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1.
Investigations about VOSCs (volatile organic sulfur compounds) have been received increasing attention for their significant contribution to the nonvolcanic background sulfate layer in the stratosphere and the earth’s radiation balance and as a potential tool to understand the carbon budget. In this study, COS and CS2 were always recorded throughout the entire rice cultivation season of 2014. COS fluxes appeared as emission in non-planted soil and as uptake in planted soil, the corresponding results were obtained as 2.66 and ?2.35 pmol·m?2·s?1, respectively. For CS2, both planted and non-planted paddy fields acted as sources with an emission rate of 1.02 pmol·m?2·s?1 and 2.40 pmol·m?2·s?1, respectively. COS emission or uptake rates showed a distinct seasonal variation, with the highest fluxes at the jointing-booting stage. COS and CS2 fluxes increased with increasing N fertilizer use because of improved plant and microbial growth and activity. Plots treated with both N and S reduced COS and CS2 fluxes slightly compared with plots with only-N treatment. Light, soil moisture or temperature showed no significant correlation with COS and CS2 fluxes, but revealed the important impacts on the magnitude and direction of gases fluxes. The results also showed that the (available) sulfur contents in soil and roots had a certain effect on VOSCs emission or uptake. Our results highlight the significance of biotic and abiotic production and consumption processes existing in the soil.  相似文献   

2.
There are large uncertainties in identifying and quantifying the natural and anthropogenic sources of chloromethanes – methyl chloride (CH3Cl), chloroform (CHCl3) and dichloromethane (CH2Cl2), which are responsible for about 15% of the total chlorine in the stratosphere. We report two years of in situ observations of these species from the AGAGE (Advanced Global Atmospheric Gas Experiment) program at Cape Grim, Tasmania (41° S, 145° E). The average background levels of CH3Cl, CHCl3 and CH2Cl2 during 1998–2000 were 551± 8, 6.3± 0.2 and 8.9± 0.2 ppt (dry air mole fractions expressed in parts per 1012) respectively, with a two-year average amplitude of the seasonal cycles in background air of 25, 1.1 and 1.5 ppt respectively. The CH3Cl and CHCl3 records at Cape Grim show clear episodes of elevated mixing ratios up to 1300 ppt and 55 ppt respectively, which are highly correlated, suggesting common source(s). Trajectory analyses show that the sources of CH3Cl and CHCl3 that are responsible for these elevated observations are located in coastal-terrestrial and/or coastal-seawater regions in Tasmania and the south-eastern Australian mainland. Elevated levels of CH2Cl2 (up to 70 ppt above background) are associated mainly with emissions from the Melbourne/Port Phillip region, a large urban/industrial complex (population 3.5 million) 300 km north of Cape Grim.Now at the Centre for Atmospheric ChemistryNow at School of Environmental Sciences  相似文献   

3.
The formation yields of nine carbonyl products are reported from the gas-phase OH radical-initiated reactions (in the presence of NO x ) and the O3 reactions with seven monoterpenes. The products were identified using GC/MS and GC-FTIR and quantified by GC-FID analyses of samples collected on Tenax solid adsorbent cartridges. The identities of products from camphene, limonene and -pinene were confirmed by comparison with authentic standards. Sufficient quantities of products from the 3-carene, limonene, -pinene, sabinene and terpinolene reactions were isolated to allow structural confirmation by proton NMR spectroscopy. The measured total carbonyl formation yields ranged from non-detectable for the OH radical reaction with camphene and the O3 reactions with 3-carene and limonene to 0.5 for the OH radical reaction with limonene and the O3 reaction with sabinene.  相似文献   

4.
The aim of the 222Rn measurements during the airborne campaign TROPOZ II, was first to help in the interpretation of the photochemical studies, and secondly to furnish a data set of 222Rn in the troposphere, for validation of atmospheric transport models. In this paper we present the 222Rn measurements, and their simulation with a 3-D atmospheric transport model based on observed winds. The 222Rn was measured using the active daughters deposit technique with isokinetic aerosol sampling. We have obtained 44 measurements distributed between 65° North and 55° South, from 1 to 11 km height. In 25% of cases, we found relatively high concentrations (> 300 mBq·scm) of 222Rn in the high troposphere (>8 km). The results of 3D simulations and the calculations of back-trajectories allow us to find the origins of the high 222Rn concentrations. The transport model reproduced most of the observed synoptic variations, but it overestimates the concentrations which implies a vertical transport of excessive velocity.  相似文献   

5.
The flux of CH4 and CO2 from termite nests into the atmosphere has been measured in a broad-leafed-type savannah in South Africa. Measurements were carried out on nests of species of six genera, i.e., Hodotermes, Macrotermes, Odontotermes, Trinervitermes, Cubitermes, and Amitermes. The flux rates of CH4 relative to the flux rate of CO2 in terms of carbon obtained for the individual species showed ratios of 2.9×10-3, 7.0×10-4, 6.7×10-5, 8.7×10-3, 2.0×10-3 and 4.2×10-3, respectively. Using data published on the assimulation efficiencies of termites, the flux of carbon as CH4 accounts for 6.0×10-5 to 2.6×10-3 of the carbon ingested which results in a global CH4 emission by termites of 2 to 5×1012 g/yr. Methane is decomposed in the soil with average decomposition rates of 52 g/m2/h. The annual CH4 consumption in the tropics and subtropics is estimated to be 21×1012 g which exceeds the CH4 emission rate by termites.  相似文献   

6.
In order to obtain field data of ocean-atmosphere gas transfer coefficients, it is preferable to measure the interfacial gas flux in the air rather than in the water. This approach has been reported in the literature for CO2. However, it is shown here that 222Rn and methyliodide, CH3I, may be more suitable gases for air-side flux measurements.  相似文献   

7.
In order to study the factors influencing the formation of the vertical component of atmospheric electric field (AEF) strength E z , the data on meteorological parameters (atmospheric pressure, air temperature, and snow depth) are applied, as well as the data of radon Rn emanation into the atmosphere. Determined is the seasonal dependence on the radon emanation to the atmospheric surface layer due to the decrease in the upper soil layer permeability in wintertime that results in the decrease in the surface layer ionization which explains the difference between the maximum and minimum values of electric field strength within the annual variations amounting to ～100 V/m for the observational period. It is demonstrated that during the negative mean diurnal temperatures (November-April), the cyclone arrival from southern directions is accompanied by significant decrease in AEF E z due to the increase in the radon flow under the influence of considerable fall of atmospheric pressure and dramatic warming by 10–15°C resulting in the increase in upper soil layer permeability.  相似文献   

8.
The absorption cross-sections of HCFC-123 (CF3–CHCl2), HCFC-141b (CH3–CFCl2) and HCFC-142b (CH3–CF2Cl) are measured between 170 and 250 nm for temperatures ranging from 295 to 210 K with uncertainties between 2 and 4%. They are compared with other available determinations. Temperature effects are discussed and parametrical formulae are proposed to compute the absorption cross-section for wavelengths and temperatures useful in atmospheric modelling calculations. Photodissociation coefficients are presented and their temperature-dependence is discussed.  相似文献   

9.
Absorption cross-sections of nine halomethanes (CCl4, CHCl3, CH2Cl2, CH3Cl, CFCl3, CF2Cl2, CF3Cl, CHFCl2, and CHF2Cl), measured between 174 and 250 nm for temperatures ranging from 225 to 295 K, are presented with uncertainties ranging from 2 to 4% and compared with previous determinations made for comparable temperature ranges.The largest temperature effect which takes place near the absorption threshold, decreases the absorption cross-section up to 50% for highly chlorinated methanes, but is negligible for molecules highly stabilized by hydrogen and/or fluorine. Extrapolated values for temperatures of aeronomical interest are presented, as well as parametrical formulas which give absorption cross-section values for given wavelength and temperature ranges.  相似文献   

10.
A 2-D meridional model for the chemistry and transport in the troposphere is used to study the seasonal variation of the concentration of organic gases like C2H2, C2H6, C3H8, C6H6, C7H8. CHCl3 and C2Cl4 at high latitudes. The anthropogenic sources for these species were estimated, and the temporal and latitudinal distribution of OH and O3 was calculated using a complex photochemical reaction system. There is fair agreement between the calculated annual variation and the measured concentrations for C2H2, C2H6, C3H8, C7H8 and C2Cl4 at Spitsbergen during July 1982 and March/April 1983, with a distinct late winter maximum and summer minimum. For CHCl3, the direct anthropogenic source is minor compared to indirect anthropogenic or natural sources. For benzene, emission in car exhaust is important, but other anthropogenic sources are required for the calculations to agree with the measurements. Measured C2H4 and C3H6 concentrations are much higher than the calculated ones based on anthropogenic emissions, and show opposite seasonal trends. This indicates biogenic sources for these compounds.A buildup of PAN (300 pptv) is calculated at high latitudes during winter. This makes it the dominant source for NOx as the temperature increases in the spring. NOx is found to be a limiting factor for O3 production at high latitudes during spring.  相似文献   

11.
In addition to increasing plant C inputs, strategies for enhancing soil C sequestration include reducing C turnover and increasing its residence time in soils. Two major mechanisms, (bio)chemical alteration and physicochemical protection, stabilize soil organic C (SOC) and thereby control its turnover. With (bio)chemical alteration, SOC is transformed by biotic and abiotic processes to chemical forms that are more resistant to decomposition and, in some cases, more easily retained by sorption to soil solids. With physicochemical protection, biochemical attack of SOC is inhibited by organomineral interactions at molecular to millimeter scales. Stabilization of otherwise decomposable SOC can occur via sorption to mineral and organic soil surfaces, occlusion within aggregates, and deposition in pores or other locations inaccessible to decomposers and extracellular enzymes. Soil structure is a master integrating variable that both controls and indicates the SOC stabilization status of a soil. One potential option for reducing SOC turnover and enhancing sequestration, is to modify the soil physicochemical environment to favor the activities of fungi. Specific practices that could accomplish this include manipulating the quality of plant C inputs, planting perennial species, minimizing tillage and other disturbances, maintaining a near-neutral soil pH and adequate amounts of exchangeable base cations (particularly calcium), ensuring adequate drainage, and minimizing erosion. In some soils, amendment with micro- and mesoporous sorbents that have a high specific surface – such as fly ash or charcoal – can be beneficial. All authors contributed equally to this article.  相似文献   

12.
Experimental field and laboratory studies on washout of radionuclides from the snow cover during snow melting were carried out in the winter of 2005/06. In the field studies, a specially equipped runoff site was used. In the laboratory conditions, the experiments were conducted using prepared soil monoliths. In the winter of 2006, 25 g/m2 of water-free cesium chloride (CsCl) and 25 g/m3 of strontium chloride (SrCl2) were put onto the snow cover surface of the runoff site. The snow surface of the soil monolith was coated with a 137Cs-bearing solution, then with SrCl2. Under experimental conditions, practically no surface runoff from the runoff site was recorded. The experiments with the soil monoliths demonstrated that the coefficient of the liquid washout of 137Cs normalized to the runoff layer was within 0.9 × 10?6–1.2 × 10?4 mm?1, and that of 90Sr normalized to the runoff layer was within 2 × 10?–1.6 × 10?4 mm?1.  相似文献   

13.
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 C6-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   

14.
Nitric oxide fluxes from soils in the Trachypogon savanna of the Orinoco basin were determined during the dry season using the static chamber method. The emission from dry soils fluctuated from 0.4 to 3 ng N m–2 s–1 and increased up to 25 ng N m–2 s–1 after moderate watering or light rain-falls (1 to 5 mm). The mean emission values are up to 6 times lower than one observed earlier at the Chaguaramas site, but up to 10 times higher than one recorded at the Guri site, indicating an important spatial variability in NO fluxes of the Venezuelan savanna region. The changes observed after the addition of nitrogen to the soil, in the form of ammonium and/or nitrate, indicate a high denitrification potential in this acidic soil. Burning of the surface vegetation produced an increase by a factor of 10 in the emission rate of NO, but the effect was relatively short in time, about 5 days. It was estimated for the savanna region that burning increases the total NO soil emission during the dry season by 15% compared to the unburnt case. Soils with termite nests emit 10 times more NO than soil without nests, but the contribution from this source is less than 2% of the total savanna soil flux.  相似文献   

15.
Atmospheric activity concentrations of 212Pb and short-lived 222Rndaughters, together with meteorological elements, have been observed continuously atthree sites at Kamisaibara Village in Japan. In addition, atmospheric activity concentrationof 222Rn, equilibrium-equivalent concentration of 222Rn and conditionsof the lower atmosphere were observed for three intensive observation periods at Akawase,one of the three sites in Kamisaibara Village. The equilibrium-equivalent concentration of222Rn is almost the same as the atmospheric activity concentration of short-lived222Rn daughters.The activity concentrations of 212Pb and the short-lived 222Rn daughtersand their ratio were low in the daytime owing to convective mixing, and high at nightowing to the surface-based inversion during periods of no precipitation. Their variationshave several patterns corresponding to the scale of the drainage wind or weak mixing.Mechanical mixing due to strong winds through both day and night during the first andsecond observation periods made the atmospheric activity concentrations of 212Pb and the short-lived 222Rn daughters continuously low. However, their ratios werecontinuously high during the first period yet continuously low during the second period.This difference can be explained by the effect ofextraction of 220Rn and 222Rndue to strong winds and snow cover. There were also cases in which the ratio of theatmospheric activity concentration of 212Pb to that of the short-lived 222Rndaughters at night was equal to or less than the ratio in the daytime. Thisinverse trend, asin the periods of no precipitation mentioned above, is considered to be due to near-neutralconditions on these nights.We find a difference in the ratio of the equilibrium-equivalent concentration of222Rn (the activity concentration of short-lived 222Rn daughters) tothe activity concentration of 222Rn during the first observation period and thatduring the second. The difference can be explained by snow cover on the ground. Wealso find differences among the ratios of the activity concentration of the short-lived222Rn daughters to that of 222Rn during the three observation periods.These differences can be explained by the submergence of paddy fields.  相似文献   

16.
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17.
A gas chromatographic study has revealed the presence in volcanic gases of a variety of volatile organic compounds. Of particular interest is the detection of such halocarbons as trichlorofluoromethane (F-11), dichlorodifluoromethane (F-12), dichlorofluoromethane (F-21), CCl4 and CHCl3. The concentrations of these compounds attaining 160 ppb in undilute solfataric gases were determined for the first time. The data obtained confirm the existence of a natural source of halocarbons that have a long lifetime in the troposphere and that play an important role in the greenhouse effect and in the catalytic cycle of destruction of stratospheric ozone.  相似文献   

18.
Concentrations of 222Rn at 0.1 m and 6.5 m height above ground level and 222Rn flux density were measured during nights characterized by strong cooling, light winds and clear sky conditions in the Carpathian Basin in Hungary. A very stable boundary layer (vSBL) formed on 14 nights between 15 August and 3 September 2009. On 12 nights, an estimated 72% (s.d. 20%) of 222Rn emitted from the surface since sunset was retained within the lowest 6.5 m above the ground until sunrise the following morning. On two nights an intermittent increase in wind speed at 9.4 m height was followed by a rise in temperature at 2.0 m height, indicating a larger atmospheric motion that resulted in 222Rn at 0.1 m around sunrise being the same as around the preceding sunset. It does not seem to be rare in a large continental basin for a vSBL to be nearly completely decoupled from the atmosphere above for the entire period from sunset to sunrise.  相似文献   

19.
Soil temperature (T S) strongly influences a wide range of biotic and abiotic processes. As an alternative to direct measurement, indirect determination of T S from meteorological parameters has been the focus of attention of environmental researchers. The main purpose of this study was to estimate daily T S at six depths (5, 10, 20, 30, 50 and 100?cm) by using a multilayer perceptron (MLP) artificial neural network (ANN) model and a multivariate linear regression (MLR) method in an arid region of Iran. Mean daily meteorological parameters including air temperature (T a), solar radiation (R S), relative humidity (RH) and precipitation (P) were used as input data to the ANN and MLR models. The model results of the MLR model were compared to those of ANN. The accuracy of the predictions was evaluated by the correlation coefficient (r), the root mean-square error (RMSE) and the mean absolute error (MAE) between the measured and predicted T S values. The results showed that the ANN method forecasts were superior to the corresponding values obtained by the MLR model. The regression analysis indicated that T a, RH, R S and P were reasonably correlated with T S at various depths, but the most effective parameters influencing T S at different depths were T a and RH.  相似文献   

20.
Long-term measurements of ambient particulate matter less than 2.5 μm in diameter (PM2.5) and its chemical compositions were performed at a rural site in Korea from December 2005 to August 2009. The average PM2.5 concentration was 31 μg m−3 for the whole sampling period, and showed a slightly downward annual trend. The major components of PM2.5 were organic carbon, SO42−, NO3−, and NH4+, which accounted for 55 % of total PM2.5 mass on average. For the top 10 % of PM2.5 samples, anionic constituents and trace elements clearly increased while carbonaceous constituents and NH4+ remained relatively constant. Both Asian dust and fog events clearly increased PM2.5 concentrations, but affected its chemical composition differently. While trace elements significantly increased during Asian dust events, NO3−, NH4+ and Cl were dramatically enhanced during fog events due to the formation of saturated or supersaturated salt solution. The back-trajectory based model, PSCF (Potential Source Contribution Function) identified the major industrial areas in Eastern China as the possible source areas for the high PM2.5 concentrations at the sampling site. Using factor analysis, soil, combustion processes, non-metal manufacture, and secondary PM2.5 sources accounted for 77 % of the total explained variance.  相似文献   

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