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  • 1
    Electronic Resource
    Electronic Resource
    Preliminary results on nitric oxide emission from a southern African savanna ecosystem (1997)
    Springer
    Nutrient cycling in agroecosystems 48 (1997), S. 123-138 
    Details
    ISSN: 1573-0867
    Keywords: Africa ; biogenic emission ; dry season ; dynamic chamber ; forest ; grassland ; groundnut ; maize ; Miombo typesavanna ecosystem ; nitric oxide ; pulsing ; sorghum ; wet season ; Zimbabwe
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract During October to December 1994, we measured diel and seasonal variability in nitric oxide (NO) exchange by a southern African savanna ecosystem (Grasslands Research Station, Marondera, Zimbabwe). A set of automated dynamic chambers was installed in three sub-sites: Miombo forest, natural grassland, and cropped soils (maize, sorghum, groundnut). The latter received a single application of commercialy available in-organic or cowdung fertilizer. The dynamic chamber system is described in detail, including correction of the resulting data for wall losses and gas-phase reactions of the NO-NO2-O3 triad. During the dry season, net vertical NO fluxes were close to the detection limit (0.44 ngN m-2s-1) regardless of vegetation type. During the transition from dry to wet season strong "pulsing" effects of the NO flux were observed: NO emissions increased by a factor of up to 60 within hours. During the wet season, NO emissions varied between the different sub-sites of the ecosystem; corresponding means are in ranking order of fertilized agricultural plots (27.2 ngN m-2 s-1), unfertilized agricultural plots (8.5 ngN m-2 s-1 ), grassland (4.4 ngN m-2 s-1 ), and Miombo forest (1.5 ngN m-2 s-1). Soil moisture was found to be the dominant factor controlling the NO fluxes. Whenever it was not limiting, the diel behaviour of NO emission followed the daily variation of soil temperature measured 1 cm below the surface.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1009765510538
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  • 2
    Electronic Resource
    Electronic Resource
    Behavior of atmospheric formic and acetic acid in the presence of hydrometeors (1992)
    Springer
    Journal of atmospheric chemistry 15 (1992), S. 101-115 
    Details
    ISSN: 1573-0662
    Keywords: Gas-liquid partitioning ; formic acid ; acetic acid ; transport
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract The partitioning of formic and acetic acid between the atmospheric liquid and gaseous phase is modelled for a range of liquid water contents. At low liquid water content, formic acid is dissolved preferentially over acetic acid. Applying these results to the analysis of processes taking place in clouds, one can explain the frequently found enrichment of formic over acetic acid in rainwater, which results from selective transport by washout. We assess the ability of dew to act as a temporary sink and source for organic acids, and propose that the diel variation of mixing ratios often found during surface measurements, may in part be due to the dissolution in dew and subsequent evaporation on the following day.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00053753
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  • 3
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    Ozone and Aitken nuclei over equatorial Africa - Airborne observations during DECAFE 88 (1992)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: Results of ozone and Aitken condensation nuclei measurements made over the rain forest in equatorial Africa during February 12-25, 1988 are presented. The results indicate the presence of a layer between 1 and 4 km altitude where these species are strongly enriched. Based on information derived from simultaneous measurements of other chemical and meteorological parameters, satellite imagery, and trajectory calculations, this enrichment is attributed to emissions from biomass burning in sub-Saharan Africa, from which ozone is formed by photochemical reactions.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 97; D6, A
    Format: text
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  • 4
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    Air chemistry over the tropical forest of Guyana (1986)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: A comparison is made of the atmospheric chemistry within and above the atmospheric boundary layer over the tropical forest of Guyana. The data were gathered by NASA during the Global Tropospheric Experiment program in 1984, with an instrumented aircraft being used to collect data at altitudes of 3.5 km and between 150-450 m. The synoptic data covered concentrations of O3, CO, dimethylsulfide (DMS), halocarbons and isoprene and three different aerosol particulate measurements (DIAL system). The forest boundary layer proved to be a significant sink for O3, and a source for substantial emissions of DMS. Isoprene emitted by the forest was photochemically oxidized and became a source of CO.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 91; 8603-861
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  • 5
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    The atmospheric sulfur cycle over the Amazon Basin. II - Wet season (1990)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: The fluxes and concentrations of atmospheric sulfur species were determined at ground level and from aircraft over the Amazon Basin during the 1987 wet season, providing a comprehensive description of the sulfur cycle over a remote tropical region. The vertical profile of dimethylsulfide (DMS) during the wet season was found to be very similar to that measured during the dry season, suggesting little seasonal variation in DMS fluxes. The concentrations of H2S were almost an order of magnitude higher than those of DMS, which makes H2S the most important biogenic source species in the atmosheric sulfur cycle over the Amazon Basin. Using the gradient-flux approach, the flux of DMS at the top of the tree canopy was estimated. The canopy was a source of DMS during the day, and a weak sink during the night. Measurements of sulfur gas emissions from soils, using the chamber method, showed very small fluxes, consistent with the hypothesis that the forest canopy is the major source of sulfur gases. The observed soil and canopy emission fluxes are similar to those measured in temperate regions. The concentrations of SO2 and sulfate aerosol in the wet season atmosphere were similar to dry season values.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 95; 16813-16
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  • 6
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    Biomass-burning emissions and associated haze layers over Amazonia (1988)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: The characteristics of haze layers, which were visually observed over the central Amazon Basin during many of the Amazon Boundary Layer Experiment 2A flights in July/August 1985, were investigated by remote and in situ measurements, using the broad range of instrumentation and sampling equipment on board the Electra aircraft. It was found that these layers strongly influenced the chemical and optical characteristics of the atmosphere over the eastern Amazon Basin. Relative to the regional background, the concentrations of CO, CO2, O3, and NO were significantly elevated in the plumes and haze layers, with the NO/CO ratio in fresh plumes much higher than in the aged haze layers. The haze aerosol was composed predominantly of organic material, NH4, K(+), NO3(-), SO4(2-), and organic anions (formate, acetate, and oxalate).
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 93; 1509-152
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  • 7
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    Vertical distribution of dimethylsulfide, sulfur dioxide, aerosol ions, and radon over the northeast Pacific Ocean (1988)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: The vertical distributions, in temperate latitudes, of dimethylsulfide (DMS), SO2, radon, methanesulfonate (MSA), nonsea-salt sulfate (nss-sulfate), and aerosol Na(+), NH4(+), and NO(-) ions were determined in samples collected by an aircraft over the northeast Pacific Ocean during May 3-12, 1985. DMS was also determined in surface seawater. It was found that DMS concentrations, both in seawater and in the atmospheric boundary layer, were significantly lower than the values reported previously for subtropical and tropical regions, reflecting the seasonal variability in the temperate North Pacific. The vertical profiles of DMS, MSA, SO2, and nss-sulfate were found to be strongly dependent on the convective stability of the atmosphere and on air mass origin. Biogenic sulfur emissions could account for most of the sulfur budget in the boundary layer, while the long-range transport of continentally derived air masses was mainly responsible for the elevated levels of both SO2 and nss-sulfate in the free troposphere.
    Keywords: GEOPHYSICS
    Type: Journal of Atmospheric Chemistry (ISSN 0167-7764); 6; 149-173
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  • 8
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    Formic and acetic acid over the central Amazon region, Brazil. I - Dry season (1988)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: The concentrations of formic and acetic acids in the gas phase, atmospheric aerosol, and rainwater samples collected in Amazonia at ground level and in the atmosphere during the Amazon Boundary Layer Experiment in July/August 1985 were analyzed by ion exchange chromatography. The diurnal behavior of both acids at ground level and their vertical distribution in the forest canopy point to the existence of vegetative sources as well as to production by chemical reactions in the atmosphere. The concentrations of formic and acetic acids in the gas phase were about 2 orders of magnitude higher than the corresponding concentrations in the atmospheric aerosol. In rainwater, the total formate and acetate represented about one half of the anion equivalents, in contrast to less than 10 percent of the soluble anionic equivalents contributed by these acids in the atmospheric aerosol. The observed levels of these ions in rainwater are considered to be the result of a combination of chemical reactions in hydrometeors and the scavenging of the gaseous acids by cloud droplets.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 93; 1616-162
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  • 9
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    The cycle of biogenic sulfur compounds over the Amazon Basin. I - Dry season (1988)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: The concentrations of SO2, methylmercaptan, dimethylsulfide, H2S, aerosol sulfate, and methanesulfonate over the Amazon Basin during the July/August dry season were determined from samples collected by the NASA research aircraft. The results indicate that biogenic emissions represent an important, if not the dominant, source of sulfur to the atmosphere over Amazonia. Per unit area, the wet continental tropics appear to have about the same reduced sulfur emission flux as the oceanic area average (about 6 nmol/sq m per min), consistent with the fact that the aerosol sulfate concentration over the Amazon Basin is similar to the excess sulfate levels over the remote oceans. However, since the wet tropical continents represent only about 3 percent of the earth's surface, their global contribution is modest; it is also small relative to the anthropogenic emissions from fossil fuel burning.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 93; 1487-149
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  • 10
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    Regional aerosol chemistry of the Amazon Basin during the dry season (1988)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: The distribution and chemical composition of the atmospheric aerosol over the Amazon Basin forest were determined during the 1985 July-August dry season, using data on the aerosol chemical constituent concentration collected during the NASA Global Tropospheric Experiment Amazon Boundary Layer Experiment 2A mission. The results of the analyses suggest that there is a remarkable compositional and spatial homogeneity of the atmospheric aerosol on an extensive regional scale. Particulate organic carbon is the dominant component of the atmospheric aerosol, exhibiting an average concentration of about 740 nmol/cu m in the mixed layer and about 220 nmol/cu m in free tropospheric air. Oxalate and SO4(2-) exhibited the greatest enrichment in the mixed layer, while Cl(-) showed essentially no enrichment. The aerosol in the Amazonian atmosphere is essentially acid-base neutral, primarily as a result of incorporation of NH(+), which is presumably derived from NH3 released by the forest ecosystem.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 93; 1499-150
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