803 research outputs found

    Hydrogen Sulfide and Radon in and Over the Western North Atlantic Ocean

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    Atmospheric measurements of radon and hydrogen sulfide, and seawater measurements of total sulfide, free sulfide, and carbonyl sulfide, were made on a cruise in the western North Atlantic Ocean (October 24 to November 9, 1989). Measured values for 222Rn ranged from 3 to 70 pCi m−3, those for atmospheric hydrogen sulfide from 1 to 85 parts per trillion, and those for dissolved total and free sulfide in seawater from 33 to 930 pmol L−1 and 0 to 73 pmol L−1, respectively. A positive correlation between 222Rn and atmospheric H2S was observed. Both 222Rn and H2S were high in air masses traced back to North America. Measurements in seawater showed that uncomplexed sulfides were approximately 13% of total sulfide at 2 m depth. Atmospheric H2S and dissolved H2S in seawater were usually not far from saturation equilibrium. Our results indicate that the ocean acted at some times as a source of atmospheric H2S but more frequently as a sink. Hydrolysis of COS and atmospheric deposition of H2S both may contribute to the budget of dissolved sulfide in seawater of the western North Atlantic Ocean. On a global scale the ocean/atmosphere exchange of H2S appears to play a minor role in the atmospheric sulfur cycle

    Nitrous oxide emissions from the Arabian Sea: A synthesis

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    We computed high-resolution (1º latitude x 1º longitude) seasonal and annual nitrous oxide (N2O) concentration fields for the Arabian Sea surface layer using a database containing more than 2400 values measured between December 1977 and July 1997. N2O concentrations are highest during the southwest (SW) monsoon along the southern Indian continental shelf. Annual emissions range from 0.33 to 0.70 Tg N2O and are dominated by fluxes from coastal regions during the SW and northeast monsoons. Our revised estimate for the annual N2O flux from the Arabian Sea is much more tightly constrained than the previous consensus derived using averaged in-situ data from a smaller number of studies. However, the tendency to focus on measurements in locally restricted features in combination with insufficient seasonal data coverage leads to considerable uncertainties of the concentration fields and thus in the flux estimates, especially in the coastal zones of the northern and eastern Arabian Sea. The overall mean relative error of the annual N2O emissions from the Arabian Sea was estimated to be at least 65%

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    Aerosol particle number size distributions and particulate light absorption at the ZOTTO tall tower (Siberia), 2006–2009

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    This paper analyses aerosol particle number size distributions, particulate absorption at 570 nm wavelength and carbon monoxide (CO) measured between September 2006 and January 2010 at heights of 50 and 300 m at the Zotino Tall Tower Facility (ZOTTO) in Siberia (60.8° N; 89.35° E). Average number, surface and volume concentrations are broadly comparable to former studies covering shorter observation periods. Fits of multiple lognormal distributions yielded three maxima in probability distribution of geometric mean diameters in the Aitken and accumulation size range and a possible secondary maximum in the nucleation size range below 25 nm. The seasonal cycle of particulate absorption shows maximum concentrations in high winter (December) and minimum concentrations in mid-summer (July). The 90th percentile, however, indicates a secondary maximum in July/August that is likely related to forest fires. The strongly combustion derived CO shows a single winter maximum and a late summer minimum, albeit with a considerably smaller seasonal swing than the particle data due to its longer atmospheric lifetime. Total volume and even more so total number show a more complex seasonal variation with maxima in winter, spring, and summer. A cluster analysis of back trajectories and vertical profiles of the pseudo-potential temperature yielded ten clusters with three levels of particle number concentration: Low concentrations in Arctic air masses (400–500 cm−3), mid-level concentrations for zonally advected air masses from westerly directions between 55° and 65° N (600–800 cm−3), and high concentrations for air masses advected from the belt of industrial and population centers in Siberia and Kazakhstan (1200 cm−3). The observational data is representative for large parts of the troposphere over Siberia and might be particularly useful for the validation of global aerosol transport models

    Does Ethylene Mediate Root Growth Inhibition by Indole-3-Acetic Acid?

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    Nitrous oxide emissions from the Arabian Sea: A synthesis

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    We computed high-resolution (1º latitude x&nbsp; 1º longitude) seasonal and annual nitrous oxide (N<sub>2</sub>O) concentration fields for the Arabian Sea surface layer using a database containing more than 2400 values measured between December 1977 and July 1997. N<sub>2</sub>O concentrations are highest during the southwest (SW) monsoon along the southern Indian continental shelf. Annual emissions range from 0.33 to 0.70 Tg N<sub>2</sub>O and are dominated by fluxes from coastal regions during the SW and northeast monsoons. Our revised estimate for the annual N<sub>2</sub>O flux from the Arabian Sea is much more tightly constrained than the previous consensus derived using averaged in-situ data from a smaller number of studies. However, the tendency to focus on measurements in locally restricted features in combination with insufficient seasonal data coverage leads to considerable uncertainties of the concentration fields and thus in the flux estimates, especially in the coastal zones of the northern and eastern Arabian Sea. The overall mean relative error of the annual N<sub>2</sub>O emissions from the Arabian Sea was estimated to be at least 65%

    Spectral light absorption by ambient aerosols influenced by biomass burning in the Amazon Basin. I: Comparison and field calibration of absorption measurement techniques

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    International audienceSpectral aerosol light absorption is an important parameter for the assessment of the radiation budget of the atmosphere. Although on-line measurement techniques for aerosol light absorption, such as the Aethalometer and the Particle Soot Absorption Photometer (PSAP), have been available for two decades, they are limited in accuracy and spectral resolution because of the need to deposit the aerosol on a filter substrate before measurement. Recently, a 7-wavelength (?) Aethalometer became commercially available, which covers the visible (VIS) to near-infrared (NIR) spectral range (?=450?950 nm), and laboratory calibration studies improved the degree of confidence in these measurement techniques. However, the applicability of the laboratory calibration factors to ambient conditions has not been investigated thoroughly yet. As part of the LBA-SMOCC (Large scale Biosphere atmosphere experiment in Amazonia ? SMOke aerosols, Clouds, rainfall and Climate) campaign from September to November 2002 in the Amazon basin we performed an extensive field calibration of a 1-? PSAP and a 7-? Aethalometer utilizing a photoacoustic spectrometer (PAS, 532 nm) as reference device. Especially during the dry period of the campaign, the aerosol population was dominated by pyrogenic emissions. The most pronounced artifact of integrating-plate type attenuation techniques (e.g. Aethalometer, PSAP) is due to multiple scattering effects within the filter matrix. For the PSAP, we essentially confirmed the laboratory calibration factor by Bond et al. (1999). On the other hand, for the Aethalometer we found a multiple scattering enhancement of 5.23 (or 4.55, if corrected for aerosol scattering), which is significantly larger than the factors previously reported (~2) for laboratory calibrations. While the exact reason for this discrepancy is unknown, the available data from the present and previous studies suggest aerosol mixing (internal versus external) as a likely cause. For Amazonian aerosol, we found no absorption enhancement due to hygroscopic particle growth in the relative humidity (RH) range between 40% and 80%. However, a substantial bias in PSAP sensitivity that correlated with both RH and temperature (T) was observed for 20%RH<30% and 24°
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