Chemical variability in the Sacramento River and in Northern San Francisco Bay

Specific conductance and concentrations of alkalinity, dissolved silica, nitrate, and ammonium were measured daily in the Sacramento River flow to northern San Francisco Bay during the rainfall seasons of 1983 and 1984 (high flow) and during late summer and early fall of 1984 (low flow). Flow and concentrations of chemical species varied in response to storm events during high flow, but flow was more variable than concentrations of chemical species. Runoff from agriculturally developed areas appeared to increase specific conductance and concentrations of alkalinity during high flow. During low flow, inputs of agricultural tailwaters caused variations in concentrations of alkalinity and dissolved silica. Dilution of municipal waste by river flow caused variability in concentrations of ammonium during both high flow and low flow. Distributions of alkalinity, dissolved silica, nitrate, and ammonium were measured in northern San Francisco Bay during late summer and fall of 1984. Changes in distributions of alkalinity in the estuary were caused by variations in alkalinity in the Sacramento River. Changes in distributions of dissolved silica, nitrate, and ammonium appeared to be primarily related to variations in supply by the river and removal by phytoplankton. Effects of removal by phytoplankton were large for ammonium and dissolved silica, but appeared relatively small for nitrate.     

Contact metamorphism/hydrothermal alteration of Tertiary basalts from the Isle of Skye,northwest Scotland

Alkali olivine basalts from Skye were simultaneously contact metamorphosed by Tertiary gabbro and granite intrusions and altered by the hydrothermal convection system that the plutons induced. Four metamorphic zones were mapped around the plutons. Furthest from the intrusions, in the primary olivine zone, metabasalts are composed of combinations of igneous olivine, augite, plagioclase, titaniferous magnetite, ilmenite, zeolites, gyrolite, sulfides, and chlorite-smectite intergrowths. Closer to the plutons, in the smectite zone, saponite and carbonate appear, primary olivine and gyrolite disappear, and zeolites decrease dramatically in abundance. Still closer to the plutons, in the amphibole zone, actinolite, edenite, chlorite, sphene, epidote, andradite, and quartz appear and saponite and chlorite-smectite intergrowths disappear. Along parts of the contact between gabbro and basalt, in the orthopyroxeneolivine zone, orthopyroxene, metamorphic olivine, and biotite appear and amphibole, chlorite, sphene, epidote, andradite, carbonate, and quartz disappear. Whole-rock chemical data indicate only minor change in the major-element chemical composition of the metabasalts during progressive metamorphism/hydrothermal alteration. Two-pyroxene eothermometry and various mineral-fluid equilibria suggest the range of peak temperatures attained in the metamorphic zones: orthopyroxene-olivine zone, 900°1, 030° C; amphibole zone, 400°–900° C; smectite and primary olivine zones, < 400° C. Mineralogical and oxygen isotopic alteration of the metabasalts were closely coupled: Basalts from the primary olivine zone with nearly unaltered igneous mineralogies have normal or near-normal wholerock ¹⁸O>+5 (SMOW); mineralogically more altered basalts from the smectite zone have whole-rock ¹⁸O=+2 to +5; still more mineralogically altered basalts from the amphibole zone (with one exception) have ¹⁸O<+ 2; completely recrystallized hornfelses from the orthopyroxene-olivine zone have ¹⁸O<0. The principal mechanism of isotope exchange between basalt and metamorphic/ hydrothermal fluid probably was heterogeneous mineralfluid reaction.Metabasalts from the orthopyroxene-olivine zone are mineralogically fresh pyroxene hornfelses that record crystallization temperatures > 1,000° C yet have highly altered whole-rock oxygen isotope compositions, ¹⁸O<0%. The hornfelses chemically interacted with metamorphic/hydrothermal fluids either at very high temperatures or while they were heated to > 1,000° C or both. Their mineralogy, however, rules out significant water-rock interaction after they cooled below 900° C. Hydrothermal convection on Skye was a two-stage process: (a) fluid flow through wall rocks initially was pervasive while they are heated; (b) fluid flow after the thermal peak in the wall rocks was sufficiently channelized that rocks such as those in the orthopyroxeneolivine zone were isolated from further fluid-rock interaction during all or almost all of the cooling history of the hydrothermal system.     

The case for a martian origin of the shergottites: nitrogen and noble gases in EETA 79001

Nitrogen and noble gases were measured in samples of a glass inclusion and the surrounding basaltic matrix from the antarctic shergottite EETA 79001. A nitrogen component trapped in the glass, but not present in the matrix, has a δ¹⁵N value at least as high as +190‰. Ratios of⁴⁰Ar/¹⁴N and¹⁵N/¹⁴N in the glass are consistent with dilution of a martian atmospheric component (δ¹⁵N = 620 ± 160‰,⁴⁰Ar/¹⁴N= 0.33 ± 0.03) by either terrestrial atmosphere adsorbed on the samples or by indigenous nitrogen from the minerals of the rock. Trapped noble gases in the glass reproduce, within error, the elemental and isotopic compositions measured in Mars' atmosphere by Viking, and are in general agreement with previous measurements except for much lower abundances of neutron-generated krypton and xenon isotopes. The most reasonable explanation at the present time for the noble gas pattern and the isotopically heavy nitrogen is that a sample of martian atmosphere has been trapped in the EETA 79001 glass, and that this meteorite, and thus the shergottites and probably the nakhlites and chassignites as well, originated on Mars.Nitrogen in the non-glassy matrix of EETA 79001 amounts to less than 0.5 ppm and has a spallation-corrected δ¹⁵N value in the range 0 to ?20‰; it may reflect indigenous nitrogen in the basalt or a mixture of indigenous and adsorbed terrestrial nitrogen. Spallogenic noble gases yield single-stage exposure ages between 400,000 and 900,000 years, depending on irradiation geometry. Trapped argon may have an unusually low³⁶Ar/³⁸Ar ratio. Trapped krypton, except for a small excess at⁸⁰Kr, is smoothly mass-fractionated with respect to either terrestrial or chondritic Kr. The trapped xenon composition is consistent with addition of neutron-capture, radiogenic and fissiogenic isotopes to a base composition resembling terrestrial atmospheric Xe. The elemental⁸⁴Kr/¹³²Xe ratio of 25 is close to the terrestrial value and very different from the chondritic ratio.     

An FTIR product study of the photooxidation of dimethyl disulfide

The products of the 254 nm photolysis of ppm levels of DMDS have been studied as a function of the O₂ partial pressure at 760 Torr (N₂ + O₂) and 298±2 K. The major sulfur containing compounds detected were SO₂ and CH₃SO₃H (methane sulfonic acid, MSA) and the major carbon containing compounds were CO, HCHO, CH₃OH and CH₃OOH (methyl hydroperoxide). Within the experimental error limits the observed sulfur and carbon balances were approximately 100%. CH₃OOH has been observed for the first time in such a photooxidation system. Its observation provides evidence for the formation of CH₃ radicals by the further oxidation of the CH₃S radicals formed in the primary photolysis step.From the behavior of the DMDS photolysis products as a function of the O₂ partial pressure, O₃ concentration and added OH radical source it is postulated that the further reactions of CH₃SOH (methyl sulfenic acid), formed in the reaction OH + CH₃SCCH₃ CH₃SOH + CH₃S, are the main source of MSA in the 254 nm photolysis of DMDS.Some of the possible implications of the results of this study for the degradation mechanisms of other atmospherically important organic sulfur compounds, in particular DMS, are briefly considered.     

Near UV absorption spectra and photolysis products of difunctional organic nitrates: Possible importance as NO x reservoirs

Difunctional organic nitrates are important products of the atmospheric reaction of NO₃ radicals with unsaturated hydrocarbons about which relatively little is known. In a continuation of the investigation of the atmospheric chemistry of such compounds, the UV absorption spectra of the following organic dinitrates and keto nitrates have been quantitively measured in the gas phase at 298±2 K and atmospheric pressure: 1,2-propandiol dinitrate, CH₃CH(ONO₂)CH₂(ONO₂); 1,2-butandiol dinitrate, CH₃CH₂CH(ONO₂)CH₂(ONO₂); 2,3-butandiol dinitrate, CH₃CH(ONO₂)CH(ONO₂)CH₃;cis 1,4-dinitrooxy-2-butene, CH₂(ONO₂)CH=CHCH₂(ONO₂); 3,4-dinitrooxy-1-butene, CH₂(ONO₂CH(ONO₂)CH=CH₂; -nitrooxy acetone, CH₃COCH₂(ONO₂); 1-nitrooxy-2-butanone, CH₃CH₂COCH₂(ONO₂); 3-nitrooxy-2-butanone, CH₃CH(ONO₂)COCH₃.Although the UV spectra of the nitrates are all very similar in shape those of the keto nitrates are red-shifted compared to the dinitrates and in the spectral range of atmospheric interest (>290 nm) their absorption cross-sections are approximately a factor of 5 higher. The cross-sections of the dinitrates are a factor of 2 higher than those reported in the literature for the corresponding alkyl mononitrates.The UV absorption cross-sections of the difunctional nitrates were used in combination with solar actinic flux data to estimate photolysis frequencies and consequently atmospheric lifetimes for these compounds. The results indicate that for the saturated difunctional nitrates studied in this work photolysis will generally be somewhat some important than reaction with OH radicals as an atmospheric removal process. However, for unsaturated nitrates loss due to reaction with OH will dominate over photolysis as an atmospheric sink.Preliminary FT-IR analyses of the photolysis products of -nitrooxy acetone, 3-nitrooxy-2-butanone and 2,3-butandiol dinitrate using both mercury and fluorescent lamps indicate that NO₂ is released in the primary step. The further reactions of the radicals thus produced result in the formation of CO, aldehydes and PAN. The possible significance of the results for difunctional organic nitrate as reservoirs for reactive odd nitrogen NO _y in the atmosphere, especially during the night, is briefly discussed.     

Verification of the Contribution of Vehicular Traffic to the Total NMVOC Emissions in Germany and the Importance of the NO3 Chemistry in the City Air

In 1997 and 1998 several field campaigns for monitoring non-methane volatile organic compounds (NMVOCs) and nitrogen oxides (NO_x) were carried out in a road traffic tunnel and in the city center of Wuppertal, Germany. C₂–C₁₀ aliphatic and aromatic hydrocarbons were monitored using a compact GC instrument. DOAS White and long path systems were used to measure aromatic hydrocarbons and oxygenated aromatic compounds. A formaldehyde monitor was used to measure formaldehyde. Chemiluminescence NO analysers with NO₂ converter were used for measuring NO and NO₂. The high mixing ratios of the NMVOCs observed in the road traffic tunnel, especially 2.9 ppbv phenol, 1.5ppbv para-cresol and 4.4 ppbv benzaldehyde, in comparison with themeasured background concentration clearly indicate that these compounds were directly emitted from road traffic. Para-Cresol was for the first timeselectively detected as primary pollutant from traffic. From the measured data a NMVOC profile of the tunnel air and the city air, normalised to benzene (ppbC/ppbC), was derived. For most compounds the observed city air NMVOC profile is almost identical with that obtained in the traffic tunnel. Since benzene originates mainly from road traffic emission, the comparison of the normalised emission ratios indicate that the road traffic emissions in Wuppertal have still the largest impact on the city air composition, which is in contrast to the German emission inventory. In both NMVOC profiles, aromatic compounds have remarkably large contributions of more than 40 ppbC%. In addtion, total NMVOC/NO_x ratios from 0.6 up to 3.0ppbC/ppb in the traffic tunnel air and 3.4± 0.5 in the city air of Wuppertal were obtained. From the observed para-cresol/toluene and ortho-cresol/toluene ratios in the city air, evidence was found thatalso during daytime NO₃ radical reactions play an important role in urban air.     

Reconstruction of urban stormwater contamination of an estuary using catchment history and sediment profile dating

Cores were collected from the length of Pakuranga estuary, a small urban estuary in Auckland, New Zealand, to determine sedimentation and contaminant history, and in particular the impact of urbanization. Catchment sediment loads for the most recent history (1953–1995), including urbanization since 1960, were reconstructed using the landcover history and soil erosion modeling. Pollen and¹⁴C dating and pre-urban landcover history were used to reconstruct early estuary sedimentation (i.e., post-3000 yr BP to 1960). Heavy metal concentrations, particle size,¹³⁷Cs, pollen, and catchment sediment loads were all needed to disentangle the complex estuarine response to urbanization.¹³⁷Cs profiles did not reflect the historical fallout pattern, but deposition of¹³⁷Cs-labelled eroded catchment soil, coinciding with peaks in urban construction. Temporal variations in stormwater¹³⁷Cs concentrations are likely due to varying contributions from¹³⁷Cs-rich topsoil and¹³⁷Cs-poor subsoils. A similar pattern was observed in heavy-metal concentrations and attributed to street runoff rather than topsoil being diluted by metal-poor subsoils. Dating of the sediment profiles showed that during urbanization sedimentation rates in the tidal creek and estuary were higher than sedimentation rates associated with past agricultural landuse and the original forest landcover. Urbanization has brought about substantial environmental changes in the upper estuary through continued infilling of shallow, intertidal areas, contamination by heavy metals to levels of ecological concern, sediment textural changes, and rapid mangrove colonization of formerly bare intertidal sediments.