A comparison between natural and anthropogenic emissions of the reduced sulfur compounds H2S, COS, and CS2 in a tropical industrialized region

Extensive ambient concentration and flux measurements have been performed in the heavily polluted region of Cubatão/Brazil. Substantial contribution of anthropogenic sources to the local reduced sulfur burden has been observed. As a result of this atmospheric sulfur burden average gas exchange between vegetated soils and the atmosphere shows net deposition. Based mainly on own field measurements a local budget for H₂S, COS, and CS₂ has been made up in order to calculate anthropogenic emissions. All major sources and sinks in the chosen atmospheric reservoir (24×20×1 km) have been taken into account. Due to the small reservoir size fluxes across its boundaries are dominant sources and sinks. The differences between outflux and influx therefore account for the unknown anthropogenic emissions which have been determined to be 80±10 (H₂S), 66±15 (COS), and 29±6 Mmol year^-1 (CS₂). Other sources and sinks like natural emissions, chemical conversion, and dry deposition turned out to be of minor importance on a local scale. In fact, inside the investigated reservoir natural emissions were below 0.5% of anthropogenic emissions. Anthropogenic emissions of H₂S, COS, and CS₂ quantified in this work have been compared with global emission estimates for these compounds made by other authors. We conclude that global anthropogenic emissions of reduced sulfur compounds especially of COS and CS₂ are currently under-estimated.     

The effect of nitrogen fertilization on the COS and CS2 emissions from temperature forest soils

The net fluxes of carbonyl sulfide (COS) and carbon disulfide (CS₂) to the atmosphere from nitrogen amended and unamended deciduous and coniferous forest soils were measured during the spring of 1986. We found that emissions of these gases from acidic forest soils were substantially increased after nitrogen fertilization. The total (COS+CS₂) emissions were increased by nearly a factor of three in the hardwood stand and were more than doubled in the pine stand. Furthermore, vegetation type appeared to have an influence on which was the dominant sulfur gas released from the forest soils. The added nitrogen caused a dramatic increase in COS emissions from the hardwood stand (a factor of three increase), while CS₂ emissions from this site were not affected. We observed the opposite response in the pine stand; that is, the nitrogen fertilization had no affect on COS emissions, but did stimulate CS₂ emissions (a factor of more than nine increase).     

Quantification of ecosystem carbon exchange characteristics in a dominant subtropical evergreen forest ecosystem

CO₂ fluxes were measured continuously for three years (2003?C2005) using the eddy covariance technique for the canopy layer with a height of 27 m above the ground in a dominant subtropical evergreen forest in Dinghushan, South China. By applying gapfilling methods, we quantified the different components of the carbon fluxes (net ecosystem exchange (NEE)), gross primary production (GPP) and ecosystem respiration (R_eco) in order to assess the effects of meteorological variables on these fluxes and the atmospherecanopy interactions on the forest carbon cycle. Our results showed that monthly average daily maximum net CO₂ exchange of the whole ecosystem varied from ?3.79 to ?14.24 ??mol m^?2 s^?1 and was linearly related to photosynthetic active radiation. The Dinghushan forest acted as a net carbon sink of ?488 g C m^?2 y^?1, with a GPP of 1448 g Cm^?2 y^?1, and a R_eco of 961 g C m^?2 y^?1. Using a carboxylase-based model, we compared the predicted fluxes of CO₂ with measurements. GPP was modelled as 1443 g C m^?2 y^?1, and the model inversion results helped to explain ca. 90% of temporal variability of the measured ecosystem fluxes. Contribution of CO₂ fluxes in the subtropical forest in the dry season (October-March) was 62.2% of the annual total from the whole forest ecosystem. On average, 43.3% of the net annual carbon sink occurred between October and December, indicating that this time period is an important stage for uptake of CO₂ by the forest ecosystem from the atmosphere. Carbon uptake in the evergreen forest ecosystem is an indicator of the interaction of between the atmosphere and the canopy, especially in terms of driving climate factors such as temperature and rainfall events. We found that the Dinghushan evergreen forest is acting as a carbon sink almost year-round. The study can improve the evaluation of the net carbon uptake of tropical monsoon evergreen forest ecosystem in south China region under climate change conditions.     

Continuous measurement of methane flux over a larch forest using a relaxed eddy accumulation method

We measured the methane flux of a forest canopy throughout a year using a relaxed eddy accumulation (REA) method. This sampling system was carefully validated against heat and CO₂ fluxes measured by the eddy covariance method. Although the sampling system was robust, there were large uncertainties in the measured methane fluxes because of the limited precision of the methane gas analyzer. Based on the spectral characteristics of signals from the methane analyzer and the diurnal variations in the standard deviation of the vertical wind velocity, we found the daytime and nighttime precision of half-hourly methane flux measurements to be approximately 1.2 and 0.7?μg?CH₄?m^?2?s^?1, respectively. Additional uncertainties caused by the dilution effect were estimated to affect the accuracy by as much as 0.21?μg?CH₄?m^?2?s^?1 on a half-hourly basis. Diurnal and seasonal variations were observed in the measured fluxes. The biological emission from plant leaves was not observed in our studies, and thus could be negligible at the canopy-scale exchange. The annual methane sink was 835?±?175?mg?CH₄?m^?2?year^?1 (8.35?kg?CH₄?ha^?1?year^?1), which was comparable to the flux range of 379–2,478?mg?CH₄?m^?2?year^?1 previously measured in other Japanese forest soils. This study indicated that the REA method could be a promising technique to measure canopy scale methane fluxes over forests, but further improvement of precision of the analyzer will be required.     

The measurement of natural sulfur emissions from soils and vegetation: Three sites in the Eastern United States revisited

Sulfur fluxes from bare soils, naturally vegetated surfaces and from several agricultural crops were measured at two mid-continent sites (Ames, Iowa and Celeryville, Ohio) and from one salt water marsh site (Cedar Island, North Carolina) during a field program conducted jointly by the NOAA Aeronomy Laboratory, Washington State University Laboratory for Atmospheric Research and University of Idaho Department of Chemistry during July and August 1985. The sites were chosen specifically because they had been characterized by previous studies (Anejaet al., 1979; Adamset al., 1980, 1981). The NOAA gas chromatographic/dynamic-enclosure measurements yielded bare soil surfaces fluxes from the mid-continent sites composed predominantly of COS, H₂S, CH₃–S–CH₃ (DMS) and CS₂, all of which were strongly correlated with air temperature. Net fluxes of approximately 5 and 15 ng S/m² min were observed in Iowa and Ohio, respectively, at appropriate weighted mean July temperatures. These fluxes are roughly a factor of 10 smaller than the earlier measurements, the greatest difference being in the measurement of the H₂S flux. The presence of growing vegetation was observed to measurably increase the flux of H₂S, significantly increase that of DMS and to decrease that of COS. Sulfur fluxes in the Cedar Island environs were observed to be both spatially and temporally much more variable and to include CH₃SH as a measurable contributor. Net fluxes, composed predominantly of DMS and H₂S, were estimated to be about 300 ngS/m²min during August; again about a factor of 10 lower than previous estimates. All measurements were corroborated to within about a factor of 2 by those of the other participating laboratories.     

Determination of Atmospheric Sulfur Compounds Near a Volcanic Area in Greece

Volcanoes have been identified as an important natural source of sulfur compounds such as H₂S, CS₂, SO₂ and COS. The emission of volcanic sulfur compounds lead to the formation of sulfate aerosol and contribute to the acidity of precipitation. Two weekly measuring campaigns have been performed in the non-erupting volcanic area of Sousaki, Korinthou, to determine the concentration levels of the above-mentioned compounds in the region, while meteorological parameters were also recorded. The samplings have been performed during in a 24 h basis, covering two seasons of the year, a week in August 1998 and a week in January 1999. Reduced sulfur compounds were determined by a simple method of gas chromatography. Quality assurance procedure showed a very good precision and accuracy of the method utilized for the sulfur compounds determination. In accordance with literature, H₂S was the dominant sulfur compound at the volcano area, while COS, and CS₂ didn't present significantly high values. Nevertheless, the concentration levels of the above pollutants are varying depending on the volcano magnitude and status (active, extinct).     

Laboratory studies of some environmental variables controlling sulfur emissions from plants

Several trace sulfur gases that can have a significant influence on atmospheric chemistry are emitted from biological systems. In order to begin to address biological questions on the mechnisms of production of such gases, laboratory-scale experiments have been developed that reproduce such emissions under controlled conditions. Using a flux chamber technique, flats containing soil, or soil plus plants were sampled for the net fluxes of sulfur gases. The major sulfur gas emitted from all the plants tested (corn, alfalfa, and wheat) was dimethyl sulfide (DMS). Alfalfa and wheat also emitted lesser amounts of methanethiol, variable amounls of hydrogen sulfide, and in some experiments wheat emitted carbon disulfide. The use of a plant incubator allowed a systematic study of the effects of variables such as temperature, photon flux, and carbon dioxide levels, on these emissions. Fluxes of all the emitted sulfur gases increased exponentially with increasing air temperature, and increased with increasing photon flux up to a saturation level of \~300 E/m^–2 sec^-1. Three to four-fold changes in DMS flux were observed during light to dark or dark to light transitions. By varying the CO₂ content of the chamber flush gas, it was shown that the observed sulfur fluxes from corn and alfalfa were not related to the CO₂ concentration. Growing these crop plants through holes in a Teflon soil-covering film allowed a separate determination of soil and foliage emissions and substantiation of the light dependent uptake of COS by growing vegetation observed in previous field studies.     

Emissions of marine biogenic sulfur to the atmosphere of northern Europe

Measurements of DMS and other reduced sulfur compounds in surface waters have been carried out from a helicopter in the seas surrounding Scandinavia. Average summer time concentrations of DMS ranged from 70 to 150 ngS L^-1. Simultaneous measurements of biological and physical parameters revealed no correlation between DMS and phytoplankton species, species assemblages, total phytoplankton biomass, chlorophyll a, temperature, and salinity. The only exception was a correlation between DMS concentration, Chrysochromulina spp. belonging to the Prymnesiophyceae, and salinity over a narrow range of salinity in the Baltic Sea.The flux of reduced sulfur to the atmosphere in July in this region is estimated to be 120–170 gS m^-2 d^-1 from the Baltic, 240–810 in the Kattegat/Skagerrak, and 120–690 in the North Sea. Annual fluxes are roughly 100 times higher than these daily fluxes. On an annual basis, biogenic sulfur emissions from the coastal seas are negligible (<1%) compared to the anthropogenic emissions in northern Europe. However, during the summer months, the biogenic sulfur emissions from the seas surrounding the Scandinavian peninsula are estimated to be as high as 20–70% of the anthropogenic emissions in Scandinavia. This makes it of interest to incorporate the biogenic emissions in calculations of long-range transport and deposition of sulfur within the region.Other volatile sulfur species, mainly methyl mercaptan, contribute about 10% of the total flux of reduced sulfur. Estimated fluxes of CS₂ to the atmosphere ranged from 1 gS m^-2 d^-1 in the Baltic Sea to 6 gS m^-2 d^-1 in the North Sea. No emissions for H₂S or COS were detected.     

锡林浩特草原CO2通量特征及其影响因素分析

利用锡林浩特国家气候观象台开路涡度相关系统、辐射土壤观测系统,测得的长期连续通量观测数据,对锡林浩特草原2009—2011年期间的CO₂通量观测特征进行了分析。结果表明:CO₂通量存在明显的年际、季节和日变化特征。3 a中NEE年际变率达到200 g·m^-2,季节变率最大达到460 g·m^-2,日变化幅度生长季最大达到0.25 mg·m^-2·s^-1。通过不同时间尺度碳通量与温度、水分、辐射等环境因子的分析,认为CO₂通量日变化主要受温度和光合有效辐射影响,而季节变化和年变化主要受降水和土壤含水量的影响。降水强度及时间分布是制约牧草CO₂吸收的关键因素,大于15%的土壤含水量有利于促进牧草生长。     

Emission of nitric oxide from soils and termite nests in a Trachypogon savanna of the Orinoco basin

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.     

Methods for Estimating Air–Sea Fluxes of CO<Subscript>2</Subscript> Using High-Frequency Measurements

The most direct method for flux estimation uses eddy covariance, which is also the most commonly used method for land-based measurements of surface fluxes. Moving platforms are frequently used to make measurements over the sea, in which case motion can disturb the measurements. An alternative method for flux estimation should be considered if the effects of platform motion cannot be properly corrected for. Three methods for estimating CO₂ fluxes are studied here: the eddy-covariance, the inertial-dissipation, and the cospectral-peak methods. High-frequency measurements made at the land-based Östergarnsholm marine station in the Baltic Sea and measurements made from a ship during the Galathea 3 expedition are used. The Kolmogorov constant for CO₂, used in the inertial-dissipation method, is estimated to be 0.68 and is determined using direct flux measurements made at the Östergarnsholm site. The cospectral-peak method, originally developed for neutral stratification, is modified to be applicable in all stratifications. With these modifications, the CO₂ fluxes estimated using the three methods agree well. Using data from the Östergarnsholm site, the mean absolute error between the eddy-covariance and inertial-dissipation methods is 0.25 μmol  m^?2 s^?1. The corresponding mean absolute error between the eddy-covariance and cospectral-peak methods is 0.26 μmol m^?2 s^?1, while between the inertial-dissipation and cospectral-peak methods it is 0.14 μmol m^?2 s^?1.     

Limitations of an Eddy-Covariance System in Measuring Low Ammonia Fluxes

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.

     

A nocturnal atmospheric loss of CH<Subscript>2</Subscript>I<Subscript>2</Subscript> in the remote marine boundary layer

Ocean emissions of inorganic and organic iodine compounds drive the biogeochemical cycle of iodine and produce reactive ozone-destroying iodine radicals that influence the oxidizing capacity of the atmosphere. Di-iodomethane (CH₂I₂) and chloro-iodomethane (CH₂ICl) are the two most important organic iodine precursors in the marine boundary layer. Ship-borne measurements made during the TORERO (Tropical Ocean tRoposphere Exchange of Reactive halogens and Oxygenated VOC) field campaign in the east tropical Pacific Ocean in January/February 2012 revealed strong diurnal cycles of CH₂I₂ and CH₂ICl in air and of CH₂I₂ in seawater. Both compounds are known to undergo rapid photolysis during the day, but models assume no night-time atmospheric losses. Surprisingly, the diurnal cycle of CH₂I₂ was lower in amplitude than that of CH₂ICl, despite its faster photolysis rate. We speculate that night-time loss of CH₂I₂ occurs due to reaction with NO₃ radicals. Indirect results from a laboratory study under ambient atmospheric boundary layer conditions indicate a k _CH2I2+NO3 of ≤4 × 10^?13 cm³ molecule^?1 s^?1; a previous kinetic study carried out at ≤100 Torr found k _CH2I2+NO3 of 4 × 10^?13 cm³ molecule^?1 s^?1. Using the 1-dimensional atmospheric THAMO model driven by sea-air fluxes calculated from the seawater and air measurements (averaging 1.8 +/? 0.8 nmol m^?2 d^?1 for CH₂I₂ and 3.7 +/? 0.8 nmol m^?2 d^?1 for CH₂ICl), we show that the model overestimates night-time CH₂I₂ by >60 % but reaches good agreement with the measurements when the CH₂I₂ + NO₃ reaction is included at 2–4 × 10^?13 cm³ molecule^?1 s^?1. We conclude that the reaction has a significant effect on CH₂I₂ and helps reconcile observed and modeled concentrations. We recommend further direct measurements of this reaction under atmospheric conditions, including of product branching ratios.     

Eddy correlation measurements of CO2, latent heat,and sensible heat fluxes over a crop surface

Eddy correlation equipment was used to measure mass and energy fluxes over a soybean crop. A rapid response CO₂ sensor, a drag anemometer, a Lyman-alpha hygrometer and a fine wire thermocouple were used to sense the fluctuating quantities.Diurnal fluxes of sensible heat, latent heat and CO₂ were calculated from these data. Energy budget closure was obtained by summing the sensible and latent heat fluxes determined by eddy correlation which balanced the sum of net radiation and soil heat flux. Peak daytime CO₂ fluxes were near 1.0 mg m^–2 (ground area) s^–1.The eddy correlation technique was also employed in this study to measure nocturnal CO₂ fluxes caused by respiration from plants, soil, and roots. These CO₂ fluxes ranged from - 0.1 to - 0.25 mg m^–2s^–1.From the data collected over mature soybeans, a relationship between CO₂ flux and photosynthetically active radiation (PAR) was developed. The crop did not appear to be light-saturated at PAR flux densities < 1800 Ei m^–2 s^–1. The light compensation point was found to be about 160 Ei m^–2 s^–1.Published as Paper No. 7402, Journal Series, Nebraska Agricultural Experiment Station. The work reported here was conducted under Nebraska Agricultural Experiment Station Project 27-003 and Regional Research Project 11–33.Post-doctoral Research Associate, Professor and Professor, respectively. Center for Agricultural Meteorology and Climatology, Institute of Agriculture and Natural Resources, University of Nebraska, Lincoln, NE 68583-0728.     

Carbon dioxide exchange in a temperate grassland ecosystem

Carbon dioxide exchange was measured, using the eddy correlation technique, over a tallgrass prairie in northeastern Kansas, U.S.A., during a six-month period in 1987. The diurnal patterns of daytime and nocturnal CO₂ fluxes are presented on eight selected days. These days were distributed throughout most of the growing season and covered a wide range of meteorological and soil water conditions. The midday CO₂ flux reached a maximum of 1.3 mg m^-2 (ground area) s^-1 during early July and was near zero during the dry period in late July. The dependence of the daytime carbon dioxide exchange on pertinent controlling variables, particularly photosynthetically active radiation, vapor pressure deficit and soil water content is discussed. The nocturnal CO₂ flux (soil plus plant respiration) averaged -0.4 mg m^-2 (ground area) s^-1 during early July and was about -0.2 mg m^-2 s^-1 during the dry period.Published as Paper No. 9061, Journal Series, Agricultural Research Division, University of Nebraska-Lincoln, U.S.A.Research Associate and Professor, respectively.     

Characteristics and sources of inertia-gravity waves revealed in the KEOP-2007 radiosonde data

Characteristics and sources of inertia-gravity waves are investigated using high-resolution radiosonde data observed at ten stations in Korea during 15 June to 15 July 2007. The wave analyses are performed in the lower stratospheric region (Z = 17–30 km). The average intrinsic frequency, vertical wavelength, and horizontal wavelength for the observed waves are 2.77f (where f is the Coriolis parameter), 2.58 km, and 620.11 km, respectively. The average eastward and westward momentum fluxes are 0.005 m² s^?2 and ?0.003 m² s^?2, respectively, and the average northward and southward momentum fluxes are 0.007 m² s^?2 and ?0.002 m² s^?2, respectively. To understand the propagation and the sources of the observed gravity waves, a three-dimensional ray-tracing model is used. The observed gravity waves are classified into two groups based on the existence of convection when and where the rays reach altitudes of 6–13 km. Sources are mostly located in the northeast and southeast of the observation stations below Z = 5 km for the convection-related cases (CONV), while those for the other cases (NCONV) are located in the northeast and southeast of the observation stations above Z = 20 km. The average intrinsic frequency and vertical wavelength of the CONV cases are somewhat larger than those of the NCONV cases. The average potential, kinetic, and total wave energies of the CONV cases are less than those of the NCONV cases.     

梯度法观测大气与森林生态系统间羰基硫(COS)的交换通量

本工作用梯度法测定了大气与其下垫的森林间ＣＯＳ的交换通量。测量在德国哥廷根大学的一座５０ｍ高的森林观测塔上进行，该塔坐落在德国中部的Ｓｏｌｌｉｎｇ自然保护区的森林中。观测现场生长着树龄分别为１２０ａ和８０ａ的山毛榉和云杉。树冠线约２８ｍ高。在塔上离地面３２ｍ，３８ｍ和５０ｍ的地方用冷以法同时采集了空气样品。样品用气相色谱－火焰光度检测法测定。ＣＯＳ通量由其梯度及扩散系数求出。扩散系数由与ＣＯＳ一起测得的感热和水蒸气通量导出。在稳定边界层条件下共获得２０条廓线。每条廓线都显示ＣＯＳ浓度随高度下降而降低的趋势，说明森林吸收ＣＯＳ。总的结果表明，ＣＯＳ向森林中的平均输送通量为（１４３±５４）ｎｇＣＯＳｍ－２·ｓ－１．     

Carbonyl sulfide emissions from biomass burning in the tropics

Carbonyl sulfide emissions from biomass burning have been studied during field experiments conducted both in an African savanna area (Ivory Coast) and rice fields, central highland pine forest and savanna areas in Viet-Nam. During these experiments CO₂, CO and C₂H₂ or CH₄ have also been also monitored. COS values range from 0.6 ppbv outside the fires to 73 ppbv in the plumes. Significant correlations have been observed between concentrations of COS and CO (R ²=0.92,n=25) and COS and C₂H₂ (R ²=0.79,n=26) indicating a COS production during the smoldering combustion. COS/CO₂ emission factors (COS/CO₂) during field experiments ranged from 1.2 to 61×10^–6 (11.4×10^–6 mean value). COS emission by biomass burning was estimated to be up to 0.05 Tg S/yr in tropics and up to 0.07 Tg S/yr on a global basis, contributing thus about 10% to the global COS flux. Based on the S/C ratio measured in the dry plant biomass and the COS/CO₂ emission factor, COS can account for only about 7% of the sulfur emitted in the atmosphere by biomass burning.     

A study to explain the emission of nitric oxide from a marsh soil

In the period 18–21 September 1989, soil NO emission was studied at Halvergate Marshes, Norfolk (U.K.) within the framework of the BIATEX-LOVENOX joint field experiment. Using a dynamic chamber technique, 186 measurements at four plots were performed showing a net NO flux of 7.2–14.6×10^–12 kgN m^–2 s^–1. Soil samples from a soil profile (1.0 m) at a representative site and from the uppermost layer (0.1 m) of each of the four plots were sent to the laboratory for (a) detailed physical and chemical soil analysis, (b) determination of NO production rates, NO uptake rate constants, and NO compensation mixing ratios, and (c) characterization of the microbial processes involved. A diffusive model (Galbally and Johansson, 1989) was applied to the laboratory results to infer NO fluxes of the individual soil samples. When we compared these fluxes with those measured in the field, we found agreement within a factor 2–4. Furthermore, laboratory studies showed, that NO was produced and consumed only in the upper soil layer (0–0.1 m depth) and that the NO production and consumption activities observed in the Halvergate marsh soil were most probably due to the anaerobic metabolism of denitrifying bacteria operating in anaerobic microniches within the generally aerobic soil.