U. Kuhn

Global budget of atmospheric carbonyl sulfide: Temporal and spatial variations of the dominant sources and sinks

[1] The spatial and temporal variability of the global fluxes of carbonyl sulfide (COS) is discussed together with possible implications for total column atmospheric COS loading. The input of COS into the atmosphere is calculated as the sum of all known direct sources of COS plus the conversion of carbon disulfide (CS 2 ) and dimethyl sulfide (DMS) to COS by atmospheric oxidation processes. Recent models are used to predict COS, CS 2 , and DMS release from the oceans and COS uptake by soils, plants, and oceans. This forward approach to constructing global integrated COS fluxes has a large associated range of uncertainty. The best guess global annual-integrated COS net flux estimate does not differ from zero within the range of estimated uncertainty, consistent with the observed absence of long-term trends in atmospheric COS loading. Interestingly, the hemispheric time-dependent monthly fluxes are very close in phase for the Northern and Southern Hemispheres. The monthly variation of the Northern Hemisphere flux seems to be driven primarily by high COS vegetation uptake in summer, while the monthly variation of the Southern Hemisphere flux appears to be driven mostly by high oceanic fluxes of COS, CS 2 , and DMS in summer.

Atmospheric volatile organic compounds (VOC) at a remote tropical forest site in central Amazonia

According to recent assessments, tropical woodlands contribute about half of all global natural non-methane volatile organic compound (VOC) emissions. Large uncertainties exist especially about fluxes of compounds other than isoprene and monoterpenes. During the Large-Scale Biosphere/Atmosphere Experiment in Amazonia - Cooperative LBA Airborne Regional Experiment 1998 (LBA-CLAIRE-98) campaign, we measured the atmospheric mixing ratios of different species of VOC at a ground station at Balbina, Amazonia. The station was located 100 km north of Manaus, SE of the Balbina reservoir, with 200-1000 km of pristine forest in the prevailing wind directions. Sampling methods included DNPH-coated cartridges for carbonyls and cartridges filled with graphitic carbons of different surface characteristics for other VOCs. The most prominent VOC species present in air were formaldehyde and isoprene, each up to several ppb. Concentrations of methylvinyl ketone as well as methacroleine, both oxidation products of isoprene, were relatively low, indicating a very low oxidation capacity in the lower atmospheric boundary layer, which is in agreement with a daily ozone maximum of <20 ppb. Total monoterpene concentration was below 1 ppb. We detected only very low amounts of VOC species, such as benzene, deriving exclusively from anthropogenic sources.

Patterns of CO2 exchange in biological soil crusts of successional age.

Abstract The objective of this paper was to determine whether CO 2 exchange rates could be used as an indicator for determining the state of development and species or functional composition of biological soil crusts in different successional stages. We quantified the CO 2 exchange rates, i.e., CO 2 assimilation and respiration, in samples from different microhabitats at two different sites in the Negev desert. In the successional pathway of the crust communities, the pioneers in colonising the soil surface are the cyanobacteria; green algae, mosses and lichens then follow. Physical influences such as soil structure and types, radiation intensity, and topographic traits such as slope directions that affect water availability and soil moisture, influence the successional pathways and the soil crust community. When physical conditions are the same, disturbances are key factors for a specific successional stage. We found a substantial gradient of CO 2 exchange at the Nizzana site for both respiration and photosynthesis. Samples from the sand dunes at the Nizzana site showed a pronounced activity gradient with high rates for assimilation (around 70 μmol CO 2 m −2 min −1 ) as well as respiration (60–70 μmol CO 2 m −2 min −1 ) at the base of dunes, decreasing towards the top. The soil crust samples of the Negev desert show comparable values. Hence, as ecotypes containing such biological soil crusts with dominant photosynthetically active organisms are a widespread phenomenon in desert, boreal and arctic systems, their contribution to the global cycling of trace gases and elements can be significant for global budgets.

Controlling variables for the uptake of atmospheric carbonyl sulfide by soil

Soil samples from arable land were investigated for their exchange of carbonyl sulfide (COS) with the atmosphere under controlled conditions using dynamic cuvettes in a climate chamber. The investigated soil type acted as a significant sink for the trace gas COS. Atmospheric COS mixing ratios, temperature, and soil water content were found to be the physicochemical parameters controlling the uptake. Emission was never observed under conditions representative of a natural environment. The observed compensation point (i.e., an ambient concentration where the consumption and production balance each other and the net flux is zero) for the uptake was about 53 parts per trillion. Uptake rates ranged between 1.5 and 10.3 pmol m−2 s−1. The consumption of COS by the soil sample depended on the physiological activity of the microorganisms in the soil, as indicated by a clear optimum temperature and by a drastic inhibition in the presence of the enzyme inhibitor 6-ethoxy-2-benzothiazole-2-sulfonamide (EZ), a specific inhibitor for carbonic anhydrase.

Carbonyl sulfide exchange on an ecosystem scale: soil represents a dominant sink for atmospheric COS

The soil/plant/atmosphere exchange of carbonyl sulfide (COS) was investigated in an open oak woodland ecosystem at a rural site in northern California. Measurements of atmospheric concentrations of COS were made in June and in December 1994. We found a significant diel cycle with a drop of COS levels by approximately 150 ppt during the night in both seasons. The mean COS daytime background mixing ratios showed a distinct seasonal di⁄erence with 465

Net ecosystem fluxes of isoprene over tropical South America inferred from Global Ozone Monitoring Experiment (GOME) observations of HCHO columns

77 ppt in summer and 375

Exchange of short‐chain monocarboxylic acids by vegetation at a remote tropical forest site in Amazonia

56 ppt in winter. The nighttime bulk COS flux into the ecosystem was estimated using a micrometeorological model. To address the observed depletion of COS during stable nocturnal boundary layer conditions, the potential of various ecosystem compartments to act as a sink for COS was investigated. Studies using dynamic enclosures flushed with ambient air excluded vegetation as an important sink during nighttime due to high stomatal resistance. Results from soil chamber measurements indicate that the soil can act as a dominant sink for atmospheric COS. ( 1999 Elsevier Science Ltd. All rights reserved.

Methanol emissions from deciduous tree species: dependence on temperature and light intensity

Click Here JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 113, D20304, doi:10.1029/2008JD009863, 2008 for Full Article Net ecosystem fluxes of isoprene over tropical South America inferred from Global Ozone Monitoring Experiment (GOME) observations of HCHO columns Michael P. Barkley, 1 Paul I. Palmer, 1 Uwe Kuhn, 2,3 Juergen Kesselmeier, 2 Kelly Chance, 4 Thomas P. Kurosu, 4 Randall V. Martin, 4,5 Detlev Helmig, 6 and Alex Guenther 7 Received 24 January 2008; revised 17 June 2008; accepted 22 July 2008; published 17 October 2008. [ 1 ] We estimate isoprene emissions over tropical South America during 1997–2001 using column measurements of formaldehyde (HCHO) from the Global Ozone Monitoring Experiment (GOME) satellite instrument, the GEOS-Chem chemistry transport model, and the MEGAN (Model of Emissions of Gases and Aerosols from Nature) bottom-up isoprene inventory. GEOS-Chem is qualitatively consistent with in situ ground-based and aircraft concentration profiles of isoprene and HCHO, and GOME HCHO column data (r = 0.41; bias = +35%), but has less skill in reproducing wet season observations. Observed variability of GOME HCHO columns over South America is determined largely by isoprene and biomass burning. We find that the column contributions from other biogenic volatile organic compounds (VOC) are typically smaller than the column fitting uncertainty. HCHO columns influenced by biomass burning are removed using Along Track Scanning Radiometer (ATSR) firecounts and GOME NO 2 columns. We find that South America can be split into eastern and western regions, with fires concentrated over the eastern region. A monthly mean linear transfer function, determined by GEOS-Chem, is used to infer isoprene emissions from observed HCHO columns. The seasonal variation of GOME isoprene emissions over the western region is broadly consistent with MEGAN (r = 0.41; bias = 25%), with largest isoprene emissions during the dry season when the observed variability is consistent with knowledge of temperature dependence. During the wet season, other unknown factors play a significant role in determining observed variability. Citation: Barkley, M. P., P. I. Palmer, U. Kuhn, J. Kesselmeier, K. Chance, T. P. Kurosu, R. V. Martin, D. Helmig, and A. Guenther (2008), Net ecosystem fluxes of isoprene over tropical South America inferred from Global Ozone Monitoring Experiment (GOME) observations of HCHO columns, J. Geophys. Res., 113, D20304, doi:10.1029/2008JD009863. 1. Introduction [ 2 ] Tropical terrestrial ecosystems are a significant source of biogenic volatile organic compounds (BVOCs). The dominant nonmethane BVOC is isoprene (C 5 H 8 ), which represents almost half of the global annual nonmethane VOC flux [Guenther et al., 1995, 2006]. Tropical ecosystems contribute nearly 75% of the global atmospheric isoprene School of GeoSciences, University of Edinburgh, Edinburgh, UK. Biogeochemistry Department, Max Planck Institute for Chemistry, Mainz, Germany. Now at Agroscope Reckenholz-Taenikon Research Station, Zurich, Switzerland. Atomic and Molecular Physics Division, Harvard-Smithsonian Center for Astrophysics, Cambridge, Massachusetts, USA. Department of Physics and Atmospheric Science, Dalhousie University, Halifax, Nova Scotia, Canada. INSTAAR, University of Colorado, Boulder, Colorado, USA. Biosphere-Atmosphere Interactions Group, Atmospheric Chemistry Division, NCAR, Boulder, Colorado, USA. Copyright 2008 by the American Geophysical Union. 0148-0227/08/2008JD009863

EXCHANGE OF SHORT-CHAIN ALDEHYDES BETWEEN AMAZONIAN VEGETATION AND THE ATMOSPHERE

09.00 budget [Guenther et al., 2006], reflecting a year-long growing season, warm temperatures, and high solar insola- tion. The high VOC loading and favorable atmospheric conditions (high concentrations of the hydroxyl radical, OH) ensures that the tropics also exert considerable influ- ence on global tropospheric photochemistry [Andreae and Crutzen, 1997]. Isoprene has a strong influence on the oxidation capacity of the atmospheric boundary layer [Poisson et al., 2000; Monson and Holland, 2001], and can contribute to the formation of tropospheric ozone [Wang and Shallcross, 2000; Sanderson et al., 2003] and be a precursor of secondary organic aerosol [Claeys et al., 2004; Henze and Seinfeld, 2006], thereby playing a signif- icant role in determining Earth’s climate. Isoprene emis- sions also represent a significant loss of fixed carbon from the terrestrial biosphere, relative to the net biome produc- tivity [Kesselmeier et al., 2002a]. [ 3 ] Global and regional isoprene emissions, determined by bottom-up models constrained by sparse in situ data, are poorly known [Guenther et al., 1995, 2006; Potter et al., D20304 1 of 24

Environmental variables controlling the uptake of carbonyl sulfide by lichens

[1] As part of the project LBA-EUSTACH (European Studies on Trace gases and Atmospheric Chemistry as a contribution to the Large-Scale Biosphere-Atmosphere experiment in Amazonia), the exchange of formic acid and acetic acid between vegetation and the atmosphere was investigated in the wet-to-dry season transition and the dry-to-wet season transition periods in 1999 in Rondonia, Brazil. Direct exchange measurements on the branch level mainly exhibited uptake of formic acid and acetic acid for all plant species in both seasons, although diel, seasonal, and interspecies variations were observed. Even though other physiological and physico-chemical parameters may have contributed, the uptake of organic acids was found to be primarily a function of the ambient atmospheric mixing ratios. The linear dependence suggests a bidirectional exchange behavior of the plants and calculated deposition velocities (0.17-0.23 cm s -1 ), compensation point mixing ratios (0.16-0.30 ppb), and potential emission rates under purified air conditions (0.013-0.031 nmol m -2 s -1 ) are discussed. Vertical profile measurements in and above the primary forest canopy further strengthened the assumption that the forest is rather a sink than a source for organic acids. The generally lower mixing ratios observed within the canopy were indicative of an uptake by vegetation and/or the soil surface. Continuous measurements of the ambient atmospheric mixing ratios at the canopy top revealed strong diel variations in both seasons and a marked seasonality with higher mixing ratios during the dry season, both being mirrored in the variation of observed uptake rates of the plants. High atmospheric concentrations during the dry season were attributed to biomass burning. During the wet season, when biomass burning activity was low, indirect emission by the vegetation, i.e., photochemical oxidation of primarily emitted biogenic reactive hydrocarbons, was assumed to dominantly contribute to the atmospheric burden of the organic acids. The high degree of correlation between atmospheric formic acid and acetic acid indicated that similar atmospheric processes were affecting their mixing ratios.