Now showing items 1-20 of 129

• Nitrogen oxides in the Arctic troposphere

Nitrogen oxides play a critical role in tropospheric photochemistry. In order to characterize these compounds in the arctic troposphere, ground-level concentrations of total reactive nitrogen (NO$\sb{y}$) and NO were determined over an extended period at a site near Barrow, Alaska. A high-sensitivity instrument developed for this purpose was used in three measurement campaigns: summer 1988, spring 1989, and March-December 1990. During the 1990 campaign, the detection limit for NO was 3-10 pptv (depending on averaging period), and the NO$\sb{y}$ uncertainty was $\pm$26%. A screening algorithm was applied to the data to eliminate effects from local (Barrow) sources, and the remaining data were divided into "background periods" (unaffected by local or regional NO$\sb{x}$ sources), and "events" (periods when emissions from a regional NO$\sb{x}$ source--the Prudhoe Bay oil-producing region--apparently impacted Barrow). These measurements revealed a sharp seasonal cycle of background NO$\sb{y}$ concentrations, with high values in early spring (median 560-620 pptv) and $\sim$70 pptv (median) during summer. This cycle is similar to that of other compounds in arctic haze but is partially attributed to a reduction in NO$\sb{y}$ lifetime due to organic nitrate decomposition as temperatures and insolation increased. Evidence indicates that the springtime arctic NO$\sb{y}$ reservoir was primarily composed of stable removal-resistant species, including PAN and other organic nitrates. PAN decomposition as temperatures rose in late spring likely caused an observed pulse of NO to $\sim$35 pptv (maximum hourly average); hourly-average NO concentrations were otherwise generally $<$8 pptv. NO$\sb{x}$ production from PAN decomposition due to the onset of spring or southward advection may affect springtime O$\sb3$ levels both in the Arctic and in the northern mid-latitudes. NO$\sb{y}$ and O$\sb3$ concentrations were positively correlated during summer, possibly indicating long-range transport of both and/or the presence of a mid-tropospheric NO$\sb{y}$ reservoir combined with a stratospheric O$\sb3$ source. A number of events with substantially elevated NO$\sb{y}$ concentrations (to 16 ppbv) were observed in air not impacted by emissions from the town of Barrow. Substantial evidence indicates that these events were a result of NO$\sb{x}$ emissions from the Prudhoe Bay region ($\sim$300 km to the ESE), which is also expected to affect measurements of other compounds at the Barrow site.
• Stabilization of secondary structure of synthetic Alzheimer beta-amyloid protein analogs in the presence of aluminum (III) ions

The gradual accretion of fibrillar protein deposits in a tissue or organ is a hallmark of all amyloidogenic diseases. These deposits accumulate as senile plaques and cerebrovascular deposits in the brain and are characteristics of Alzheimer's disease. A majority of the brain amyloid deposits consist of a 40 amino acid protein, the Alzheimer $\beta$-protein, A$\beta$P, which in a soluble form is ubiquitous in biological tissues. In order to provide a more detailed understanding of the structural transformations of soluble A$\beta$P, sequence analogs derived from $\beta$1-40, and having His $\to$ Arg, and scL-Asp- $\to$ scD-Asp substitutions were synthesized. The kinetic variations of $\beta$1-40 and $\beta$6-25 were studied using amide circular dichroism spectroscopy by monitoring ellipticity changes of the peptide backbone. In both peptides, the gradual loss of secondary structure was a multiphasic process which was also dependent on concentration. The circular dichroism titrations with metal ions revealed the involvement of at least two ions in the conformational transitions of $\beta$1-40 and $\beta$6-25. The association of Al(III) with scL-Asp $\to$ scD-Asp derived analogs caused surprising conformational changes in $\beta$6-25, which were distinct from $\beta$1-40. Microheterogeneous products corresponding to Al(III)-bound peptide species were resolvable on the reversed-phase surface. The association of aluminum was investigated by low field $\sp{27}$Al nuclear magnetic resonance spectroscopy. The signal corresponding to Al(III)-bound peptide species revealed that at least four Al(III) ions were bound to $\beta$1-40 and $\beta$6-25 between pH 5 and 6. Moreover, $\beta$1-40 effectively competed with EDTA to bind with Al(III). This study also describes a strategy which resolved the band broadening in reversed-phase high-performance liquid chromatography of $\beta$1-40 and derived analogs. Chromatographic parameters related to interactive contact area of $\beta$1-40 and derived analogs were determined on reversed-phase matrix. The peptides were bound to the reversed-phase surface in their monomeric form. Slow partition kinetics appear to contribute to significant band broadening, which suggests a secondary retention effect--indicating a conformational change due to unfolding on the stationary phase surface.
• Nitrogen oxide photochemistry in high northern latitudes during spring

The transport of NOy reservoir species from midlatitudes into the Arctic and the thermal and photochemical breakup of these species has been proposed to be the most important NOx source during spring, and may have an important influence on the ozone budget. This has not yet been shown to be correct. The objective of this research is to understand the sources of NOx and ozone in high latitudes during spring. To measure NOx, a high sensitivity chemiluminescence NO detector and a photolytic converter for NO$\sb2$ were constructed. The detection limits for NO and NO$\sb2$ were 1.70 and 5.67 part per trillion (pptv) in a one-hour average, respectively. Springtime NOx measurements were carried out concurrently with measurements of ozone, PAN, J(NO$\sb2$), and other species during 1994 at the Zeppelin station on Svalbard, and during 1993 and 1995 at Poker Flat, Alaska. The median mixing ratios of NOx, PAN and ozone at Svalbard were 23.7, 237.0 pptv, and 39.0 parts per billion (ppbv), respectively. During a few ozone depletion events in the Arctic marine boundary layer ozone and NOx mixing ratios were as low as 4 ppbv and 0.9 pptv, respectively. Halogen chemistry is probably responsible for both effects. The median NOx, PAN and ozone mixing ratios at Poker Flat were 79.5 pptv, 85.9 pptv, and 40.6 ppbv, respectively. During April and May diurnal cycles of PAN, ozone and temperature were observed and anticorrelated with the water mixing ratio. We interpret this to be the result of mixing with higher layers of the troposphere during the day. At both locations thermal PAN decomposition was an important NOx source. At Svalbard PAN decomposition was small, and the in-situ ozone production rates are an insignificant contribution to the ozone budget. Because of the higher temperatures, PAN decomposition rates, NOx mixing ratios, and in-situ ozone production rates are higher at Poker Flat. A contribution from this production to the overall ozone budget was visible during some periods. These results indicate that stable ozone precursors which are transported into the Arctic from anthropogenic sources can influence the ozone budget in high latitudes.
• Oceanic emissions of sulfur: Application of new techniques

Sulfur gases and aerosols are important in the atmosphere because they play major roles in acid rain, arctic haze, air pollution, and climate. Globally, man-made and natural sulfur emissions are comparable in magnitude. The major natural source is dimethyl sulfide (DMS) from the oceans, where it originates from the degradation of dimethysulfonioproprionate (DMSP), a compound produced by marine phytoplankton. Global budgets of natural sulfur emissions are uncertain because of (1) the uncertainty in the traditional method used to estimate DMS sea-to-air flux, and (2) the spatial and temporal variability of DMS sea-to-air flux. We have worked to lessen the uncertainty on both fronts. The commonly used method for estimating DMS sea-to-air flux is certain to a factor of two, at best. We used a novel instrumental technique to measure, for the first time, sulfur gas concentration fluctuations in the marine boundary layer. The measured concentration fluctuations were then used with two established micrometeorological techniques to estimate sea-to-air flux of sulfur. Both methods appear to be more accurate than the commonly used one. The analytical instrument we used in our studies shows potential as a direct flux measurement device. High primary productivity in high-latitude oceans suggests a potentially large DMS source from northern oceans. To begin to investigate this hypothesis, we have measured DMS in the air over northern oceans around Alaska. For integrating and extrapolating field measurements over larger areas and longer time periods, we have developed a model of DMS ocean mixing, biological production, and sea-to-air flux of DMS. The model's main utility is in gaining intuition on which parameters are most important to DMS sea-to-air flux. This information, along with a direct flux measurement capability, are crucial steps toward the long-term goal of remotely sensing DMS flux. A remote sensing approach will mitigate the problems of spatial and temporal variability. The new developments in methodology, field sampling, and modeling put forth in this thesis are tools we have used to better understand and quantify sulfur gas emissions from northern oceans, which appear to be a significant source of sulfur to the global atmosphere.
• Molecular systematics and biogeography of long-tailed shrews (Insectivora: Sorex) and northern flying squirrels (Rodentia: Glaucomys)

Insight into phylogenetic and biogeographic relationships among several mammalian taxa in western North America was provided with DNA sequences of two mitochondrial genes (cytochrome b and ND4). Members of two species complexes of long-tailed shrews (genus Sorex ) and northern flying squirrels (genus Glaucomys) were examined, and a common theme of responses to past climate change and glacial cycles was evident. Diversification events indicated by the DNA sequences provide new perspectives regarding the deep and shallow history of these taxa. Analysis of seven species of the Sorex cinereus complex (and related species) revealed two major clades within the complex, Northern and Southern. These generally corroborate proposed morphological relationships and correspond to broadly defined habitat affiliations (xeric and mesic), respectively. Within the Northern clade, amphiberingian species represented a monophyletic group suggesting Beringia was a center of endemism. Next, five species of the S. vagrans complex and related species were assessed. Significant molecular variation was revealed that does not correspond to morphological differences within the complex. Two major clades within S. monticolus were observed, a widespread Continental clade (Arizona to Alaska, including S. neomexicanus) and a restricted Coastal clade (Oregon to southeast Alaska, including S. bairdi and S. pacificus). A regional examination of genetic variation in the northern flying squirrel in southeast Alaska was also performed. Results suggested that southern islands in the Alexander Archipelago were the result of recent colonization (founder event). Finally, a comparative phylogeographic analysis of a reduced data set (S. monticolus), a molecular data set for the American Pine Marten, Martes americana, and other published molecular studies were used to reexamine the role of glacial refugia in the biogeography of the north Pacific coast. Previous ideas regarding purported refugia may be overstated and may be the result of limited geographic sampling. This thesis provides new perspectives on processes (e.g., post-glacial colonization) driving mammalian phylogenetic and biogeographic structuring in western North America.
• New instrumentation for the detection of sulfur dioxide in the remote atmosphere

Sulfur gases are an important chemical component of the atmosphere. Gaseous sulfur compounds effect the acidity of rainwater and are important precursors to aerosol particles which affect public health, climate and visibility of scenic vistas such as the Grand Canyon. Sulfate aerosols are also known to participate in ozone catalysis in the stratosphere. A vast majority of the gaseous sulfur cycling through the atmosphere will exist as sulfur dioxide (SO2) at some time during its atmospheric lifetime. Since SO 2 is a primary component of the atmospheric sulfur cycle, quality measurements of this gas are important to understanding the cycling of sulfur through the atmosphere. The mixing ratio of SO2 in the atmosphere can be as low as a few 10's of parts-per-trillion by volume (pptv) in unpolluted areas and as high as 100's of parts-per-billion by volume (ppbv) near industrial centers. Obtaining SO2 measurements with mixing ratios that can differ by 105 in magnitude is a difficult task, especially for mixing ratios less than a few hundred pptv. The Diffusion Denuder/Sulfur Chemiluminescence Detector (DD/SCD) was developed further and tested in a rigorously blind comparison under controlled laboratory conditions. The DD/SCD exhibited excellent sensitivity and little-to-no interference from other trace gases. The DD/SCD performance was comparable to that of other state-of-the-art instruments developed for measuring SO 2 in the remote atmosphere. The Continuous SO2 Detector was developed to overcome the limitation of long sampling times (4 to 90 minutes) inherent in the DD/SCD and other state-of-the-art techniques. The Continuous SO2 Detector (CSD) was developed based on the design of the DD/SCD, but has been optimized for sensitive, high-time resolved measurements of SO2 in air. Sensitive, high-time resolved measurements would be beneficial for studying atmospheric SO2 over large geographical areas from a moving sampling platform such as an aircraft. The current prototype of the CSD is capable of measuring SO2 at mixing ratios of less than 100 pptv on the order of seconds. The DD/SCD, CSD and an automated, computer controlled dynamic dilution system described in this thesis represent a suite of instruments for the measurement of SO2 in the remote atmosphere.
• Investigations into model systems of neurodegeneration: Organotypic brain slice culture and in vivo microdialysis

The mechanisms behind neurodegeneration in disease and injury have yet to be fully defined. Many in vitro and in vivo model systems, have been developed to investigate the mechanisms of neurotoxicity and its relation to human disease and injury. There are a few resounding connections between most types of neurological disorder; namely oxidative stress and inflammation. The glutamate receptor agonist, N-methyl-D-aspartate, can be used to imitate excitotoxicity during stroke as it overstimulates the glutamate receptor, leading to rises in intracellular calcium levels, which in turn lead to oxidative stress within the cell. Amyloid-beta protein (Abeta) a useful in many of its isoforms in creating in vitro model systems of Alzheimer's disease (AD). Abeta can directly cause the production of potentially harmful free radicals. This study investigates the formation of model systems of neurodegeneration: in vivo microdialysis and organotypic brain slices culture in order to assess the role of oxidative stress and inflammation morphologically and biochemically. The effect of melatonin, an endogenous antioxident, on oxidative stress associated with NMDA and Abeta neurotoxicity was determined through morphological analysis and biochemical markers of oxidative stress. This study reports that both NMDA and Abeta(25--35) cause oxidative stress in an organotypic brain slice culture model system of stroke and Alzheimer's disease as established by: (1) morphological analysis of tissue and ultrastructure, (2) redox-active assay, (3) heme-oxygenase assay, (4) 8-hydroxyguanosine assay and (5) interleukin IL-1beta and IL-6 assay (Abeta only) These investigations also demonstrate that melatonin can attenuate the oxidative stress associated with NMDA and Abeta exposure. These findings expand upon previous evidence from cell culture analysis of oxidative stress induced by NMDA and Abeta. Therefore, this evidence supports the theory that oxidative stress is involved in neurodegeneration in both excitotoxicity in stroke and in Abeta-mediated damage in Alzheimer's disease, and that endogenous antioxidant treatment may be a useful therapeutic approach in such injury and disease.
• A toxicity assessment of total dissolved solid ions in mine effluent using two common bioassays: the 22-hour MicroTox assay and a S. carpricornutum growth assay

This research evaluated two microassays and a synthetic TDS standard to measure the effects of elevated TDS from mine effluent on biota of freshwater systems. Field samples from Red Dog and Fort Knox mines were tested on Selenastrum capricornutum and the MicroTox assay, and compared to the synthetic standard. Results indicate that the synthetic TDS standard is a poor representation of produced waters with similar total TDS concentrations. Additionally, no correlation was found between the toxicological responses of the two assays. Principle component analysis found the MicroTox assay to be most sensitive to cadmium and chloride. At concentrations present in the field samples, there does not appear to be a relationship between toxicity and TDS as measured on these assays.
• Distribution of hexachlorobenzene concentrations in spruce needle samples across Alaska

The global distribution of persistent organic pollutants has initiated considerable effort towards understanding long range atmospheric transport and partitioning of these potentially damaging compounds. Apparent latitude dependent concentration gradients of organic pollutants in otherwise pristine environments has given rise to a global fractionation model, coined the cold finger effect. According to the cold finger theory, semi-volatile persistent organic pollutant will show a preference for partitioning from the atmosphere to the ground and vegetation at northern latitudes. Here we present a study of hexachlorobenzene in spruce needle samples across Alaska, which offers a large range of climates, from its southern coastal rain forests to the northern arctic. The large variation in climate across Alaska should result in a measurable latitude dependent concentration gradient for HCB, if the cold finger effect is being realized. Spruce needle samples were extracted, cleaned, and analyzed by GC/MS. According to principle component regression analysis, HCB concentrations in all the spruce needle samples across Alaska show a strong positive correlation with lipid content of the needles. The HCB concentrations also show two distinct latitude trends. The spruce needle samples taken from the coast to approximately 63° north show relatively high HCB concentrations and a possible negative correlation with latitude. The samples between 63° and 68° north show a definite positive correlation between HCB concentration and latitude, which is consistent with the cold finger effect.
• Benzene as an indoor air pollutant in Fairbanks, Alaska

Benzene is a known carcinogen found in gasoline, automobile exhaust, cigarette smoke, and organic solvents. Previous studies suggest that sources of chemicals within the home are the major factors influencing personal exposure to benzene. Indoor air was sampled for benzene in order to determine the concentrations present in Fairbanks homes, and to indentify what factors might be associated with higher concentrations. Sampling sites were limited to homes with attached garages and with no smokers in the household. A wide range of benzene concentrations was observed in the eight homes sampled. The highest concentration was about 70 ppbv, and the concentration in most homes was at or above 4 ppbv. The primary source of benzene appears to be gasoline, most likely from small engines (such as lawnmowers) stored in the attached garage. More sites, including homes with attached garages that contain various numbers of small engines, need to be sampled to confirm these conclusions.
• Nitrogen oxide photochemistry in marine air over the eastern Pacific

Models predict that photochemistry is the primary contribution to the observed spring surface ozone maxima in the Northern Hemisphere. Nitrogen oxides (NOx) are the limiting reagents for photochemical ozone production. This fact leads to an apparent paradox, because the short lifetime of NOx should lead to a low mixing ratio of NOx far from source regions. However, chemical reservoirs of NOx such as peroxyacetyl nitrate (PAN) may provide a transport pathway for delivering NOx to 'clean' marine Pacific air masses. A coastal site in Washington, was chosen to investigate the relationship of NOx, PAN and ozone in marine air from the Pacific during two consecutive spring campaigns in 1997 and 1998. In this work, we develop a simple PAN decomposition model and comparie the modeled to the measured PAN mixing ratios. We estimate ozone formation using the deviation in the measured NO to NO₂ ratio, from the Leighton cycle.
• Phytochemistry and chemosystematics of Artemisia arctica in Alaska

Artemisia L. (Asteraceae - Anthemideae) is a large and taxonomically complex genus occurring widely throughout the northern hemisphere. Chemical investigations in this genus have mainly been stimulated by the economic and/or medicinal importance of many of its members. This chemical knowledge has also provided useful criteria for resolving systematic uncertainties within the genus. Alaskan Artemisia species are little known chemically despite their historic and contemporary medicinal use. Therefore, an investigation of the chemistry of Alaskan Artemisia arctica was initiated with the dual purpose of searching for structurally novel and/or biologically active compounds and contributing additional criteria for systematic studies of this taxon. Collections of A. arctica from four different geographic locations in Alaska were analyzed for chemical characters and biological activity. The roots and leaves afforded one novel acetylenic isocoumarin, in addition to several known acetylenic and non-acetylenic compounds. The biological and systematic significance of these results are discussed.
• Development of a Fe Boltzmann temperature lidar

An iron Boltzmann temperature lidar allows the measurement of temperatures and iron densities in the mesopause region (8̃0-100 km). This thesis describes the initial development of a new Boltzmann temperature lidar at Poker Flat Research Range. An excimer-pumped dye laser system was installed in April 1999. During 1999 and 2000 this system was calibrated against the resident sodium system. Observations of iron were made in the winter of 2000 and spring 2001. Temperature measurements were made in December of 2000. The thesis presents an operational analysis of the lidar system performance and a scientific analysis of the data obtained. the midwinter temperature measurements indicate the mesopause is above the mesospheric iron layer at this high-latitude site. The new lidar is an important development as it can be combined with Rayleigh lidar measurements to provide direct temperature profile soundings over the 30 to 90 km altitude range.
• Neuroprotection in the hibernating brain: tissue trauma and glutamate studied by microdialysis

Hibernation, a natural model of tolerance to 'cerebral ischemia', represents a state of pronounced fluctuation in cerebral blood flow where no brain damage occurs. This study systematically investigates the brain tissue response of hibernating and euthermic arctic ground squirrels to CNS trauma, modeled by insertion of microdialysis probes. The effect of glutamate, an excitatory amino acid neurotransmitter, on the cellular response and the origin of the significant amount of gltuamate were determined by quantitative microdialysis study. The present results indicate in euthermic brain tissue a typical inflammatory tissue response evidenced by the presence of activated microglia and astrocytes and the oxidative stress response. However, this response was profoundly suppressed in hibernating animals. Importantly, the progressive increase in [glu]dia is not necessarily associated with the enhanced tissue response observed in euthermic animals and could be avoided by using sterile microdialysis technique, which suggests a microbial origin of glutamate.
• Assessment of total mercury and methyl mercury in selected subsistence fish in Western Alaska

Total Hg (THg) and methylmercury (MeHg) were examined in muscle and liver samples of salmon species (Chinook: Oncorhynchus tshawytscha; Chum: O. keta; Sockeye: O. nerka; Coho: O. kisutch) and freshwater fish species (Pike: Esox lucius; Grayling: Thymallus arcticus; Whitefish: Caregonus nelsoni) collected in 1999 and 2000 from the Western Alaska rivers (Yukon, Kuskokwim, Nushagak and Kvichak). The THg in salmon muscles has a mean value of 62 ng/g (ww). In Pike muscles, THg has a mean value of 879 ng/g. The mean concentrations of THg in Grayling and Whitefish muscle are 153 ng/g and 32 ng/g respectively. In salmon muscle and liver the MeHg levels constitute 77% and 62% of the THg levels, respectively. In Pike muscle the MeHg levels constitute 100% of the THg levels. A significant correlation between Hg levels and fish length was found. Calculated consumption limits indicate that children may consume 0.05-1.5 kg of fish per month, depending on the species consumed. The study suggests that, from 1979 to 1998, nearly 21 kg of MeHg was transported by Sockeye salmon to the Alaskan rivers of the Bering Sea east coast.
• The origin and composition of aerosols in the Alaskan airshed

Since the Alaskan airshed north of the Alaska Range receives a substantial portion of its anthropogenic aerosol and gaseous pollutants through long-range transport, Alaskan air quality is influenced to an unusually high degree by the political and economic events of other countries. An understanding of the political and economic forces at work in the various circumpolar nations is key to an understanding of the observed decline in Arctic haze, the present state of Arctic air pollution, and likely future developments. It is shown in this thesis that Arctic haze has declined in Interior Alaska over the last decade and a half. This decline appears to be driven by the widespread emission reductions which have occurred in North America, Europe, and the former Soviet Union (FSU) between 1988 and 1998. If true, this linkage indicates that the story of Arctic haze is not yet a post-mortem. EMEP projections for 2005 foresee a continuing decline in emissions across Europe and a leveling off in North America, but emissions in the European FSU are expected to double by 2005. Events in the FSU, and perhaps Asia as well, threaten to abrogate any further progress made by Europe and North America and could perhaps revive the phenomenon.
• Phytochemical investigation of Colophospermum mopane

A previously partially-characterized diterpene alcohol was isolated from Colophospermum mopane, and its structure completely elucidated. A second novel diterpene alcohol, structurally related to the first, was also fully characterized by NMR spectroscopy. A proposed precursor of the diterpenes, a mixed pair of diterpene aldehydes, was isolated, and upon reduction yielded a mixture of both diterpene alcohols. These diterpenes represent important 'missing' links in the biogenesis of 9,13-epoxylabdanes. Seeds of C. mopane were grown in greenhouse conditions to determine when these diterpenes were produced. Two sesquiterpenes and two diterpenes were quantified by GC-MS. Seedlings grown from seeds rinsed in hexane grew faster and produced terpenoids sooner than the control group. It is likely that C. mopane seeds have terpenoids present in concentrations high enough to minimize competition from herbaceous perennials, at the cost of some degree of auto-toxicity, so rinsing promotes growth and terpenoid production.
• The synthesis of single-isomer cyclodextrins for the enantiomeric separation of sulfoxides and sulfoximines

Chiral sulfoxides belong to the class of chiral organosulfur compounds that are widely used in asymmetric synthesis. Their application as chiral synthons has become a well established and reliable strategy. This is mainly due to their availability and high asymmetric induction exerted by the chiral sulfinyl group. Equally important in making effective use of these reagents is the ability to efficiently separate these compounds and to be able to determine the enantiomeric excess of one enantiomer over the other. In this research effort, the investigator proposes the synthesis of single isomer cyclodextrins in order to develop an effective method to determine enantiomeric excess in mixtures of sulfoxide and sulfoximine enantiomers. These single-isomer cyclodextrins are employed as chiral resolving agents in capillary electrophoresis for the enantiomeric separation of chiral sulfoxide derivatives.
• The application of cavity ring-down spectroscopy to determine nitrate radical concentrations in the atmosphere

The nitrate radical, NO₃, is a potent atmospheric oxidant. Current NO₃ measurement methods average NO₃ concentrations over several kilometer pathlengths. Recent modeling studies predict that NO₃'s distribution is vertically inhomogenous, causing previous NO₃ observations to not be representative of its atmospheric chemistry. In-situ measurements offer a test of these modeling predictions and a better understanding of NO₃ chemistry. In this thesis, we describe construction of an instrument capable of detecting NO₃ in-situ. This sensor is based upon cavity ring-down spectroscopy. Our initial work demonstrated that CRDS could sensitively detect NO₃. We then built and tested a field prototype during June 2001, successfully detecting NO₃ in the field. CRDS observations were compared to path averaged NO₃ observations. Similar time behavior of both signals indicated that the techniques were observing NO₃. A consistent difference in signal levels indicated that the two techniques were not sampling a homogeneous air mass.