William D. Long

Hydration Rate of Obsidian

The hydration rates of 12 obsidian samples of different chemical compositions were measured at temperatures from 95� to 245�C. An expression relating hydration rate to temperature was derived for each sample. The SiO2 content and refractive index are related to the hydration rate, as are the CaO, MgO, and original water contents. With this information it is possible to calculate the hydration rate of a sample from its silica content, refractive index, or chemical index and a knowledge of the effective temperature at which the hydration occurred. The effective hydration temperature can be either measured or approximated from weather records. Rates have been calculated by both methods, and the results show that weather records can give a good approximation to the true EHT, particularly in tropical and subtropical climates. If one determines the EHT by any of the methods suggested, and also measures or knows the rate of hydration of the particular obsidian used, it should be possible to carry out absolute dating to � 10 percent of the true age over periods as short as several years and as long as millions of years.

HYDRATION OF NATURAL GLASS AND FORMATION OF PERLITE

The hydration rate of rhyolitic glass has been determined at temperatures ranging from 5° C to 100° C. The relationship between the depth of hydration, x, and time, t is x 2 = kt; k varies from 0.4 μ 2 /10 3 years at 5° C to 10 4 μ 2 /10 3 years at 100° C; k is independent of the water pressure from a few hundredths of a centimeter to 1 atm. water pressure. The activation energy of hydration is about 20 kcal/mole. The determined hydration rates are consistent with the observation that perlite commonly forms by the hydration of shattered rhyolitic glass, either during the late cooling of a deposit or after the deposit has cooled to a surficial temperature.

Terpenes emitted from agricultural species found in California's Central Valley

More than a dozen monoterpenes have been identified as emissions from agricultural and natural plant species occupying large acreages in the Central Valley of California, including as dominant emissions camphene, 2-carene, Δ3-carene, limonene, myrcene, trans-ocimene, β-phellandrene, α-pinene, β-pinene, sabinene, γ-terpinene, and terpinolene. Isoprene was not a significant emission from any of the crop species examined but was emitted by a Valley Oak. In addition to the monoterpenes, sesquiterpenes were emitted from approximately one third of the species investigated, in some cases at higher levels than the monoterpene emissions from the same plant. The possible contributions of these biogenic emissions to the ozone exceedances in the Central Valley should be considered in planning future emission control strategies.

Rate Constants for the Gas-Phase Reactions of OH Radicals with Dimethyl Phosphonate over the Temperature Range of 278-351 K and for a Series of Other Organophosphorus Compounds at ∼280 K

Rate constants for the gas-phase reactions of OH radicals with dimethyl phosphonate [DMHP; (CH3O)2P(O)H] were measured over the temperature range of 278-351 K at atmospheric pressure of air using a relative rate method with 4-methyl-2-pentanone as the reference compound. The Arrhenius expression obtained was 1.01 x 10(-12) e((474 +/- 159)/T) cm(3) molecule(-1) s(-1), where the indicated error is two least-squares standard deviations and does not include uncertainties in the rate constants for the reference compound. Rate constants for the gas-phase reactions of OH radicals with dimethyl methylphosphonate [DMMP, (CH3O)2P(O)CH3], dimethyl ethylphosphonate [DMEP, (CH3O)2P(O)C2H5], diethyl methylphosphonate [DEMP, (C2H5O)2P(O)CH3], diethyl ethylphosphonate [DEEP, (C2H5O)2P(O)C2H5], and triethyl phosphate [TEP, (C2H5O)3PO] were also measured at 278 and/or 283 K for comparison with a previous study (Aschmann, S. M.; Long, W. D.; Atkinson, R. J. Phys. Chem. A, 2006, 110, 7393). With the experimental procedures employed, experiments conducted at temperatures below the dew point where a water film was present on the outside of the Teflon reaction chamber resulted in measured rate constants which were significantly higher than those expected from the extrapolation of rate data obtained at temperatures (283-348 K) above the dew point. Using rate constants measured at > or = 283 K, the resulting Arrhenius expressions (in cm(3) molecule(-1) s(-1) units) are 6.25 x 10(-14) e((1538 +/- 112)/T) for DMMP (283-348 K), 9.03 x 10(-14) e((1539 +/- 27)/T) for DMEP (283-348 K), 4.35 x 10(-13) e((1444 +/- 148)/T) for DEMP (283-348 K), 4.08 x 10(-13) e((1485 +/- 328)/T) for DEEP (283-348 K), and 4.07 x 10(-13) e((1448 +/- 145)/T) for TEP (283-347 K), where the indicated errors are as above. Aerosol formation at 296 +/- 2 K from the reactions of OH radicals with these organophosphorus compounds was relatively minor, with aerosol yields of < or = 8% in all cases.

Obsidian Hydration Dates Glacial Loading

Three different groups of hydration rinds have been measured on thin sections of obsidian from Obsidian Cliff, Yellowstone National Park, Wyoming. The average thickness of the thickest (oldest) group of hydration rinds is 16.3 micrometers and can be related to the original emplacement of the flow 176,000 years ago (potassium-argon age). In addition to these original surfaces, most thin sections show cracks and surfaces which have average hydration rind thicknesses of 14.5 and 7.9 micrometers. These later two hydration rinds compare closely in thickness with those on obsidian pebbles in the Bull Lake and Pinedale terminal moraines in the West Yellowstone Basin, which are 14 to 15 and 7 to 8 micrometers thick, respectively. The later cracks are thought to have been formed by glacial loading during the Bull Lake and Pinedale glaciations, when an estimated 800 meters of ice covered the Obsidian Cliff flow.

Atmospheric Chemistry of Dichlorvos

Dichlorvos [2,2-dichlorovinyl dimethyl phosphate, (CH(3)O)(2)P(O)OCH═CCl(2)] is a relatively volatile in-use insecticide. Rate constants for its reaction with OH radicals have been measured over the temperature range 296-348 K and atmospheric pressure of air using a relative rate method. The rate expression obtained was 3.53 × 10(-13) e((1367±239)/T) cm(3) molecule(-1) s(-1), with a 298 K rate constant of (3.5 ± 0.7) × 10(-11) cm(3) molecule(-1) s(-1), where the error in the 298 K rate constant is the estimated overall uncertainty. In addition, rate constants for the reactions of NO(3) radicals and O(3) with dichlorvos, of (2.5 ± 0.5) × 10(-13) cm(3) molecule(-1) s(-1) and (1.7 ± 1.0) × 10(-19) cm(3) molecule(-1) s(-1), respectively, were measured at 296 ± 2 K. Products of the OH and NO(3) radical-initiated reactions were investigated using in situ atmospheric pressure ionization mass spectrometry (API-MS) and (OH radical reaction only) in situ Fourier transform infrared (FT-IR) spectroscopy. For the OH radical reaction, the major initial products were CO, phosgene [C(O)Cl(2)] and dimethyl phosphate [(CH(3)O)(2)P(O)OH], with equal (to within ±10%) formation yields of CO and C(O)Cl(2). The API-MS analyses were consistent with formation of (CH(3)O)(2)P(O)OH from both the OH and NO(3) radical-initiated reactions. In the atmosphere, the dominant chemical loss processes for dichlorvos will be daytime reaction with OH radicals and nighttime reaction with NO(3) radicals, with an estimated lifetime of a few hours.

Kinetics of the gas-phase reactions of OH and NO3 radicals and O3 with 1,4-thioxane and 1,4-dithiane.

Rate constants for the gas-phase reactions of the cyclic organosulfur compounds 1,4-thioxane and 1,4-dithiane with NO(3) radicals and O(3) have been measured at 296 +/- 2 K, and rate constants for their reactions with OH radicals have been measured over the temperature range 278-350 K. Relative rate methods were used to measure rate constants for the OH radical and NO(3) radical reactions. The OH radical reaction in the presence of NO(x) and, to a lesser extent, the NO(3) radical reaction were subject to secondary reactions leading to additional removal of 1,4-thioxane and/or 1,4-dithiane. The rate constants obtained for the NO(3) radical and O(3) reactions at 296 +/- 2 K were (5.1 +/- 1.1) x 10(-14) cm(3) molecule(-1) s(-1) and <2 x 10(-19) cm(3) molecule(-1) s(-1), respectively, for 1,4-thioxane and (5.9 +/- 1.8) x 10(-14) cm(3) molecule(-1) s(-1) and <2.5 x 10(-19) cm(3) molecule(-1) s(-1), respectively, for 1,4-dithiane. For the OH radical reactions, the temperature-dependent rate expressions obtained were k(OH + 1,4-thioxane) = 2.54 x 10(-12) e((619+/-51)/T) cm(3) molecule(-1) s(-1) (278-349 K) and k(OH + 1,4-dithiane) = 3.71 x 10(-12) e((621+/-163)/T) cm(3) molecule(-1) s(-1) (278-350 K), with 298 K rate constants of (2.03 +/- 0.41) x 10(-11) cm(3) molecule(-1) s(-1) for 1,4-thioxane and (2.98 +/- 0.75) x 10(-11) cm(3) molecule(-1) s(-1) for 1,4-dithiane. For the experimental conditions employed, aerosol formation from the OH radical-initiated reactions of both 1,4-thioxane and 1,4-dithiane was important, accounting for approximately 60% of the organosulfur compounds reacted in both the presence and absence of NO(x). The data obtained here for 1,4-thioxane and 1,4-dithiane are compared with literature data for the corresponding reactions of simple acyclic alkyl sulfides and ethers.

Kinetics and Products of the Gas-Phase Reactions of Divinyl Sulfoxide with OH and NO3 Radicals and O3

Using relative rate methods, rate constants for the gas-phase reactions of divinyl sulfoxide [CH 2CHS(O)CHCH 2; DVSO] with NO 3 radicals and O 3 have been measured at 296 +/- 2 K, and rate constants for the reaction with OH radicals have been measured over the temperature range of 277-349 K. Rate constants obtained for the NO 3 radical and O 3 reactions at 296 +/- 2 K were (6.1 +/- 1.4) x 10 (-16) and (4.3 +/- 1.0) x 10 (-19) cm (3) molecule (-1) s (-1), respectively. For the OH radical reaction, the temperature-dependent rate expression obtained was k = 4.17 x 10 (-12)e ((858 +/- 141)/ T ) cm (3) molecule (-1) s (-1) with a 298 K rate constant of (7.43 +/- 0.71) x 10 (-11) cm (3) molecule (-1) s (-1), where, in all cases, the errors are two standard deviations and do not include the uncertainties in the rate constants for the reference compounds. Divinyl sulfone was observed as a minor product of both the OH radical and NO 3 radical reactions at 296 +/- 2 K. Using in situ Fourier transform infrared spectroscopy, CO, CO 2, SO 2, HCHO, and divinyl sulfone were observed as products of the OH radical reaction, with molar formation yields of 35 +/- 11, 2.2 +/- 0.8, 33 +/- 4, 54 +/- 6, and 5.4 +/- 0.8%, respectively, in air. For the experimental conditions employed, aerosol formation from the OH radical-initiated reaction of DVSO in the presence of NO was minor, being approximately 1.5%. The data obtained here for DVSO are compared with literature data for the corresponding reactions of dimethyl sulfoxide.