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1.
Micrometeorological flux-gradient and nocturnal boundary layer methods were combined with Fourier transform infrared (FTIR) spectroscopy for high-precision trace gas analysis to measure fluxes of the trace gases CO 2, CH 4 and N 2O between agricultural fields and the atmosphere. The FTIR measurements were fully automated and routinely obtained a precision of 0.1–0.2% for several weeks during a measurement campaign in October 1995. In flux-gradient measurements, vertical profiles of the trace gases were measured every 30 min from the ground to 22 m. When combined with independent micrometeorological measurements of water vapour fluxes, trace gas fluxes from the underlying surface could be determined. In the nocturnal boundary layer method the rate of change in mass storage in the 0–22 m layer was combined with fluxes measured at 22 m to estimate surface fluxes. Daytime fluxes for CO 2 were −0.78±0.40 (1 σ) mg CO 2 m −2 s −1. Daytime fluxes of N 2O and CH 4 were very small and difficult to measure reliably using the flux-gradient technique, despite the high precision of the concentration measurements. Mean daytime flux for N 2O was 17±48 ng N m −2 s −1, while the corresponding flux for CH 4 was 47±410 ng CH 4 m −2 s −1. The mean nighttime flux of CO 2 estimated using the nocturnal boundary layer method was +0.15±0.05 mg CO 2 m −2 s −1, in good agreement with chamber measurements of respiration rates. Nighttime fluxes of CH 4 and N 2O from the nocturnal boundary layer method were 109±69 ng CH 4 m −2 s −1 and 2±3.2 ng N m −2 s −1, respectively, in good agreement with chamber measurements and inventory estimates based on the sheep and cattle stocking rates in the region. The suitability of FTIR-based methods for long term monitoring of spatially and temporally averaged flux measurements is discussed. 相似文献
2.
We present measurements of several trace gases made at a subtropical coastal site in Hong Kong in October and November 1997. The gases include O 3, CO, SO 2, and NO x. The surface measurement data are compared with those from an aircraft study [Kok et al. J. Geophys. Res. 102 (D15) (1997) 19043–19057], and a subset of the latter is used to show the vertical distribution of the trace gases in the boundary layer. During the study period, averaged concentrations at the surface site for O 3, CO, NO x, and SO 2 were 50, 298, 2.75, and 1.65 ppbv, respectively. Their atmospheric abundance and diurnal pattern are similar to those found in the “polluted” rural areas in North America. The measured trace gases are fairly well mixed in the coastal boundary layer in the warm South China region. Large variability is indicated from the data. Examination of 10-day, isentropic back trajectories shows that the measured trace gases are influenced by maritime air masses, outflow of pollution-laden continental air, and the mixing of the two. The trajectories capture the contrasting chemical features of the large-scale air masses impacting on the study area. CO, NO x and SO 2 all show higher concentrations in the strong outflow of continental air, as expected, than those in the marine category. Compared with previously reported values for the western Pacific, the much higher levels found in the marine trajectories in our study suggest the impacts of regional and/or sub-regional emissions on the measured trace gases at the study site. The presence of abundant O 3 and other chemically active trace gases in the autumn season, coupled with high solar radiation and warm weather, suggests that the South China Sea is a photochemically active region important for studying the chemical transformation of pollutants emitted from the Asian continent. 相似文献
3.
Having a quantitative understanding of the carbon cycle in forests is of great importance for predicting global warming issues. Carbon dioxide production in soil is the largest CO 2 source in forests, and exhibits large temporal and spatial variations. Continuous observation of soil CO 2 flux at many sites over a forest is therefore necessary to obtain representative soil CO 2 fluxes for the forest. In this study, a gradient method to measure soil CO 2 flux indirectly from soil radon and CO 2 measurements was theoretically modified to conveniently measure the soil CO 2 flux from soil radon and CO 2 concentrations measured at one soil depth. To experimentally test the modified method, a field observation was conducted continuously in a forest over a 31-day period.Since changes in the soil water content near the soil surface were small throughout the observation, a constant effective diffusivity for CO 2 was assumed for the soil CO 2 flux estimation. The soil CO 2 flux was then calculated as the product of the effective diffusivity and the gradient of the soil CO 2 concentration, each calculated from soil radon and CO 2 concentrations. The estimated flux ranged from 1.9 to 5.8 μmol m ?2 s ?1, and, correlating well with the reference value, measured with a conventional ventilated-chamber method. We therefore conclude that the modified gradient method based on the measurement of soil CO 2 and radon concentration at one depth is reliable, at least under conditions where the change in the soil water content is small. 相似文献
4.
The emissions of exhaust gases (NO x , SO 2, VOCs, and CO 2) and particles (e.g., PM) from ships traversing Busan Port in Korea were estimated over three different years (the years 2006, 2008, and 2009). This analysis was performed according to the ship operational modes (“at sea,” “maneuvering,” and “in port”) and ship types based on an activity-based method. The ship emissions for current (base year 2009) and future scenarios (years 2020 and 2050) were also compared. The annual emissions of SO 2, VOCs, PM, and CO 2 were highest (9.6?×?10 3, 374, 1.2?×?10 3, and 5.6?×?10 5 ton year ?1, respectively) in 2008. In contrast, the annual NO x emissions were highest (11.7?×?10 3 ton year ?1) in 2006 due mainly to the high NO x emission factor. The emissions of air pollutants for each ship operational mode differed considerably, with the largest emission observed in “in port” mode. In addition, the largest fraction (approximately 45–67 %) of the emissions of all air pollutants during the study period was emitted from container ships. The future ship emissions of most pollutants (except for SO 2 and PM) in 2020 and 2050 are estimated to be 1.4–1.8 and 4.7–6.1 times higher than those in 2009 (base year), respectively. 相似文献
5.
A decentralized emission inventories are prepared for road transport sector of India in order to design and implement suitable technologies and policies for appropriate mitigation measures. Globalization and liberalization policies of the government in 90's have increased the number of road vehicles nearly 92.6% from 1980–1981 to 2003–2004. These vehicles mainly consume non-renewable fossil fuels, and are a major contributor of green house gases, particularly CO 2 emission. This paper focuses on the statewise road transport emissions (CO 2, CH 4, CO, NO x, N 2O, SO 2, PM and HC), using region specific mass emission factors for each type of vehicles. The country level emissions (CO 2, CH 4, CO, NO x, N 2O, SO 2 and NMVOC) are calculated for railways, shipping and airway, based on fuel types. In India, transport sector emits an estimated 258.10 Tg of CO 2, of which 94.5% was contributed by road transport (2003–2004). Among all the states and Union Territories, Maharashtra's contribution is the largest, 28.85 Tg (11.8%) of CO 2, followed by Tamil Nadu 26.41 Tg (10.8%), Gujarat 23.31 Tg (9.6%), Uttar Pradesh 17.42 Tg (7.1%), Rajasthan 15.17 Tg (6.22%) and, Karnataka 15.09 Tg (6.19%). These six states account for 51.8% of the CO 2 emissions from road transport. 相似文献
6.
Forty operational measurements by aircraft are described, which were performed during 1985–1987. The purpose was to obtain an overall picture of transboundary transports of SO 2, NOx sulfate, nitrate and O 3 between the F.R.G. and its neighbours. Transboundary fluxes were calculated by means of measurement results with respect to the concentrations of the considered pollutants, depth of the planetary boundary layer, wind speed and wind direction. The largest SO 2 fluxes have been observed across the eastern border of the F.R.G., during periods characterized by easterly winds (300–2500 ton SO 2 h −1 across a 500–600 km border section). The major fraction of this SO 2 appeared to have originated from the easterly neighbours of the F.R.G. and to a lesser extent also from countries further eastward. During easterly winds it has been observed that SO 2, which originated from countries east of the F.R.G., contributed considerably to SO 2 fluxes across the western border to countries west of the F.R.G. The results of the measurement flights as presented have provided valuable indications about transboundary transports of pollutants despite considerable uncertainties in the fluxes due to inaccuracies in the concentration profiles, wind data and depth of the planetary boundary layer. 相似文献
7.
The quantitative assessment of landfill gas emissions is essential to assess the performance of the landfill cover and gas collection system. The relative error of the measured surface emission of landfill gas may be induced by the static flux chamber technique. This study aims to quantify effects of the size of the chamber, the insertion depth, pressure differential on the relative errors by using an integrated approach of in situ tests, and numerical modeling. A field experiment study of landfill gas emission is conducted by using a static chamber at one landfill site in Xi’an, Northwest China. Additionally, a two-dimensional axisymmetric numerical model for multi-component gas transport in the soil and the static chamber is developed based on the dusty-gas model (DGM). The proposed model is validated by the field data obtained in this study and a set of experimental data in the literature. The results show that DGM model has a better capacity to predict gas transport under a wider range of permeability compared to Blanc’s method. This is due to the fact that DGM model can explain the interaction among gases (e.g., CH4, CO2, O2, and N2) and the Knudsen diffusion process while these mechanisms are not included in Blanc’s model. Increasing the size and the insertion depth of static chambers can reduce the relative error for the flux of CH4 and CO2. For example, increasing the height of chambers from 0.55 to 1.1 m can decrease relative errors of CH4 and CO2 flux by 17% and 18%, respectively. Moreover, we find that gas emission fluxes for the case with positive pressure differential (?Pin-out) are greater than that of the case without considering pressure fluctuations. The Monte Carlo method was adopted to carry out the statistical analysis for quantifying the range of relative errors. The agreement of the measured field data and predicted results demonstrated that the proposed model has the capacity to quantify the emission of landfill gas from the landfill cover systems. 相似文献
8.
Using proton transfer reaction mass spectrometry equipped with a quadrupol mass analyser to quantify the biosphere-atmosphere exchange of volatile organic compounds (VOC), concentrations of different VOC are measured sequentially. Depending on how many VOC species are targeted and their respective integration times, each VOC is measured at repeat rates on the order of a few seconds. This represents an order of magnitude longer sample interval compared to the standard eddy covariance (EC) method (5–20 Hz sampling rates). Here we simulate the effect of disjunct sampling on EC flux estimates by decreasing the time resolution of CO 2 and H 2O concentrations measured at 20 Hz above a temperate mountain grassland in the Austrian Alps. Fluxes for one month are calculated with the standard EC method and compared to fluxes calculated based on the disjunct data (1, 3 and 5 s sampling rates) using the following approaches: i) imputation of missing concentrations based on the nearest neighbouring samples (iDEC nn), ii) imputation by linear interpolation (iDEC li), and iii) virtual disjunct EC (vDEC), i.e. flux calculation based solely on the disjunct concentrations. It is shown that the two imputation methods result in additional low-pass filtering, longer lag times (as determined with the maximum cross-correlation method) and a flux loss of 3–30% as compared to the standard EC method. A novel procedure, based on a transfer function approach, which specifically corrects for the effect of data treatment, was developed, resulting in improved correspondence (to within 2%). The vDEC method yields fluxes which approximate the true (20 Hz) fluxes to within 3–7% and it is this approach we recommend because it involves no additional empirical corrections. The only drawback of the vDEC method is the noisy nature of the cross-correlations, which poses problems with lag determination – practical approaches to overcome this limitation are discussed. 相似文献
9.
With rising concentrations of both atmospheric carbon dioxide (CO 2) and tropospheric ozone (O 3), it is important to better understand the interacting effects of these two trace gases on plant physiology affecting land-atmosphere gas exchange. We investigated the effect of growth under elevated CO 2 and O 3, singly and in combination, on the primary short-term stomatal response to CO 2 concentration in paper birch at the Aspen FACE experiment. Leaves from trees grown in elevated CO 2 and/or O 3 exhibited weaker short-term responses of stomatal conductance to both an increase and a decrease in CO 2 concentration from current ambient level. The impairement of the stomatal CO 2 response by O 3 most likely developed progressively over the growing season as assessed by sap flux measurements. Our results suggest that expectations of plant water-savings and reduced stomatal air pollution uptake under rising atmospheric CO 2 may not hold for northern hardwood forests under concurrently rising tropospheric O 3. 相似文献
10.
Leaf injury data from acute and chronic exposure studies of Dare soybean were regressed against the logarithms of exposure time and O 3 and SO 2 concentrations to develop a new two-pollutant leaf injury model (which explains 88% of the variance) and to calculate the parameters of best fit for this new model and a previously developed one-pollutant model. Using the calculated parameters, the percentage of leaf surface Injured over a growing season by O 3, SO 2, or both simultaneously was estimated for an ambient air sampling site located 2 miles from a coal burning power plant. For this site, the one- and two-pollutant models predicted that SO 2 effects would be negligible If SO 2 concentrations never exceeded the National Ambient Air Quality Standard (NAAQS) of 0.50 ppm, averaged over 3 h. However, calculations suggest that O 3 may injure up to 24% of Dare soybean leaf surface over a growing season even though the O 3 NAAQS of 0.12 ppm, averaged over 1 h, is never exceeded. Because the 3 h SO 2 standard is exceeded at very few places, the O 3 model is usually sufficient to estimate Dare soybean leaf Injury. Leaf injury is estimated by taking the logarithm of the summation of each daytime hour’s exponentiated O 3 concentration (c) measured at an ambient air sampling site over a growing season. This is expressed as: z = -0.0828 + 0.4876 in (Σ co 3 2.618), where z is the Gaussian transform of percent leaf injury. The methods developed in this paper, using Dare soybean data as an example, may apply to other plants. 相似文献
11.
Human activities have increased anthropogenic CO2 emissions, which are believed to play important roles in global warming. The spatiotemporal variations of CO2 concentration and flux at fine spatial scales in aquaculture ponds remain unclear, particularly in China, the country with the largest aquaculture. In this study, the plot-scale spatiotemporal variations of water CO2 concentration and flux, both within and among ponds, were researched in shrimp ponds in Shanyutan Wetland, Min River Estuary, Southeast China. The average water CO2 concentration and flux across the water–air interface in the shrimp ponds over the shrimp farming period varied from 22.79?±?0.54 to 186.66?±?8.71 μmol L?1 and from ??0.50?±?0.04 to 2.87?±?0.78 mol m?2 day?1, respectively. There was no remarkable difference in CO2 concentration and flux within the ponds, but significantly spatiotemporal differences in CO2 flux were observed between shrimp ponds. Chlorophyll a, pH, salinity, air temperature, and morphometry were the important factors driving the spatiotemporal patterns of CO2 flux in the shrimp ponds. Our findings highlighted the importance and spatiotemporal variations of CO2 flux in the important coastal ecosystems. 相似文献
12.
Poplar shoots were exposed for 3–4 weeks to filtered air, ambient (maximum values 50–60 nl ℓ -1) or two times ambient O 3-concentrations under controlled environmental conditions in fumigation chambers. A sensitive (Populus nigra ‘Brandaris’) and a tolerant (P. euramericana ‘Robusta’) cultivar were used. At regular intervals the uptake of O 3, transpiration and CO 2 assimilation rate ( Pn) of full-grown leaves were measured with leaf cuvettes. For unaffected leaves, the measured flux of O 3 into the leaves appeared to be larger than can be calculated using the stomatal conductance for O 3 ( gs,o) estimated from the transpiration rates of the same leaves. Resistance analysis revealed that the difference was partly a result of a reaction with the external leaf surface. However, when the O 3 flux into the leaf was corrected for this reaction, it was still larger than can be estimated using gs,o. As a consequence, negative residual or internal resistances ( ri) for O 3 transport into the leaves were assessed. It is postulated that O 3 molecules moving into the leaf follow a shorter pathway than effluxing H 2O-molecules. P. ‘Brandaris’ leaves showed a reduction in Pn after 12 days of exposure to ambient O 3-concentrations, whereas for P. ‘Robusta’ a reduction in Pn was only observed at two times ambient concentrations. A simultaneous decline in the O 3-flux was found in both cases. The decline occurred before a decrease in gs,o was observed suggesting that the O 3 flux into the affected leaves was first hindered by internal factors. The measured flux of the affected leaves became smaller than the flux estimated using gs,o and, consequently, positive ri-values were estimated. The change in ri suggests that O 3 molecules not only penetrated deeper into the leaf, but also were accumulating at a prolonged exposure. Our results indicate that ri may be a potentially important component of the overall resistance for O 3-uptake, which may have important consequences for estimating O 3 uptake from water vapour flux data. 相似文献
13.
ABSTRACT This paper presents a technique for the complete, simultaneous decomposition of CO 2, SO 2, and NO x, as well as the simultaneous removal of fly ash by ultra-high voltage pulse activation. Ultra-high voltage narrow pulse is used to make the gases in the reactor become active molecules, which are then dissociated into nonpoisonous gas molecules and solid particles under the control of a directional reaction model. By using a sufficient charge and a strong electric field, the fly ash can be removed. It becomes the carrier of C and S, and its efficiency is 99.5%. Owing to the action of catalyst B (using Ni as the mother's body), the activation energy of CO 2, SO 2, and NO x gases is reduced in great magnitude, and their removal efficiency can reach 75~90% at normal pressure and 180 °C. 相似文献
14.
Ozone (O 3) fluxes above a temperate mountain grassland were measured by means of the eddy covariance (EC) method using a slow-response O 3 analyser. The resultant flux loss was corrected for by a series of transfer functions which model the various sources of high- and, in particular, low-pass filtering. The resulting correction factors varied on average between 1.7 and 3.5 during night and daytime, respectively. A cospectral analysis confirmed the accuracy of this approach. O 3 fluxes were characterised by a comparatively large random uncertainty, which during daytime typically amounted to 60%. EC O 3 fluxes were compared against O 3 flux measurements made concurrently with the flux-gradient (FG) method. The two methods generally agreed well, except for a period between sunrise and early afternoon, when the FG method was suspected of being affected by the presence of photochemical sources/sinks. O 3 flux magnitudes and deposition velocities determined with the EC method compared nicely with the available literature from grassland studies. We conclude that our understanding of the causes and consequences of various sources of flux loss (associated with any EC system) has sufficiently matured so that also less-than-ideal instrumentation may be used in EC flux applications, albeit at the cost of relatively large empirical corrections. 相似文献
15.
During the summertime of 2007/2008, carbon dioxide (CO 2) and methane (CH 4) fluxes across air–water interface were investigated in the littoral zones of Lake Mochou and Lake Tuanjie, east Antarctica, using a static chamber technique. The mean fluxes of CO 2 and CH 4 were ?70.8 mgCO 2 m ?2 h ?1 and 144.6 μgCH 4 m ?2 h ?1, respectively, in the littoral zone of Lake Mochou; The mean fluxes were ?36.9 mgCO 2 m ?2 h ?1 and 109.8 μgCH 4 m ?2 h ?1, respectively, in the littoral zone of Lake Tuanjie. Their fluxes showed large temporal and spatial dynamics. The CO 2 fluxes showed a significantly negative correlation with daily total radiation (DTR) and a weakly negative correlation with air temperature and water temperature, indicating that sunlight intensity controlled the magnitude of CO 2 fluxes from the open lakes. The CH 4 fluxes significantly correlated with local air temperature, water table and total dissolved solids (TDS), indicating that they were the predominant factors influencing CH 4 fluxes. Summertime CO 2 budgets in the littoral zones of Lake Mochou and Lake Tuanjie were estimated to be ?152.9 gCO 2 m ?2 and ?79.7 gCO 2 m ?2, respectively, and net CH 4 emissions were estimated to be 312.3 mgCH 4 m ?2 and 237.2 mgCH 4 m ?2, respectively. Our results show that shallow, open, alga-rich lakes might be strong summertime CO 2 absorbers and small CH 4 emitters during the open water in coastal Antarctica. 相似文献
16.
Agricultural practices affect the production and emission of carbon dioxide (CO 2) from paddy soils. It is crucial to understand the effects of tillage and N fertilization on soil CO 2 flux and its influencing factors for a better comprehension of carbon dynamics in subtropical paddy ecosystems. A 2-yr field study was conducted to assess the effects of tillage (conventional tillage [CT] and no-tillage [NT]) and N fertilization (0 and 210 kg N ha ?1) on soil CO 2 fluxes during the 2008 and 2009 rice growing seasons in central China. Treatments were established following a split-plot design of a randomized complete block with tillage practices as the main plot and N fertilizer level as the split-plot treatment. The soil CO 2 fluxes were measured 24 times in 2008 and 17 times in 2009. N fertilization did not affect soil CO 2 emissions while tillage affected soil CO 2 emissions, where NT had similar soil CO 2 emissions to CT in 2008, but in 2009, NT significantly increased soil CO 2 emissions. Cumulative CO 2 emissions were 2079–2245 kg CO 2–C ha ?1 from NT treatments, and 2084–2141 kg CO 2–C ha ?1 from CT treatments in 2008, and were 1257–1401 kg CO 2–C ha ?1 from NT treatments, and 1003–1034 kg CO 2–C ha ?1 from CT treatments in 2009, respectively. Cumulative CO 2 emissions were significantly related to aboveground biomass and soil organic C. Before drainage of paddy fields, soil CO 2 fluxes were significantly related to soil temperature with correlation coefficients ( R) of 0.67–0.87 in 2008 and 0.69–0.85 in 2009; moreover, the Q 10 values ranged from 1.28 to 1.55 and from 2.10 to 5.21 in 2009, respectively. Our results suggested that NT rice production system appeared to be ineffective in decreasing carbon emission, which suggested that CO 2 emissions from integrated rice-based system should be taken into account to assess effects of tillage. 相似文献
17.
The technique includes the use of two chromatographic columns in series to separate O 2, N 2, CO, CO 2, H 2O, H 2S, SO 2 and CH 3SH. Column 1, containing Triton 45 on Chromosorb, separates H 2O, H 2S, SO 2 and CH 3SH. Column 2, packed with Molecular Sieve, separates O 2, N 2, CO and CO 2. The conditions required to obtain adequate sensitivity and separation are discussed. 相似文献
18.
The effect of elevated CO 2 and O 3 on apparent quantum yield ( ?), maximum photosynthesis ( Pmax), carboxylation efficiency ( Vcmax) and electron transport capacity ( Jmax) at different canopy locations was studied in two aspen ( Populus tremuloides) clones of contrasting O 3 tolerance. Local light climate at every leaf was characterized as fraction of above-canopy photosynthetic photon flux density (%PPFD). Elevated CO 2 alone did not affect ? or Pmax, and increased Jmax in the O 3-sensitive, but not in the O 3-tolerant clone. Elevated O 3 decreased leaf chlorophyll content and all photosynthetic parameters, particularly in the lower canopy, and the negative impact of O 3 increased through time. Significant interaction effect, whereby the negative impact of elevated O 3 was exaggerated by elevated CO 2 was seen in Chl, N and Jmax, and occurred in both O 3-tolerant and O 3-sensitive clones. The clonal differences in the level of CO 2 × O 3 interaction suggest a relationship between photosynthetic acclimation and background O 3 concentration. 相似文献
19.
A new sampling device is described for the simultaneous collection of NH 3, HNO 3, HCl, SO 2 and H 2O 2 in ambient air. The apparatus is based on air sampling by two parallel annular denuder tubes. The gases are collected by absorption in solutions present in the annulus of the denuder tubes. After a sampling time of 30 min at flow rate of 32 ℓ min −1 the solutions are extracted from the denuders and analyzed off-line. The detection limits of NH 3, HNO 3, HCL and SO 2 are in the order of 0.1–0.5 μm −3. For H 2O 2 the detection limit is 0.01 μm −3. The reproducibility is 5–10% at the level of ambient air concentrations. Comparison of this novel technique with existing methods gives satisfactory results. The compact set-up offers the possibility of field experiments without the need of extensive equipment. 相似文献
20.
A study was conducted by the Atmospheric Environment Service (AES) to compute the transboundary sulphur flux between eastern Canada and the eastern United States on a monthly and annual basis for the years 1980–1983.The S fluxes were calculated using the AES Lagrangian model. SO 2 and SO 4 concentrations were computed at 16 line segment mid-points along the Canada-U.S. border from western Ontario through Quebec to the Maritimes. Sulphur fluxes were determined at 6-h intervals and summed temporally and spatially to obtain the total transboundary S flux. By using only the Canadian and only the U.S. emissions, the total S flux contributions from each country could be determined.Canadian and U.S. emissions declined from 1980 to 1983 by 20% and 11%, respectively, then increased slightly in 1983. The total annual S flux from the U.S. to Canada ranged from 1.86 Mt S (1980) to 1.61 Mt S (1983) while the flux from Canada to the U.S. ranged from 0.75 Mt S (1980) to 0.52 Mt S (1982). Fluxes between both countries were highest (lowest) in the winter (summer) because of the stronger (lighter) winds and higher (lower) SO 2 concentrations. However, SO 4 mass flux peaked in summer and early fall because of higher chemical conversion rates.Annual transboundary fluxes were observed to change by up to 20% in response to emissions changes and meteorological variability and these two influences should be considered together when assessing flux changes. 相似文献
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