Emission Of Volatile Sulfur Compounds Research Articles

Eutrophication levels increase sulfur biotransformation and emissions from sediments of Lake Taihu

Eutrophication can stimulate the emissions of volatile sulfur compounds (VSCs) accompanied by variations in environmental variables in lakes. However, the effects of eutrophication on VSC emissions from lake sediments as well as the underlying mechanisms remain unclear. In this study, depth gradient sediments at different eutrophication levels and seasons were collected from Lake Taihu to investigate the response of sulfur biotransformation in the sediments to eutrophication based on the analysis of environmental variables, microbial activity, abundance and community structure. H2S and CS2 were the main VSCs produced from the lake sediments, with the production rates of 2.3–7.9 and 1.2–3.9 ng g−1 h−1 in August, respectively, which were higher than those in March, mainly due to the increasing activity and abundance of sulfate-reducing bacteria (SRB) at high temperatures. The VSC production rates from the sediments increased with lake eutrophication level. Higher VSC production rates were detected in surface sediments in eutrophic regions but in deep sediments in oligotrophic regions. Sulfuricurvum, Thiobacillus and Sulfuricella were the main sulfur-oxidizing bacteria (SOB) in the sediments, while Desulfatiglans and Desulfobacca were the predominant SRB. Organic matter, Fe3+, NO3−-N and total sulfur had significant influences on the microbial communities in the sediments. Partial least squares path modelling showed that the trophic level index could stimulate VSC emissions from lake sediments by influencing the activities and abundances of SOB and SRB. These findings indicated that sediments contributed substantially to VSC emissions from eutrophic lakes, especially surface sediments, and sediment dredging might be an effective way to mitigate VSC emissions from eutrophic lakes.

Effects of Bifidobacterium lactis HN019 and Lactobacillus acidophilus NCFM on volatile sulfur compounds produced by oral anaerobes

Halitosis is a term that refers to an unpleasant or foul odor originating from oral cavity, which is mainly caused by volatile sulfur compounds (VSCs) produced by oral anaerobes such as Porphyromonas gingivalis, Fusobacterium nucleatum, Treponema denticola and Prevotella intermedia. General therapies, such as tooth and tongue brushing or usage of bacteriostat can hardly provide a harmless and continuous therapeutic effect on halitosis. Recent evidence has suggested the potential clinical application value of probiotics in the treatment of halitosis. In this study, Bifidobacterium lactis HN019 and Lactobacillus acidophilus NCFM were identified from four kinds of probiotics and the antimicrobial activities against pathogens related to halitosis and inhibitory effects on VSCs were investigated. The results showed that B. lactis HN019 and L. acidophilus NCFM exhibited superior bacteriostatic action against pathogens related to halitosis and showed remarkable inhibitory effect on the production and emission of VSCs. These findings suggest that B. lactis HN019 and L. acidophilus NCFM may serve as promising parts of a successful halitosis manage plan.

Estimation of sulfur fate and contribution to VSC emissions from lakes during algae decay

Algae decay is an important process influencing environmental variables and emissions of volatile sulfur compounds (VSCs) in eutrophic lakes. However, effects of algae decay on VSC emissions from eutrophic lakes as well as fate of algae-derived sulfur remain poorly understood. In this study, simulated algae-sediment systems were used to explore the flow and distribution of sulfur during algae decay. VSCs including hydrogen sulfide (H2S), methanethiol (CH3SH), carbon disulfide (CS2) and dimethyl sulfide ((CH3)2S) were detected during algae decay, which increased with algae biomass and eutrophic levels in lakes. During algae decay, the highest H2S, CH3SH and (CH3)2S emission rates of 10.45, 21.82 and 43.26 μg d−1 occurred in the first 1–2 days, respectively, while the highest CS2 emission rates were observed between days 8 and 11. The maximum emissions of H2S and CS2 from algae decay were estimated at 0.51 and 0.35 mg m−2 d−1 in Lake Taihu, accounting for 1.57% and 0.69% of the total H2S and CS2 emissions of in situ, respectively. Algae decay could significantly increase the contents of total sulfur and total carbon in sediments by 2.90%–21.11% and 4.23%–45.05%, respectively. The VSC emissions during algae decay could be predicted using the multiple regression models with the contents of total carbon, total nitrogen and sulfur-containing compounds in sediments. Partial least squares path modelling demonstrated that algae decay had a low direct effect on VSC emissions with a strength of 0.06, while it had a significant influence on environmental variables with a strength of 0.63, which could affect VSC emissions with a strength of 0.85, indicating VSC emissions from eutrophic lakes were affected by the environmental variables rather than the direct influence of algae decay. These findings illustrated the mechanisms of VSC emissions during algae decay and provided insights into VSC control and mitigation for eutrophic lakes.

Inhibitory Effects of the Addition of KNO3 on Volatile Sulfur Compound Emissions during Sewage Sludge Composting.

Odor released from the sewage sludge composting process often has a negative impact on the sewage sludge treatment facility and becomes a hindrance to promoting compost technology. This study investigated the effect of adding KNO3 on the emissions of volatile sulfur compounds, such as hydrogen sulfide (H2S), dimethyl sulfide (DMS), and carbon disulfide (CS2), during sewage sludge composting and on the physicochemical properties of compost products, such as arylsulfatase activity, available sulfur, total sulfur, moisture content, and germination index. The results showed that the addition of KNO3 could inhibit the emissions of volatile sulfur compounds during composting. KNO3 can also increase the heating rate and peak temperature of the compost pile and reduce the available sulfur loss. The addition of 4% and 8% KNO3 had the best effect on H2S emissions, and it reduced the emissions of H2S during composting by 19.5% and 20.0%, respectively. The addition of 4% KNO3 had the best effect on DMS and CS2 emissions, and it reduced the emissions of DMS and CS2 by 75.8% and 63.0%, respectively. Furthermore, adding 4% KNO3 had the best effect from the perspective of improving the germination index of the compost.

Occurrence and emissions of volatile sulfur compounds in the Changjiang estuary and the adjacent East China Sea

Volatile organic sulfur compounds (VSCs) are key components of the oceanic and atmospheric sulfur cycle. Here, we investigated the distributions of three major VSCs, such as carbon disulfide (CS2), dimethyl sulfide (DMS), and carbonyl sulfide (COS), and estimated their sea-to-air fluxes in the Changjiang Estuary and the adjacent East China Sea from July 20 to August 3, 2017. The DMS, COS, and CS2 surface water concentration ranges were 0.22–18.62, 0.06–0.77, and 0.02–0.3 nmol L−1, respectively. The distributions of VSCs were related to environmental and biological factors. In contrast to DMS, COS and CS2 concentrations generally decreased from the estuary to offshore waters. A significant correlation was observed between chlorophyll a and CS2 concentration, suggesting that CS2 production may be related to phytoplankton growth. Moreover, a positive correlation was observed between CS2 and DMS, indicating that they might share similar production pathways. COS was the most abundant VSC in the atmosphere, with an average concentration of 422.9 ± 301.8 ppt, but its distribution was likely influenced by anthropogenic activities. The average COS, DMS, and CS2 sea-to-air fluxes were 0.98 ± 0.98, 4.38 ± 6.42, and 0.05 ± 0.05 μmol m−2 d−1. The Changjiang Estuary and the adjacent East China Sea are important sources of atmospheric VSCs. These results will help us to better understand global VSC cycling between the oceanic atmosphere and bodies of water.

Effects of ocean warming and coral bleaching on aerosol emissions in the Great Barrier Reef, Australia

It is proposed that emissions of volatile sulfur compounds by coral reefs contribute to the formation of a biologically-derived feedback on sea surface temperature (SST) through the formation of marine biogenic aerosol (MBA). The direction and strength of this feedback remains uncertain and constitutes a fundamental constraint on predicting the ability of corals to cope with future ocean warming. We investigate the effects of elevated SST and irradiance on satellite-derived fine-mode aerosol optical depth (AOD) throughout the Great Barrier Reef, Australia (GBR) over an 18-year time period. AOD is positively correlated with SST and irradiance and increases two-fold during spring and summer with high frequency variability. As the influence of non-biogenic and distant aerosol sources are found to be negligible, the results support recent findings that the 2,300 km stretch of coral reefs can be a substantial source of biogenic aerosol and thus, influence local ocean albedo. Importantly however, a tipping point in the coral stress response is identified, whereby thermal stress reaches a point that exceeds the capacity of corals to influence local atmospheric properties. Beyond this point, corals may become more susceptible to permanent damage with increasing stress, with potential implications for mass coral bleaching events.

Emission characteristics of volatile sulfur compounds (VSCs) from a municipal sewage sludge aerobic composting plant

The emission of volatile sulfur compounds (VSCs) causing strong odors is a major problem in municipal sewage sludge composting plants (MSSACPs). Improving the knowledge on characteristics of VSCs emission in MSAACPs is of particular significance to elimate odors, but the studies conducted on-site to identify them are scarce. To this purpose, characteristics of VSCs emission were studied on-site from a MSSACP during different ambient temperatures corresponding with seasonal variations. Results reveal that (1) the total emission of VSCs which included methyl disulfide (DMDS), methyl sulfide (DMS), carbon disulfide, methyl mercaptan, and hydrogen sulfide (H2S) was 561.89 mg/dry kg in summer, 358.45 mg/dry kg in spring, and 215.52 mg/dry kg in winter, and the greatest amounts of VSCs were emitted during the mesophilic and pre-thermophilic phases; (2) although DMDS and DMS contributed the most towards total VSCs emissions during winter (81.93%), spring (82.55%), and summer (83.90%), their odor contributions were less than that of H2S; (3) in summer, the odor nuisance of total VSCs was higher than that in winter and spring; (4) sulfur loss in the form of VSCs emissions and total sulfur loss both increased with rising ambient temperatures during the sewage sludge aerobic composting. Results obtained in this study will be beneficial towards the elimation of odors released from MSSACPs.

Real-time quantification of emissions of volatile organic compounds from land spreading of pig slurry measured by PTR-MS and wind tunnels

Volatile organic compounds (VOC) and hydrogen sulfide are emitted from land spreading of manure slurry to the atmosphere and contribute to odour nuisance, particle formation and tropospheric ozone formation. Data on emissions is almost non-existing partly due to lack of suitable quantitative methods for measuring emissions in full scale. Here we present a method based on application of wind tunnels for simulation of air exchange combined with the use of online mass spectrometry (PTR-MS). The focus was on odorous VOC but all relevant VOC were included. A method for quantification of VOC emission based on calculated proton-transfer reaction rate constants was validated by comparison to reference concentrations for typical VOC emitted from pig manure slurry. Wall losses of volatile sulfur compounds in the wind tunnels were assessed to be insignificant and recoveries >95% were observed for these compounds. An influence of air exchange rate was clearly observed highlighting the need to identify realistic air exchange rates for future application of the method. Emission data was obtained for spreading of pig manure slurry as an example of an important source of gases. Emissions were monitored for ~37 h following land spreading and time-resolved emission data was presented for the first time. Highest emissions were observed for short-chain volatile carboxylic acids (C2–C6) with acetic acid being the most abundant compound. Emission peaks were observed immediately following application and were followed by declining emissions until the second day at which emissions reached a second peak for several compounds. This second emission peak was speculated to be caused by a temperature-induced diurnal effect. Emissions of volatile sulfur compounds occurred on a short time-scale and ceased shortly after application. Odour activity values were dominated by C4–C5 carboxylic acids and 4-methylphenol with a less pronounced influence of 4-methylphenol on day 2.

Emissions of volatile sulfur compounds (VSCs) throughout wastewater biosolids processing

Volatile sulfur compounds (VSCs) are important contributors to nuisance odours from the processing of wastewater sludge and biosolids. However, emission characteristics are difficult to predict as they vary between sites and are likely to be affected by biosolids processing configuration and operation. VSC emissions from biosolids throughout 6 wastewater treatment plants (WWTPs) in Sydney, Australia were examined in this study. H2S was the VSC found at the highest concentrations throughout the WWTPs, with concentrations ranging from 7 to 39,000μg/m3. Based on odour activity values (OAVs), H2S was typically also the most dominant odorant. However, methyl mercaptan (MeSH) was also found to be sensorially important in the biosolids storage areas given its low odour detection threshold (ODT). High concentrations of VOSCs such as MeSH in the storage areas were shown to potentially interfere with H2S measurements using the Jerome 631-X H2S sensor and these interferences should be investigated in more detail. The VSC composition of emissions varied throughout biosolids processing as well as between the different WWTPs. The primary sludge and biosolids after dewatering and during storage, were key stages producing nuisance odours as judged by the determination of OAVs. Cluster analysis was used to group sampling locations according to VSC emissions. These groups were typically the dewatered and stored biosolids, primary and thickened primary sludge, and waste activated sludge (WAS), thickened WAS, digested sludge and centrate. Effects of biosolids composition and process operation on VSC emissions were evaluated using best subset regression. Emissions from the primary sludge were dominated by H2S and appeared to be affected by the presence of organic matter, pH and Fe content. While volatile organic sulfur compounds (VOSCs) emitted from the produced biosolids were shown to be correlated with upstream factors such as Fe and Al salt dosing, anaerobic digestion and dewatering parameters.

Emission of Volatile Organic Compounds as Affected by Rate of Application of Cattle Manure

<abstract> Beef cattle manure can serve as a valuable nutrient source for crop production. However, emissions of volatile organic compounds (VOCs) following land application may pose a potential off-site odor concern. This study was conducted to evaluate the effects of land application method, N application rate, soil moisture content, and time since manure application on VOC emissions. Manure from cattle fed a diet containing 30% wet distillers grains was applied to a cropland area at rates required to meet the 0.5, 1, or 2 year N requirement for corn. Land application methods included surface-applying manure (i.e., no tillage) or incorporating manure using disk tillage. The effect of soil moisture content on VOC emissions was determined by adding water to the experimental plots approximately 24 h after manure application. Volatile sulfur compounds (i.e., dimethyl disulfide and dimethyl trisulfide), isovaleric acid, and butyric acid contributed 43.4%, 14.0%, and 13.9%, respectively, of the total measured odor activity value (OAV). Emissions of each of the principal VOC odor compounds were reduced by manure incorporation. In general, no significant differences in VOC measurements of volatile fatty acids (VFAs) and aromatic compounds were found among varying manure application rates. However, an increase in emissions of volatile sulfur compounds resulted from increased manure application. Measurements of VFAs and aromatic compounds usually decreased and sulfide emissions increased following the application of water. Application method, N application rate, soil moisture content, and time since application may all influence VOC emissions following land application of cattle manure.

Inhibitory Effect of Enterococcus faecium WB2000 on Volatile Sulfur Compound Production by Porphyromonas gingivalis.

Volatile sulfur compounds (VSCs) produced by oral anaerobes are the major compounds responsible for oral malodor. Enterococcus faecium WB2000 is recognized as an antiplaque probiotic bacterium. In this study, the effect of E. faecium WB2000 on VSC production by Porphyromonas gingivalis was evaluated, and the mechanism of inhibition of oral malodor was investigated. P. gingivalis ATCC 33277 was cultured in the presence of four lactic acid bacteria, including E. faecium WB2000. Subsequently, P. gingivalis ATCC 33277, W50, W83, and two clinical isolates were cultured in the presence or absence of E. faecium WB2000, and the emission of VSCs from spent culture medium was measured by gas chromatography. The number of P. gingivalis ATCC 33277 in mixed culture with E. faecium WB2000 decreased at 6 h, and the rate of decrease was higher than that in mixed cultures with the other lactic acid bacteria. The numbers of five P. gingivalis strains decreased at similar rates in mixed culture with E. faecium WB2000. The concentration of methyl mercaptan was lower in spent culture medium from P. gingivalis and E. faecium WB2000 cultures compared with that from P. gingivalis alone. Therefore, E. faecium WB2000 may reduce oral malodor by inhibiting the growth of P. gingivalis and neutralizing methyl mercaptan.

Emission of volatile sulfur compounds during composting of municipal solid waste (MSW)

Volatile sulfur compounds (VSCs) are the main source for malodor from composting plants. In this study, the VSCs generated from composting of 15–80mm municipal solid waste (T0), kitchen waste (T1) and kitchen waste mixed dry cornstalks (T2) were measured in 60L reactors with forced aeration for a period of 30days. The VSCs detected in all treatments were hydrogen sulfide (H2S), methyl mercaptan (MM), dimethyl sulfide (DMS), carbon bisulfide (CS2) and dimethyl disulfide (DMDS). Over 90% of the VSCs emissions occurred during the first 15days, and reached their peak values at days 4–7. The emission profiles of five VSCs species were significantly correlated with internal materials temperature and outlet O2 concentration (p<0.05). Total emissions of the VSCs were 216.1, 379.3 and 126.0mgkg−1 (dry matter) for T0, T1 and T2, respectively. Among the five VSCs, H2S was the most abundant compound with 39.0–43.0% of total VSCs released. Composting of kitchen waste from separate collection posed a negative influence on the VSC and leachate production because of its high moisture content. An addition of dry cornstalks at a mixing ratio of 4:1 (wet weight) could significantly reduce the VSCs emissions and avoid leachate. Compared to pure kitchen waste, VSCs were reduced 66.8%.

PTR-MS measurement of partition coefficients of reduced volatile sulfur compounds in liquids from biotrickling filters

Biological air filtration for reduction of emissions of volatile sulfur compounds (e.g., hydrogen sulfide, methanethiol and dimethyl sulfide) from livestock production facilities is challenged by poor partitioning of these compounds into the aqueous biofilm or filter trickling water. In this study, Henry’s law constants of reduced volatile sulfur compounds were measured for deionized water, biotrickling filter liquids (from the first and second stages of a two-stage biotrickling filter), and NaCl solutions by a dynamic method using Proton-Transfer-Reaction Mass Spectrometry (PTR-MS) at a temperature range of 3–45°C. NaCl solutions were used to estimate salting-out constants up to an ionic strength of 0.7M in order to evaluate the effect of ionic strength on partitioning between air and biofilter liquids. Thermodynamic parameters (enthalpy and entropy of phase exchange) were obtained from the measured partition coefficients as a function of temperature. The results show that the partition coefficients of organic sulfur compounds in the biotrickling filter liquids were generally very close to the corresponding partition coefficients in deionized water. Based on the estimated ionic strength of biofilter liquids, it is assessed that salting-out effects are of no importance for these compounds. For H2S, a higher enthalpy of air–liquid partitioning was observed for 2nd stage filter liquid, but not for 1st stage filter liquid. In general, the results show that co-solute effects for sulfur compounds can be neglected in numerical biofilter models and that the uptake of volatile sulfur compounds in biotrickling filter liquids cannot be increased by decreasing ionic strength.

Sulfur Turnover and Emissions during Storage of Cattle Slurry: Effects of Acidification and Sulfur Addition

Slurry acidification using sulfuric acid reduces ammonia emissions but also affects sulfur (S) cycling. Emission of sulfur is a source of malodor and reduces the sulfur fertilizer value of the slurry. We investigated the effect of sulfate and methionine amendments, alone or in combination with acidification, on sulfur transformations in slurry and emissions of volatile sulfur compounds (VSC) during storage of fresh and aged cattle slurry. When pH was lowered to 5.5 it resulted in an almost complete inhibition of sulfate reduction. There was a huge emission of hydrogen sulfide (HS) with addition of sulfate and methionine ( < 0.01). Methanethiol (MT) was emitted in treatments with addition of methionine, especially when simultaneously acidified ( < 0.01). The large HS production in the sulfate-amended slurries resulted in little accumulation of MT and dimethyl sulfide (DMS) under neutral conditions, in contrast to acidic conditions where the degradation was inhibited and both MT and DMS accumulated. Based on odor activity values, untreated slurry had little odor development from S compounds, especially the aged slurry. Acidification did not significantly increase odor contribution from any of the compounds in fresh or aged slurry. Generally, addition of a sulfate increased the contribution from HS dramatically, whereas acidification lowered the HS contribution but increased that of MT. Thus, acidification of slurry with sulfuric acid may potentially produce more odor from S compounds than untreated slurry.

REMOTE SENSING OF OCEANIC BIOLOGY IN RELATION TO GLOBAL CLIMATE CHANGE

Journal of PhycologyVolume 28, Issue 5 p. 579-590 REMOTE SENSING OF OCEANIC BIOLOGY IN RELATION TO GLOBAL CLIMATE CHANGE Jim Aiken, Jim Aiken Natural Environmental Research Council, Plymouth Marine Laboratory, Prospect Place West Hoe, Plymouth, United Kindgom PL1 3DHSearch for more papers by this authorGerald F. Moore, Gerald F. Moore Natural Environmental Research Council, Plymouth Marine Laboratory, Prospect Place West Hoe, Plymouth, United Kindgom PL1 3DHSearch for more papers by this authorPatrick M. Hotligan, Patrick M. Hotligan Natural Environmental Research Council, Plymouth Marine Laboratory, Prospect Place West Hoe, Plymouth, United Kindgom PL1 3DHSearch for more papers by this author Jim Aiken, Jim Aiken Natural Environmental Research Council, Plymouth Marine Laboratory, Prospect Place West Hoe, Plymouth, United Kindgom PL1 3DHSearch for more papers by this authorGerald F. Moore, Gerald F. Moore Natural Environmental Research Council, Plymouth Marine Laboratory, Prospect Place West Hoe, Plymouth, United Kindgom PL1 3DHSearch for more papers by this authorPatrick M. Hotligan, Patrick M. Hotligan Natural Environmental Research Council, Plymouth Marine Laboratory, Prospect Place West Hoe, Plymouth, United Kindgom PL1 3DHSearch for more papers by this author First published: October 1992 https://doi.org/10.1111/j.0022-3646.1992.00579.xCitations: 50 We are grateful for access to the NASA aircraft data set from the NABE, May 1989 and thank Dr. Frank Hoge (NASA), Dr. Bob Swift (NASA) and our collaborator Dr. Jim Yoder (University of Rhode Island) for making these data available. This work is part of the Biogeochemical Ocean Flux Study of the Natural Environment Research Council, Plymouth Marine Laboratory, Plymouth, UK. Question (Malin et al.): What is the potential of the SeaWiFS satellite for giving insight into the global emission of volatile sulfur compounds? Answer: The pigment 19′ hexanolyoxyfucoxanthin (HEX) is a main accessory pigment in both E. huxleyi and Phaeocystis, and a linear relationship has been established between HEX and DMS in the water in several geographical locations (including Antarctica). Detection of the pigment is possible by differential absorption at 555 nm and another wavelength. Although there are several other taxa-specific pigments that absorb at the same wavelength, the observed scattering properties (e.g. for coccolithophores) and auxilliary information, on season, location etc., should allow us to be more specific. The air-sea exchange of DMS is related to the sea state (wave height and surface roughness), which will not be available from the SeaWiFS satellite but may be available from other satellite sensors, such as the scatterometer on ERS-1 operating concurrently. AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature Volume28, Issue5October 1992Pages 579-590 RelatedInformation

Evolution of Volatile Sulfur Compounds during Laboratory-Scale Incubations and Indoor Preparation of Compost Used as a Substrate in Mushroom Cultivation

Volatile sulfur compounds are known to be produced during the preparation of compost used as a substrate in mushroom cultivation. Because they cause odor problems, attempts have been made to reduce the production of these compounds. The influences of temperature and various additions on the production of volatile sulfur compounds from composting material were tested on laboratory-scale preparations. The production of H(2)S, COS, CH(3)SH, and (CH(3))(2)S was proven to be a biological process with an optimal temperature that coincides with the optimal temperature for biological activity. The formation of CS(2) and (CH(3))(2)S(2) was shown to be a nonbiological process. The emission of volatile sulfur compounds during the indoor preparation of mushroom compost appeared to be remarkably reduced (about 90%) as compared with the emission during the conventional outdoor process. Introduction of this indoor composting process would result in a significant reduction in environmental pollution.

Emission of Volatile Sulfur Compounds from Spruce Trees

Spruce (Picea Abies L.) trees from the same clone were supplied with different, but low, amounts of plant available sulfate in the soil (9.7-18.1 milligrams per 100 grams of soil). Branches attached to the trees were enclosed in a dynamic gas exchange cuvette and analyzed for the emission of volatile sulfur compounds. Independent of the sulfate supply in the soil, H(2)S was the predominant reduced sulfur compound continuously emitted from the branches with high rates during the day and low rates in the night. In the light, as well as in the dark, the rates of H(2)S emission increased exponentially with increasing water vapor flux from the needles. Approximately 1 nanomole of H(2)S was found to be emitted per mole of water. When stomata were closed completely, only minute emission of H(2)S was observed. Apparently, H(2)S emission from the needles is highly dependent on stromatal aperture, and permeation through the cuticle is negligible. In several experiments, small amounts of dimethylsulfide and carbonylsulfide were also detected in a portion of the samples. However, SO(2) was the only sulfur compound consistently emitted from branches of spruce trees in addition to H(2)S. Emission of SO(2) mainly proceeded via an outburst starting before the beginning of the light period. The total amount of SO(2) emitted from the needles during this outburst was correlated with the plant available sulfate in the soil. The diurnal changes in sulfur metabolism that may result in an outburst of SO(2) are discussed.