ethanol, acetone, and propanal. Both anthropogenic and biogenic sources exist for these OVOCs and their role in atmospheric chemistry is important. The OVOCs of interest here are found in very low concentrations in ambient air (low ppbv to high pptv) and thus provide unique challenges for analysis by GC-C-IRMS. To address the challenges of measuring OVOCs, a Hewlett Packard 6890 gas chromatograph interfaced with a Europa Scientific Geo 20-20 IRMS was modified to accept ambient atmospheric samples. To sharpen peak shape all dead volume within the system was minimized; starting with the addition of a fused silica combustion tube (0.25 mm i.d.) containing Cu, Pt, or Ni wires (0.1 mm dia.). To assist water removal from the sample stream before delivery to the IRMS a small volume nafion dryer (0.20 mm i.d.) and a water-trap submersed in a dry-ice / acetone slurry were tested individually. Deactivated fused silica (0.1 mm i.d.) joins the custom designed open split to the ion source and effectively decreases dead volume while maintaining chromatographic separation and desired source pressure. To decrease the variability of the instrumentation, and to increase the total amount of carbon at the ion source, total carrier gas flow is reduced to 0.7 mL/min. Reference gas addition is manually facilitated by a six port rotary valve upstream of the open split and delivers diluted CO2 reference gas (0.1% CO2 in He) directly to the ion source while maintaining continuous flow conditions from the gas chromatograph. Experimental results of initial biogenic source sampling will be presented and future directions will be discussed.

Analytical Chemistry, 2010

We present a new method for analyzing the δ 13 C isotopic composition of several oxygenated volat... more We present a new method for analyzing the δ 13 C isotopic composition of several oxygenated volatile organic compounds (OVOCs) from direct sources and ambient atmospheric samples. Guided by the requirements for analysis of trace components in air, a gas chromatograph isotope ratio mass spectrometer (GC-IRMS) system was developed with the goal of increasing sensitivity, reducing dead-volume and peak band broadening, optimizing combustion and water removal, and decreasing the split ratio to the isotope ratio mass spectrometer (IRMS). The technique relies on a twostage preconcentration system, a low-volume capillary reactor and water trap, and a balanced reference gas delivery system. The instrument's measurement precision is 0.6 to 2.9‰ (1σ), and results indicate that negligible sample fractionation occurs during gas sampling. Measured δ 13 C values have a minor dependence on sample size; linearity for acetone was 0.06‰ ng C-1 and was best over 1-10 ng C. Sensitivity is ∼10 times greater than similar instrumentation designs, incorporates the use of a diluted working reference gas (0.1% CO 2), and requires collection of >0.7 ng C to produce accurate and precise results. With this detection limit, a 1.0 L sample of ambient air provides sufficient carbon for isotopic analysis. Emissions from vegetation and vehicle exhaust are compared and show clear differences in isotopic signatures. Ambient samples collected in metropolitan Miami and the Everglades National Park can be differentiated and reflect multiple sources and sinks affecting a single sampling location. Vehicle exhaust emissions of ethanol, and those collected in metropolitan Miami, have anomalously enriched δ 13 C values ranging from-5.0 to-17.2‰; we attribute this result to ethanol's origin from corn and use as an additive in automotive fuels.

ABSTRACT Determining delta13C values for reduced hydrocarbons in atmospheric samples is emerging ... more ABSTRACT Determining delta13C values for reduced hydrocarbons in atmospheric samples is emerging as an important area of interest in isotopic analytical chemistry. The importance of stable isotopic data stems from its ability to differentiate between multiple sources and allows for an assessment of changing source structure and source strength in a constantly changing environment. Though much stable isotopic work is available for CH4 and other volatile organic compounds (VOCs), particularly non-methane hydrocarbons (NMHCs), few studies have focused on oxygenated volatile organic compounds (OVOCs) such as methanol, ethanol, acetone, and MEK. Both anthropogenic and biogenic sources exist for these OVOCs and their role in atmospheric chemistry is important. The OVOCs of interest here are found in low concentrations in ambient air (low ppbv to high pptv) and thus provide unique challenges for analysis by gas chromatography - isotope ratio mass spectrometry (GC-IRMS). Presented here, is a first look at measured delta13C values for various sources of OVOCs to the atmosphere and includes a small survey of tropical vegetation and transportation sources. In addition to these sources, ambient samples from metropolitan Miami and Everglades National Park will be compared. We will also discuss challenges associated with these measurements and the steps taken to overcome them.

ABSTRACT Determining delta13C values for reduced hydrocarbons in atmospheric samples is emerging ... more ABSTRACT Determining delta13C values for reduced hydrocarbons in atmospheric samples is emerging as an important area of interest in isotopic analytical chemistry. The importance of stable isotopic data stems from its ability to differentiate between multiple sources and allows for an assessment of changing source structure and source strength in a constantly changing environment. Though much stable isotopic work is available for CH4 and other volatile organic compounds (VOCs), particularly non-methane hydrocarbons (NMHCs), few studies have focused on oxygenated volatile organic compounds (OVOCs) such as methanol, ethanol, acetone, and MEK. Both anthropogenic and biogenic sources exist for these OVOCs and their role in atmospheric chemistry is important. The OVOCs of interest here are found in low concentrations in ambient air (low ppbv to high pptv) and thus provide unique challenges for analysis by gas chromatography - isotope ratio mass spectrometry (GC-IRMS). Presented here, is a first look at measured delta13C values for various sources of OVOCs to the atmosphere and includes a small survey of tropical vegetation and transportation sources. In addition to these sources, ambient samples from metropolitan Miami and Everglades National Park will be compared. We will also discuss challenges associated with these measurements and the steps taken to overcome them.

Summary • Plant production of methanol (MeOH) is a poorly understood aspect of metabolism, and un... more Summary • Plant production of methanol (MeOH) is a poorly understood aspect of metabolism, and understanding MeOH production in plants is crucial for modeling MeOH emissions. Here, we have examined the source of MeOH emissions from mature and immature leaves and whether pectin methylesterase (PME) activity is a good predictor of MeOH emission. We also investigated the significance of belowground MeOH production for mature leaf emissions. • We present measurements of MeOH emission, PME activity, and MeOH concentration in mature and immature tissues of tomato (Lycopersicon esculentum). We also present stable carbon isotopic signatures of MeOH emission and the pectin methoxyl pool. • Our results suggest that below-ground MeOH production was not the dominant contributor to daytime MeOH emissions from mature and immature leaves. Stable carbon isotopic signatures of mature and immature leaf MeOH were similar, suggesting that they were derived from the same pathway. Foliar PME activity was...

ABSTRACT Phytogenic methanol is the dominant source of methanol to the atmosphere, where it is th... more ABSTRACT Phytogenic methanol is the dominant source of methanol to the atmosphere, where it is the second most abundant organic compound. Beyond methanol’s role in atmospheric chemistry, it is an indicator of plant function and is linked to plant wound response. Methanol emissions are considered to be a by-product of cell wall expansion and, more specifically, the demethylation of pectin by pectin methylesterase (PME) in cell walls. Production of methanol was investigated in mature and immature tomato Lycopersicon esculentum via measurement of methanol flux, foliar PME activity, and methanol extraction from leaf, root, and stem tissues. δ13C values for mature and immature methanol emissions were also measured using a GC-IRMS system. Environmental control over methanol production and emission was studied by changing temperature and light while holding stomatal conductance constant. As seen previously, mature leaf methanol emissions were significantly less than immature emissions. Surprisingly, preliminary results suggest mature leaf methanol production to be similar to immature leaves, indicating an enhanced metabolic sink for methanol in mature leaves. These data enhance our understanding of methanol production, a term which is not well constrained in current methanol flux models.

We present a new method for analyzing the δ13C isotopic composition of several oxygenated volatil... more We present a new method for analyzing the δ13C isotopic composition of several oxygenated volatile organic compounds (OVOCs) from direct sources and ambient atmospheric samples. Guided by the requirements for analysis of trace components in air, a gas chromatograph isotope ratio mass spectrometer (GC-IRMS) system was developed with the goal of increasing sensitivity, reducing dead-volume and peak band broadening, optimizing combustion and water removal, and decreasing the split ratio to the isotope ratio mass spectrometer (IRMS). The technique relies on a twostage preconcentration system, a low-volume capillary reactor and water trap, and a balanced reference gas delivery system. The instrument’s measurement precision is 0.6 to 2.9‰ (1σ), and results indicate that negligible sample fractionation occurs during gas sampling. Measured δ13C values have a minor dependence on sample size; linearity for acetone was 0.06‰ ng C-1 and was best over 1-10 ng C. Sensitivity is ∼10 times greater ...

Introduction Methyl tertiary butyl ether (MTBE) (Fig. 1) is an oxygenated volatile organic compou... more Introduction Methyl tertiary butyl ether (MTBE) (Fig. 1) is an oxygenated volatile organic compound (OVOC) added to gasoline to either increase the oxygenated content and/or to increase the octane rating. MTBE is currently added to fuels in Mexico and Asia in the range of 2-7%. Only small quantities of MTBE are found in fuels in the United States because of extensive regulatory action restricting its use. MTBE is short lived in the atmosphere (~3.5 days) with losses due primarily to reaction with the OH radical. It is an exclusive indicator of tailpipe and evaporative emissions and unlike acetylene, is not emitted from biomass burning. In combination with other collected data, MTBE measured during the MIRAGE and INTEX-B studies and the CLIVAR P16N oceanographic cruise is useful for differentiating and quantifying important VOC emission sources from Mexico and Asia.

ABSTRACT Recent advances in optical spectroscopy techniques have provided an alternative to stabl... more ABSTRACT Recent advances in optical spectroscopy techniques have provided an alternative to stable isotope ratio mass spectrometry (SIRMS) techniques as a means of measuring delta13C in CO2. Low cost, ease of use, portability, and easier maintenance have made cavity ringdown spectroscopy (CRDS) an increasingly popular alternative to traditional SIRMS methods. Our recent experiences with two Picarro CRDS analyzers (G1101-i) for CO2 show instrument accuracy and precision to be influenced by gas composition and humidity levels. In some instances, these effects are large and limit the utility of the instrument unless appropriate calibration procedures are performed. We will discuss the results of experiments with sample gases other than air, including those containing different nitrogen-oxygen ratios and helium. The effect of different humidity levels and CO2 concentrations will also be addressed. These issues raise important concerns in using the CRDS in a range of environments in which there are varying concentrations of oxygen and for applications in which the CRDS is used as a detector interfaced to preparative instrumentation such as elemental analyzers.

Science of The Total Environment

Ethanol is currently receiving increased attention because of its use as a biofuel or fuel additi... more Ethanol is currently receiving increased attention because of its use as a biofuel or fuel additive and because of its influence on air quality. We used stable isotopic ratio measurements of (13)C/(12)C in ethanol emitted from vehicles and a small group of tropical plants to establish ethanol's δ(13)C end-member signatures. Ethanol emitted in exhaust is distinctly different from that emitted by tropical plants and can serve as a unique stable isotopic tracer for transportation-related inputs to the atmosphere. Ethanol's unique isotopic signature in fuel is related to corn, a C4 plant and the primary source of ethanol in the U.S. We estimated a kinetic isotope effect (KIE) for ethanol's oxidative loss in the atmosphere and used previous assumptions with respect to the fractionation that may occur during wet and dry deposition. A small number of interpretive model calculations were used for source apportionment of ethanol and to understand the associated effects resulting from atmospheric removal. The models incorporated our end-member signatures and ambient measurements of ethanol, known or estimated source strengths and removal magnitudes, and estimated KIEs associated with atmospheric removal processes for ethanol. We compared transportation-related ethanol signatures to those from biogenic sources and used a set of ambient measurements to apportion each source contribution in Miami, Florida-a moderately polluted, but well ventilated urban location.

Science of The Total Environment, May 1, 2022

There is concern about the buildup of plastic waste in soil, their degradation into microplastics... more There is concern about the buildup of plastic waste in soil, their degradation into microplastics, and their potential to interfere with the natural processing of soil organic carbon and other nutrient cycling processes. Here we used scanning electron microscopy (SEM) and 13C isotope ratio mass spectrometry to determine if precut consumer plastics comprised of either high density polyethylene (HDPE), a blend of linear low density polyethylene and low density polyethylene (L/LDPE), or polyethylene terephthalate (PETE) would degrade or transform during a short-term, 32 day, exposure to soil or sludge in laboratory microcosms. SEM confirmed morphological changes occurred to all plastics, but the attachment of biofilm and presence of microorganisms mostly favored PETE and HDPE surfaces. These observations support the idea that abiotic and/or biotic processes may degrade plastics in soil; however distinguishable and significant changes in mean stable isotopic values (Dd 13C) of ~0.2-0.7‰ were only observed for exposed PETE and HDPE. This indicates that each plastic's degradation in soil may be dependent on their physical and chemical properties, with L/LDPE being more resistant and less prone to degradation compared to the others, and less dependent on the environmental conditions or properties of the soil or sludge. Our experiments were short-term and while the mechanisms of degradation are not clear, the results provide strong motivation for further studies of plastic fate and processing in soil systems. Direct mechanistic studies using stable isotopic approaches in combination with other characterizations and techniques are clearly warranted and may lead to a significant enhancement in our present understanding of the interactions and dynamics of plastics in the soil environment.

AGUFM, Dec 1, 2009

ABSTRACT Phytogenic methanol is the dominant source of methanol to the atmosphere, where it is th... more ABSTRACT Phytogenic methanol is the dominant source of methanol to the atmosphere, where it is the second most abundant organic compound. Beyond methanol’s role in atmospheric chemistry, it is an indicator of plant function and is linked to plant wound response. Methanol emissions are considered to be a by-product of cell wall expansion and, more specifically, the demethylation of pectin by pectin methylesterase (PME) in cell walls. Production of methanol was investigated in mature and immature tomato Lycopersicon esculentum via measurement of methanol flux, foliar PME activity, and methanol extraction from leaf, root, and stem tissues. δ13C values for mature and immature methanol emissions were also measured using a GC-IRMS system. Environmental control over methanol production and emission was studied by changing temperature and light while holding stomatal conductance constant. As seen previously, mature leaf methanol emissions were significantly less than immature emissions. Surprisingly, preliminary results suggest mature leaf methanol production to be similar to immature leaves, indicating an enhanced metabolic sink for methanol in mature leaves. These data enhance our understanding of methanol production, a term which is not well constrained in current methanol flux models.

Environmental Science & Technology, Jun 30, 2011

Analytical Chemistry, Jul 20, 2010

We present a new method for analyzing the delta(13)C isotopic composition of several oxygenated v... more We present a new method for analyzing the delta(13)C isotopic composition of several oxygenated volatile organic compounds (OVOCs) from direct sources and ambient atmospheric samples. Guided by the requirements for analysis of trace components in air, a gas chromatograph isotope ratio mass spectrometer (GC-IRMS) system was developed with the goal of increasing sensitivity, reducing dead-volume and peak band broadening, optimizing combustion and water removal, and decreasing the split ratio to the isotope ratio mass spectrometer (IRMS). The technique relies on a two-stage preconcentration system, a low-volume capillary reactor and water trap, and a balanced reference gas delivery system. The instrument's measurement precision is 0.6 to 2.9 per thousand (1sigma), and results indicate that negligible sample fractionation occurs during gas sampling. Measured delta(13)C values have a minor dependence on sample size; linearity for acetone was 0.06 per thousand ng C(-1) and was best over 1-10 ng C. Sensitivity is approximately 10 times greater than similar instrumentation designs, incorporates the use of a diluted working reference gas (0.1% CO(2)), and requires collection of >0.7 ng C to produce accurate and precise results. With this detection limit, a 1.0 L sample of ambient air provides sufficient carbon for isotopic analysis. Emissions from vegetation and vehicle exhaust are compared and show clear differences in isotopic signatures. Ambient samples collected in metropolitan Miami and the Everglades National Park can be differentiated and reflect multiple sources and sinks affecting a single sampling location. Vehicle exhaust emissions of ethanol, and those collected in metropolitan Miami, have anomalously enriched delta(13)C values ranging from -5.0 to -17.2 per thousand; we attribute this result to ethanol's origin from corn and use as an additive in automotive fuels.

AGU Spring Meeting Abstracts, May 1, 2007

AGUFM, Dec 1, 2008

Determining delta13C values for reduced hydrocarbons in atmospheric samples is emerging as an imp... more Determining delta13C values for reduced hydrocarbons in atmospheric samples is emerging as an important area of interest in isotopic analytical chemistry. The importance of stable isotopic data stems from its usefulness to differentiate between multiple sources and allows for an assessment of changing source structure and source strength in a constantly changing environment. Though much stable isotopic work is available on CH4 and other VOCs, particularly NMHCs, few studies have focused on oxygenated volatile organic compounds (OVOCs) such as methanol, ethanol, acetone, and propanal. Both anthropogenic and biogenic sources exist for these OVOCs and their role in atmospheric chemistry is important. The OVOCs of interest here are found in very low concentrations in ambient air (low ppbv to high pptv) and thus provide unique challenges for analysis by GC-C-IRMS. To address the challenges of measuring OVOCs, a Hewlett Packard 6890 gas chromatograph interfaced with a Europa Scientific Geo 20-20 IRMS was modified to accept ambient atmospheric samples. To sharpen peak shape all dead volume within the system was minimized; starting with the addition of a fused silica combustion tube (0.25 mm i.d.) containing Cu, Pt, or Ni wires (0.1 mm dia.). To assist water removal from the sample stream before delivery to the IRMS a small volume nafion dryer (0.20 mm i.d.) and a water-trap submersed in a dry-ice / acetone slurry were tested individually. Deactivated fused silica (0.1 mm i.d.) joins the custom designed open split to the ion source and effectively decreases dead volume while maintaining chromatographic separation and desired source pressure. To decrease the variability of the instrumentation, and to increase the total amount of carbon at the ion source, total carrier gas flow is reduced to 0.7 mL/min. Reference gas addition is manually facilitated by a six port rotary valve upstream of the open split and delivers diluted CO2 reference gas (0.1% CO2 in He) directly to the ion source while maintaining continuous flow conditions from the gas chromatograph. Experimental results of initial biogenic source sampling will be presented and future directions will be discussed.

Analytical Chemistry, 2010

We present a new method for analyzing the δ 13 C isotopic composition of several oxygenated volat... more We present a new method for analyzing the δ 13 C isotopic composition of several oxygenated volatile organic compounds (OVOCs) from direct sources and ambient atmospheric samples. Guided by the requirements for analysis of trace components in air, a gas chromatograph isotope ratio mass spectrometer (GC-IRMS) system was developed with the goal of increasing sensitivity, reducing dead-volume and peak band broadening, optimizing combustion and water removal, and decreasing the split ratio to the isotope ratio mass spectrometer (IRMS). The technique relies on a twostage preconcentration system, a low-volume capillary reactor and water trap, and a balanced reference gas delivery system. The instrument's measurement precision is 0.6 to 2.9‰ (1σ), and results indicate that negligible sample fractionation occurs during gas sampling. Measured δ 13 C values have a minor dependence on sample size; linearity for acetone was 0.06‰ ng C-1 and was best over 1-10 ng C. Sensitivity is ∼10 times greater than similar instrumentation designs, incorporates the use of a diluted working reference gas (0.1% CO 2), and requires collection of >0.7 ng C to produce accurate and precise results. With this detection limit, a 1.0 L sample of ambient air provides sufficient carbon for isotopic analysis. Emissions from vegetation and vehicle exhaust are compared and show clear differences in isotopic signatures. Ambient samples collected in metropolitan Miami and the Everglades National Park can be differentiated and reflect multiple sources and sinks affecting a single sampling location. Vehicle exhaust emissions of ethanol, and those collected in metropolitan Miami, have anomalously enriched δ 13 C values ranging from-5.0 to-17.2‰; we attribute this result to ethanol's origin from corn and use as an additive in automotive fuels.

ABSTRACT Determining delta13C values for reduced hydrocarbons in atmospheric samples is emerging ... more ABSTRACT Determining delta13C values for reduced hydrocarbons in atmospheric samples is emerging as an important area of interest in isotopic analytical chemistry. The importance of stable isotopic data stems from its ability to differentiate between multiple sources and allows for an assessment of changing source structure and source strength in a constantly changing environment. Though much stable isotopic work is available for CH4 and other volatile organic compounds (VOCs), particularly non-methane hydrocarbons (NMHCs), few studies have focused on oxygenated volatile organic compounds (OVOCs) such as methanol, ethanol, acetone, and MEK. Both anthropogenic and biogenic sources exist for these OVOCs and their role in atmospheric chemistry is important. The OVOCs of interest here are found in low concentrations in ambient air (low ppbv to high pptv) and thus provide unique challenges for analysis by gas chromatography - isotope ratio mass spectrometry (GC-IRMS). Presented here, is a first look at measured delta13C values for various sources of OVOCs to the atmosphere and includes a small survey of tropical vegetation and transportation sources. In addition to these sources, ambient samples from metropolitan Miami and Everglades National Park will be compared. We will also discuss challenges associated with these measurements and the steps taken to overcome them.

ABSTRACT Determining delta13C values for reduced hydrocarbons in atmospheric samples is emerging ... more ABSTRACT Determining delta13C values for reduced hydrocarbons in atmospheric samples is emerging as an important area of interest in isotopic analytical chemistry. The importance of stable isotopic data stems from its ability to differentiate between multiple sources and allows for an assessment of changing source structure and source strength in a constantly changing environment. Though much stable isotopic work is available for CH4 and other volatile organic compounds (VOCs), particularly non-methane hydrocarbons (NMHCs), few studies have focused on oxygenated volatile organic compounds (OVOCs) such as methanol, ethanol, acetone, and MEK. Both anthropogenic and biogenic sources exist for these OVOCs and their role in atmospheric chemistry is important. The OVOCs of interest here are found in low concentrations in ambient air (low ppbv to high pptv) and thus provide unique challenges for analysis by gas chromatography - isotope ratio mass spectrometry (GC-IRMS). Presented here, is a first look at measured delta13C values for various sources of OVOCs to the atmosphere and includes a small survey of tropical vegetation and transportation sources. In addition to these sources, ambient samples from metropolitan Miami and Everglades National Park will be compared. We will also discuss challenges associated with these measurements and the steps taken to overcome them.

Summary • Plant production of methanol (MeOH) is a poorly understood aspect of metabolism, and un... more Summary • Plant production of methanol (MeOH) is a poorly understood aspect of metabolism, and understanding MeOH production in plants is crucial for modeling MeOH emissions. Here, we have examined the source of MeOH emissions from mature and immature leaves and whether pectin methylesterase (PME) activity is a good predictor of MeOH emission. We also investigated the significance of belowground MeOH production for mature leaf emissions. • We present measurements of MeOH emission, PME activity, and MeOH concentration in mature and immature tissues of tomato (Lycopersicon esculentum). We also present stable carbon isotopic signatures of MeOH emission and the pectin methoxyl pool. • Our results suggest that below-ground MeOH production was not the dominant contributor to daytime MeOH emissions from mature and immature leaves. Stable carbon isotopic signatures of mature and immature leaf MeOH were similar, suggesting that they were derived from the same pathway. Foliar PME activity was...

ABSTRACT Phytogenic methanol is the dominant source of methanol to the atmosphere, where it is th... more ABSTRACT Phytogenic methanol is the dominant source of methanol to the atmosphere, where it is the second most abundant organic compound. Beyond methanol’s role in atmospheric chemistry, it is an indicator of plant function and is linked to plant wound response. Methanol emissions are considered to be a by-product of cell wall expansion and, more specifically, the demethylation of pectin by pectin methylesterase (PME) in cell walls. Production of methanol was investigated in mature and immature tomato Lycopersicon esculentum via measurement of methanol flux, foliar PME activity, and methanol extraction from leaf, root, and stem tissues. δ13C values for mature and immature methanol emissions were also measured using a GC-IRMS system. Environmental control over methanol production and emission was studied by changing temperature and light while holding stomatal conductance constant. As seen previously, mature leaf methanol emissions were significantly less than immature emissions. Surprisingly, preliminary results suggest mature leaf methanol production to be similar to immature leaves, indicating an enhanced metabolic sink for methanol in mature leaves. These data enhance our understanding of methanol production, a term which is not well constrained in current methanol flux models.

We present a new method for analyzing the δ13C isotopic composition of several oxygenated volatil... more We present a new method for analyzing the δ13C isotopic composition of several oxygenated volatile organic compounds (OVOCs) from direct sources and ambient atmospheric samples. Guided by the requirements for analysis of trace components in air, a gas chromatograph isotope ratio mass spectrometer (GC-IRMS) system was developed with the goal of increasing sensitivity, reducing dead-volume and peak band broadening, optimizing combustion and water removal, and decreasing the split ratio to the isotope ratio mass spectrometer (IRMS). The technique relies on a twostage preconcentration system, a low-volume capillary reactor and water trap, and a balanced reference gas delivery system. The instrument’s measurement precision is 0.6 to 2.9‰ (1σ), and results indicate that negligible sample fractionation occurs during gas sampling. Measured δ13C values have a minor dependence on sample size; linearity for acetone was 0.06‰ ng C-1 and was best over 1-10 ng C. Sensitivity is ∼10 times greater ...

Introduction Methyl tertiary butyl ether (MTBE) (Fig. 1) is an oxygenated volatile organic compou... more Introduction Methyl tertiary butyl ether (MTBE) (Fig. 1) is an oxygenated volatile organic compound (OVOC) added to gasoline to either increase the oxygenated content and/or to increase the octane rating. MTBE is currently added to fuels in Mexico and Asia in the range of 2-7%. Only small quantities of MTBE are found in fuels in the United States because of extensive regulatory action restricting its use. MTBE is short lived in the atmosphere (~3.5 days) with losses due primarily to reaction with the OH radical. It is an exclusive indicator of tailpipe and evaporative emissions and unlike acetylene, is not emitted from biomass burning. In combination with other collected data, MTBE measured during the MIRAGE and INTEX-B studies and the CLIVAR P16N oceanographic cruise is useful for differentiating and quantifying important VOC emission sources from Mexico and Asia.

ABSTRACT Recent advances in optical spectroscopy techniques have provided an alternative to stabl... more ABSTRACT Recent advances in optical spectroscopy techniques have provided an alternative to stable isotope ratio mass spectrometry (SIRMS) techniques as a means of measuring delta13C in CO2. Low cost, ease of use, portability, and easier maintenance have made cavity ringdown spectroscopy (CRDS) an increasingly popular alternative to traditional SIRMS methods. Our recent experiences with two Picarro CRDS analyzers (G1101-i) for CO2 show instrument accuracy and precision to be influenced by gas composition and humidity levels. In some instances, these effects are large and limit the utility of the instrument unless appropriate calibration procedures are performed. We will discuss the results of experiments with sample gases other than air, including those containing different nitrogen-oxygen ratios and helium. The effect of different humidity levels and CO2 concentrations will also be addressed. These issues raise important concerns in using the CRDS in a range of environments in which there are varying concentrations of oxygen and for applications in which the CRDS is used as a detector interfaced to preparative instrumentation such as elemental analyzers.

Science of The Total Environment

Ethanol is currently receiving increased attention because of its use as a biofuel or fuel additi... more Ethanol is currently receiving increased attention because of its use as a biofuel or fuel additive and because of its influence on air quality. We used stable isotopic ratio measurements of (13)C/(12)C in ethanol emitted from vehicles and a small group of tropical plants to establish ethanol's δ(13)C end-member signatures. Ethanol emitted in exhaust is distinctly different from that emitted by tropical plants and can serve as a unique stable isotopic tracer for transportation-related inputs to the atmosphere. Ethanol's unique isotopic signature in fuel is related to corn, a C4 plant and the primary source of ethanol in the U.S. We estimated a kinetic isotope effect (KIE) for ethanol's oxidative loss in the atmosphere and used previous assumptions with respect to the fractionation that may occur during wet and dry deposition. A small number of interpretive model calculations were used for source apportionment of ethanol and to understand the associated effects resulting from atmospheric removal. The models incorporated our end-member signatures and ambient measurements of ethanol, known or estimated source strengths and removal magnitudes, and estimated KIEs associated with atmospheric removal processes for ethanol. We compared transportation-related ethanol signatures to those from biogenic sources and used a set of ambient measurements to apportion each source contribution in Miami, Florida-a moderately polluted, but well ventilated urban location.