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1.
Addition of different forms of nitrogen fertilizer to cultivated soil is known to affect carbon dioxide (CO2) and nitrous oxide (N2O) emissions. In this study, the effect of urea, wastewater sludge and vermicompost on emissions of CO2 and N2O in soil cultivated with bean was investigated. Beans were cultivated in the greenhouse in three consecutive experiments, fertilized with or without wastewater sludge at two application rates (33 and 55 Mg fresh wastewater sludge ha− 1, i.e. 48 and 80 kg N ha− 1 considering a N mineralization rate of 40%), vermicompost derived from the wastewater sludge (212 Mg ha− 1, i.e. 80 kg N ha− 1) or urea (170 kg ha− 1, i.e. 80 kg N ha− 1), while pH, electrolytic conductivity (EC), inorganic nitrogen and CO2 and N2O emissions were monitored. Vermicompost added to soil increased EC at onset of the experiment, but thereafter values were similar to the other treatments. Most of the NO3 was taken up by the plants, although some was leached from the upper to the lower soil layer. CO2 emission was 375 C kg ha− 1 y− 1 in the unamended soil, 340 kg C ha− 1 y− 1 in the urea-amended soil and 839 kg ha− 1 y− 1 in the vermicompost-amended soil. N2O emission was 2.92 kg N ha− 1 y− 1 in soil amended with 55 Mg wastewater sludge ha− 1, but only 0.03 kg N ha− 1 y− 1 in the unamended soil. The emission of CO2 was affected by the phenological stage of the plant while organic fertilizer increased the CO2 and N2O emission, and the yield per plant. Environmental and economic implications must to be considered to decide how many, how often and what kind of organic fertilizer could be used to increase yields, while limiting soil deterioration and greenhouse gas emissions.  相似文献   

2.
Emission of N2O and CH4 from a constructed wetland in southeastern Norway   总被引:1,自引:0,他引:1  
The Skjønhaug constructed wetland (CW) is a free surface water (FSW) wetland polishing chemically treated municipal wastewater in southeastern Norway and consists of three ponds as well as trickling, unsaturated filters with light weight aggregates (LWA). Fluxes of nitrous oxide (N2O) and methane (CH4) have been measured during the autumn, winter and summer from all three ponds as well as from the unsaturated filters. Physicochemical parameters of the water have been measured at the same localities. The large temporal and spatial variation of N2O fluxes was found to cover a range of − 0.49 to 110 mg N2O–N m− 2 day−1, while the fluxes of CH4 was found to cover a range of − 1.2 to 1900 mg m− 2 day− 1. Thus, both emission and consumption occurred. Regarding fluxes of N2O there was a significant difference between the summer, winter and autumn, with the highest emissions occurring during the autumn. The fluxes of CH4 were, on the other hand, not significantly different with regard to seasons. Both the emissions of N2O and CH4 were positively influenced by the amount of total organic carbon (TOC). The measured fluxes of N2O and CH4 are in the same range as those reported from other CWs treating wastewater. There was an approximately equal contribution to the global warming potential from N2O and CH4.  相似文献   

3.
Experiments were performed to study the airflow rates (AFRs) in a naturally ventilated building through four summer seasons and three winter seasons. The AFRs were determined using heat balance (HB), tracer gas technique (TGT) and CO2-balance as averages of the values of all experiments carried out through the different seasons. The statistical analyses were correlation analysis, regression model and t-test. Continuous measurements of gaseous concentrations (NH3, CH4, CO2 and N2O) and temperatures inside and outside the building were performed. The HB showed slightly acceptable results through summer seasons and unsatisfactory results through winter seasons. The CO2-balance showed unexpected high differences to the other methods in some cases. The TGT showed reliable results compared to HB and CO2-balance. The AFRs, subject to TGT, were 0.12 m3 s−1 m−2, 1.15 m3 s−1 cow−1, 0.88 m3 s−1 LU−1, 56 h−1, 395 m3 s−1 and 470 kg s−1 through summer seasons, and 0.08 m3 s−1 m−2, 0.83 m3 s−1 cow−1, 0.64 m3 s−1 LU−1 39 h−1, 275 m3 s−1 and 328 kg s−1 through winter seasons. The AFRs are not independent values, rather they were estimated for specific reference values, which are: area, cow and LU as well as rates. The emission rates through summer seasons, subject to TGT, were 9.4, 40, 3538 and 2.3 g h−1 cow−1; and through winter seasons were 4.8, 19, 2332 and 2.6 g h−1 cow−1, for NH3, CH4, CO2 and N2O, respectively.  相似文献   

4.
Gross CO2 and CH4 emissions (degassing and diffusion from the reservoir) and the carbon balance were assessed in 2009-2010 in two Southeast Asian sub-tropical reservoirs: the Nam Ngum and Nam Leuk Reservoirs (Lao PDR). These two reservoirs are within the same climatic area but differ mainly in age, size, residence time and initial biomass stock. The Nam Leuk Reservoir was impounded in 1999 after partial vegetation clearance and burning. However, GHG emissions are still significant 10 years after impoundment. CH4 diffusive flux ranged from 0.8 (January 2010) to 11.9 mmol m− 2 d− 1 (April 2009) and CO2 diffusive flux ranged from - 10.6 (October 2009) to 38.2 mmol m− 2 d− 1 (April 2009). These values are comparable to other tropical reservoirs. Moreover, degassing fluxes at the outlet of the powerhouse downstream of the turbines were very low. The tentative annual carbon balance calculation indicates that this reservoir was a carbon source with an annual carbon export (atmosphere + downstream river) of about 2.2 ± 1.0 GgC yr− 1.The Nam Ngum Reservoir was impounded in 1971 without any significant biomass removal. Diffusive and degassing CO2 and CH4 fluxes were lower than for other tropical reservoirs. Particularly, CO2 diffusive fluxes were always negative with values ranging from - 21.2 (April 2009) to - 2.7 mmol m−2 d−1 (January 2010). CH4 diffusive flux ranged from 0.1 (October 2009) to 0.6 mmol m−2 d−1 (April 2009) and no degassing downstream of the turbines was measured. As a consequence of these low values, the reservoir was a carbon sink with an estimated annual uptake of - 53 ± 35 GgC yr−1.  相似文献   

5.
Wood ash (3.1, 3.3 or 6.6 tonnes dry weight ha− 1) was used to fertilize two drained and forested peatland sites in southern Sweden. The sites were chosen to represent the Swedish peatlands that are most suitable for ash fertilization, with respect to stand growth response. The fluxes of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) from the forest floor, measured using opaque static chambers, were monitored at both sites during 2004 and 2005 and at one of the sites during the period 1 October 2007-1 October 2008. No significant (p > 0.05) changes in forest floor greenhouse gas exchange were detected. The annual emissions of CO2 from the sites varied between 6.4 and 15.4 tonnes ha− 1, while the CH4 fluxes varied between 1.9 and 12.5 kg ha− 1. The emissions of N2O were negligible. Ash fertilization increased soil pH at a depth of 0-0.05 m by up to 0.9 units (p < 0.01) at one site, 5 years after application, and by 0.4 units (p < 0.05) at the other site, 4 years after application. Over the first 5 years after fertilization, the mean annual tree stand basal area increment was significantly larger (p < 0.05) at the highest ash dose plots compared with control plots (0.64 m2 ha− 1 year− 1 and 0.52 m2 ha− 1 year− 1, respectively). The stand biomass, which was calculated using tree biomass functions, was not significantly affected by the ash treatment. The groundwater levels during the 2008 growing season were lower in the high ash dose plots than in the corresponding control plots (p < 0.05), indicating increased evapotranspiration as a result of increased tree growth. The larger basal area increment and the lowered groundwater levels in the high ash dose plots suggest that fertilization promoted tree growth, while not affecting greenhouse gas emissions.  相似文献   

6.
Annual paddy rice-winter wheat rotation constitutes one of the typical cropping systems in southeast China, in which various water regimes are currently practiced during the rice-growing season, including continuous flooding (F), flooding-midseason drainage-reflooding (F-D-F), and flooding-midseason drainage-reflooding and moisture but without waterlogging (F-D-F-M). We conducted a field experiment in a rice-winter wheat rotation system to gain an insight into the water regime-specific emission factors and background emissions of nitrous oxide (N2O) over the whole annual cycle. While flooding led to an unpronounced N2O emission during the rice-growing season, it incurred substantial N2O emission during the following non-rice season. During the non-rice season, N2O fluxes were, on average, 2.61 and 2.48 mg N2O-N m2 day− 1 for the 250 kg N ha− 1 applied plots preceded by the F and F-D-F water regimes, which are 56% and 49% higher than those by the F-D-F-M water regime, respectively. For the annual rotation system experienced by continuous flooding during the rice-growing season, the relationship between N2O emission and nitrogen input predicted the emission factor and background emission of N2O to be 0.87% and 1.77 kg N2O-N ha− 1, respectively. For the plots experienced by the water regimes of F-D-F and F-D-F-M, the emission factors of N2O averaged 0.97% and 0.85%, with background N2O emissions of 2.00 kg N2O-N ha− 1 and 1.61 kg N2O-N ha− 1 for the annual rotation system, respectively. Annual direct N2O-N emission was estimated to be 98.1 Gg yr− 1 in Chinese rice-based cropping systems in the 1990s, consisting of 32.3 Gg during the rice-growing season and 65.8 Gg during the non-rice season, which accounts for 25-35% of the annual total emission from croplands in China.  相似文献   

7.
To assess the atmospheric environmental impacts of anthropogenic reactive nitrogen in the fast-developing Eastern China region, we measured atmospheric concentrations of nitrogen dioxide (NO2) and ammonia (NH3) as well as the wet deposition of inorganic nitrogen (NO3 and NH4+) and dissolved organic nitrogen (DON) levels in a typical agricultural catchment in Jiangsu Province, China, from October 2007 to September 2008. The annual average gaseous concentrations of NO2 and NH3 were 42.2 μg m3 and 4.5 μg m3 (0 °C, 760 mm Hg), respectively, whereas those of NO3, NH4+, and DON in the rainwater within the study catchment were 1.3, 1.3, and 0.5 mg N L1, respectively. No clear difference in gaseous NO2 concentrations and nitrogen concentrations in collected rainwater was found between the crop field and residential sites, but the average NH3 concentration of 5.4 μg m3 in residential sites was significantly higher than that in field sites (4.1 μg m3). Total depositions were 40 kg N ha1 yr1 for crop field sites and 30 kg N ha1 yr1 for residential sites, in which dry depositions (NO2 and NH3) were 7.6 kg N ha1 yr1 for crop field sites and 1.9 kg N ha1 yr1 for residential sites. The DON in the rainwater accounted for 16% of the total wet nitrogen deposition. Oxidized N (NO3 in the precipitation and gaseous NO2) was the dominant form of nitrogen deposition in the studied region, indicating that reactive forms of nitrogen created from urban areas contribute greatly to N deposition in the rural area evaluated in this study.  相似文献   

8.
PM2.5 (particle with an aerodynamic diameter less than 2.5 µm) was measured in different microenvironments of Hong Kong (including one urban tunnel, one Hong Kong/Mainland boundary roadside site, two urban roadside sites, and one urban ambient site) in 2003. The concentrations of organic carbon (OC), elemental carbon (EC), water-soluble ions, and up to 40 elements (Na to U) were determined. The average PM2.5 mass concentrations were 229 ± 90, 129 ± 95, 69 ± 12, 49 ± 18 µg m− 3 in the urban tunnel, cross boundary roadside, urban roadside, and urban ambient environments, respectively. Carbonaceous particles (sum of organic material [OM] and EC) were the dominant constituents, on average, accounting for ∼ 82% of PM2.5 emissions in the tunnel, ∼ 70% at the three roadside sites, and ∼ 48% at the ambient site, respectively. The OC/EC ratios were 0.6 ± 0.2 and 0.8 ± 0.1 at the tunnel and roadside sites, respectively, suggesting carbonaceous aerosols were mainly from vehicle exhausts. Higher OC/EC ratio (1.9 ± 0.7) occurred at the ambient site, indicating contributions from secondary organic aerosols. The PM2.5 emission factor for on-road diesel-fueled vehicles in the urban area of Hong Kong was 257 ± 31 mg veh− 1 km− 1, with a composition of ∼ 51% EC, ∼ 26% OC, and ∼ 9% SO4=. The other inorganic ions and elements made up ∼ 11% of the total PM2.5 emissions. OC composed the largest fraction (∼ 51%) in gasoline and liquid petroleum gas (LPG) emissions, followed by EC (∼ 19%). Diesel engines showed higher emission rates than did gasoline and LPG engines for most pollutants, except for V, Br, Sb, and Ba.  相似文献   

9.
Constructed wetlands are nowadays successfully employed as an alternative technology for wastewater and sewage sludge treatment. In these systems organic matter and nutrients are transformed and removed by a variety of microbial reaction and gaseous compounds such as methane (CH4) and nitrous oxide (N2O) may be released to the atmosphere. The aim of this work is to introduce a method to determine greenhouse gas emissions from sludge treatment wetlands (STW) and use the method in a full-scale system. Sampling and analysing techniques used to determine greenhouse gas emissions from croplands and natural wetlands were successfully adapted to the quantification of CH4 and N2O emissions from an STW. Gas emissions were measured using the static chamber technique in 9 points of the STW during 13 days. The spatial variation in the emission along the wetland did not follow some specific pattern found for the temporal variation in the fluxes. Emissions ranged from 10 to 5400 mgCH4/m2 d and from 20 to 950 mgN2O/m2 d, depending on the feeding events. The comparison between the CH4 and N2O emissions of different sludge management options shows that STW have the lowest atmospheric impact in terms of CO2 equivalent emissions (Global warming potential with time horizon of 100 years): 17 kgCO2eq/PE y for STW, 36 kgCO2eq/PE y for centrifuge and 162 kgCO2eq/PE y for untreated sludge transport, PE means Population Equivalent.  相似文献   

10.
With the aim to determine the presence of individual nitro-PAH contained in particles in the atmosphere of Mexico City, a monitoring campaign for particulate matter (PM10 and PM2.5) was carried out in Northern Mexico City, from April 2006 to February 2007. The PM10 annual median concentration was 65.2 μg m− 3 associated to 7.6 μg m− 3 of solvent-extractable organic matter (SEOM) corresponding to 11.4% of the PM10 concentration and 38.6 μg m− 3 with 5.9 μg m− 3 SEOM corresponding to 15.2% for PM2.5. PM concentration and SEOM varied with the season and the particle size. The quantification of nitro-polycyclic aromatic hydrocarbons (nitro-PAH) was developed through the standards addition method under two schemes: reference standard with and without matrix, the former giving the best results. The recovery percentages varied with the extraction method within the 52 to 97% range depending on each nitro-PAH. The determination of the latter was effected with and without sample purification, also termed fractioning, giving similar results. 8 nitro-PAH were quantified, and their sum ranged from 111 to 819 pg m− 3 for PM10 and from 58 to 383 pg m− 3 for PM2.5, depending on the season. The greatest concentration was for 9-Nitroanthracene in PM10 and PM2.5, detected during the cold-dry season, with a median (10th-90th percentiles) concentration in 235 pg m− 3 (66-449 pg m− 3) for PM10 and 73 pg m− 3 (18-117 pg m− 3) for PM2.5. The correlation among mass concentrations of the nitro-PAH and criteria pollutants was statistically significant for some nitro-PAH with PM10, SEOM in PM10, SEOM in PM2.5, NOX, NO2 and CO, suggesting either sources, primary or secondary origin. The measured concentrations of nitro-PAH were higher than those reported in other countries, but lower than those from Chinese cities. Knowledge of nitro-PAH atmospheric concentrations can aid during the surveillance of diseases (cardiovascular and cancer risk) associated with these exposures.  相似文献   

11.
Riparian wetlands bordering intensively managed agricultural fields can act as biological filters that retain and transform agrochemicals such as nitrate and pesticides. Nitrate removal in wetlands has usually been attributed to denitrification processes which in turn imply the production of greenhouse gases (CO2 and N2O). Denitrification processes were studied in the Salburua wetland (northern Spain) by using undisturbed soil columns which were subsequently divided into three sections corresponding to A-, Bg- and B2g-soil horizons. Soil horizons were subjected to leaching with a 200 mg NO3 L− 1 solution (rate: 90 mL day− 1) for 125 days at two different temperatures (10 and 20 °C), using a new experimental design for leaching assays which enabled not only to evaluate leachate composition but also to measure gas emissions during the leaching process. Column leachate samples were analyzed for NO3 concentration, NH4+ concentration, and dissolved organic carbon. Emissions of greenhouse gases (CO2 and N2O) were determined in the undisturbed soil columns. The A horizon at 20 °C showed the highest rates of NO3 removal (1.56 mg N-NO3 kg−1 DW soil day− 1) and CO2 and N2O production (5.89 mg CO2 kg−1 DW soil day− 1 and 55.71 μg N-N2O kg−1 DW soil day− 1). For the Salburua wetland riparian soil, we estimated a potential nitrate removal capacity of 1012 kg N-NO3 ha− 1 year− 1, and potential greenhouse gas emissions of 5620 kg CO2 ha− 1 year− 1 and 240 kg N-N2O ha− 1 year− 1.  相似文献   

12.
The degradation of four pharmaceutical compounds (PhACs), ibuprofen (IBU), diphenhydramine (DP), phenazone (PZ), and phenytoin (PHT) was investigated via ultraviolet (UV) photolysis and UV/H2O2 process with a low-pressure (LP) UV lamp. For each PhAC tested, direct photolysis quantum yields at 254 nm were found to be ranging from 6.32 × 10−2 to 2.79 × 10−1 mol E−1 at pH 7. The second-order rate constants of the reaction between the PhACs and OH were determined to be from 4.86 × 109 to 6.67 × 109 M−1 s−1 by using a competition kinetic model which utilized para-chlorobenzoic acid (pCBA) as a reference compound. The overall effect of OH radical scavenging from humic acid (HA) and anions HCO3, NO3 was measured utilizing ROH,UV method through examining the aqueous photodegradation of pCBA as a probe compound. Moreover, these fundamental direct and indirect photolysis parameters were applied in the model prediction for oxidation rate constants of the PhACs in UV/H2O2 process. It was found that the predicted oxidation rate constants approximated the observed ones. The results indicated that the new ROH,UV probe compound method was applicable for measuring background OH radical scavenging effects in water treatment process of UV/H2O2. Furthermore, by GC-MS analysis, most of the intermediates created during the photodegradation of the selected PhACs in UV/H2O2 process were identified. For the photodegradation of PZ, a competition mechanism existed between the direct UV photolysis and the oxidation of OH. An appropriate dosage of H2O2 could hinder the occurrence of the direct photolysis.  相似文献   

13.
This study assesses individual-vehicle molecular hydrogen (H2) emissions in exhaust gas from current gasoline and diesel vehicles measured on a chassis dynamometer. Absolute H2 emissions were found to be highest for motorcycles and scooters (141 ± 38.6 mg km− 1), approximately 5 times higher than for gasoline-powered automobiles (26.5 ± 12.1 mg km− 1). All diesel-powered vehicles emitted marginal amounts of H2 (∼ 0.1 mg km− 1). For automobiles, the highest emission factors were observed for sub-cycles subject to a cold-start (mean of 53.1 ± 17.0 mg km− 1). High speeds also caused elevated H2 emission factors for sub-cycles reaching at least 150 km h− 1 (mean of 40.4 ± 7.1 mg km− 1). We show that H2/CO ratios (mol mol− 1) from gasoline-powered vehicles are variable (sub-cycle means of 0.44-5.69) and are typically higher (mean for automobiles 1.02, for 2-wheelers 0.59) than previous atmospheric ratios characteristic of traffic-influenced measurements. The lowest mean individual sub-cycle ratios, which correspond to high absolute emissions of both H2 and CO, were observed during cold starts (for automobiles 0.48, for 2-wheelers 0.44) and at high vehicle speeds (for automobiles 0.73, for 2-wheelers 0.45). This finding illustrates the importance of these conditions to observed H2/CO ratios in ambient air. Overall, 2-wheelers displayed lower H2/CO ratios (0.48-0.69) than those from gasoline-powered automobiles (0.75-3.18). This observation, along with the lower H2/CO ratios observed through studies without catalytic converters, suggests that less developed (e.g. 2-wheelers) and older vehicle technologies are largely responsible for the atmospheric H2/CO ratios reported in past literature.  相似文献   

14.
This study was aimed to understand the spatial variation of CH4 emissions from alpine wetlands in Southwest China on a field-scale in two phenological seasons, namely the peak growing season and the spring thaw. Methane emission rates were measured at 30 plots, which included three kinds of environmental types: dry hummock, Carex muliensis and Eleocharis valleculosa sites. There were highly spatial variations of methane emissions among and within different environmental types in both phenological seasons. Mean methane emission rates ranged from 1.1 to 37.0 mg CH4 m− 2 h− 1 in the peak growing season and from 0.004 to 0.691 mg CH4 m− 2 h− 1 in the spring thaw. In the peak growing season, coefficients of variation (CV) averaged 38% among environmental types and 64% within environmental types; while in the spring thaw, CV were on the average 61% among environmental types and 96% within environmental types. The key influencing factors were the standing water table and the plant community height in the peak growing season, while in the spring thaw, no significant correlations between factors and methane emissions were found.  相似文献   

15.
Treatment of fresh air in ventilation systems for air-conditioned offices consumes a significant amount of energy and affects the indoor air quality (IAQ). In this study, energy impact on the ventilation systems was examined against certain IAQ objectives for indoor airborne bacteria exposure risk in air-conditioned offices of Hong Kong. The relationship between thermal energy consumptions and indoor airborne bacteria exposure levels based on regional surveys was investigated. The thermal energy consumptions of ventilation systems operating for carbon dioxide (CO2) exposure concentrations between 800 and 1200 ppmv for typical office buildings and the corresponding failure probability against some target bacteria exposure levels were evaluated. The results showed that, for a reference indoor environment at a CO2 exposure concentration of 1000 ppmv, the predicted average thermal energy saving of ventilation system for a unit increment of the expected risk of unsatisfactory IAQ of 1% was 55 MJ m−2 yr−1 and for a unit decrement of 1%, the predicted additional thermal energy consumption was 58 MJ m−2 yr−1 respectively. This study would be a useful source of reference in evaluation of the energy performance of ventilation strategies in air-conditioned offices at a quantified exposure risk of airborne bacteria.  相似文献   

16.
Atmospheric deposition of different types of aerosols over the southern East Sea has received little attention in terms of seawater biogeochemistry. We investigated the concentrations of water-soluble ions (NO3, NH4+ and nss-SO42−) in the aerosols associated with air mass transport patterns arriving at the east coast of Korea, adjacent to the southern East Sea, in order to determine source regions affecting chemical composition of aerosols and to assess the atmospheric pathway as a significant controlling mechanism of the biogeochemistry in this marginal sea. Concentrations of certain elements (Al, Na, Ca, V, Zn and Pb) together with the water-soluble ions were measured in the aerosol samples (n = 34) collected during the period March 2002-February 2003. The geometric mean concentrations of the water-soluble ions were NO3 2.98 (0.56-16.22), NH4+ 1.42 (0.37-6.73) and nss-SO42− 2.47 (0.17-17.35) μg m− 3. The backward trajectories revealed that air masses passing slowly over eastern China contributed more to increases in the concentrations of water-soluble ions than those associated with fast-moving northwesterly and maritime winds. Therefore, the correlation between the NH4+ and NO3+ concentrations increased, suggesting that gas-phase NH3 and HNO3 was forming fine-mode NH4NO3. The atmospheric N input accounted for ∼ 10% of new production over the southern East Sea on an annual scale, while it accounted for over ∼ 25% of new production during the water column stratification seasons (summer and early fall).  相似文献   

17.
The study focuses on the role of the fired clay brick making industry (BMI) on deforestation and greenhouse gas (GHG) emissions in Sudan. The BMI is based on numerous kilns that use biomass fuel, mainly wood which is largely harvested unsustainably. This results in potential deforestation and land degradation. Fuelwood consumption data was collected using interviews and questionnaires from 25 BMI enterprises in three administrative regions, namely Khartoum, Kassala and Gezira. Annual fuelwood consumption data (t dm yr− 1) was converted into harvested biomass (m3) using a wood density value of 0.65 t dm m− 3. For annual GHG estimations, the methodological approach outlined by the Intergovernmental Panel on Climate Change (IPCC) was used. According to our results, the annual deforestation associated with the BMI for the whole of Sudan is 508.4 × 103 m3 of wood biomass, including 267.6 × 103 m3 round wood and 240.8 × 103 m3 branches and small trees. Total GHG emissions from the Sudanese BMI are estimated at 378 028 t CO2, 15 554 t CO, 1778 t CH4, 442 t NOX, 288 t NO and 12 t N2O per annum. The combined CO2-equivalent (global warming potential for 100-year time horizon) of the GHG emissions (excluding NOX and NO) is 455 666 t yr− 1. While these emissions form only a small part of Sudan's total GHG emissions, the associated deforestation and land degradation is of concern and effort should be made for greater use of sustainable forest resources and management.  相似文献   

18.
This paper reports the potential of heterogeneous photocatalysis as an advanced oxidation technology for removal of toluene from air using TiO2 as a photocatalyst in building materials. First, the photocatalytic activity of two types of TiO2 containing building materials, i.e. roofing tiles and corrugated sheets, has been investigated at ambient conditions (T=25.0 °C; relative humidity RH=47%; toluene inlet concentration [TOL]in=17–35 ppbv). Toluene removal efficiencies up to 63% were observed at a gas residence time (τ) of 17 s. Second, the effect of RH (1–77%), [TOL]in (23–465 ppmv) and τ (17–115 s) on toluene removal has been systematically investigated using TiO2 containing roofing tiles as photocatalytic building materials. Results revealed lower toluene removal efficiencies at higher RH and [TOL]in, whereas a positive effect was observed with increased τ. Under optimal conditions, toluene removal efficiencies up to 78±2% and elimination rates higher than 100 mg h−1 m−2 roofing tile were obtained. A decline in photocatalytic activity by a factor of 2 was observed after operation at gas residence times shorter than 69 s and [TOL]in higher than 76 ppmv. Washing the building materials with deionized water, simulating rainfall, could partially (i.e. by a factor 1.3) regenerate the catalyst activity.  相似文献   

19.
W.H. Chin  J.L. Harris 《Water research》2009,43(16):3940-3947
Greywater treatment by UVC/H2O2 was investigated with regard to the removal of chemical oxygen demand (COD). A COD reduction from 225 to 30 mg l−1 (overall removal of 87%) was achieved after settling overnight and subsequent irradiation for 3 h with 10 mM H2O2. Most of the contaminants were removed by oxidation since only 13% COD was removed by settlement.The removal of COD in the greywater followed a second-order kinetic equation, r = 0.0637[COD][H2O2], up to 10 mM H2O2. A slightly enhanced COD removal was observed at the initial pH of 10 compared with pH 3 and 7. This was attributed to the dissociation of H2O2 to O2H. The treatment was not affected by total concentration of carbonate (cT) of at least 3 mM, above which operation between pH 3 and 5 was essential. The initial biodegradability of the settled greywater (as BOD5:COD) was 0.22. After 2 h UVC/H2O2 treatment, a higher proportion of the residual contaminants was biodegradable (BOD5:COD = 0.41) which indicated its potential as a pre-treatment for a biological process.  相似文献   

20.
The multi-annual carbon budget of a peat-covered catchment   总被引:1,自引:0,他引:1  
This study estimates the complete carbon budget of an 11.4 km2 peat-covered catchment in Northern England. The budget considers both fluvial and gaseous carbon fluxes and includes estimates of particulate organic carbon (POC); dissolved organic carbon (DOC); excess dissolved CO2; release of methane (CH4); net ecosystem respiration of CO2; and uptake of CO2 by primary productivity. All components except CH4 were measured directly in the catchment and annual carbon budgets were calculated for the catchment between 1993 and 2005 using both extrapolation and interpolation methods. The study shows that: Over the 13 year study period the total carbon balance varied between a net sink of − 20 to − 91 Mg C/km2/yr. The biggest component of this budget is the uptake of carbon by primary productivity (− 178 Mg C/km2/yr) and in most years the second largest component is the loss of DOC from the peat profile (+ 39 Mg C/km2/yr). Direct exchanges of C with the atmosphere average − 89 Mg C/km2/yr in the catchment. Extrapolating the general findings of the carbon budget across all UK peatlands results in an approximate carbon balance of − 1.2 Tg C/yr (± 0.4 Pg C/yr) which is larger than previously reported values. Carbon budgets should always be reported with a clear statement of the techniques used and errors involved as this is significant when comparing results across studies.  相似文献   

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