Peter J. Milne

Measurement of vertical distribution of isoprene in surface seawater, its chemical fate, and its emission from several phytoplankton monocultures

Abstract Concurrent measurements of isoprene (2-methyl-1,3-butadiene) in seawater together with atmospheric concentrations in the Gulf Stream off the Florida coast were made. Florida Straits surface water concentrations of isoprene varied between 9.8 and 50.8 pmol 1 −1 . Surface water isoprene concentrations showed a positive correlation with measured chlorophyll fluorescence, consistent with the biogenic origin of this non-methane hydrocarbon. Depth profiles showed a maximum in isoprene concentration similar to that of biological productivity as indicated by chlorophyll fluorescence. Daytime atmospheric mixing ratios of isoprene were never above 11 parts-per-trillion (pptv) and eight of eleven samples taken were below the ~ 5 pptv detection limit. Using an estimated value of the Henrys law constant ( K H ~ 3.1) a supersaturation of surface seawater of 2 to 3 orders of magnitude is estimated. Laboratory grown monocultures of several common phytoplankton species showed production of isoprene. Processes controlling the isoprene concentration in the photic zone of the ocean and the marine boundary layer are discussed. A calculation using a simple time dependent photochemical box model confirmed that isoprene is rapidly consumed by its reaction with the OH radical in the marine atmosphere.

Observations of nonmethane hydrocarbons and oxygenated volatile organic compounds at a rural site in the southeastern United States

Measurements of an extensive range of nonmethane hydrocarbons (NMHCs) including alkanes, alkenes, and aromatics, and oxygenated volatile organic compounds (OVOCs) including alcohols, ketones, and aldehydes were conducted for several weeks during the summer of 1995 as part of the Southern Oxidants Study (SOS) at a rural experimental site (Youth, Inc.) 32 km southeast of Nashville, Tennessee, in the southeastern United States. These measurements were conducted to (1) determine the absolute magnitude and variability of oxygenated compounds found in a contemporary rural region; (2) assess the importance of the measured ambient levels of OVOCs on a photochemical reactivity basis relative to the more commonly determined NMHCs; and (3) to evaluate our ability to accurately measure oxygenates by the current techniques employed under a field study scenario. Several other physical (temperature, insolation, etc.), meteorological (wind velocity, wind direction, atmospheric structure, and boundary layer height), and chemical (criterion pollutants, NOx, SO2, CO, O3, etc.) parameters were measured concurrently with the NMHC and OVOC measurements. During the study period, OVOCs were consistently the dominant compounds present, and methanol and acetone had the highest mixing ratios. Although OVOCs made up the majority of the volatile organic compound component on a mass basis, a substantial sink for OH was isoprene and its immediate oxidation products, methacrolein and methyl vinyl ketone. In combination with CO and formaldehyde, these compounds comprised about 85% of the observed OH reactivity at the site. Acetaldehyde and methanol were responsible for an additional 10%, with the NMHCs and remaining OVOCs making up the final 5% of the measured OH reactivity at the site. These observed patterns reinforce recent studies which find OVOCs to be an important component of the rural troposphere.

Extraction of chromophoric humic substances from seawater

Chromophoric humic substances were extracted from seawater using hydrophobic solid-phase extraction, ultrafiltration, and a hydrophobic macroreticular resin (XAD-2). Four criteria were used to evaluate the efficiency of extraction: (1) UV-visible absorbance, (2) dissolved organic matter fluorescence, (3) capacity for photoproduction of H2O2, and (4) retention of total organic carbon. Extraction efficiencies for solid-phase media followed the order C18 > C8 > cyclohexyl (CH) > phenyl (PH)=C2. The extent of removal of humic substances from seawater decreased between 70 and 40% with volume extracted and varied with the source of water. Using our criteria, extraction of humic substances with C18 solid phase was between 22 and 84% more effective than with XAD-2. Concentration of humic substances by ultrafiltration was more efficient with membranes of molecular weight cut-off values of 500 than 5000. C18 solid-phase extraction of humic substances was as effective as ultrafiltration. Seawater reconstituted with humic substances extracted by C18 solid-phase extraction and by ultrafiltration had properties that were between 90 and 101% of those of the original water samples. Our results indicate that extraction of humic substances from seawater is most conveniently achieved by using C18 solid-phase extraction. A scaled-up version of this procedure has been used for the extraction of chromophoric humic substances from large volumes (1001) of coastal and open-ocean water.

The ionization of boric acid in NaCl, NaCaCl and NaMgCl solutions at 25°C

Abstract The stoichiometric pK ★ for the ionization of boric acid has been determined from emf measurements in pure NaCl solution and in NaCl solution with small amounts of added CaCl2 and MgCl2 from I = 0.5 to 6.0 molal at 25°C. Our results in NaCl media at low concentrations are in good agreement (±0.01 pK units) with the results of Owen and King (1943). From the values of the pK★ we have determined the Pitzer parameters β 0 , β 1 and Co for the interactions of Ca2+ and Mg2+ with B(OH)4−. Ion pairing constants for the interaction of borate ion with Ca2+ and Mg2+ were also determined from I = 0.5 to 6 m and values were extrapolated to pure water. These interactions are weak and the pK s in water and in NaCl solution are in reasonable agreement with values of other workers. Pitzer terms (β[MA]Cl0) for the interaction of [MA] ion pairs with Cl− were also determined. The pK HA ★ data can be fitted within experimental error with one less parameter using the combined ion pairing/Pitzer approach than when using the Pitzer formalism alone. We, thus, favor the combined approach for calculating the ionic interactions in these solutions.

Amino acid nitrogen in atmospheric aerosols: occurrence, sources and photochemical modification

The presence of amino acids in atmospheric precipitation and aerosols has been noted for many years, yet relatively little is known about these or other nitrogen containing organic compounds in the atmosphere. Marine and continental rainwater analyses indicate that atmospheric aerosols, and subsequently atmospheric precipitation, may contain substantial levels of free and combined amino acids. The most likely source of amino N in the remote marine atmosphere appears to be the injection of proteinaceous material through the action of bursting bubbles at the sea-air interface or the long range transport from terrestrial sources. The capacity of these substrates to undergo photooxidation and photodegradation in the atmosphere to simpler species, such as ammonium ions, carboxylic acids, and for the S containing amino acids, oxidized forms of sulfur, has received little attention from atmospheric chemists. The photochemistry of covalently bound amino groups, particularly as found in peptides and amino acids, is discussed here with the purpose of summarizing what is known of their occurrence and their possible importance to atmospheric chemistry.

Interstitial laser hyperthermia model development for minimally invasive therapy of breast carcinoma.

BACKGROUND This investigation describes the preclinical development of a laser fiberoptic interstitial delivery system for the thermal destruction of small breast cancers. We propose adaptation of this technology to stereotactic mammographic instrumentation currently employed for diagnostic core biopsy to thermally ablate a site of disease with maximal treatment efficacy, minimal observable superficial change, reduced patient trauma, and lowered overall treatment costs. STUDY DESIGN Laser hyperthermia is a clinical modality that seeks to achieve tumor destruction through controlled tissue heating. The advantage of laser-induced hyperthermia over traditionally used heat sources such as ultrasound, microwave, or radiowave radiation lies in the ability to focus heat localization to the specific tumor tissue site. Neodymium:yttrium aluminum garnet (Nd:YAG) laser light transmitted through a fiberoptic cable to a diffusing quartz tip can induce such temperature increases leading to localized tissue destruction. Because breast cancer occurs with greatest frequency in the mature woman whose breast tissue has undergone glandular involution with fatty replacement, this study concentrates on determining the resultant laser energy heat distribution within fat and fibrofatty tissue. This investigation studied the time-temperature responses of ex vivo human breast and porcine fibrofatty tissue, which led to an in vivo subcutaneous porcine model for the practical demonstration of a laser hyperthermia treatment of small volumes of porcine mammary chain tissue. RESULTS Spatial recordings of the resultant temperature fields through time exhibited similar, reproducible thermal profiles in both ex vivo human breast and subcutaneous porcine fat. In vivo laser-produced temperature fields in porcine subcutaneous fat were comparable to those in the ex vivo analyses, and showed a histologically, sharply defined, and controllable volume of necrosis with no injury to adjacent tissues or to overlying skin. CONCLUSIONS Interstitially placed, fiberoptically delivered Nd:YAG laser energy is capable of controlled tissue denaturation to a defined volume for the treatment of small breast cancers. It is hoped that this minimally invasive approach, with further investigation and refinement, may lead to the effective treatment of small, well-defined breast cancers that are commonly diagnosed through stereographic mammography and stereotactic core biopsy. The juxtaposition of such a localized treatment modality with these increasingly used diagnostic tools is of considerable promise.

Mississippi River flood waters that reached the Gulf Stream

Distributions of physical, biological, and chemical parameters in florida Keys coastal waters seaward of the reef track were surveyed on September 9 to 13, 1993, as part of a coordinated multidisciplinary study of surface transport processes. A band of low-salinity water was observed along the shoreward side of the florida Current over the downstream extent of the survey from Miami to Key West. Biological and chemical indicators within the band, together with its large volume, satellite imagery, and a surface drifter trajectory suggested the recent Mississippi River flood as the source.

In Situ temperature measurements with thermocouple probes during laser interstitial thermotherapy (LITT): Quantification and correction of a measurement artifact

Background and Objective: The purpose of this work was to quantify the magnitude of an artifact induced by stainless steel thermocouple probes in temperature measurements made in situ during experimental laser interstitial thermo‐therapy (LITT). A procedure for correction of this observational error is outlined.

Photoproduction of nonmethane hydrocarbons (NMHCs) in seawater

Abstract Nonmethane hydrocarbons (NMHCs) are emitted into the atmosphere from the oceans surface. Although the oceanic contribution to the global NMHC budget is considered minor relative to other sources, it is one of the least well measured or understood. The major compounds emitted are a series of C2–C4 alkenes. Due to their ubiquitous presence in seawater, their high reactivity in the atmosphere, and the important role they play in the atmospheric chemistry in remote regions of the globe, the processes responsible for their formation and fate warrant examination. To ascertain the role of photoprocesses in NMHC formation in surface waters, laboratory experiments were conducted to determine the magnitude and wavelength dependence of NMHC photoproduction for a range of water types. Photochemical transformation of dissolved organic matter (DOM) present in surface seawater results in the production of the C2–C4 alkenes in the surface ocean with the UV portion (295–340 nm) of the solar spectrum controlling the bulk of this production. Under summer sunlight intensities in Miami, FL, net photoproduction rates for ethene, the dominant photoproduced NMHC in surface seawater, varied from 0.220 pmol l−1 min−1 for transparent oligotrophic waters to 6.11 pmol l−1 min−1 for highly colored estuarine waters. Apparent quantum yields of photoproduction varied from 10−9 to 10−7 depending on water type, wavelength of light and individual compound.

The solubility of calcite, strontianite and witherite in NaCl solutions at 25°C

Abstract The solubility of CaCO 3 (calcite), SiCO 3 (strontianite), and BaCO 3 (witherite) has been determined in NaCl solutions from 0.1 to 6 m at 25°C. Activity coefficients estimated from Pitzers equations with higher order interaction terms (θ and Ψ) were used to extrapolate the results to infinite dilution. Thermodynamic values of pK sp = 8.46 ± 0.03,9.13 ± 0.03 and 8.56 ± 0.04 were found, respectively, for CaCO 3 , SrCO 3 and BaCO 3 at 25°C. These results are in reasonable agreement with literature data. Since Pitzer parameters for the interactions of CO 3 2− with Ca 2+ , Sr 2+ and Ba 2+ were not used, our results indicate that they are not necessary at low values of P co2 .