Atmospheric Sciences VI
Presiding: D L Savoie, Marine and Atmospheric Chemistry, University of Miami; L T Steyaert, USGS
A54B-01 15:30h
Historical Land Cover and Biophysical Parameter Data to Study the Consequences of Land Use Change within the Eastern United States
Previous studies have demonstrated the utility of historical land cover data in regional climate modeling sensitivity tests to help quantify the effects of land use change on land surface processes, weather, and climate variability. Land use history is also important for long-term net carbon flux studies. In order to address these types of climate change research issues, historical land cover and biophysical parameter datasets were developed to investigate the consequences of land use change on land-atmosphere interactions within the eastern United States. This reconstructed land cover analysis, which was performed at four separate time-slices (mid-1600s, 1850, 1920, and 1992), resulted in 5-km gridded datasets for the land area to the east of the U.S. Great Plains. The temporal trajectory of land cover change was mapped by a set of consistently-defined land surface parameter classes that are designed for use in a regional land-atmosphere modeling system. Preliminary diagnostic analysis of land cover change and associated biophysical parameter fields in this region suggests significant implications for the land surface energy balance due to, for example, the magnitude of changes in land surface albedo and roughness. As part of land surface process research with these historical datasets, a regional climate modeling system could be coupled with impact assessment models to investigate potential land use change effects on managed ecosystems and climate including feedbacks.
A54B-02 15:45h
Global Patterns in Human Harvests of Net Primary Production
Humans have a major impact on Earth's ecosystems. Quantifying this impact often involves measuring the fraction of the planet's net primary production (NPP) that humanity appropriates for its own use. Here we measure NPP harvested (NPPh) or the amount of renewable terrestrial organic carbon directly (or indirectly through domestic animals) removed from the landscape and used by people for food, fuel, or fabrication or directly destroyed by burning in the field during 1997. This measure captures only part of NPP appropriated by humans because it does not include NPP appropriated by changes in land use or cover. Nevertheless, it is an important measure because subtracting it from the amount of NPP actually generated on the landscape (NPPact) yields the amount of NPP remaining for other species (NPPt). This presentation contains global maps at 0.5 degree lat./long. resolution identifying (a) source areas and amounts of NPPh, (b) amounts of NPPact, and (c) amounts of NPPt. Our intermediate value of annual global NPPh is 4.3 Pg C per yr or 7.4 percent of NPPact. These estimates are consistent with earlier estimates of NPPh once differences in time and biomass pools are considered. NPPh's shares of NPPact vary spatially both by region and by NPPact. Based on our intermediate value of NPPh, for example, NPPh's shares of NPPact are, on average, 4.8 percent in tropical zones, but 10.9 percent in temperate zones. Areas where NPPh leaves relatively little NPPt (less than 290 g C per square m per yr on average) for other species include portions of Bangladesh, Belgium, China, Egypt, Germany, India, Myanmar (Burma), Nigeria, Pakistan, Poland, the Netherlands, Thailand, the U.S. (e.g., the Midwest), and Vietnam. We also find that in areas where NPPh > 0, the relationship between NPPh's shares of NPPact and NPPact is inverse. This has some important implications for an important measure of biodiversity, species richness, or the number of species of a defined taxon occurring in a defined area. According to the species-energy hypothesis, species richness is positively related to the amount of energy remaining in an ecosystem, i.e., NPPt. Despite controversy regarding the form and cause of species-energy relationships, reviews of the literature indicate that the relationship between species richness and energy is often monotonically increasing, especially at regional, continental, and global scales. Our results imply that humans leave relatively less NPPt (as a percent share of NPPact) on average for low-productivity ecosystems than for high-productivity ecosystems. This suggests, therefore, that humans have reduced species richness of relatively low-productivity ecosystems in temperate and tropical zones more than relatively high-productivity ecosystems in tropical zones.
A54B-03 16:00h
Optical Properties of Saharan Dust Over the North Atlantic Ocean
During several intensive field experiments over the tropical North Atlantic, we used a variety of instruments to make extensive measurements of the chemical, physical and optical properties of aerosols in the marine boundary layer at Barbados and Puerto Rico and in the free troposphere at Izaña, Tenerife, Canary Islands. The ultimate objective of this work is to determine the mean physical and optical properties of aerosols from specific sources and to assess the variations of these properties as a function of meteorological parameters. Major aerosol sources for this region include Saharan dust, sea-salt, and pollution from Europe and North Africa. This information is critical to properly estimating the affect of aerosols on the propogation of radiation through the atmosphere. Cl-, NO3-, SO4=, Na+, NH4+, and mineral dust are based on 12 or 24-hour high volume bulk aerosol samples. Spectrally-resolved (300-1100 nm at 10 nm intervals) light absorption was measured on portions of the bulk filter using a diffuse reflectance technique. Aerosol light scatter and backscatter were measured at 450, 550, 700 nm wavelengths using a TSI 3563 Integrating Nephelometer; the high frequency data were subsequently averaged over the time periods of the bulk aerosol collections. At Izaña, the mass scattering efficiency of Saharan dust increases from 0.43 m2/g at 450 nm to 0.50 at 550 nm to 0.54 at 700 nm. Over the western Atlantic, the mass scattering efficiencies are about 20% higher (about 0.60 m2/g at 550 nm) as a consequence of the loss of the largest dust particles (greater than about 6 um diameter) which have a substantial affect on the mass but make only a minor contribution to the total light scatter. The mass absorption efficiency of Saharan dust is virtually constant across the region but decreases from 0.20 m2/g at 450 nm to 0.09 at 550 to 0.025 at 700. Because absorption follows the mass-partile size distribution, losses of the large particles affects mass and absorption similarly and these affects cancel in the absorption/mass ratio. Because total pollutant particle mass was not measured, total scattering by dry total pollutant particles is presented per gram of sulfate. At Izaña during summer 1997, total pollutant scattering decreased from 10.7 m2/g-sulfate at 450 nm to 4.4 at 700 nm, comparable results were obtained during summer 1995. The projects under which these data were collected were funded by NSF-Atmospheric Chemistry, the Navy (ONR), and NASA (TOMS).
A54B-04 16:15h
Human and Animal Wastes: Implications for Atmospheric N2O and NOx
More than 220 TgN are processed annually through the global agriculture/animal/human food chain. It is suggested that aerobic denitrification, reduction of nitrite formed in the first stage of nitrification, is an important source not only of global N2O but also of NOx. A simple top-down method indicates a globally averaged yield of 2% for N2O emitted as a consequence of human disturbances to the global nitrogen cycle. This yield can account not only for the contemporary budget of atmospheric N2O but also for trends observed over the past 1000 years. The associated microbial source of NOx is estimated assuming a NOx/N2O ratio of 3, consistent with results from a variety of laboratory and field studies. This source is significant, particularly for large developing countries such as China and India for which its contribution is comparable to that from fossil fuel.
A54B-05 16:30h
Measurement and Experimental Validation of N2O Formation and Emission in Domestic Wastewater
Ammonium nitrogen, in the form of highly soluble ion (NH4+), is one of the characteristic contaminants of industrial effluents, of untreated municipal discharges and of anaerobic and/or facultative municipal WWTPs effluents, where there is no removal of NH4+. In this case, N2O formation and emission may end up being more severe than in advanced treatment systems, although this occurs outside of the installation's physical boundaries, i.e., when the nitrogen-rich discharge is returned to a receiving body of water where natural and non-selective N/D processes are stimulated. There is however, great uncertainty on the quantification of N2O emissions from surface waters, because most studies of N2O formation have been carried out in groundwater, mouths of rivers, inland seas, and stagnant waters, which often have more favorable conditions for N2O formation: restricted availability of oxygen, greater presence of nitrifying micro-organisms, and high levels of alkalinity. Furthermore, the high solubility of N2O in water favors high concentrations of this gas in infiltrated and ground water and thus tends to remain in liquid phase until it finds the right conditions for its release into the atmosphere (Bowden & Bormann, 1986; Yoshinari et al, 1997; Bateman & Hiscock, 2001). Recently, thanks to the notable evolution of the isotopic monitoring of contaminants, and laser spectroscopy it has been possible to identify several preferential paths in the biochemical transformation of nitrogen and its derivatives in situ. Everything seems to indicate that the non-selective nitrification of the ammonium ion is the principal path of N2O formation in water systems (Ueda et al, 1993; Kim & Craig, 1993; Bateman & Hiscock, 2001). As part of the proposed Rio Frio Wastewater Treatment and Carbon Offset Project, nitrogen in the effluent will be removed through a combination of aoxic and anoxic treatment steps. Measurements have been designed to determine the background emissions of N2O in the rivershed receiving the effluent of the plant as well as at the plant site, before and afetr construction of a nitrogen removal scheme at the plant. The measurements constitute a first of a kind combination of laser spectroscopy, gas chromatography and mass spectrometry to measure N2O in river-shed wide area, at an accuracy required to document emission reductions of N2O. The measurements will also contribute to a better understanding of the mechanism of formation of N2O and to the determination of N2O emission factors. This paper describes the measurement systems designed for the purpose and the monitoring protocols that would be used to document the baseline and emission reductions of N2O. The results are expected to influence climate policy as it relates to N2O emissions from wastewater treatment plants.
A54B-06 16:45h
Global Trends in Tropospheric Water Vapor from 1995 to 2003: The GOME Water Vapor Climatology
We present trend analysis of total column tropospheric water vapor (WV) measured by the Global Ozone Monitoring Experiment (GOME) between August 1995 and August 2003. The GOME instrument measures WV in the visible region of the spectrum and provides total column values over all surface types in cloud free situations. Monthly mean values from GOME are therefore suitable for model evaluations of General Circulation and Chemical Transport Models (GCMs and CTMs) and for the analysis of climate change. We compare trend analysis from the GOME Water Vapor Climatology (GWC) Project (http://www1.mpch-mainz.mpg.de/~saphire/gome_igam/) to data compiled from other satellite based sensors, like the Special Sensor Microwave Imager (SSM/I), to in situ radiosonde date from the operational network, to re-analysis data from the European Center for Medium-rangeWeather Forecast (ECMWF) and to model output of CTMs and GCMs. A special focus is put on the recent strong increase of water vapor above Central Europe and Scandinavia and the impact of the 1997 to 1998 ENSO event on the observed trends in different regions of the globe. The comparisons demonstrate the potential of GOME WV data to be used as a benchmark for model evaluations of the hydrological cycle.