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1.
We measured the emissions of volatile aliphatic amines and ammonia produced by the manure of beef cattle, dairy cows, swine, laying hens and horses in livestock buildings. The amine emissions consisted almost exclusively of the three methylamines and correlated with those of ammonia. The molar emission ratios of the methylamines to ammonia, and data on NH 3 emissions from animal husbandry in Europe, together with global statistics on domestic animals, were used to estimate the global emissions of amines. Annual global methylamine-N input to the atmosphere from animal husbandry in 1988 was 0.15±0.06 TgN (Tg=10 12 g). Almost 3/4 of these emissions consisted of trimethylamine-N. This represents about half of all methylamine emissions to the atmosphere. Other sources are marine coastal waters and biomass burning.Possible reaction pathways for atmospheric methylamines are shown. Among various speculative but possible products N 2O and HCN are of interest because the emission of methylamines could contribute to the global budgets of these compounds. Maximum atmospheric N 2O production from methylamines are below 0.4 Tg N/year, which is less than 10% of the annual N 2O growth rate. Although we do not expect the methylamine emissions to contribute in a major way to the atmospheric N 2O budget, more studies are needed to establish this conclusion beyond doubt. Similar conclusions hold for HCN. 相似文献
2.
以武汉市为研究区域,基于实地调查获得典型行业污染源活动水平,以大气污染物排放清单编制技术指南为参考,利用排放因子法建立2014年武汉市大气污染源排放清单,并结合经纬度、人口密度分布、土地利用类型、道路长度等数据将排放清单进行了3 km×3 km网格化处理.结果表明,2014年武汉市SO 2、NO x、PM 10、PM 2.5、CO、BC、OC、VOCs和NH 3排放量分别为10.3、17.0、16.3、7.1、63.1、0.6、0.4、19.8和1.6万t.固定燃烧源为SO 2排放的主要来源,其贡献率约64%;移动源为NO x的主要来源,其贡献率约51%;颗粒物排放主要来源于扬尘源和工艺过程源;CO和VOCs主要来源于工艺过程源,BC和OC排放均以移动源和生物质燃烧源为主,NH 3排放主要来自农业源.污染物排放主要集中在青山区至新洲区一带. 相似文献
3.
Ammonia emissions from stored farm manures form a small but significant proportion (∼10%) of the total emitted annually from
UK sources. These emissions are regulated by factors including: the surface area of the store; the storage method; the physical
form of the stored manure and the source of manure. A method was developed to estimate in situ emissions from a range of store
types (weeping wall and earth-banked lagoon) that are currently under-represented in UK emissions estimates. Passive diffusion
samplers (Willems Badges) were used to determine vertical concentration profiles to a height of 4.5 m at a number of locations
around each slurry store. An atmospheric dispersion model was applied to estimate the contribution from emissions from other
on-farm ammonia sources to the measured data and also to determine the emission rates from the stored manure. A procedure
was applied whereby the emission rates from each source were allowed to vary and a numerical equation solver was applied to
backfit the modelled data set to the field measurements. Measurements were collected at four farms on a monthly basis throughout
the year, with each dataset being collected over 24 h. The uncertainties in the estimates of emissions from the slurry stores
during individual measurement periods typically ranged between 20–40% though higher uncertainties occurred when emission fluxes
from the stores were below 0.25 g NH 3–N m −2 day −1 and were entrained in the wakes, and mixed with the emissions, of adjacent buildings. The average emission from the farms
was 0.6 g NH 3–N m −2 day −1 which agrees with other recent data on ammonia emissions from crusted slurry stores and, though it is within the range of
data considered in the UK emissions inventory, suggests that emissions from weeping wall stores and earth-banked lagoons may
be currently overestimated in national predictions. 相似文献
4.
Humans seem to have doubled the global rate of terrestrial nitrogen fixation. Globally 50–70% (85 Tg, 1 Tg=10 12 g) of the nitrogen supplied in fertilizer (80 Tg N/a) and leguminous crops (40–80 Tg N/a) are used to feed cattle. The aim of the present study was to derive some estimates of global N 2O production from animal manure. As the parameter giving the most stable numerical basis for regional and global extrapolation we adopted the molar emission ratios of N 2O to NH 3. These ratios were measured in cattle, pig and chicken housings with different manure handling systems, in dung-heaps and in liquid manure storage tanks. Individual molar emission ratios from outside manure piles varied over two orders of magnitude, strongly dependent on the treatment of the manure. A median emission ratio of 1.6×10 -2 ( n=65) was obtained in cow-sheds with slatted floors and liquid manure stored underneath and a median ratio of 24×10 -2 ( n=31) was measured in a beef cattle housing with a solid manure handling system.We next extrapolated to global NH 3 emissions from those estimated for Europe, using N uptake by the animals as a scaling factor. Multiplication with observed N 2O to NH 3 ratios next provided some estimates of regional and global N 2O emissions. To account for the great variability of the emission ratios of N 2O/NH 3, we developed upper and lower case emission scenarios, based on lower and upper quartiles of measured emission ratios. The global emission from cattle and swine manure is in the range of 0.2–2.5 Tg N-N 2O/a, representing 44+-39% of the annual atmospheric accumulation rate. This N 2O emission arises from about 40 Tg N/a of cattle and pig manure stored in or at animal housings. We did not account for N 2O emissions from another 50 Tg N/a excreted by grazing cattle, goats and sheep, and application of the manure to agricultural fields. Our study makes it clear that major anthropogenic N 2O emissions may well arise from animal manure. The large uncertainty of emission ratios, which we encountered, show that much more intense research efforts are necessary to determine the factors that influence N 2O emissions from domestic animal manure both in order to derive a more reliable global estimate of N 2O release and to propose alternative waste treatment methods causing smaller N 2O releases. In our studies we found large enhancements in N 2O releases when straw was added to the manure, which is a rather common practice. In view of the ongoing discussion in Europe to re-install the traditional solid manure system (bed down cattle) for environmental and animal welfare reasons, it is noteworthy that our measurements indicate highest N 2O release from this particulary system.In a similar manner, but based on a smaller data set, we also estimated the release of CH 4 from cattle and swine manure and from liquid manure only to be about 9 Tg/year in good agreement with the estimate by the Environmental Protection Agency (1994) of 8.6+-2.6 Tg/year. A total annual methane release as high as 34 Tg/a was derived for solid and liquid cattle and pig manure from animals in housings. 相似文献
5.
Ammonia (NH 3) emission from wheat (November to April) and rice (July to October) crops was measured using the chemiluminescence method at a subtropical agricultural area of India during 2009?C2010. Samples were collected from the canopy height during different growth stages of wheat crop to study the variations of NH 3 emission during different growth stages of the crop. Background atmospheric concentration of NH 3 was measured at 5 m height at the study site. Background NH 3 concentration was subtracted from the NH 3 concentration at crop canopy height to estimate the emission of NH 3 from crop canopy. The NH 3 emission from the wheat crop were recorded as 33.3 to 57.0; 15.3 to 29.2; 10.3 to 28.0; 8.7 to 23.9 and 13.9 to 28.9 ??g m ?2 d ?1 during sowing, crown root initiation (CRI), panicle initiation, grain filling and maturity stages of the crop respectively. The NH 3 emission followed a diurnal pattern with significant correlation with ambient temperature at different crop growth stages. Cumulative seasonal NH 3 emission to the atmosphere was accounted for the loss of ??10% of applied N-fertilizer during the wheat crop growing period. Immediate increase in NH 3 emission was recorded from rice crop, grown under temperature gradient tunnel (TGT). However, the NH 3 emission inside the TGT decreases within 3?C4 h after the N-fertilizer application. Continuous estimation of NH 3 concentration at the crop canopy inside the TGT, suggests that the NH 3 emission to the atmosphere reaches its peak within ??20 h of N-fertilizer application and continues up to 5 d following a diurnal pattern. 相似文献
6.
Green manuring of legume crops can improve soil fertility and sustainability. To evaluate its agronomic and environmental effectiveness, gaseous losses of ammonia (NH3) in the surface layer need to be quantified by direct measurements in the field. However, the application of the eddy-covariance technique to atmospheric NH3 is challenging: its high reactivity, water solubility, and low background concentrations all hinder the response time of closed-path sensors for fast measurements of NH3 concentration. Ammonia emissions following green manuring were measured for 21 days using a flux system equipped with a fast-pulsed quantum-cascade tunable-infrared-laser spectrometer. The noisy cross-covariance function for this configuration indicates flux measurements are close to the limit of detection; the low signal-to-noise ratio further increases the uncertainties, introducing a mirroring effect on the fluxes, which results in the rapid alternation between emission and deposition, within the limit of detection (around 13 and 20 ng m?2 s?1, at the 95 and 99% confidence limits, respectively). An evaluation of the measurement errors is presented, focussing on three technical aspects of the eddy-covariance system: (1) time lag, (2) random error, and (3) limit of detection. The NH3 fluxes measured by the spectrometer are close to its limit of detection, with a random error of the same order as the flux. 相似文献
7.
基于WRF/Chem模式和雾的观测资料,开展了包含和不包含人为污染排放源两种大气背景条件下的数值模拟对比试验,在此基础上探讨了人为污染物对2009年12月1日发生在我国华北和华东地区的一次浓雾天气过程的影响机理.结果表明,在考虑污染排放源时,模式模拟的雾的空间分布和强度变化与卫星、能见度仪和微波辐射计的观测更为接近.污... 相似文献
8.
During 18–23 July 1990, 31 smoke samples were collected from an aircraft flying at low altitudes through the plumes of tropical savanna fires in the Northern Territory, Australia. The excess (above background) mixing ratios of 17 different trace gases including CO 2, CO, CH 4, several non-methane hydrocarbons (NMHC), CH 3CHO, NO
x
(– NO + NO 2), NH 3, N 2O, HCN and total unspeciated NMHC and sulphur were measured. Emission ratios relative to excess CO 2 and CO, and emission factors relative to the fuel carbon, nitrogen or sulphur content are determined for each measured species. The emission ratios and factors determined here for carbon-based gases, NO
x
, and N 2O are in good agreement with those reported from other biomass burning studies. The ammonia data represent the first such measurements from savanna fires, and indicate that NH 3 emissions are more than half the strength of NO
x
emissions. The emissions of NO
x
, NH 3, N 2O and HCN together represent only 27% of the volatilised fuel N, and are primarily NO
x
(16%) and NH 3 (9%). Similarly, only 56% of the volatilised fuel S is accounted for by our measurements of total unspeciated sulphur. 相似文献
9.
Ammonia has a short residence time in the atmosphere and rapidly neutralizes acid gases that occur near its source, requiring a rapid measurement system for ammonia and particulate ammonium concentrations to better understand their sources, temporal variation of ammonia emissions, and the formation of secondary ammonium aerosols. A semi-continuous measurement system, consisting of a diffusion scrubber, a particle growth chamber, an air-liquid separator, and a fluorescent detector, was developed to determine both gaseous ammonia (NH 3) and particulate ammonium (NH 4 + ) in PM 2.5 in the ambient atmosphere of Gwangju, South Korea, during the months of March, April, July, and September of 2007. During the sampling periods, the average concentrations of ammonia and ammonium were found to be 2.33?±?1.29 μg/m 3 and 1.89?±?0.99 μg/m 3, respectively. Although the average gaseous ammonia concentration was highest in March, the particulate ammonium concentration was higher during the warmer season, reaching 2.08?±?1.07 μg/m 3 and 2.32?±?0.94 μg/m 3 in April and July, respectively, while only 1.68?±?0.61 μg/m 3 in March and 1.24?±?0.99 μg/m 3 in September. It is proposed that the higher availability of acid species during the warmer months produced a significant amount of particulate ammonium sulfate. Diurnal fluctuation of ammonia and ammonium during the warmer months showed that their peak time occurred at approximately 10:00 am. Both ammonia and ammonium concentrations were better correlated during the warmer months than during the cooler months. Further, the data suggest that the ammonia and ammonium were measured under well dispersed conditions, and multiple sources contributed to the ammonia at the sampling site. 相似文献
10.
Using a three-dimensional (3-D) transport model of the troposphere, we calculated the global distributions of ammonia (NH 3) and ammonium (NH
4
+
), taking into account removal of NH 3 on acidic aerosols, in liquid water clouds and by reaction with OH. Our estimated global 10°×10° NH 3 emission inventory of 45 Tg N-NH 3 yr – provides a reasonable agreement between calculated wet NH
4
+
deposition and measurements and of measured and modeled NH
4
+
in aerosols, although in Africa and Asia especially discrepancies exist.NH 3 emissions from natural continental ecosystems were calculated applying a canopy compensation point and oceanic NH 3 emissions were related to those of DMS (dimethylsulfide). In many regions of the earth, the pH found in rain and cloud water can be attributed to acidity derived from NO, SO 2 and DMS emissions and alkalinity from NH 3. In the remote lower troposphere, sulfate aerosols are calculated to be almost neutralized to ammonium sulfate (NH 4) 2SO 4, whereas in the middle and upper troposphere, according to our calculations, the aerosol should be more acidic, as a result of the oxidation of DMS and SO 2 throughout the troposphere and removal of NH 3 on acidic aerosols at lower heights. Although the removal of NH 3 by reaction with the OH radical is relatively slow, the intermediate NH 2 radical can provide a substantial annual N 2O source of 0.9
–0.4
+0.9
Tg, thus contributing by ca. 5% to estimated global N 2O production. The oxidation by OH of NH 3 from anthropogenic sources accounts for 10% of the estimated total anthropogenic sources of N 2O. This source was not accounted for in previous studies, and is mainly located in the tropics, which have high NH 3 and OH concentrations. Biomass burning plumes, containing high NO
x
and NH 3 concentrations provide favourable conditions for gas phase N 2O production. This source is probably underestimated in this model study, due to the coarse resolution of the 3-D model, and the rather low biomass burning NH 3 and NO
x
emissions adopted. The estimate depends heavily on poorly known concentrations of NH 3 (and NO
x
) in the tropics, and uncertainties in the rate constants of the reactions NH 2 + NO 2 N 2O + H 2O (R4), and NH 2 + O 3 NH 2O + O 2 (R7). 相似文献
11.
The Four-Dimensional Data Assimilation was performed to evaluate source emission strengths over the United States. The USEPA Models-3 system (CMAQ/MM5/SMOKE) and ridge regression are used as the forward and inverse models, respectively. The continental US is divided into six regions, and data assimilation is performed for each region in July 2001 and January 2002. In addition, two separate scaling factors are calculated for weekdays and weekends. Results show that base emissions for CO and SO 2 sources are relatively accurate. Base emissions for PEC source are overestimated 100%, but those for POA source are underestimated up to 70% when compared with the adjusted emissions. Emissions for NH 3, NO x , and PMFINE sources are relatively accurate in July 2001, but those in January 2002 are around 100% higher than the adjusted emissions. Base VOC emissions in July 2001 are similar to the adjusted emissions but those in January 2002 are underestimated up to 70% when compared with the adjusted emissions. Though the emission adjustment itself improves the overall air quality model performance, a better improvement is expected with the modification of speciation profiles and temporal allocations in the Models-3 system, as well. 相似文献
12.
A global three-dimensional chemical transport model has been used to identify and evaluate possible candidates for the `missing' surface source required to balance the atmospheric budget of methyl bromide. Both natural and anthropogenic emissions of methyl bromide are `coloured' in the model, thus allowing the global CH 3Br distribution to be broken-down into its source components. These coloured CH 3Br tracers are then combined in various ways to create one base-line emission scenario and five further plausible scenarios. The additional emission scenarios are specifically designed to test whether the geographical distribution and seasonal cycles of additional vegetation and/or increased biomass burning emissions are consistent with atmospheric observations of methyl bromide mixing ratios. Due to an imbalance in our current understanding of the methyl bromide budget, simulated CH 3Br mixing ratios from the base-line emission scenario are significantly lower than atmospheric measurements. Both the inclusion of a vegetation source in the tropics and a double strength biomass burning source substantially improve the agreement between model simulations and atmospheric measurements compared with the base-line emission scenario. While measurement data provides useful information on global fluxes and regional CH 3Br seasonal cycles, small differences between the simulated seasonal cycles of different emission scenarios makes it difficult to distinguish between the relative likelihoods of model scenarios containing a tropical vegetation source or an increased biomass burning source. Further measurements performed in continental mid-to-high northern latitudes, central-southern Africa and South America would be of particular benefit in future attempts to constrain the location and magnitude of the natural terrestrial sources of methyl bromide. 相似文献
13.
Gaseous nitric acid and ammonia were sampled with annular denuders at a forest savannah site from April to December 1987. The analysis of the extract was made spectrophotometrically and by a selective electrode for NO 3
– and NH 4
+, respectively. Higher concentrations were observed during the vegetation burning period at the end of the dry season. In the studied savannah area, large soil emissions of NO occur during the rainy season, although very low concentrations of HNO 3 (0.035 ppb) and also of particulate NO 3
– (0.43 g m -3) were observed; it is likely that NO x are lost by fast vertical transport to the upper troposphere. During the nonburning period, the average concentration of NH 3 was 2.7 ppb, which is much lower than values given in the literature for the tropical America atmosphere. The concentrations of HNO 3 and NH 3 were always below the values needed to produce ammonium nitrate aerosols. 相似文献
14.
This paper analyses factors that contributed to the evolution of SO 2, NO x and CO 2 emissions in Europe from 1960 to 2010. Historical energy balances, along with population and economic growth data, are used to quantify the impacts of major determinants of changing emission levels, including energy intensity, conversion efficiency, fuel mix, and pollution control. Time series of emission levels are compared for countries in Western and Eastern Europe, throwing light on differences in the importance of particular emission-driving forces. Three quarters of the decline in SO 2 emissions in Western Europe resulted from a combination of reduced energy intensity and improved fuel mix, while dedicated end-of-pipe abatement measures played a dominant role in the reduction of NO x emissions. The increase in atmospheric emissions in Eastern Europe through the mid-1990s was associated with the growth of energy-intensive industries, which off-setted the positive impact of better fuel quality and changes in fuel mix. A continuous decrease in energy intensity and higher conversion efficiencies have been the main factors responsible for the moderate rate of growth of European CO 2 emissions. 相似文献
15.
Gaseous pollutants and PM 2.5 aerosol particles were investigated during a tropical storm and an air pollution episode in southern Taiwan. Field sampling and chemical analysis of particulate matter and gaseous pollutants were conducted in Daliao and Tzouying in the Kaohsiung area, using a denuder-filter pack system during the period of 22 October to 3 November 2004. Sulfate, nitrate and ammonium were the major ionic species in the PM 2.5, accounting for 46 and 39% of the PM 2.5 for Daliao and Tzouying, respectively. Higher PM 2.5, Cl ?, NO 3? and NH 4+, HNO 2 and NH 3 concentrations were found at night in both stations, whereas higher HNO 3 was found during the day. In general, higher PM 2.5, HCl, NH 3, SO 2, Cl ?, NO 3?, SO 42? and NH 4+ concentrations were found in Daliao. The synoptic weather during the experiment was first influenced by Typhoon NOCK-TEN, which resulted in the pollutant concentrations decreasing by about two-thirds. After the tropical thunderstorm system passed, the ambient air quality returned to the previous condition in 12 to 24 h. When there was a strong subsidence accompanied by a high-pressure system, a more stable environment with lower wind speed and mixing height resulted in higher PM 2.5, as well as HNO 2, NH 3, SO 42?, Cl ?, NO 3?, NH 4+ and K + concentrations during the episode days. The rainfall is mainly a scavenger of air pollutants in this study, and the stable atmospheric system and the high emission loading are the major reasons for high air pollutant concentrations. 相似文献
16.
A new complex earth system model consisting of an atmospheric general circulation model, an ocean general circulation model,
a three-dimensional ice sheet model, a marine biogeochemistry model, and a dynamic vegetation model was used to study the
long-term response to anthropogenic carbon emissions. The prescribed emissions follow estimates of past emissions for the
period 1751–2000 and standard IPCC emission scenarios up to the year 2100. After 2100, an exponential decrease of the emissions
was assumed. For each of the scenarios, a small ensemble of simulations was carried out. The North Atlantic overturning collapsed
in the high emission scenario (A2) simulations. In the low emission scenario (B1), only a temporary weakening of the deep
water formation in the North Atlantic is predicted. The moderate emission scenario (A1B) brings the system close to its bifurcation
point, with three out of five runs leading to a collapsed North Atlantic overturning circulation. The atmospheric moisture
transport predominantly contributes to the collapse of the deep water formation. In the simulations with collapsed deep water
formation in the North Atlantic a substantial cooling over parts of the North Atlantic is simulated. Anthropogenic climate
change substantially reduces the ability of land and ocean to sequester anthropogenic carbon. The simulated effect of a collapse
of the deep water formation in the North Atlantic on the atmospheric CO 2 concentration turned out to be relatively small. The volume of the Greenland ice sheet is reduced, but its contribution to
global mean sea level is almost counterbalanced by the growth of the Antarctic ice sheet due to enhanced snowfall. The modifications
of the high latitude freshwater input due to the simulated changes in mass balance of the ice sheet are one order of magnitude
smaller than the changes due to atmospheric moisture transport. After the year 3000, the global mean surface temperature is
predicted to be almost constant due to the compensating effects of decreasing atmospheric CO 2 concentrations due to oceanic uptake and delayed response to increasing atmospheric CO 2 concentrations before. 相似文献
17.
Agricultural soils are a major source of atmospheric nitrous oxide (N 2O), a potent greenhouse gas (GHG). Because N 2O emissions strongly depend on soil type, climate, and crop management, their inventory requires the combination of biophysical and economic modeling, to simulate farmers’ behavior. Here, we coupled a biophysical soil-crop model, CERES-EGC, with an economic farm type supply model, AROPAj, at the regional scale in northern France. Response curves of N 2O emissions to fertilizer nitrogen (Nf) inputs were generated with CERES-EGC, and linearized to obtain emission factors. The latter ranged from 0.001 to 0.0225 kg N 2O-N kg ???1 Nf, depending on soil and crop type, compared to the fixed 0.0125 value of the IPCC guidelines. The modeled emission factors were fed into the economic model AROPAj which relates farm-level GHG emissions to production factors. This resulted in a N 2O efflux 20% lower than with the default IPCC method. The costs of abating GHG emissions from agriculture were calculated using a first-best tax on GHG emissions, and a second-best tax on their presumed factors (livestock size and fertilizer inputs). The first-best taxation was relatively efficient, achieving an 8% reduction with a tax of 11 €/ t-CO 2-equivalent, compared to 68 €/t-CO 2 eq for the same target with the second-best scheme. 相似文献
18.
Particulate matter emissions generated by agricultural field preparation and harvesting operations were measured remotely
via aerosol lidar and sampled simultaneously with a variety of aerosol point samplers in order to quantify dust plume space
and time dynamics and particulate mass and number concentrations. Data for two cotton operations (disking, harvesting) in
a flood-irrigated field in New Mexico are presented. Dust plume dynamics varied with boundary layer meteorological conditions,
especially atmospheric stability, with plume maximum height significantly lower under stable conditions. Plume tracking indicated
little change in plume area with height under unstable conditions and plume movement depended on wind speed and direction.
Particle mass distributions indicate approximately 50% of the measured PM 10 mass was PM 2.5, significantly higher than previously reported values, possibly due to the near-source nature of the samples collected here.
Variability in plume movement matched the variability in short-term wind fluctuations and this variability helps explain why
models that utilize long-term averages perform poorly when trying to capture plume dynamics for nonsteady sources such as
tractor operations. 相似文献
19.
A coupled carbon cycle-climate model is used to compute global atmospheric CO 2 and temperature variation that would result from several future CO 2 emission scenarios. The model includes temperature and CO 2 feedbacks on the terrestrial biosphere, and temperature feedback on the oceanic uptake of CO 2. The scenarios used include cases in which fossil fuel CO 2 emissions are held constant at the 1986 value or increase by 1% yr –1 until either 2000 or 2020, followed by a gradual transition to a rate of decrease of 1 or 2% yr –1. The climatic effect of increases in non-CO 2 trace gases is included, and scenarios are considered in which these gases increase until 2075 or are stabilized once CO 2 emission reductions begin. Low and high deforestation scenarios are also considered. In all cases, results are computed for equilibrium climatic sensitivities to CO 2 doubling of 2.0 and 4.0 °C.Peak atmospheric CO 2 concentrations of 400–500 ppmv and global mean warming after 1980 of 0.6–3.2 °C occur, with maximum rates of global mean warming of 0.2–0.3 °C decade –1. The peak CO 2 concentrations in these scenarios are significantly below that commonly regarded as unavoidable; further sensitivity analyses suggest that limiting atmospheric CO 2 to as little as 400 ppmv is a credible option.Two factors in the model are important in limiting atmospheric CO 2: (1) the airborne fraction falls rapidly once emissions begin to decrease, so that total emissions (fossil fuel + land use-induced) need initially fall to only about half their present value in order to stabilize atmospheric CO 2, and (2) changes in rates of deforestation have an immediate and proportional effect on gross emissions from the biosphere, whereas the CO 2 sink due to regrowth of forests responds more slowly, so that decreases in the rate of deforestation have a disproportionately large effect on net emission.If fossil fuel emissions were to decrease at 1–2% yr –1 beginning early in the next century, emissions could decrease to the rate of CO 2 uptake by the predominantly oceanic sink within 50–100 yrs. Simulation results suggest that if subsequent emission reductions were tied to the rate of CO 2 uptake by natural CO 2 sinks, these reductions could proceed more slowly than initially while preventing further CO 2 increases, since the natural CO 2 sink strength decreases on time scales of one to several centuries. The model used here does not account for the possible effect on atmospheric CO 2 concentration of possible changes in oceanic circulation. Based on past rates of atmospheric CO 2 variation determined from polar ice cores, it appears that the largest plausible perturbation in ocean-air CO 2 flux due to changes of oceanic circulation is substantially smaller than the permitted fossil fuel CO 2 emissions under the above strategy, so tieing fossil fuel emissions to the total sink strength could provide adequate flexibility for responding to unexpected changes in oceanic CO 2 uptake caused by climatic warming-induced changes of oceanic circulation. 相似文献
20.
Emissions of oxygenated volatile organic compounds (OVOC) from several plant species were measured in continuously stirred tank reactors (CSTR). High emission pulses of OVOCs were observed when plants were exposed to stress. Absolute emission rates were highly variable ranging up to 10 –13 mol · cm –2 · s –1. The temporal shape of these emissions was described by a formalism similar to that of a consecutive reaction of pseudo first order kinetics. The main emitted OVOC was (Z)-3-hexenol together with other C 6-aldehydes and alcohols, suggesting that lipoxygenase activity on linolenic acid was mainly responsible for OVOC production. Various stress factors induced lipoxygenase activity and subsequent emissions of OVOCs. These factors were exposure to high ozone concentrations, pathogen attack, and wounding. The pattern of OVOC emissions from tobacco was similar for different stress applications and the same products of lipoxygenase activity were emitted from all investigated plant species. Our results imply that these emissions occur as general response of the plants to stress. Since plants experience various abiotic or biotic stress factors in the environment, OVOC emissions as a response to stress are likely to be of significant importance for atmospheric chemistry.Now at 相似文献
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