The first-order loss rate constant of methyl bromide was measured in surface seawater samples from the North Atlantic Ocean, Caribbean Sea, and coastal eastern Pacific Ocean during May-July 1998. A stable isotope incubation technique was used, which consisted of spiking seawater samples with ¹³CH₃Br and following the loss rate of the isotopically labeled spike with gas chromatography and isotope dilution mass spectrometry. The analysis of both filtered and unfiltered aliquots of seawater provides insight into the relative importance of chemical and particle-related (presumably biological) degradation pathways. Over the entire cruise, first-order total degradation rate constants ranged from 0.03–0.40 day⁻¹. On average, higher rate constants were observed during the last part of the cruise in the Caribbean Sea (mean 0.34 day⁻¹) and coastal Pacific waters (0.31 day⁻¹), than in the earlier passage through the North Atlantic Ocean (0.18 day⁻¹, legs 1 and 3). In the warm waters of the Caribbean Sea and the Pacific, total degradation rate constants were controlled primarily by chemical losses (0.30 and 0.25 day⁻¹, respectively). In the colder Atlantic waters the average chemical loss rate constant was lower (0.11 day⁻¹), and biological losses constituted a significant fraction of the total loss rate constant (35%). Chemical loss rate constants varied strongly with water temperature, in good agreement with previous determinations of the rate constant for methyl bromide removal from seawater due to chloride substitution and hydrolysis. Biological losses were detected in most of the water samples analyzed, suggesting that the biological capability to degrade methyl bromide is ubiquitous in the oceans. Rate constants for biological removal exhibited no apparent relationship to seawater temperature, salinity, chlorophyll, or bacterial counts.

A stable isotope tracer technique was used to investigate the loss rate of methyl bromide in surface ocean waters. Unfiltered and 0.2 μm-filtered or autoclaved aliquants of Biscayne Bay seawater samples were spiked with ¹³CH₃Br at roughly 10–100 times ambient concentrations (50–800 pM) and incubated for 10–30 hours. The concentration of ¹³CH₃Br was monitored using gas chromatography with isotope dilution mass spectrometry, with CD₃Br as the isotope spike. Removal rates in unfiltered aliquants were significantly faster than in the 0.2 μm-filtered or autoclaved aliquants, indicating that some of the loss of methyl bromide was associated with particulate matter. Filtration experiments indicate that the particulate material responsible for methyl bromide loss is between 0.2 and 1.2 μm in diameter, suggesting that bacteria are likely to be responsible. The particulate-related removal of methyl bromide was inhibited by autoclaving, supporting a biological mechanism.

This dissertation involves measurements of ethane and carbon monoxide in the air trapped in polar firn (porous ice) and ice cores from Greenland and Antarctica. Ethane and carbon monoxide are reactive trace gases that are involved in tropospheric ozone formation and impact the atmosphere's oxidative capacity. The major sources of these gases are from anthropogenic fossil fuel use, biofuel use, and biomass burning. Ethane fossil fuel emissions are mainly from evaporative emissions associated with the production, processing and transmission of fossil fuels. Carbon monoxide emissions are primarily due to fossil fuel combustion and atmospheric hydrocarbon oxidation. In this study, past atmospheric levels of ethane and carbon monoxide are reconstructed from polar firn air to examine man's impact on their global budgets.

Antarctic and Greenland firn air measurements show that ethane levels rose globally during the twentieth century, reached a peak in the 1980s, followed by a decline to their present-day levels. Ethane emissions reconstructions suggest that the ethane decline since 1980 was likely due to a reduction in fossil fuel emissions. The firn-air based ethane emissions histories suggest the slowdown in the atmospheric methane growth rate during the 1980s and 1990s was also due to reductions in fossil fuel emissions, possibly as a result of capture, recovery, and/or storage of natural gas that was previously vented or flared. In order to develop longer atmospheric histories, ethane was analyzed in air extracted from bubbles in Antarctic ice cores. Both dry extraction and wet extraction procedures were utilized in this study. The results indicate that preindustrial (1000-1900 AD) ethane levels over Antarctica were 40-50% lower than today.

Carbon monoxide levels increased by roughly 40% from 1920-1980, with near zero growth after the 1990s, based on the South Pole firn air reconstructions. The rate of CO rise during the mid-twentieth century was faster than the rate of methane rise during the same period. Modeling studies show that the twentieth century CO trends at high latitudes in each hemisphere can be explained by changes in anthropogenic fossil fuel emissions. The timing of the peak and decline in the anthropogenic CO emissions reconstructions is consistent with the implementation of clean air policies in the US and Europe.

Biomass burning plays a major role in atmospheric chemistry, carbon cycling, and climate. To understand and better predict how biomass burning may change in the future, it is important to investigate how biomass burning has varied in the past. Proxy records of biomass burning over long time periods are necessary to identify the link between biomass burning and climate. This information is needed by Earth system models to make accurate projections about future climate change and biomass burning.

In this dissertation, new ice core measurements are used to reconstruct biomass burning variability over the last 2,000 years. The trace gases ethane and acetylene are released to the atmosphere during biomass burning events. New analytical techniques utilizing a wet-extraction method coupled with gas-chromatography and high-resolution mass spectrometry analysis were developed to measure these gases in polar ice cores. The abundance of ethane and acetylene were measured in ice cores from Summit, Greenland, West Antarctic Ice Sheet (WAIS) Divide, Antarctica, and South Pole, Antarctica.

The ice core ethane and acetylene records exhibit similar temporal variability over the 2,000-year period. Over Greenland, little variability is observed in the ethane and acetylene levels. Over Antarctica, they both decline substainitally after 1500 CE, ethane by roughly 30% and acetylene by 50%. Using chemistry transport modeling, this decline in Antarctic ethane and acetylene was attributed to a decline in biomass burning emissions in the non-boreal (tropical) biome, rather than the boreal forests, from the warmer Medieval Period to the cooler Little Ice Age.

My study presents the first millennial scale record of these trace gases in polar ice cores and demonstrates that long-term paleo-climate records from these reactive, trace-level gases are attainable. The results show spatial and temporal variability in biomass burning emissions which were likely driven by climate. More work is needed to extend these records further back in time to periods where there is less influence by human activity and where there is a broader range of climatic variation in order to fully tease apart and quantify the climatic, rather than human, controls over fire in order to aid in validation of Earth system models.

Measurements of atmospheric dimethylsulfide (DMS), hydrogen sulfide (H₂S), and carbon disulfide (CS₂) were made over the North and South Atlantic Ocean as part of the Global Tropospheric Experiment/Chemical Instrumentation Test and Evaluation (GTE/CITE 3) project. DMS and CS₂ samples were collected and analyzed using an automated gas chromatography/flame photometric detection system with a sampling frequency of 10 min. H₂S samples were collected using silver nitrate impregnated filters and analyzed by fluorescence quenching. The DMS data from both hemispheres have a bimodal distribution. Over the North Atlantic this reflects the difference between marine and continental air masses. Over the South Atlantic it may reflect differences in the sea surface source of DMS, corresponding to different air mass source regions. The median boundary layer H₂S and CS₂ levels were significantly higher in the northern hemisphere than the southern hemisphere, reflecting the higher frequency of samples influenced by pollutant and/or coastal emissions. Composite vertical profiles of DMS and H₂S are similar to each other, and are consistent with a sea surface source. Vertical profiles of CS₂ have maxima in the free troposphere, implicating a continental source. The low levels of H₂S and CS₂ found in the southern hemisphere constrain the role of these compounds in global budgets to significantly less than previously estimated.

Methanesulfonate (MSA) in ice cores has attracted attention as a possible tracer of past oceanic emissions of dimethylsulfide (DMS). After sulfate MSA is the second most prevalent aerosol oxidation product of DMS, but in contrast to sulfate, DMS oxidation is the only known source of MSA. The hypothesis by Charlson et al., [1987] of a climate feedback mechanism with sulfur emissions from marine phytoplankton influencing the cloud albedo adds to the interest in establishing long records of MSA and non-seasalt sulfate spanning large climatic changes. Records of MSA and non-seasalt sulfate covering time periods from a few years to thousands of year have been extracted from antarctic ice cores [Ivey et al., 1986; Saigne and Legrand, 1987; Legrand and Feniet-Saigne, 1991; Mulvaney et al., 1992] but only the record from the Vostok ice core [Legrand et al., 1991] covers a full glacial cycle. The concentrations of MSA and non-seasalt sulfate in Antarctica have been found to increase under glacial conditions. Here we present the first Northern Hemisphere record of MSA, and the first continuous record of non-seasalt sulfate, both extracted from the Renland ice core, East Greenland. The records are extending from the Holocene to the Eem interglacial 130,000 years B.P. The contrast to the Southern Hemisphere records is striking, with a decreasing concentration of MSA with the advance of glaciation but an increasing concentration of non-seasalt sulfate. A strong linear relationship is found in the Renland ice core between the ratio of MSA to non-seasalt sulfate and the temperature, with higher ratios associated with warmer climatic stages, while the opposite relationship to temperature is found in the Vostok ice core. A more complicated picture is emerging of the use of MSA in ice cores as a quantitative tracer which suggests that previous interpretations can have been overly simplistic.