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1.
Microorganisms are responsible for the mineralisation of organic nitrogen in soils. NH
+4
can be further oxidised to NO3
− during nitrification and NO3
− can be reduced to gaseous nitrogen compounds during denitrification. During both processes, nitrous oxide (N2O), which is known as greenhouse gas, can be lost from the ecosystem. The aim of this study was to quantify N2O emissions and the internal microbial N cycle including net N mineralisation and net nitrification in a montane forest ecosystem in the North Tyrolean Limestone Alps during an 18-month measurement period and to estimate the importance of these fluxes in comparison with other components of the N cycle. Gas samples were taken every 2 weeks using the closed chamber method. Additionally, CO2 emission rates were measured to estimate soil respiration activity. Net mineralisation and net nitrification rates were determined by the buried bag method every month. Ion exchange resin bags were used to determine the N availability in the root zone. Mean N2O emission rate was 0.9 kg N ha−a−, which corresponds to 5 % of the N deposited in the forest ecosystem. The main influencing factors were air and soil temperature and NO
−3
accumulated on the ion exchange resin bags. In the course of net ammonification, 14 kg NH
+4
−N ha− were produced per year. About the same amount of NO
−3
−N was formed during nitrification, indicating a rather complete nitrification going on at the site. NO
t-3
concentrations found on the ion exchange resin bags were about 3 times as high as NO
t-3
produced during net nitrification, indicating substantial NO
t-3
immobilisation. The results of this study indicate significant nitrification activities taking place at the Mühleggerköpfl. 相似文献
2.
Land use conversion and fertilization have been widely reported to be important managements affecting the exchanges of greenhouse gases between soil and atmosphere. For comprehensive assessment of methane (CH 4) and nitrous oxide (N 2O) fluxes from hilly red soil induced by land use conversion and fertilization, a 14-month continuous field measurement was conducted on the newly converted citrus orchard plots with fertilization (OF) and without fertilization (ONF) and the conventional paddy plots with fertilization (PF) and without fertilization (PNF). Our results showed that land use conversion from paddy to orchard reduced the CH 4 fluxes at the expense of increasing the N 2O fluxes. Furthermore, fertilization significantly decreased the CH 4 fluxes from paddy soils in the second stage after conversion, but it failed to affect the CH 4 fluxes from orchard soils, whereas fertilizer applied to orchard and paddy increased soil N 2O emissions by 68 and 113.9 %, respectively. Thus, cumulative CH 4 emissions from the OF were 100 % lower, and N 2O emissions were 421 % higher than those from the PF. Although cumulative N 2O emissions were stimulated in the newly converted orchard, the strong reduction of CH 4 led to lower global warming potentials (GWPs) as compared to the paddy. Besides, fertilization in orchard increased GWPs but decreased GWPs of paddy soils. In addition, measurement of soil moisture, temperature, dissolved carbon contents (DOCs), and ammonia (NH 4 +-N) and nitrate (NO 3 ?-N) contents indicated a significant variation in soil properties and contributed to variations in soil CH 4 and N 2O fluxes. Results of this study suggest that land use conversion from paddy to orchard would benefit for reconciling greenhouse gas mitigation and citrus orchard cultivation would be a better agricultural system in the hilly red soils in terms of greenhouse gas emission. Moreover, selected fertilizer rate applied to paddy would lead to lower GWPs of CH 4 and N 2O. Nevertheless, more field measurements from newly converted orchard are highly needed to gain an insight into national and global accounting of CH 4 and N 2O emissions. 相似文献
3.
Introduction Trends in precipitation pH and conductivity during 1992?C2009, and in ionic compositions from January 2007 to June 2009, are reported from Lushan Mountain, one of the highest mountains in mid-east China. Annual mean pH was in the range of 4.35?C5.01 and showed a statistically very significant ( P?0.01) decreasing trend with time. Annual mean conductivity showed a statistically significant ( P?0.05) increasing trend, although this was not the case for non-H conductivity. Increasing rainwater acidity was mainly caused by increasing amounts of acid substances entering the rain. The trends in precipitation pH and conductivity were directly associated with energy consumption. Results and discussions Over the period of study, Lushan Mountain received more rainfall in spring and summer. The pH values varied seasonally with winter minima. The winter multiyear seasonal mean pH was 4.35. The corresponding summer value was 4.88. SO 4 2? and NO 3 ? were the main anions, and NH 4 + and Ca 2+ the main cations. The anion to cation ratio was 0.8?C1.0, and that of [SO 4 2? ] to [NO 3 ? ] was 2.4-3.0, much lower than that of the 1980s. However, sulfuric acid was still the main acid present. The ratio of [NH 4 + ] to [Ca 2+] was about 1.0, suggesting that these two alkaline substances provided close acid neutralizing capacity. The ratio of [Cl ?] to [Na +] was about 0.67, somewhat lower than that of natural precipitation. Conclusions Ionic composition varied seasonally and was closely correlated to the amounts of rainfall and pollution. Trajectory analyses showed that the trajectories to Lushan Mountain could be classified in six clusters and trajectories originating from the South Sea and the areas surrounding Lushan Mountain had the greatest impacts on precipitation chemistry. 相似文献
4.
Background PM 10 aerosol samples were simultaneously collected at two urban and one urban background sites in Fuzhou city during two sampling campaigns in summer and winter. PM 10 mass concentrations and chemical compositions were determined. Methods Water-soluble inorganic ions (Cl ?, NO 3 ? , SO 4 2? , NH 4 + , K +, Na +, Ca 2+, and Mg 2+), carbonaceous species (elemental carbon and organic carbon), and elements (Al, Si, Mg, K, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, As, Se, Br, and Pb) were detected using ion chromatography, thermal/optical reflectance, and proton-induced X-ray emission methods, respectively. Results PM 10 mass concentrations, as well as most of the chemical components, were significantly increased from urban background to urban sites, which were due to enhanced anthropogenic activities in urban areas. Elements, carbonaceous species, and most of the ions were more uniformly distributed at different types of sites in winter, whereas secondary ion SO 4 2? , NO 3 ? , and NH 4 + showed more evident urban-background contrast in this season. The chemical mass closure indicated that mineral dust, organic matters, and sulfate were the most abundant components in PM 10. The sum of individually measured components accounted for 86.9?C97.7% of the total measured PM 10 concentration, and the discrepancy was larger in urban area than in urban background area. Conclusion According to the principal component analysis?Cmultivariate linear regression model, mineral dust, secondary inorganic ions, sea salt, and motor vehicle were mainly responsible for the PM 10 particles in Fuzhou atmosphere, and contributed 19.9%, 53.3%, 21.3%, and 5.5% of PM 10, respectively. 相似文献
5.
Studies of forest nitrogen (N) budgets generally measure inputs from the atmosphere in wet and dry deposition and outputs via hydrologic export. Although denitrification has been shown to be important in many wetland ecosystems, emission of N oxides from forest soils is an important, and often overlooked, component of an ecosystem N budget. During 1 year (2002–03), emissions of nitric oxide (NO) and nitrous oxide (N 2O) were measured from Sessile oak and Norway spruce forest soils in northeast Hungary. Accumulation in small static chambers followed by gas chromatography-mass spectrometry detection was used for the estimation of N 2O emission flux. Because there are rapid chemical reactions of NO and ozone, small dynamic chambers were used for in situ NO flux measurements. Average soil emissions of NO were 1.2 and 2.1 μg N m −2 h −1, and for N 2O were 15 and 20 μg N m −2 h −1, for spruce and oak soils, respectively. Due to the relatively high soil water content, and low C/N ratio in soil, denitrification processes dominate, resulting in an order of magnitude greater N 2O emission rate compared to NO. The previously determined N balance between the atmosphere and the forest ecosystem was re-calculated using these soil emission figures. The total (dry+wet) atmospheric N-deposition to the soil was 1.42 and 1.59 g N m −2 yr −1 for spruce and oak, respectively, while the soil emissions are 0.14 and 0.20 g N m −2 yr −1. Thus, about 10–13% of N compounds deposited to the soil, mostly as and , were transformed in the soil and emitted back to the atmosphere, mostly as greenhouse gas (N 2O). 相似文献
6.
The present study aims to investigate the EDTA catalyzed reduction of nitrate (NO 3 ? ) by zero-valent bimetallic (Fe?CAg) nanoparticles (ZVBMNPs) in aqueous medium and to enumerate the effect of temperature, solution pH, ZVBMNPs dose and EDTA concentration on NO 3 ? reduction. Batch experimental data were generated using a four-factor Box?CBehnken design. Optimization modeling was performed using the response surface method for maximizing the reduction of NO 3 ? by ZVBMNPs. Significance of the independent variables and their interactions were tested by the analysis of variance and t test statistics. The model predicted maximum reduction capacity (340.15?mg?g ?1 NO 3 ? ) under the optimum conditions of temperature, 60?°C; pH?4; dose, 1.0?g?l ?1; and EDTA concentration, 2.0?mmol?l ?1 was very close to the experimental value (338.62?mg?g ?1) and about 16?% higher than the experimentally determined capacity (291.32?mg?g ?1). Study demonstrated that ZVBMNPs had higher reduction efficiency than Fe 0 nanoparticles for NO 3 ? . EDTA significantly enhanced the NO 3 ? reduction by ZVBMNPs. The EDTA catalyzed reduction of NO 3 ? by ZVBMNPs can be employed for the effective decontamination of water. 相似文献
7.
The wetlands play an important role in global carbon and nitrogen storage, and they are also natural sources of greenhouse gases such as methane (CH 4) and nitrous oxide (N 2O). Land-use change is an important factor affecting the exchange of greenhouse gases between wetlands and the atmosphere. However, few studies have investigated the effect of land-use change on CH 4 and N 2O emissions from freshwater marsh in China. Therefore, a field study was carried out over a year to investigate the seasonal changes of the emissions of CH 4 and N 2O at three sites ( Deyeuxia angustifolia marsh, dryland and rice field) in the Sanjiang Plain of Northeast China. Marsh was the source of CH 4 showing a distinct temporal variation. Maximum fluxes occurred in June and the highest value was 20.69 ± 2.57 mg CH 4 m ?2 h ?1. The seasonal change of N 2O fluxes from marsh was not obvious, consisted of a series of emission pulses. The marsh acted as a N 2O sink during winter, while became a N 2O source in the growing season. The results showed that gas exchange between soil/snow and the atmosphere in the winter season contributed greatly to the annual budgets. The winter season CH 4 flux was about 3.24% of the annual flux and the winter uptake of N 2O accounted for 13.70% of the growing-season emission. Conversion marsh to dryland resulted in a shift from a strong CH 4 source to a weak sink (from 199.12 ± 39.04 to ?1.37 ± 0.68 kg CH 4 ha ?1 yr ?1), while increased N 2O emissions somewhat (from 4.07 ± 1.72 to 4.90 ± 1.52 kg N 2O ha ?1 yr ?1). Conversion marsh to rice field significantly decreased CH 4 emission from 199.12 ± 39.04 to 94.82 ± 9.86 kg CH 4 ha ?1 yr ?1 and N 2O emission from 4.07 ± 1.72 to 2.09 ± 0.79 kg N 2O ha ?1 yr ?1. 相似文献
8.
In a laboratory study we investigated 1) the potential production of nitrous oxide (N 2O), methane (CH 4) and carbon dioxide (CO 2) and 2) the effect of nitrate (NO 3?) and anaerobic N 2O development on CH 4 production in sediment from a recently recreated free surface water wetland (FSWW) and in soil from an adjacent meadow. We designed an experiment where production of greenhouse gases was registered at the time of maximum net development of N 2O. We made additions of biodegradable carbon (glucose) and/or NO 3? to sediment and soil slurries and incubated them at four temperatures (4, 13, 20, 28 °C). Gas production from both substrates was positively correlated with temperature. We also found that the sediment produced more N 2O than the soil. N 2O production in sediment was NO 3? limited, whereas in soil carbon availability was lower and only combined additions of NO 3? and glucose supported increased N 2O development. CH 4 production was generally low and did not differ between soil and sediment. Nor did glucose addition increase CH 4 rates. The results suggest that neither soil nor sediment environment did support development of methanogenic populations. There were no clear effects of NO 3? on CH 4 production. However, the highest records of CH 4 were found in incubations with low N 2O production, which indicates that N 2O might be toxic to methanogens. In summary, our study showed that transforming meadows into FSWWs implies a risk of increased N 2O emissions. This does not seem to be valid for CH 4. However, since N 2O is almost always produced wherever NO 3? is denitrified, increased N 2O production in wetlands leads to reduced rates in downstream environments. Hence, we conclude that when balancing NO 3? retention and global warming aspects, we find no reason to discourage future creation or restoration of wetlands. 相似文献
9.
In coastal Antarctica, freezing and thawing influence many physical, chemical and biological processes for ice-free tundra ecosystems, including the production of greenhouse gases (GHGs). In this study, penguin guanos and ornithogenic soil cores were collected from four penguin colonies and one seal colony in coastal Antarctica, and experimentally subjected to three freezing–thawing cycles (FTCs) under ambient air and under N 2. We investigated the effects of FTCs on the emissions of three GHGs including nitrous oxide (N 2O), carbon dioxide (CO 2) and methane (CH 4). The GHG emission rates were extremely low in frozen penguin guanos or ornithogenic soils. However, there was a fast increase in the emission rates of three GHGs following thawing. During FTCs, cumulative N 2O emissions from ornithogenic soils were greatly higher than those from penguin guanos under ambient air or under N 2. The highest N 2O cumulative emission of 138.24 μg N 2O–N kg ?1 was observed from seal colony soils. Cumulative CO 2 and CH 4 emissions from penguin guanos were one to three orders of magnitude higher than those from ornithogenic soils. The highest cumulative CO 2 (433.0 mgCO 2–C kg ?1) and CH 4 (2.9 mgCH 4–C kg ?1) emissions occurred in emperor penguin guanos. Penguin guano was a stronger emitter for CH 4 and CO 2 while ornithogenic soil was a stronger emitter for N 2O during FTCs. CO 2 and CH 4 fluxes had a correlation with total organic carbon (TOC) and soil/guano moisture (M c) in penguin guanos and ornithogenic soils. The specific CO 2–C production rate (CO 2–C/TOC) indicated that the bioavailability of TOC was markedly larger in penguin guanos than in ornithogenic soils during FTCs. This study showed that FTC-released organic C and N from sea animal excreta may play a significant role in FTC-related GHG emissions, which may account for a large proportion of annual fluxes from tundra ecosystems in coastal Antarctica. 相似文献
10.
Purpose This study contains some new findings connected to the photolysis of the drug paracetamol (hereinafter APAP) especially in light of estimating natural conditions, and it will offer information to better evaluate environmental problems connected with this widely used analgesic agent. Only a few studies, so far, have focussed on the photodegradation process of APAP in the natural environment, and the question about the role of the colored/chromophoric dissolved organic matter (CDOM) and nitrate (NO 3 ? ) as photoinductors is almost open. Methods APAP dissolved in freshwater and pure laboratory water in the presence and absence of CDOM and NO 3 ? ions was irradiated using weak-energy photon energies simulating natural conditions. Results CDOM and NO 3 ? as photoinductors produced only the slow phototransformation of APAP under weak energy radiation, and APAP seemed to be practically resistant to direct photolysis under weak radiant energies available in natural conditions. The estimated reaction efficiencies, in addition to half-lives, speak for that NO 3 ? and CDOM do not act as quite independent photoinductors but their effect in conjunction (CDOM?CNO 3 ? ?Cwater) is stronger than the separate ones. The principal phototransformation intermediates of APAP were mono-hydroxy derivatives, depending on available photon energies formed via ortho- or meta-hydroxylation, possessing substantial power of resistance to further specific transformation reactions. Conclusions The estimated half-life of the phototransformation of APAP in the natural aqueous environment and in the presence of suitable photoinductors will be about 30?days or more. 相似文献
11.
Although the effect of volatile organic compounds (VOCs) on the oxidation of dissolved sulfur dioxide by oxygen has been the subject of many investigations, this is the first study which examines the effect of a large number of precisely 16 hydroxy compounds. The kinetics both in the absence and the presence of VOCs was defined by rate laws ( A and B): A $$ \hbox{-} \mathrm{d}\left[\mathrm{S}\left(\mathrm{IV}\right)\right]/\mathrm{dt}={R}_o={k}_o\left[\mathrm{S}\left(\mathrm{IV}\right)\right] $$ B $$ \hbox{-} \mathrm{d}\left[\mathrm{S}\left(\mathrm{IV}\right)\right]/\mathrm{dt}={R}_i={k}_i\left[\mathrm{S}\left(\mathrm{IV}\right)\right] $$ where R o and k o are the initial rate and first-order rate constant, respectively, in the absence of VOCs, R i , and k i are the initial rate and the first-order rate constant, respectively, in the presence of VOCs, and [S(IV)] is the concentration of dissolved sulfur dioxide, sulfur(IV). The nature of the dependence of k i on the concentration of inhibitor, [Inh], was defined by Eq. ( C). C $$ {k}_i={k}_0/\left(1+B\left[\mathrm{Inh}\right]\right) $$ where B is an empirical inhibition parameter. The values of B have been determined from the plots of 1/ k i versus [Inh]. Among aliphatic and aromatic hydroxy compounds studied, t-butyl alcohol and pinacol were without any inhibition effect due to the absence of secondary or tertiary hydrogen. The values of inhibition parameter, B, were related to k inh , the rate constant for the reaction of SO 4 ? radical with the inhibitor, by Eq. ( D). D $$ B=\left(9\pm 2\right)\times 1{0}^{-4}\times {k}_{inh} $$ Equation ( D) may be used to calculate the values of either of B or k inh provided that the other is known. The extent of inhibition depends on the value of the composite term, B[Inh]. However, in accordance with Eq. ( C), the extent of inhibition would be sizeable and measurable when B[Inh]?>?0.1 and oxidation of S(IV) would be almost completely stopped when B[Inh]?≥?10. B[Inh] value can be used as a guide whether the reaction step: SO 4 ??+?organics? \( \overset{k_{inh}}{\to } \) ?SO 4 2??+?non-chain products: should be included in the multiphase models or not. 相似文献
12.
Municipal solid waste landfills are the significant anthropogenic sources of N 2O due to the cooxidation of ammonia by methane-oxidizing bacteria in cover soils. Such bacteria could be developed through CH 4 fumigation, as evidenced by both laboratory incubation and field measurement. During a 10-day incubation with leachate addition, the average N 2O fluxes in the soil samples, collected from the three selected landfill covers, were multiplied by 1.75 ( p < 0.01), 3.56 ( p < 0.01), and 2.12 ( p < 0.01) from the soil samples preincubated with 5% CH 4 for three months when compared with the control, respectively. Among the three selected landfill sites, N 2O fluxes in two landfill sites were significantly correlated with the variations of the CH 4 emissions without landfill gas recovery ( p < 0.001). N 2O fluxes were also elevated by the increase of the CH 4 emissions with landfill gas recovery in another landfill site ( p > 0.05). The annual average N 2O flux was 176 ± 566 μg N 2O–N m ?2 h ?1 ( p < 0.01) from sandy soil–covered landfill site, which was 72% ( p < 0.05) and 173% ( p < 0.01) lower than the other two clay soil covered landfill sites, respectively. The magnitude order of N 2O emissions in three landfill sites was also coincident by the results of laboratory incubation, suggesting the sandy soil cover could mitigate landfill N 2O emissions. 相似文献
13.
This article reports a dataset on 8 years of monitoring carbon fluxes in a subarctic palsa mire based on micrometeorological eddy covariance measurements. The mire is a complex with wet minerotrophic areas and elevated dry palsa as well as intermediate sub-ecosystems. The measurements document primarily the emission originating from the wet parts of the mire dominated by a rather homogenous cover of Eriophorum angustifolium. The CO 2/CH 4 flux measurements performed during the years 2001–2008 showed that the areas represented in the measurements were a relatively stable sink of carbon with an average annual rate of uptake amounting to on average ?46 g C m ?2 y ?1 including an equally stable loss through CH 4 emissions (18–22 g CH 4–C m ?2 y ?1). This consistent carbon sink combined with substantial CH 4 emissions is most likely what is to be expected as the permafrost under palsa mires degrades in response to climate warming. 相似文献
14.
Understanding the removal mechanisms and kinetics of trace tetracycline by activated sludge is critical to both evaluation of tetracycline elimination in sewage treatment plants and risk assessment/management of tetracycline released to soil environment due to the application of biosolids as fertilizer. Adsorption is found to be the primary removal mechanism while biodegradation, volatilization, and hydrolysis can be ignored in this study. Adsorption kinetics was well described by pseudo-second-order model. Faster adsorption rate ( k 2?=?2.04?×?10 ?2?g?min ?1?μg ?1) and greater adsorption capacity ( q e?=?38.8 μg?g ?1) were found in activated sludge treating freshwater sewage. Different adsorption rate and adsorption capacity resulted from chemical properties of sewage matrix rather than activated sludge surface characteristics. The decrease of tetracycline adsorption in saline sewage was mainly due to Mg 2+ which significantly reduced adsorption distribution coefficient ( K d) from 12,990?±?260 to 4,690?±?180 L?kg ?1. Species-specific adsorption distribution coefficients followed the order of $ K_{\mathrm{d}}^{{ + 00}} \gg K_{\mathrm{d}}^{{ + - 0}} > K_{\mathrm{d}}^{{ + - - }} $ . Contribution of zwitterionic tetracycline to the overall adsorption was >90 % in the actual pH range in aeration tank. Adsorption of tetracycline in a wide range of temperature (10 to 35 °C) followed the Freundlich adsorption isotherm well. 相似文献
15.
The spatial variability of carbon dioxide (CO 2), methane (CH 4), and nitrous oxide (N 2O) fluxes from forest soil with high nitrogen (N) deposition was investigated at a rolling hill region in Japan. Gas fluxes were measured on July 25th and December 5th, 2008 at 100 points within a 100 × 100 m grid. Slope direction and position influenced soil characteristics and site-specific emissions were found. The CO 2 flux showed no topological difference in July, but was significantly lower in December for north-slope with coniferous trees. Spatial dependency of CH 4 fluxes was stronger than that of CO 2 or N 2O and showed a significantly higher uptake in hill top, and emissions in the valley indicating strong influence of water status. N 2O fluxes showed no spatial dependency and exhibited high hot spots at different topology in July and December. The high N deposition led to high N 2O fluxes and emphasized the spatial variability. 相似文献
16.
Purpose Bacterial community structure and the chemical components in aerosols caused by rotating brushes in an Orbal oxidation ditch were assessed in a Beijing municipal wastewater treatment plant. Methods Air samples were collected at different distances from the aerosol-generating rotating brushes. Molecular culture-independent methods were used to characterize the community structure of the airborne bacteria in each sample regardless of cell culturability. A clone library of 16S rDNA directly amplified from air DNA of each sample was constructed and sequenced to analyze the community composition and diversity. Insoluble particles and water-soluble ions emitted with microorganisms in aerosols were analysis by a scanning electron microscope together with energy dispersive X-ray spectroscopy and ion chromatogram analyzer. Results In total, most of the identified bacteria were Proteobacteria. The majority of sequences near the rotating brushes (the main source of the bioaerosols) were Proteobacteria (62.97 %) with ??-(18.52 %) and ??-(44.45?%) subgroups and Bacteroidetes (29.63 %). Complex patterns were observed for each sampling location, suggesting a highly diverse community structure, comparable to that found in water in the Orbal oxidation ditch. Accompany with microorganisms, 46.36???g/m 3 of SO 4 2? , 29.35???g/m 3 of Cl ?, 21.51???g/m 3 of NO 3 ? , 19.76???g/m 3 of NH 4 + , 11.42???g/m 3 of PO 4 3? , 6.18???g/m 3 of NO 2 ? , and elements of Mg, Cl, K, Na, Fe, S, and P were detected from the air near the aerosols source. Conclusions Differences in the structure of the bacterial communities and chemical components in the aerosols observed between sampling sites indicated important site-related variability. The composition of microorganisms in water was one of the most important sources of bacterial communities in bioaerosols. Chemical components in bioaerosols may provide a media for airborne microorganism attachment, as well as a suitable microenvironment for their growth and survival in the air. This study will be benefit for the formulation of pollution standards, especially for aerosols, that take into account plant workers?? health. 相似文献
17.
Acrylate esters are α,β-unsaturated esters that contain vinyl groups directly attached to the carbonyl carbon. These compounds are widely used in the production of plastics and resins. Atmospheric degradation processes of these compounds are currently not well understood. The kinetics of the gas phase reactions of OH radicals with methyl 3-methylacrylate and methyl 3,3-dimethylacrylate were determined using the relative rate technique in a 50 L Pyrex photoreactor using in situ FTIR spectroscopy at room temperature (298?±?2 K) and atmospheric pressure (708?±?8 Torr) with air as the bath gas. Rate coefficients obtained were (in units cm 3 molecule ?1 s ?1): (3.27?±?0.33)?×?10 ?11 and (4.43?±?0.42)?×?10 ?11, for CH 3CH═CHC(O)OCH 3 and (CH 3) 2CH═CHC(O)OCH 3, respectively. The same technique was used to study the gas phase reactions of hexyl acrylate and ethyl hexyl acrylate with OH radicals and Cl atoms. In the experiments with Cl, N 2 and air were used as the bath gases. The following rate coefficients were obtained (in cm 3 molecule ?1 s ?1): k 3 (CH 2═CHC(O)O(CH 2) 5CH 3?+?Cl)?=?(3.31?±?0.31)?×?10 ?10, k 4(CH 2═CHC(O)OCH 2CH(CH 2CH 3)(CH 2) 3CH 3?+?Cl)?=?(3.46?±?0.31)?×?10 ?10, k 5(CH 2═CHC(O)O(CH 2) 5CH 3?+?OH)?=?(2.28?±?0.23)?×?10 ?11, and k 6(CH 2═CHC(O)OCH 2CH(CH 2CH 3)(CH 2) 3CH 3?+?OH)?=?(2.74?±?0.26)?×?10 ?11. The reactivity increased with the number of methyl substituents on the double bond and with the chain length of the alkyl group in –C(O)OR. Estimations of the atmospheric lifetimes clearly indicate that the dominant atmospheric loss process for these compounds is their daytime reaction with the hydroxyl radical. In coastal areas and in some polluted environments, Cl atom-initiated degradation of these compounds can be significant, if not dominant. Maximum Incremental Reactivity (MIR) index and global warming potential (GWP) were also calculated, and it was concluded that these compounds have significant MIR values, but they do not influence global warming. 相似文献
18.
As a convenient method, the closed chamber method has been applied to determine gaseous emission fluxes from fully open animal feeding operations despite the measured fluxes being theoretically affected by deployment time, wind speed over the emitting surface and detected gas mass. This laboratory study evaluated the effects of deployment time (0 to 120 min) and external surface wind speed (ESWS) (0.00, 0.25, 0.50, 0.75, 1.00, 1.50 and 2.00 m sec -1) on the measurement accuracy of a 300 mm (diameter) × 400 mm (height) (D300×H400) closed chamber using methane (CH 4), nitrous oxide (N 2O) and sulfur hexafluoride (SF 6) as reference gases. The results showed that the overall deviation ratio between the measured and reference CH 4 fluxes ranged from 9.99 % to -37.32 % and the flux was overestimated in the first 20 min. The measured N 2O and SF 6 emissions were smaller than the reference fluxes using the chamber. N 2O measurement accuracy decreased from -14.47 to -35.09% with deployment time extended to 120 min, while SF 6 accuracy sharply increased in the first 40 min, with the deviation stabilizing at approximately -5.00%. CH 4, N 2O and SF 6 measurements were significantly affected by deployment time and ESWS (P<0.05), and the interaction of those two factors greatly influenced CH 4 and SF 6 measurements (P<0.05). With the D300×H400 closed chamber, deployment times of 20 to 30 min and 10 to 20 min are recommended to measure CH 4 and N 2O, respectively, from the open operations of dairy farms under wind speeds lower than 2 m sec -1. Implications: This study recommended the suitable deployment times and wind speeds for using a D300 × H400 closed chamber to measure CH4, N2O, and SF6 in an open system, such as a dairy open lot and manure stockpile, to help researchers and other related industry workers get accurate data for gas emission rate. Deployment times of 20 to 30 min and 10 to 20 min were recommended to measure CH4 and N2O emissions using the D300 × H400 closed chamber, respectively, from the open operations of dairy farms under wind speeds lower than 2 m sec?1. For the measurement of SF6, a typical tracer gas, a deployment of 70 to 90 min was suggested. 相似文献
19.
To investigate the spatial and seasonal variations of nitrous oxide (N 2O) fluxes and understand the key controlling factors, we explored N 2O fluxes and environmental variables in high marsh (HM), middle marsh (MM), low marsh (LM), and mudflat (MF) in the Yellow River estuary throughout a year. Fluxes of N 2O differed significantly between sampling periods as well as between sampling positions. During all times of day and the seasons measured, N 2O fluxes ranged from ?0.0051 to 0.0805 mg N 2O m ?2 h ?1, and high N 2O emissions occurred during spring (0.0278 mg N 2O m ?2 h ?1) and winter (0.0139 mg N 2O m ?2 h ?1) while low fluxes were observed during summer (0.0065 mg N 2O m ?2 h ?1) and autumn (0.0060 mg N 2O m ?2 h ?1). The annual average N 2O flux from the intertidal zone was 0.0117 mg N 2O m ?2 h ?1, and the cumulative N 2O emission throughout a year was 113.03 mg N 2O m ?2, indicating that coastal marsh acted as N 2O source. Over all seasons, N 2O fluxes from the four marshes were significantly different ( p?<?0.05), in the order of HM (0.0256?±?0.0040 mg N 2O m ?2 h ?1)?>?MF (0.0107?±?0.0027 mg N 2O m ?2 h ?1)?>?LM (0.0073?±?0.0020 mg N 2O m ?2 h ?1)?>?MM (0.0026?±?0.0011 mg N 2O m ?2 h ?1). Temporal variations of N 2O emissions were related to the vegetations ( Suaeda salsa, Phragmites australis, and Tamarix chinensis) and the limited C and mineral N in soils during summer and autumn and the frequent freeze/thaw cycles in soils during spring and winter, while spatial variations were mainly affected by tidal fluctuation and plant composition at spatial scale. This study indicated the importance of seasonal N 2O contributions (particularly during non-growing season) to the estimation of local N 2O inventory, and highlighted both the large spatial variation of N 2O fluxes across the coastal marsh (CV?=?158.31 %) and the potential effect of exogenous nitrogen loading to the Yellow River estuary on N 2O emission should be considered before the annual or local N 2O inventory was evaluated accurately. 相似文献
20.
Emissions of CH 4 and N 2O related to private pig farming under a tropical climate in Uvéa Island were studied in this paper. Physicochemical soil parameters such as nitrate, nitrite, ammonium, Kjeldahl nitrogen, total organic carbon, pH and moisture were measured. Gaseous soil emissions as well as physicochemical parameters were compared in two private pig farming strategies encountered on this island on two different soils (calcareous and ferralitic) in order to determine the best pig farming management: in small concrete pens or in large land pens. Ammonium levels were higher in control areas while nitrate and nitrite levels were higher in soils with pig slurry inputs, indicating that nitrification was the predominant process related to N 2O emissions. Nitrate contents in soils near concrete pens were important (≥55 μg N/g) and can thus be a threat for the groundwater. For both pig farming strategies, N 2O and CH 4 fluxes can reach high levels up to 1 mg N/m 2/h and 1 mg C/m 2/h, respectively. CH 4 emissions near concrete pens were very high (≥10.4 mg C/m 2/h). Former land pens converted into agricultural land recover low N 2O emission rates (≤0.03 mg N/m 2/h), and methane uptake dominates. N 2O emissions were related to nitrate content whereas CH 4 emissions were found to be moisture dependent. As a result relating to the physicochemical parameters as well as to the gaseous emissions, we demonstrate that pig farming in large land pens is the best strategy for sustainable family pig breeding in Uvéa Islands and therefore in similar small tropical islands. 相似文献
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