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91.
Katsunori Tanaka Natsuko Yoshifuji Nobuaki Tanaka Katsushige Shiraki Chatchai Tantasirin Masakazu Suzuki 《Ecological modelling》2009
A soil–plant–air continuum multilayer model was used to numerically simulate canopy net assimilation (An), evapotranspiration (ET), and soil moisture in a deciduous teak plantation in a dry tropical climate of northern Thailand to examine the influence of soil drought on An. The timings of leaf flush and the end of the canopy duration period (CDP) were also investigated from the perspective of the temporal positive carbon gain. Two numerical experiments with different seasonal patterns of leaf area index (LAI) were carried out using above-canopy hydrometeorological data as input data. The first experiment involved seasonally varying LAI estimated based on time-series of radiative transmittance through the canopy, and the second experiment applied an annually constant LAI. The first simulation captured the measured seasonal changes in soil surface moisture; the simulated transpiration agreed with seasonal changes in heat pulse velocity, corresponding to the water use of individual trees, and the simulated An became slightly negative. However, in the second simulation, An became negative in the dry season because the decline in stomatal conductance due to severe soil drought limited the assimilation, and the simultaneous increase in leaf temperature increased dark respiration. Thus, these experiments revealed that the leaflessness in the dry season is reasonable for carbon gain and emphasized the unfavorable soil water status for carbon gain in the dry season. Examining the duration of positive An (DPA) in the second simulation showed that the start of the longest DPA (LDPA) in a year approached the timing of leaf flush in the teak plantation after the spring equinox. On the other hand, the end appeared earlier than that of all CDPs. This result is consistent with the sap flow stopping earlier than the complete leaf fall, implying that the carbon assimilation period ends before the completion of defoliation. The model sensitivity analysis in the second simulation suggests that a smaller LAI and slower maximum rate of carboxylation likely extend the LDPA because soil water from the surface to rooting depth is maintained longer at levels adequate for carbon gain by decreased canopy transpiration. The experiments also suggest that lower soil hydraulic conductivity and deeper rooting depth can postpone the end of the LDPA by increasing soil water retention and the soil water capacity, respectively. 相似文献
92.
93.
Allen AG Machado CM Cardoso AA 《Environmental pollution (Barking, Essex : 1987)》2011,159(5):1190-1197
Increased reactive nitrogen (Nr) deposition due to expansion of agro-industry was investigated considering emission sources, atmospheric transport and chemical reactions. Measurements of the main inorganic nitrogen species (NO2, NH3, HNO3, and aerosol nitrate and ammonium) were made over a period of one year at six sites distributed across an area of ∼130,000 km2 in southeast Brazil. Oxidized species were estimated to account for ∼90% of dry deposited Nr, due to the region’s large emissions of nitrogen oxides from biomass burning and road transport. NO2-N was important closer to urban areas, however overall HNO3-N represented the largest component of dry deposited Nr. A simple mathematical modeling procedure was developed to enable estimates of total Nr dry deposition to be made from knowledge of NO2 concentrations. The technique, whose accuracy here ranged from <1% to 29%, provides a useful new tool for the mapping of reactive nitrogen deposition. 相似文献
94.
Al-Momani IF Momani KA Jaradat QM Massadeh AM Yousef YA Alomary AA 《Environmental monitoring and assessment》2008,136(1-3):209-218
Wet and dry deposition samples were collected in the capital of Jordan, Amman. Concentrations of Al, Ba, Bi, Cd, Co, Cr, Cu,
Mn, Mo, Ni, Pb, Sb, V, Zn, Fe, Sr, Mg2+, Ca2+, Na+, K+, Cl−, NO3
− and SO4
2−, along with pH were determined in collected samples. Mean trace metal concentrations were similar or less than those reported
for other urban regions worldwide, while concentrations of Ca2+ and SO4
2− were among the highest. High Ca2+ concentrations were attributed to the calcareous nature of the local soil and to the influence of the Saharan dust. However,
high SO4
2− concentrations were attributed to the influence of both anthropogenic and natural sources. Except for Cl−, NO3
−, SO4
2− and Cu, monthly dry deposition fluxes of all measured species were higher than wet deposition fluxes. The annual wet deposition
fluxes of trace metals were much lower than those reported for other urban areas worldwide. 相似文献
95.
Atmospheric concentrations of nitric acid (HNO3), sulfur dioxide (SO2), particulate nitrate and particulate sulfate on the urban- and mountain-facing sides of Mt. Gokurakuji were measured from November 2002 to October 2003, in order to evaluate
the effects of anthropogenic activity on air quality and dry deposited nitrate and sulfate on the surfaces of pine foliage.
The results showed that HNO3, SO2 and concentrations were significantly higher (P < 0.05) on the urban-facing side (1.54, 2.48 and 0.65 μg m−3, respectively) than the mountain-facing side (0.67, 1.19 and 0.37 μg m−3, respectively), while concentrations did not differ significantly between the two sides (urban-facing: 2.80 μg m−3; mountain−facing: 2.05 μg m−3). Indirect estimates of dry deposition rates of nitrate and sulfate to the surfaces of pine foliage based on the measured
concentrations approximately agreed with the measured values determined by the foliar rinsing technique in a previous study.
It was found that HNO3 was the major source (approximately 80%) of dry deposited nitrate on pine foliage, while the contribution from was about equal to that from SO2. In conclusion, HNO3 and SO2 appear to be dominant species reflecting higher dry deposition rates of nitrate and sulfate on the urban-facing side compared
to the mountain-facing side of Mt. Gokurakuji. 相似文献
96.
Dry deposition and soil-air gas exchange of polychlorinated biphenyls (PCBs) in an industrial area 总被引:3,自引:0,他引:3
Bozlaker A Odabasi M Muezzinoglu A 《Environmental pollution (Barking, Essex : 1987)》2008,156(3):784-793
Ambient air and dry deposition, and soil samples were collected at the Aliaga industrial site in Izmir, Turkey. Atmospheric total (particle + gas) ∑41-PCB concentrations were higher in summer (3370 ± 1617 pg m−3, average + SD) than in winter (1164 ± 618 pg m−3), probably due to increased volatilization with temperature. Average particulate ∑41-PCBs dry deposition fluxes were 349 ± 183 and 469 ± 328 ng m−2 day−1 in summer and winter, respectively. Overall average particulate deposition velocity was 5.5 ± 3.5 cm s−1. The spatial distribution of ∑41-PCB soil concentrations (n = 48) showed that the iron-steel plants, ship dismantling facilities, refinery and petrochemicals complex are the major sources in the area. Calculated air-soil exchange fluxes indicated that the contaminated soil is a secondary source to the atmosphere for lighter PCBs and as a sink for heavier ones. Comparable magnitude of gas exchange and dry particle deposition fluxes indicated that both mechanisms are equally important for PCB movement between air and soil in Aliaga. 相似文献
97.
Dragutin T. Mihailovic Kiran Alapaty Zorica Podrascanin 《Environmental science and pollution research international》2009,16(2):144-151
Background, aim, and scope Improving the parameterization of processes in the atmospheric boundary layer (ABL) and surface layer, in air quality and
chemical transport models. To do so, an asymmetrical, convective, non-local scheme, with varying upward mixing rates is combined
with the non-local, turbulent, kinetic energy scheme for vertical diffusion (COM). For designing it, a function depending
on the dimensionless height to the power four in the ABL is suggested, which is empirically derived. Also, we suggested a
new method for calculating the in-canopy resistance for dry deposition over a vegetated surface.
Materials and methods The upward mixing rate forming the surface layer is parameterized using the sensible heat flux and the friction and convective
velocities. Upward mixing rates varying with height are scaled with an amount of turbulent kinetic energy in layer, while
the downward mixing rates are derived from mass conservation. The vertical eddy diffusivity is parameterized using the mean
turbulent velocity scale that is obtained by the vertical integration within the ABL. In-canopy resistance is calculated by
integration of inverse turbulent transfer coefficient inside the canopy from the effective ground roughness length to the
canopy source height and, further, from its the canopy height.
Results This combination of schemes provides a less rapid mass transport out of surface layer into other layers, during convective
and non-convective periods, than other local and non-local schemes parameterizing mixing processes in the ABL. The suggested
method for calculating the in-canopy resistance for calculating the dry deposition over a vegetated surface differs remarkably
from the commonly used one, particularly over forest vegetation.
Discussion In this paper, we studied the performance of a non-local, turbulent, kinetic energy scheme for vertical diffusion combined
with a non-local, convective mixing scheme with varying upward mixing in the atmospheric boundary layer (COM) and its impact
on the concentration of pollutants calculated with chemical and air-quality models. In addition, this scheme was also compared
with a commonly used, local, eddy-diffusivity scheme. Simulated concentrations of NO2 by the COM scheme and new parameterization of the in-canopy resistance are closer to the observations when compared to those
obtained from using the local eddy-diffusivity scheme.
Conclusions Concentrations calculated with the COM scheme and new parameterization of in-canopy resistance, are in general higher and
closer to the observations than those obtained by the local, eddy-diffusivity scheme (on the order of 15–22%).
Recommendations and perspectives To examine the performance of the scheme, simulated and measured concentrations of a pollutant (NO2) were compared for the years 1999 and 2002. The comparison was made for the entire domain used in simulations performed by
the chemical European Monitoring and Evaluation Program Unified model (version UNI-ACID, rv2.0) where schemes were incorporated. 相似文献
98.
Cryogenic distillation columns are generally subjected to high-pressure loadings during the natural gas purification process. The high-pressure conditions inside the column cause safety risk e.g. rupture. When an emergency arises, blowdown is a typical way of minimizing the failure hazard. However, blowdown at the cryogenic conditions involves dry ice formation due to the rapid decrease in temperature driven by the Joule-Thomson effect. The dry ice formation intensifies the failure hazard due to the orifice blockage. Therefore, optimization of blowdown parameters is necessary to avoid the dry ice formation. So far, very limited studies are available in the literature for the blowdown of CO₂-CH₄ mixture, especially at the cryogenic conditions. In this study, a computational investigation followed by the experimental validation is accomplished to analyze the dry ice formation during blowdown of CO₂-CH₄ binary mixture from the cryogenic distillation column. The composition of mixture, orifice size, and initial conditions inside vessel have a high impact on blowdown path. A 3.00 mm orifice is the most suitable size for the blowdown at cryogenic conditions as it doesn't promote solidification and discharges the inventory quickly. Based on the experimental observation, an empirical correlation is also developed to instantly find out the optimum blowdown parameters. 相似文献
99.
100.