Martin D. King

Extinction of UV radiation in Arctic snow at Alert, Canada (82°N)

Extinction of ultraviolet (UV) and visible radiation (300–548 nm) in snowpack is reported for surface snow used in snow-atmosphere exchange experiments during the Polar Sunrise Experiment ALERT 2000 (Canadian Forces Station Alert, Canada). The UV penetration distance is reported as the e-folding depth (the depth over which the monochromatic light irradiance decreases by a factor of e) for 2 nm wavelength intervals. Values in the range 5–6 cm are obtained for a uniform snowpack in the wavelength region between the ozone absorption edge in the UV and green light in the visible. Experimental evidence shows at most a weak dependence of the asymptotic e-folding depth on the solar zenith angle. Comparison of these data to previous studies indicates that the e-folding depths vary greatly between sites, most probably due to variations in impurities at each of the sites. These data imply that approximately 85% of a photochemical reaction occurs in the top 10 cm of snowpack at this site.

Snow-pile and chamber experiments during the Polar Sunrise Experiment ‘Alert 2000’: exploration of nitrogen chemistry

Abstract Snow chamber and snow-pile experiments performed during the ‘Alert 2000’ campaign show significant release of NO, NO 2 , and HONO in steady ratios under the influence of irradiation. Both light and a minimal degree of heating are required to produce this effect. We suggest diffusion and re-distribution of NO 3 − in the form of HNO 3 as an important step in the mechanism of active nitrogen release from the snowpack.

Frontier molecular orbital correlations for predicting rate constants between alkenes and the tropospheric oxidants NO3, OH and O3

Two types of correlation relating the value of the energy of the highest occupied molecular orbital (HOMO) of an alkene to the logarithm of its rate constant for reaction with NO3, OH or O3 have been formulated. Both correlations have been shown to be consistent with frontier molecular orbital theory. The correlation can be used to predict the rate constants for the reaction of an alkene with NO3, OH or O3 by calculating the value of the HOMO energy of the alkene. The accuracy of these predictions is quoted as a 48, 40 and 97% minimum probability that the predicted rate constant for reaction of an alkene with NO3, O3 and OH, respectively, will be within a factor of two of the measured rate constant. This probability is increased to a minimum of 73, 80 and approaches 100% for the reactions of NO3, O3 and OH, respectively, with conjugated dienes.

The pedosedimentary evolution and chronology of Tortugas, a Late Quaternary type-site of the northern Pampa, Argentina

New micromorphological, magnetic susceptibility, geochemical and geochronological data have been collected from Tortugas, a key Late Quaternary type-site of the northern Pampa (Argentina), thus enabling the detailed reconstruction of the pedogenic and sedimentary history of this loess–paleosol sequence. Paleosols developed in the Ceres Formation and the overlying lower member of the Tezanos Pinto Formation retain evidence for leaching, bioturbation and particularly clay translocation processes being dominant. Both paleosols are truncated: evidence for water sorting and sediment reworking, as well as continued bioturbation and redistribution of carbonates, suggests that intervening depositional phases were complex. The previously recorded ‘Hypsithermal Soil’ developed in the upper member of the Tezanos Pinto Formation has similar characteristics to the buried paleosols, yet does not appear to have been truncated at this site and is only covered by a thin layer of sediment (San Guillermo Formation). This latter unit has been pedogenically welded onto the ‘Hypsithermal Soil’, thus creating the present-day surface soil (complex). A series of optically stimulated luminescence dates from throughout the sequence provide a stratigraphically consistent chronological framework (ca. 1–150 ka) for the pedosedimentary reconstruction, yet conflict with the previously reported thermoluminescence-based chronology for the site and region (ca. 1–90 ka).

Organochlorine pesticide air-water exchange and bioconcentration in krill in the Ross Sea.

Mean hexachlorobenzene (HCB) and hexachlorocyclohexane (HCH) concentrations, measured in seawater and air samples, confirmed the decline in levels of these compounds in Antarctic air and water. However, low alpha/gamma-HCH ratios in air at the beginning of the sampling period suggest a predominance of fresh lindane entering the Antarctic atmosphere during the Austral spring probably due to current use in the Southern Hemisphere. Water-air fugacity ratios demonstrate the potential for HCH gas deposition to coastal Antarctic seas, while the water-air fugacity ratios for HCB imply that volatilization does not account for the observed decrease of HCB in surface seawater. HCH concentrations found in krill samples were correlated with seawater concentrations indicative of bioconcentration of HCHs from seawater.

A kinetic study of the reactions of NO3 with methyl vinyl ketone, methacrolein, acrolein, methyl acrylate and methyl methacrylate

Absolute and relative-rate techniques have been used to obtain rate coefficients for the reactions: NO3+CH3C(O)CHCH2→products (1), NO3+CH2C(CH3)CHO→products (2), NO3+CH2CHCHO→ products (3), and NO3+CH2CHC(O)OCH3→products (4). The reaction NO3+CH2C(CH3)C(O)OCH3→ products (5), has been investigated by a relative-rate method only. The rate coefficients obtained by the relative-rate method at T=296±2 K and P=760 Torr are k1=(4.7±1.7)×10-16 cm3 molecule-1 s-1, k2=(3.7±1.0)×10-15 cm3 molecule-1 s-1, k3=(1.1±0.4)×10-15 cm3 molecule-1 s-1, k4=(1.0±0.6)×10-16 cm3 molecule-1 s-1 and k5=(3.6±1.3)×10-15 cm3 molecule-1 s-1. The rate coefficients determined by the discharge-flow technique at low pressure (P=1–10 Torr) and at T=293–303 K are k1=(3.2±0.6)×10-16 cm3 molecule-1 s-1, k2=(9.6±2.0)×10-15 cm3 molecule-1 s-1, k3=(8.9±2.8)×10-15 cm3 molecule-1 s-1, k4=(1.9±0.4)×10-16 cm3 molecule-1 s-1. The discrepancy between the values obtained from the relative-rate technique and the absolute technique are discussed and explained in terms of interference in the absolute study caused by secondary chemistry and fast-reacting impurities. Product studies reveal that methyl glyoxal is a product of reactions (1) and (2) along with peroxymethacryloyl nitrate (MPAN) for reaction (2) in air. A diurnally varying boundary-layer model suggests that reaction (2) is an important loss process for methacrolein and that it can lead to the generation of OH at night.

The modulation of Ca2+-ATPase activity of sarcoplasmic reticulum by membrane cholesterol. The effect of enzyme coupling

The Ca2+-ATPase activity of sarcoplasmic reticulum is relatively low (less than 2 I.U.) in vesicles where enzyme activity is geared to calcium accumulation. Modulation of membrane fluidity by enriching the membrane with cholesterol has no significant effect on enzyme activity. Collapsing the Ca2+ gradient with the calcium ionophore, A23187, unmasks the inhibitory effect of membrane cholesterol on enzyme activity.

Is the reaction between CH3C(O)O2 and NO3 important in the night-time troposphere?

A discharge-flow system equipped with a laser-induced fluorescence (LIF) cell to detect NO2 and a multi-pass absorption cell to detect NO3 has been used to study the reaction CH3C(O)O2+ NO3→ CH3C(O)O + NO2+ O2(1) at T= 403–443 K and P= 2–2.4 Torr. The rate constant was found to be independent of temperature with a value of k1=(4 ± 1)× 10–12 cm3 molecule–1 s–1. The likely mechanism for the reaction is discussed. The atmospheric implications of reaction (1) are investigated using a range of models and several case studies are presented, comparing model results with actual field measurements. It is concluded that reaction (1) participates in a cycle which can generate OH at night. This reaction cycle (see text) can operate throughout the continental boundary layer, but may even occur in remote regions.

An experimental study of the gas-phase reaction of the NO3 radical with α,β-unsaturated carbonyl compounds

The relative-rate technique has been used to obtain rate coefficients for the reaction between the NO3 radical and α,β-unsaturated esters and ketones: methyl E-2-butenoate (k1), methyl 3-methyl-2-butenoate (k2), methyl E-2-methyl-2-butenoate (k3), 3-methyl-3-buten-2-one (k4), E-3-penten-2-one (k5), 4-methyl-3-penten-2-one (k6), and E-3-methyl-3-penten-2-one (k7). The rate constants obtained by the relative-rate method at T = 298 ± 2 K and P = 760 ± 5 Torr (N2 as bath gas) are: k1 = (1.85 ± 0.56) × 10−15 cm3 molecule−1 s−1, k2 = (1.41 ± 0.23) × 10−14 cm3 molecule−1 s−1, k3 = (4.91 ± 1.15) × 10−14 cm3 molecule−1 s−1, k4 = (8.27 ± 6.44) × 10−15 cm3 molecule−1 s−1, k5 = (1.03 ± 0.31) × 10−14 cm3 molecule−1 s−1, k6 = (1.44 ± 0.26) × 10−13 cm3 molecule−1 s−1 and k7 = (1.55 ± 0.20) × 10−13 cm3 molecule−1 s−1. The rate constants are used to show the effect of increased substitution at the carbon–carbon double bond. Group-reactivity factors for the ketone and ester groups are also determined. Atmospheric lifetimes of the compounds against night-time attack by NO3 are estimated.

Reaction of a Phospholipid Monolayer with Gas-Phase Ozone at the Air—Water Interface: Measurement of Surface Excess and Surface Pressure in Real Time

The reaction between gas-phase ozone and monolayers of the unsaturated lipid 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine, POPC, on aqueous solutions has been studied in real time using neutron reflection and surface pressure measurements. The reaction between ozone and lung surfactant, which contains POPC, leads to decreased pulmonary function, but little is known about the changes that occur to the interfacial material as a result of oxidation. The results reveal that the initial reaction of ozone with POPC leads to a rapid increase in surface pressure followed by a slow decrease to very low values. The neutron reflection measurements, performed on an isotopologue of POPC with a selectively deuterated palmitoyl strand, reveal that the reaction leads to loss of this strand from the air-water interface, suggesting either solubilization of the product lipid or degradation of the palmitoyl strand by a reactive species. Reactions of (1)H-POPC on D(2)O reveal that the headgroup region of the lipids in aqueous solution is not dramatically perturbed by the reaction of POPC monolayers with ozone supporting degradation of the palmitoyl strand rather than solubilization. The results are consistent with the reaction of ozone with the oleoyl strand of POPC at the air-water interface leading to the formation of OH radicals. The highly reactive OH radicals produced can then go on to react with the saturated palmitoyl strands leading to the formation of oxidized lipids with shorter alkyl tails.