Radon-222 (Rn-222) is used as a transport tracer of forest canopy-atmosphere CO 2 exchange in an old-growth, tropical rain forest site near km 67 of the Tapajós National Forest, Pará, Brazil. Initial results, from month-long periods at the end of the wet season (June-July) and the end of the dry season (November-December) in 2001, demonstrate the potential of new Rn measurement instruments and methods to quantify mass transport processes between forest canopies and the atmosphere. Gas exchange rates yield mean canopy air residence times ranging from minutes during turbulent daytime hours to greater than 12 h during calm nights. Rn is an effective tracer for net ecosystem exchange of CO 2 (CO 2 NEE) during calm, night-time hours when eddy covariance-based NEE measurements are less certain because of low atmospheric turbulence. Rn-derived night-time CO 2 NEE (9.00 AE 0.99 lmol m À2 s À1 in the wet season, 6.39 AE 0.59 in the dry season) was significantly higher than raw uncorrected, eddy covariance-derived CO 2 NEE (5.96 AE 0.51 wet season, 5.57 AE 0.53 dry season), but agrees with corrected eddy covariance results (8.65 AE 1.07 wet season, 6.56 AE 0.73 dry season) derived by filtering out lower NEE values obtained during calm periods using independent meteorological criteria. The Rn CO 2 results suggest that uncorrected eddy covariance values underestimate night-time CO 2 loss at this site. If generalizable to other sites, these observations indicate that previous reports of strong net CO 2 uptake in Amazonian terra firme forest may be overestimated.

The kinetics of the reactions of hydroxyl radical with n-octane (k1), n-nonane (k2), and n-decane (k3) at 240-340 K and a total pressure of approximately 1 Torr has been studied using relative rate combined with discharge flow and mass spectrometer (RR/DF/MS) technique. The rate constant for these reactions was found to be positively dependent on temperature, with an Arrhenius expression of k1 = (2.27 +/- 0.21) x 10(-11)exp[(-296 +/- 27)/T], k2 = (4.35 +/- 0.49) x 10(-11)exp[(-411 +/- 32)/T], and k3 = (2.26 +/- 0.28) x 10(-11)exp[(-160 +/- 36)/T] cm3 molecule(-1) s(-1) (uncertainties taken as 2sigma), respectively. Our results are in good agreement with previous studies at and above room temperature using different techniques. Assuming that the reaction of alkane with hydroxyl radical is the predominant form for loss of these alkanes in the troposphere, the atmospheric lifetime for n-octane, n-nonane, and n-decane is estimated to be about 43, 35, and 28 h, respectively.

A tunable quantum-cascade (QC) laser has been flown on NASA's ER-2 high-altitude aircraft to produce the first atmospheric gas measurements with this newly invented device, an important milestone in the QC laser's future planetary, industrial, and commercial applications. Using a cryogenically cooled QC laser during a series of 20 aircraft flights beginning in September 1999 and extending through March 2000, we took measurements of methane (CH(4)) and nitrous oxide (N(2)O) gas up to ~20 km in the stratosphere over North America, Scandinavia, and Russia. The QC laser operating near an 8-mum wavelength was produced by the groups of Capasso and Cho of Bell Laboratories, Lucent Technologies, where QC lasers were invented in 1994. Compared with its companion lead salt diode lasers that were also flown on these flights, the single-mode QC laser cooled to 82 K and produced higher output power (10 mW), narrower laser linewidth (17 MHz), increased measurement precision (a factor of 3), and better spectral stability (~0.1 cm(-1) K). The sensitivity of the QC laser channel was estimated to correspond to a minimum-detectable mixing ratio for methane of approximately 2 parts per billion by volume.

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2, 3). Pseudocontact shifts result from direct interaction between the magnetic dipoles of the unpaired electrons of the paramagnetic metal and the magnetic dipoles of the ligand nuclei (8-10). The pseudocontact interaction is transmitted through space, even when there is no covalent bonding (11), and is attenuated as the distance from the paramagnetic ion increases. Thus the magnitudes of the downfield shifts for the nonequivalent carbon-bonded protons of alcohols bonded to Eu(DPM)3 depend mainly on the distance between the europium and the protons.The dependence of the shift gradient for a particular proton on the distance from the hydroxyl group should prove use-