Search

Your search keyword '"Fan, Song-Miao"' showing total 49 results
Start Over Author "Fan, Song-Miao"
49 results on '"Fan, Song-Miao"'

1. Regional budgets for nitrogen oxides from continental sources: Variations of rates for oxidation and deposition with season and distance from source regions

Author

Munger, J. William, Fan, Song-Miao, Bakwin, Peter S., Goulden, Mike L., Goldstein, Allen. H., Colman, Albert S., and Wofsy, Steven C.

Subjects
constituent sources and sinks, Troposphere, pollution, chemistry
Abstract

Measurements of nitrogen deposition and concentrations of NO, NO2, NO y (total oxidized N), and O3 have been made at Harvard Forest in central Massachusetts since 1990 to define the atmospheric budget for reactive N near a major source region. Total (wet plus dry) reactive N deposition for the period 1990–1996 averaged 47 mmol m−2 yr−1 (126 μmol m−2 d−1, 6.4 kg N ha−1 yr−1), with 34% contributed by dry deposition. Atmospheric input adds about 12% to the N made available annually by mineralization in the forest soil. The corresponding deposition rate at a distant site, Schefferville, Quebec, was 20 mmol m−2 d−1 during summer 1990. Both heterogeneous and homogeneous reactions efficiently convert NO x to HNO3 in the boundary layer. HNO3 is subsequently removed rapidly by either dry deposition or precipitation. The characteristic (e-folding) time for NO x oxidation ranges from 0.30 days in summer, when OH radical is abundant, to ∼1.5 days in the winter, when heterogeneous reactions are dominant and O3 concentrations are lowest. The characteristic time for removal of NO x oxidation products (defined as NO y minus NO x) from the boundary layer by wet and dry deposition is ∼1 day, except in winter when it decreases to 0.6 day. Biogenic hydrocarbons contribute to N deposition through formation of organic nitrates but are also precursors of reservoir species, such as peroxyacetylnitrate, that may be exported from the region. A simple model assuming pseudo first-order rates for oxidation of NO x, followed by deposition, predicts that 45% of NO x in the northeastern U.S. boundary layer is removed in 1 day during summer and 27% is removed in winter. It takes 3.5 and 5 days for 95% removal in summer and winter, respectively.

Published
1998

2. Physiological responses of a black spruce forest to weather

Author

Goulden, Michael L., Daube, Bruce C., Fan, Song-Miao, Sutton, Douglas J., Bazzaz, Ammar, Munger, J. William, and Wofsy, Steven C.

Subjects
plant ecology, Biosphere/atmosphere interactions, evapotranspiration
Abstract

We used eddy covariance to measure the net exchange of CO2 between the atmosphere and a black spruce (Picea mariana) forest in Manitoba for 16,500 hours from March 16, 1994 to October 31, 1996. We then partitioned net exchange into gross photosynthesis and respiration by estimating daytime respiration as a function of temperature, and used these data to define the physiological responses of the forest to weather. The annual rates of gross production and respiration by the forest were both around 8 t C ha−1 yr−1. Both photosynthetic and respiratory response were reduced in winter, recovered with warming in spring, and varied little in summer. Respiration in mid summer increased with air temperature (T air) at a Q 10 of around 2 to a rate of 2–8 μmol m−2 s−1 at 15°C. Gross photosynthesis at high light (photon flux density (PPFD) greater than 600 μmol m−2 s−1) was negligible at Tair < 0°C, increased linearly with Tair from 0° to 14°C, and was relatively insensitive to T air > 14°C. Gross CO2 uptake at T air > 14°C increased with increasing light at an ecosystem-level quantum yield of 0.05 mol CO2 mol−1 photons before saturating at an uptake rate of 8–18 μmol m−2 s−1 at PPFDs greater than 500–700 μmol m−2 s−1. Photosynthesis in summer did not appear limited by high evaporative demand or soil water depletion.

Published
1997

4. Emission of nitric oxide (NO) from tropical forest soils and exchange of NO between the forest canopy and atmospheric boundary layers

Author

Bakwin, Peter S, Wofsy, Steven C, Fan, Song-Miao, Keller, Michael, Trumbore, Susan E, and Da Costa, Jose Maria

Subjects
boundary layer, canopy, clay, dry season, nitric oxide, rain forest, tropical forest soil, wet season, Brazil, Amazon
Abstract

Emissions of NO from soils in the Amazon rain forest were measured at 66 locations (224 measurements) using an enclosure technique, and continuous vertical profiles of NO and O3 were measured between the ground and 41-m altitude. Fluxes of NO averaged 8.9 (±1.5) × 109 molecules cm−2 s−1 from the dominant (yellow clay) soils of the region, with larger fluxes (33.7 (±6.5) × 109 molecules cm−2 s−1) observed from adjacent white sand soils. Fluxes from clay soils were lower by more than a factor of 5 than fluxes observed during the dry season at a nearby site. Low soil emission rates were reflected in lower concentrations of NO at the top of the forest canopy in the wet season, only 30–50 pptv (parts per trillion by volume) during the daytime. The measured fluxes are consistent with chemical mass balances for NO within the forest canopy, calculated from the NO and O3 profiles taken at night, and with observations of NO between 150 and 5000 m altitude (A. L. Torres and K. R. Hooks, unpublished manuscript, 1989). Measurements of NO emission rates from soil plots fertilized using NaNO3, NH4Cl or sucrose indicated that a reductive pathway (denitrification) may have been primarily responsible for production of the NO released by both clay and sand soils.

Published
1990

8. Measurements of NO(x) and NO(y) concentrations and fluxes over Arctic tundra

Author

Bakwin, Peter S, Wofsy, Steven C, Fan, Song-Miao, and Fitzjarrald, David R

Subjects
Geophysics
Abstract

Measurements of the atmospheric concentrations of NO, NO2, total NO(y), and O3 were made during the NASA Arctic Boundary Layer Expedition (ABLE 3A) at a remote location in a tundra bog ecosystem in southeastern Alaska during the growing season (July-August 1988). Concentrations of NO(x) and NO(y) were found to be very low compared to other remote continental sites, indicating that anthropogenic influences were small at this site during this time of year. The NO(y) emission rate from the soil were 0.13 +/- 0.05 x 10 exp 9 molecules/sq cm/s. Direct measurements of the flux of total NO(y) were made for the first time, indicating downward flux of NO(y) at all times of day, with maximum deposition of 2.5 +/- 0.9 x 10 exp 9 molecules/sq cm/s in the afternoon. Deposition of HNO3 appears to dominate the atmosphere/surface exchange of NO(y). The mean dry deposition rate of NO(y) to the tundra was 1.8 +/- 1.0 x 10 exp 9 molecules/sq cm/s.

Published
1992

9. Biosphere/atmosphere CO2 exchange in tundra ecosystems - Community characteristics and relationships with multispectral surface reflectance

Author

Whiting, Gary J, Bartlett, David S, Fan, Song-Miao, Bakwin, Peter S, and Wofsy, Steven C

Subjects
Geophysics
Abstract

CO2 exchange rates were measured at selected tundra sites near Bethel, Alaska using portable, climate-controlled, instrumented enclosures. The empirically modeled exchange rate for a representative area of vegetated tundra was 1.2 +/- 1.2 g/sq m/d, compared to a tower-measured exchange over the same time period of 1.1 +.0- 1.2 g/sq m/d. Net exchange in response to varying light levels was compared to wet meadow and dry upland tundra, and to the net exchange measured by the micrometeoroidal tower technique. The multispectral reflectance properties of the sites were measured and related to exchange rates in order to provide a quantitative foundation for the use of satellite remote sensing to monitor biosphere/atmosphere CO2 exchange in the tundra biome.

Published
1992

10. Measurements of reactive nitrogen oxides (NO/y/) within and above a tropical forest canopy in the wet season

Author

Bakwin, Peter S, Wofsy, Steven C, and Fan, Song-Miao

Subjects
Geophysics
Abstract

Measurements of ambient concentrations of reactive nitrogen oxides were made in the Amazon rain forest, near Manaus, Brazil, continuously at 39 m (above the canopy), and on several days and nights at 19 m (within the canopy). Concentrations were very low, typically 100-700 pptv, except for brief periods when up to 5000 pptv of NO(y) was observed, indicating polluted air from the urban area of Manaus. The forest was a net sink for NO(y) with the NO(y) flux = -7.6 + or - 5.0) x 10 to the 9th molecules/sq cm per sec in unpolluted periods, even though soils emitted NO at a significant rate (8.9 + or - 1.5 x 10 to the 9th molecules/sq cm per sec). The deposition rate for NO(y) appeared to be much larger during the daytime than at night, suggesting that uptake was controlled either by plant processes (stomatal opening) or by supply of reactive components of NO(y) (e.g., HNO3) during the daytime. Implications for regional and global atmospheric chemistry are discussed.

Published
1990

11. Atmosphere-biosphere exchange of CO2 and O3 in the Central Amazon Forest

Author

Fan, Song-Miao, Wofsy, Steven C, Bakwin, Peter S, Jacob, Daniel J, and Fitzjarrald, David R

Subjects
Meteorology And Climatology
Abstract

An eddy correlation measurement of O3 deposition and CO2 exchange at a level 10 m above the canopy of the Amazon forest, conducted as part of the NASA/INPE ABLE2b mission during the wet season of 1987, is presented. It was found that the ecosystem exchange of CO2 undergoes a well-defined diurnal variation driven by the input of solar radiation. A curvilinear relationship was found between solar irradiance and uptake of CO2, with net CO2 uptake at a given solar irradiance equal to rates observed over forests in other climate zones. The carbon balance of the system appeared sensitive to cloud cover on the time scale of the experiment, suggesting that global carbon storage might be affected by changes in insolation associated with tropical climate fluctuations. The forest was found to be an efficient sink for O3 during the day, and evidence indicates that the Amazon forests could be a significant sink for global ozone during the nine-month wet period and that deforestation could dramatically alter O3 budgets.

Published
1990

12. Terrestrial carbon sink in the Northern Hemisphere estimated from the atmospheric CO2 difference between Mauna Loa and the South Pole since 1959

Author

Fan, Song-Miao, Blaine, Tegan L., and Sarmiento, Jorge L.

Subjects
Atmospheric Science
Abstract

The diVerence between Mauna Loa and South Pole atmospheric CO2 concentrations from 1959 to the present scales linearly with CO2emissions from fossil fuel burning and cement production (together called fossil CO2). An extrapolation to zero fossil CO2 emission has been used to suggest that the atmospheric CO2 concentration at Mauna Loa was 0.8 ppm less than that at the South Pole before the industrial revolution, associated with a northward atmospheric transport of about 1 Gt C yr−1 (Keeling et al. 1989a). Mass conservation requires an equal southward transport in the ocean. However, our ocean general circulation and biogeochemistry model predicts a much smaller pre-industrial carbon transport. Here, we present a new analysis of the Mauna Loa and South Pole CO2 data, using a general circulation model and a 2-box model of the atmosphere. It is suggested that the present CO2 diVerence between Mauna Loa and the South Pole is caused by, in addition to fossil CO2 sources and sinks, a pre-industrial interhemispheric flux of 0.5–0.7 Gt C yr−1, and a terrestrial sink of 0.8–1.2 Gt C yr−1 in the mid-latitude Northern Hemisphere, balanced by a tropical deforestation source that has been operating continuously in the period from 1959 to the present.DOI: 10.1034/j.1600-0889.1999.t01-4-00001.x

Published
1999

15. Three-dimensional transport and concentration of SF6

Author

Denning, A. Scott, Holzer, Mark, Gurney, Kevin R., Heimann, Martin, Law, Rachel M., Rayner, Peter J., Fung, Inez Y., Fan, Song-Miao, Taguchi, Shoichi, Friedlingstein, Pierre, Balkanski, Yves, Taylor, John, Maiss, Manfred, and Levin, Ingeborg

Abstract

Sulfur hexafluoride (SF6) is an excellent tracer of large-scale atmospheric transport, because it has slowly increasing sources mostly confined to northern midlatitudes, and has a lifetime of thousands of years. We have simulated the emissions, transport, and concentration of SF6 for a 5-year period, and compared the results with atmospheric observations. In addition, we have performed an intercomparison of interhemispheric transport among 11 models to investigate the reasons for the differences among the simulations. Most of the models are reasonably successful at simulating the observed meridional gradient of SF6 in the remote marine boundary layer, though there is less agreement at continental sites. Models that compare well to observations in the remote marine boundary layer tend to systematically overestimate SF6 at continental locations in source regions, suggesting that vertical trapping rather than meridional transport may be a dominant control on the simulated meridional gradient. The vertical structure of simulated SF6 in the models supports this interpretation. Some of the models perform quite well in terms of the simulated seasonal cycle at remote locations, while others do not. Interhemispheric exchange time varies by a factor of 2 when estimated from 1-dimensional meridional profiles at the surface, as has been done for observations. The agreement among models is better when the global surface mean mole fraction is used, and better still when the full 3-dimensional mean mixing ratio is used. The ranking of the interhemispheric exchange time among the models is not sensitive to the change from station values to surface means, but is very sensitive to the change from surface means to the full 3-dimensional tracer fields. This strengthens the argument that vertical redistribution dominates over interhemispheric transport in determining the meridional gradient at the surface. Vertically integrated meridional transport in the models is divided roughly equally into transport by the mean motion, the standing eddies, and the transient eddies. The vertically integrated mass flux is a good index of the degree to which resolved advection vs. parameterized diffusion accomplishes the meridional transport of SF6. Observational programs could provide a much better constraint on simulated chemical tracer transport if they included regular sampling of vertical profiles of nonreactive trace gases over source regions and meridional profiles in the middle to upper troposphere. Further analysis of the SF6simulations will focus on the subgrid-scale parameterized transports.DOI: 10.1034/j.1600-0889.1999.00012.x

Published
2011

16. Three-dimensional transport and concentration of SF 6 A model intercomparison study (TransCom 2)

Author

Denning, A. Scott, Holzer, Mark, Gurney, Kevin, Heimann, Martin, Law, Rachel, Rayner, Peter, Fung, Inez, Fan, Song-Miao, Taguchi, Shoichi, Friedlingstein, Pierre, Balkanski, Yves, Taylor, John, Maiss, Manfred, Levin, Ingeborg, Adaptive Behaviour Research Group (ABRG), University of Sheffield [Sheffield], Max-Planck-Institut für Biogeochemie (MPI-BGC), School of Earth Sciences [Melbourne], Faculty of Science [Melbourne], University of Melbourne-University of Melbourne, Department of Earth and Planetary Science [UC Berkeley] (EPS), University of California [Berkeley], University of California-University of California, College of Engineering, Mathematics and Physical Sciences [Exeter] (EMPS), University of Exeter, Laboratoire des Sciences du Climat et de l'Environnement [Gif-sur-Yvette] (LSCE), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ), Modelling the Earth Response to Multiple Anthropogenic Interactions and Dynamics (MERMAID), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ), Institut für Umweltphysik [Heidelberg], Universität Heidelberg [Heidelberg], University of California [Berkeley] (UC Berkeley), University of California (UC)-University of California (UC), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), and Universität Heidelberg [Heidelberg] = Heidelberg University

Subjects
[SDU.OCEAN]Sciences of the Universe [physics]/Ocean, Atmosphere, [SDU.STU.CL]Sciences of the Universe [physics]/Earth Sciences/Climatology, [SDE.MCG]Environmental Sciences/Global Changes, [SDE]Environmental Sciences
Abstract

International audience; Sulfur hexafluoride (SF6) is an excellent tracer of large-scale atmospheric transport, because it has slowly increasing sources mostly confined to northern midlatitudes, and has a lifetime of thousands of years. We have simulated the emissions, transport, and concentration of SF6 for a 5-year period, and compared the results with atmospheric observations. In addition, we have performed an intercomparison of interhemispheric transport among 11 models to investigate the reasons for the differences among the simulations. Most of the models are reasonably Successful at simulating the observed meridional gradient of SF6 in the remote marine boundary layer, though there is less agreement at continental sites. Models that compare well to observations in the remote marine boundary layer tend to systematically overestimate SF6 at continental locations in source regions, suggesting that vertical trapping rather than meridional transport may be a dominant control on the simulated meridional gradient. The vertical structure of simulated SF6 in the models supports this interpretation. Some of the models perform quite well in terms of the simulated seasonal cycle at remote locations, while others do not. Interhemispheric exchange time varies by a factor of 2 when estimated from 1-dimensional meridional profiles at the surface, as has been done for observations. The agreement among models is better when the global surface mean mole fraction is used, and better still when the full 3-dimensional mean mixing ratio is used. The ranking of the interhemispheric exchange time among the models is not sensitive to the change from station values to surface means, but is very sensitive to the change from surface means to the full 3-dimensional tracer fields. This strengthens the argument that vertical redistribution dominates over interhemispheric transport in determining the meridional gradient at the surface. Vertically integrated meridional transport in the models is divided roughly equally into transport by the mean motion, the standing eddies, and the transient eddies. The vertically integrated mass flux is a good index of the degree to which resolved advection vs. parameterized diffusion accomplishes the meridional transport of SF6. Observational programs could provide a much better constraint on simulated chemical tracer transport if they included regular sampling of vertical profiles of nonreactive trace gases over source regions and meridional profiles in the middle to upper troposphere. Further analysis of the SF6 simulations will focus on the subgrid-scale parameterized transports.

Published
1999

23. Measurements and models of the atmospheric Ar/N2ratio

Author

Battle, Mark, primary, Bender, Michael, additional, Hendricks, Melissa B., additional, Ho, David T., additional, Mika, Robert, additional, McKinley, Galen, additional, Fan, Song-Miao, additional, Blaine, Tegan, additional, and Keeling, Ralph F., additional

Published
2003
Full Text
View/download PDF

29. Three-dimensional transport and concentration of SF6. A model intercomparison study (TransCom 2)

Author

DENNING, A. SCOTT, primary, HOLZER, MARK., additional, GURNEY, KEVIN R., additional, HEIMANN, MARTIN, additional, LAW, RACHEL M., additional, RAYNER, PETER J., additional, FUNG, INEZ Y., additional, FAN, SONG-MIAO, additional, TAGUCHI, SHOICHI, additional, FRIEDLINGSTEIN, PIERRE, additional, BALKANSKI, YVES, additional, TAYLOR, JOHN, additional, MAISS, MANFRED, additional, and LEVIN, INGEBORG, additional

Published
1999
Full Text
View/download PDF

39. Three-dimensional transport and concentration of SF6.

Author

DENNING, A. SCOTT, HOLZER, MARK., GURNEY, KEVIN R., HEIMANN, MARTIN, LAW, RACHEL M., RAYNER, PETER J., FUNG, INEZ Y., FAN, SONG-MIAO, TAGUCHI, SHOICHI, FRIEDLINGSTEIN, PIERRE, BALKANSKI, YVES, TAYLOR, JOHN, MAISS, MANFRED, and LEVIN, INGEBORG

Published
1999
Full Text
View/download PDF

44. Terrestrial carbon sink in the Northern Hemisphere estimated from the atmospheric CO2difference between Mauna Loa and the South Pole since 1959

Author

FAN, SONG‐MIAO., BLAINE, TEGAN L., and SARMIENTO, JORGE L.

Abstract

The diVerence between Mauna Loa and South Pole atmospheric CO2concentrations from 1959 to the present scales linearly with CO2emissions from fossil fuel burning and cement production (together called fossil CO2). An extrapolation to zero fossil CO2emission has been used to suggest that the atmospheric CO2concentration at Mauna Loa was 0.8 ppm less than that at the South Pole before the industrial revolution, associated with a northward atmospheric transport of about 1 Gt C yr−1(Keeling et al. 1989a). Mass conservation requires an equal southward transport in the ocean. However, our ocean general circulation and biogeochemistry model predicts a much smaller pre‐industrial carbon transport. Here, we present a new analysis of the Mauna Loa and South Pole CO2data, using a general circulation model and a 2‐box model of the atmosphere. It is suggested that the present CO2diVerence between Mauna Loa and the South Pole is caused by, in addition to fossil CO2sources and sinks, a pre‐industrial interhemispheric flux of 0.5–0.7 Gt C yr−1, and a terrestrial sink of 0.8–1.2 Gt C yr−1in the mid‐latitude Northern Hemisphere, balanced by a tropical deforestation source that has been operating continuously in the period from 1959 to the present.

Published
1999
Full Text
View/download PDF

45. Three-dimensional transport and concentration of SF6A model intercomparison study (TransCom 2)

Author

Denning, A. Scott, Holzer, Mark, Gurney, Kevin R., Heimann, Martin, Law, Rachel M., Rayner, Peter J., Fung, Inez Y., Fan, Song-Miao, Taguchi, Shoichi, Friedlingstein, Pierre, Balkanski, Yves, Taylor, John, Maiss, Manfred, and Levin, Ingeborg

Abstract

Sulfur hexafluoride (SF6) is an excellent tracer of large-scale atmospheric transport, because it has slowly increasing sources mostly confined to northern midlatitudes, and has a lifetime of thousands of years. We have simulated the emissions, transport, and concentration of SF6for a 5-year period, and compared the results with atmospheric observations. In addition, we have performed an intercomparison of interhemispheric transport among 11 models to investigate the reasons for the differences among the simulations. Most of the models are reasonably successful at simulating the observed meridional gradient of SF6in the remote marine boundary layer, though there is less agreement at continental sites. Models that compare well to observations in the remote marine boundary layer tend to systematically overestimate SF6at continental locations in source regions, suggesting that vertical trapping rather than meridional transport may be a dominant control on the simulated meridional gradient. The vertical structure of simulated SF6in the models supports this interpretation. Some of the models perform quite well in terms of the simulated seasonal cycle at remote locations, while others do not. Interhemispheric exchange time varies by a factor of 2 when estimated from 1-dimensional meridional profiles at the surface, as has been done for observations. The agreement among models is better when the global surface mean mole fraction is used, and better still when the full 3-dimensional mean mixing ratio is used. The ranking of the interhemispheric exchange time among the models is not sensitive to the change from station values to surface means, but is very sensitive to the change from surface means to the full 3-dimensional tracer fields. This strengthens the argument that vertical redistribution dominates over interhemispheric transport in determining the meridional gradient at the surface. Vertically integrated meridional transport in the models is divided roughly equally into transport by the mean motion, the standing eddies, and the transient eddies. The vertically integrated mass flux is a good index of the degree to which resolved advection vs. parameterized diffusion accomplishes the meridional transport of SF6. Observational programs could provide a much better constraint on simulated chemical tracer transport if they included regular sampling of vertical profiles of nonreactive trace gases over source regions and meridional profiles in the middle to upper troposphere. Further analysis of the SF6simulations will focus on the subgrid-scale parameterized transports.

Published
1999
Full Text
View/download PDF

46. Atmosphere-biosphere exchange of CO 2 and O 3 in the central Amazon Forest

Author

Fan, Song-Miao, Wofsy, Steven Charles, Bakwin, Peter S., Jacob, Daniel James, and Fitzjarrald, David Roy

Abstract

Measurements of vertical fluxes for CO2 and O3 were made at a level 10 m above the canopy of the Amazon forest during the wet season, using eddy correlation techniques. Vertical profiles of CO2 and O3 were recorded continuously from above the canopy to the soil surface, and forest floor respiration was measured using soil enclosures. Nocturnal respiration of CO2 by the forest ecosystem averaged 2.57 kgC/ha/h, with about 85% from the forest floor. During the daytime, CO2 was taken up at a mean rate of 4.4 kgC/ha/h. Net ecosystem uptake of carbon dioxide increased with solar flux by 0.015 (kgC/ha/h)/(W m−2), corresponding to fixation of 0.0076 moles CO2 per mole photons (about 0.017 moles CO2 per mole of absorbed photons at photosynthetically active wavelengths). The relationship between net ecosystem exchange and solar flux was virtually the same in the Amazon forest as in forests in Canada (Desjardins et al., 1982, 1985) and Tennessee (Baldocchi et al., 1987a,b). The relatively high efficiency for utilization of light (about 30% of the theoretical maximum) and the strong dependence of net CO2 uptake on solar flux suggest that light may significantly regulate net ecosystem exchange and carbon storage in the tropical forest. Changes in the distribution of cloud cover, associated for example with climatic shifts, might induce globally significant changes in carbon storage. Rates for uptake of O3 averaged 2.3×1011 molecules cm−2s−1 in the daytime (10 hours, 700–1700 hours), dropping by roughly a factor of 10 during the 14 hours from dusk to dawn. The mean O3 deposition velocity at 40 m was 0.26 cm s−1 in the night and 1.8 cm s−1 in the day. Diurnal variation of O3 deposition was regulated both by stratification of the atmospheric boundary layer and by stomatal response to light and water deficit. The total flux of O3 to the forest was limited largely by supply from the free troposphere above. Deposition of O3 to the forest canopy appears to be a regionally, and perhaps globally, important sink for tropospheric O3., Engineering and Applied Sciences

Published
1990
Full Text
View/download PDF

Catalog

Books, media, physical & digital resources
See catalog results