Volatile Organic Compounds In Soil Research Articles

Water-Enhanced Flux Changes under Dynamic Temperatures in the Vertical Vapor-Phase Diffusive Transport of Volatile Organic Compounds in Near-Surface Soil Environments

The quantitative understanding of the transport behavior of volatile organic compounds (VOCs) in near-surface soils is highly important in light of the potential impacts of soil VOC emissions on the air quality and climate. Previous studies have suggested that temperature changes affect the transport behavior; however, the effects are not well understood. Indeed, much larger changes in the VOC flux under in situ dynamic temperatures than those expected from the temperature dependence of the diffusion coefficients of VOCs in the air have been suggested but rarely investigated experimentally. Here, we present the results of a set of experiments on the upward vertical vapor-phase diffusive transport of benzene and trichloroethylene (TCE) in sandy soils with water contents ranging from an air-dried value to 10 wt% during sinusoidal temperature variation between 20 and 30 °C. In all experiments, the flux from the soil surface was correlated with the temperature, as expected. However, the changes in flux under wet conditions were unexpectedly large and increased with increasing water content; they were also larger for TCE, the volatility of which depended more strongly on the temperature. Additionally, the larger flux changes were accompanied by a recently discovered water-induced inverse correlation between temperature and flux into the overlying soil. These results demonstrated that the flux changes of VOCs under dynamic temperatures could be increased by volatilization-dissolution interactions of VOCs with water. Future extensive studies on this newly discovered phenomenon would contribute to a better understanding of the impacts of soil VOC emissions on the air quality and climate.

Short-Term Effect of Green Waste and Sludge Amendment on Soil Microbial Diversity and Volatile Organic Compound Emissions

Soil amendments with organic waste products (OWPs) have been widely supported in Europe to improve soil fertility, causing wide changes in the microbial community structure and diversity, especially in the short-term period. Those changes are known to affect the volatile organic compound (VOC) emissions by soil. This work aimed to characterize, in terms of quantity and composition, the effect of green waste and sludge (GWS) application on soil VOC emissions and microbial community 49 h after the last GWS application. Two different soil samples were compared to test the effect of the soil history on VOC emissions and microbial communities. For this reason, we chose a soil that received GWS input for 20 years (GWS sample) and one that did not receive any organic input during the same period (CN sample). Furthermore, samples were manipulated to generate three microbial dilution diversity gradients (low, medium, and high). Results showed that Bacteroidetes phyla took advantage of the GWS application in all samples, increasing their relative abundance by 22% after 49 h, while the Proteobacteria phylum was penalized by the GWS amendment, passing from 58% to 49% relative abundance 49 h after the GWS application. Microbial structure differences between microbial diversity dilution levels remained even after the GWS application. GWS amendment induced a change in the emitted VOC profiles, especially in samples used to receiving GWS. GWS amendment doubled the VOC emissions from samples used to receiving GWS after 49 h. Finally, the microbial community was strongly correlated to the VOC emissions. Firmicutes, Proteobacteria, Actinobacteria, and Crenarchaeota were positively correlated (Pearson coefficient > 0.6), while other phyla, such as Bacteroidetes and Verrucomicrobia, were found to be negatively correlated (Pearson coefficient < −0.6) to the VOC emissions. After the addition of GWS, these correlations shifted from positive to negative and from negative to positive.

Method validation for the determination of aniline and 3,3’-dichlorobenzidine by gas chromatography-mass spectrometry

This article uses and validates the analytical methods for the determination of aniline and 3,3’-dichlorobenzidine in soil by gas chromatography-mass spectrometry, and discusses the determination of semi volatile organic compounds in soil by gas chromatography-mass spectrometry. The feasibility of the application. The results showed that the semi volatile organic compounds aniline and 3,3’-dichlorobenzidine target corresponding to the internal standard response value and concentration showed a good linear relationship, the correlation coefficient was between 0.9997 and 0.9983 respectively; the detection limit was 0.04 mg, respectively/kg and 0.04mg/kg, the limits of quantification are 0.2mg/kg and 0.2mg/kg; the relative standard deviations of the two semi-volatile organic compounds in the precision are 2.5∼16.9% and 3.6∼6.2%, respectively; the accuracy is 2 The recovery rates of these volatile organic compounds were 64.5-83.9% and 72.6-74.3%, respectively. The verification results show that the linear relationship, detection limit, precision and accuracy all meet the requirements of “Determination of Semi-volatile Organic Compounds in Soils and Sediments by Gas Chromatography-Mass Spectrometry” (HJ 834-2017). Using gas chromatography-mass spectrometry technology can achieve fast, accurate and sensitive detection of target substances, and can meet the detection requirements of trace semi-volatile organic compounds, so this method can be better applied to the detection of soil and other environments.

Profiling soil volatile organic compounds after N fertilization in a soil grown with Rosmarinus officinalis

The biogenic volatile organic compounds (BVOCs) emissions from cultivated plants-soil systems and N fertilization's role on these emissions are mostly unknown. This study aimed to elucidate the BVOCs emissions from a plant-soil system receiving N fertilization using Rosmarinus officinalis as a model case study. We put forward the hypothesis that N fertilization changes the BVOCs emissions patterns irrespectively the presence of Rosmarinus officinalis and that the emissions are related to N availability and bacterial abundance. To test our hypothesis, we established a microcosm (glass static chambers) study in a fully randomized design with four treatments: soil (S), soil and plant (S + P), soil and fertilizer (S + F), soil, plant, and fertilizer (S + P + F); using NH4NO3 as N source. BVOCs were sampled from the microcosms, using the static headspace sampling technique with a solid-phase microextraction (SPME) device and analyzed by gas chromatography–mass spectrometry (HS-SPME-GC–MS). Sampling occurred 1, 2, 3, 4, 7, 10, 15, 17, 22, 25, and 31 days after applying the NH4NO3 and besides BVOCs, we measured soil NH4+ and NO3− concentration as well as 16S rRNA bacterial abundance. Time drives a significant portion of the variation in the chemical diversity and quantity of the different VOCs found throughout the experiment (PERMANOVA; R2 = 0.28, p < 0.001); however, this was dependent on the presence of plant and fertilizer leading to a significant interaction (PERMANOVA; R2 = 0.33, p < 0.001). Individual BVOCs emissions were strongly affected by nitrogen fertilization, plant presence and declined during the time. The most dominant BVOCs detected were benzyl alcohol, acetone, toluene, benzaldehyde, and caprolactam. Interestingly, the BVOCs concentration was negatively associated with soil concentration to NH4+, NO3− and total bacterial abundance.

Volatile organic compounds (VOCs) allow sensitive differentiation of biological soil quality

Understanding the change in function of the biological community under different soil conditions is key to effective soil quality monitoring and mitigation of soil degradation. Current measures of biological soil quality suffer from drawbacks with most techniques having high expense, low throughput or a narrow focus on one component of the community. The aim of this study was to assess the use of volatilomics as a method to profile the soil microbial community and compare the technique to phospholipid fatty acid (PLFA) profiling as a measure of biological soil quality. An agricultural grassland soil (Eutric Cambisol) was subjected to a range of stresses in replicate laboratory mesocosms. Treatments included the imposition of hypoxia/anoxia by flooding with freshwater or saltwater in the presence or absence of plant residues. The volatile organic compound (VOC) and PLFA profile of each treatment was then compared to unamended mesocosms. We hypothesized that the VOC fingerprint of soil would be highly responsive to changes in microbial metabolic status/functioning and thus provide a complementary approach to PLFAs for evaluating soil biological health. We also hypothesized that the VOC profile would have greater discriminatory power than PLFAs for determining differences between soil treatments. A headspace solid phase microextraction (HSSPME) method coupled with gas chromatography quadrupole-time of flight mass spectrometry (GC/Q-TOFMS) was used to analyse the broad spectrum of VOCs produced by each soil. Across all soil treatments 514 unique VOC peaks were detected. Overall, VOCs showed greater sensitivity than the PLFA analysis in separating soil quality treatments. Eighteen individual VOCs were identified which were primarily responsible for this separation (e.g. indole, α-ionone, isophorone, 3-octanone, p-cresol, 2-ethyl-phenol). Anaerobic soils amended with residues showed the greatest separation from other treatments, with most of this differentiation associated with ten individual VOCs. The anaerobic soils also showed a significant reduction in the number of VOCs emitted but an increase in total VOC emissions. In conclusion, our findings provide evidence that soil VOCs rapidly respond to changes in soil quality and therefore hold great potential as a novel functionally relevant diagnostic measure of biological soil quality.

Soil organic matter determination based on artificial olfactory system and PLSR-BPNN

Soil organic matter (SOM) is a key indicator of soil fertility. For accurate measurement of SOM, a novel method based on an artificial olfactory system (AOS) was proposed. The response curves of soil volatile organic compounds (VOCs) were measured using a metal-oxide semiconductor sensor array, and four features (including maximum value, mean differential coefficient, response area, and the transient value at the 20th second) were obtained from the curves and used to build olfactory feature space. Then, prediction models were established using the pattern recognition algorithm. To further enhance the accuracy of AOS measurement, we used Monte Carlo cross-validation (MCCV) to identify and eliminate the abnormal samples of the soil olfactory feature space. Then, the dimension reduction method of the genetic algorithm (GA)back-propagation (BP) was used to find the appropriate feature vectors, and two types of hybrid models were presented. One was the support vector machine (SVM) and group method of data handling (GMDH) combined model—SVM-GMDH. The other was a combination of partial least squares regression (PLSR) and back-propagation neural network (BPNN)—PLSR-BPNN. The forecasting performances of three single models (BPNN, PLSR, support vector regression: SVR) and two combined models (PLSR-BPNN, SVM-GMDH) were comparatively evaluated. The evaluation indices included coefficient of determination (R 2), root mean square error (RMSE), ratio of performance to deviation and relative prediction error (RPE). It was found that the predictive capabilities of all five tested models were improved after elimination of abnormal samples and feature reduction. Moreover, PLSR-BPNN performed the best in predicting SOM concentrations, with R 2 = 0.952, RMSE = 1.771, PRD = 4.291, and slight variation of RPE within 0–0.185, and thus can offer a reference for predicting SOM via AOS.

Method Verification of Soil Volatile Organic Compounds

In this paper, purge-and-trap / gas chromatography-mass spectrometry is used to verify the analysis of six volatile organic compounds in soil, including 1,1-dichloropropene, benzene, and 1,2-dichloroethane. The feasibility of purge and trap / gas chromatography-mass spectrometry for the determination of VOCs in land Engineering was discussed. The results show that in the linear relationship, the response value and concentration of the volatile organic target object show a good linear relationship with a correlation coefficient of 0.9951 to 0.9996; the detection limit is 0.8 to 1.9 μg/kg and the quantification limit is 3.0 to 7.6 μg/kg. The relative standard deviation of 6 volatile organic compounds in precision is: 3.0% to 12.3%; the recovery rate of 6 volatile organic compounds in accuracy is: 112.4% to 127.0%. The verification results show that the linear relationship, detection limit, precision, and accuracy all meet the requirements of “Soil and Sediment-Determination of Volatile Organic Compounds Purge and Trap Gas Chromatography/Mass Spectrometry Method” (HJ605-2011). The purge-and-trap/gas chromatography-mass spectrometry technology can be used to achieve fast, accurate and sensitive detection of target substances, and can meet the detection requirements of trace volatile organic compounds, so it can be applied to environmental testing work such as soil.

Pathogen suppression by microbial volatile organic compounds in soils.

There is increasing evidence that microbial volatile organic compounds (mVOCs) play an important role in interactions between microbes in soils. In this minireview, we zoom in on the possible role of mVOCs in the suppression of plant-pathogenic soil fungi. In particular, we have screened the literature to see what the actual evidence is that mVOCs in soil atmospheres can contribute to pathogen suppression. Furthermore, we discuss biotic and abiotic factors that influence the production of suppressive mVOCs in soils. Since microbes producing mVOCs in soils are part of microbial communities, community ecological aspects such as diversity and assembly play an important role in the composition of produced mVOC blends. These aspects have not received much attention so far. In addition, the fluctuating abiotic conditions in soils, such as changing moisture contents, influence mVOC production and activity. The biotic and abiotic complexity of the soil environment hampers the extrapolation of the production and suppressing activity of mVOCs by microbial isolates on artificial growth media. Yet, several pathogen suppressive mVOCs produced by pure cultures do also occur in soil atmospheres. Therefore, an integration of lab and field studies on the production of mVOCs is needed to understand and predict the composition and dynamics of mVOCs in soil atmospheres. This knowledge, together with the knowledge of the chemistry and physical behaviour of mVOCs in soils, forms the basis for the development of sustainable management strategies to enhance the natural control of soil-borne pathogens with mVOCs. Possibilities for the mVOC-based control of soil-borne pathogens are discussed.

Fungi Indirectly Affect Plant Root Architecture by Modulating Soil Volatile Organic Compounds.

The plant-growth modulating effect of microbial volatile organic compounds (VOCs) has been demonstrated repeatedly. This has most often been performed by exposing plants to VOC released by microbes grown on nutrient rich media. Here, we used soil instead to grow fungi of the Fusarium genus and investigate how VOCs emitted by this system influenced the development of Arabidopsis plants. The volatile profiles of Fusarium strains grown in soil and malt extract were also compared. Our results demonstrate that distinct volatile signatures can be attributed to different Fusarium genetic clades but also highlight a major influence of the growth medium on volatile emission. Furthermore, all soil-grown Fusarium isolates increased primary root length in Arabidopsis by decreasing VOC concentrations in soil. This result represents a major paradigm shift in plant-microbe interactions since growth modulating effects have been attributed so far to the emission and not the consumption of volatile signals.

Volatile Organic Compound Emissions From Soil Following Wetting Events

AbstractDynamics of carbon dioxide (CO2) emissions following the wetting of dry soil have been widely studied in field and laboratory settings. Nonmethane volatile organic compounds (VOCs) are also emitted from soil following a rain event and are evident from the characteristic smell of wet soil. Few studies have documented VOC emissions before and after soil rewetting. Soil emissions were studied using a dynamic flux chamber system purged with VOC‐free air, with identification and quantification of emissions performed by gas chromatography/mass spectrometry. All soils exhibited a rewetting‐induced pulse of VOC emissions, with VOC emissions 14 times higher (on average) in the few hours after rewetting compared to moist soils 2 days after rewetting. This VOC rewetting pulse mirrored the CO2 rewetting pulse (the so‐called “Birch Effect”) but was shorter in duration. Average VOC emissions were 5.0 ± 2.0% of CO2 emissions (molar C equivalent) and increased with increasing soil organic matter content (ρ = 0.40, ρ = 0.99 with one soil excluded). The amounts and types of VOCs varied with time since rewetting and across the five studied soil types, though acetone and small hydrocarbons were the dominant compounds emitted from all soils. Some of the VOCs emitted are likely important mediators of microbial activities and relevant to atmospheric chemical dynamics. Soil VOC emissions, similar to CO2 emissions, are strongly affected by rewetting events, and it is important to consider these rewetting dynamics when modeling soil and ecosystem VOC emissions and understand their relevance to terrestrial ecosystem functioning and atmospheric processes.

Using a multi-method approach based on soil radon deficit, resistivity, and induced polarization measurements to monitor non-aqueous phase liquid contamination in two study areas in Italy and India.

Geochemical and geophysical surveys employing radon deficit, resistivity, and induced polarization (IP) measurements were undertaken on soil contaminated with non-aqueous phase liquids (NAPLs) in two different sites in India and in Italy. Radon deficit, validated through the comparison with average soil radon in reference unpolluted areas, shows the extension of contamination in the upper part of the unsaturated aquifers. In site 1 (Italy), the spill is not recent. A residual film of kerosene covers soil grains, inhibiting their chargeability and reducing electrical resistivity difference with background unpolluted areas. No correlation between the two parameters is observed. Soil volatile organic compounds (VOCs) concentration is not linked with radon deficit, supporting the old age of the spillage. NAPL pollution in sites 2a and 2b (India) is more recent and probably still active, as demonstrated by higher values of electrical resistivity. A good correlation with IP values suggests that NAPL is still distributed as droplets or as a continuous phase in the pores, strengthening the scenario of a fresh spill or leakage. Residual fraction of gasoline in the pore space of sites 2a and 2b is respectively 1.5 and 11.8kg per cubic meter of terrain. This estimation is referred to the shallower portion of the unsaturated aquifer. Electrical resistivity is still very high indicating that the gasoline has not been strongly degraded yet. Temperature and soil water content influence differently radon deficit in the three areas, reducing soil radon concentration and partly masking the deficit in sites 2a and 2b.

Profiling of soil volatile organic compounds after long-term application of inorganic, organic and organic-inorganic mixed fertilizers and their effect on plant growth

The complexity of soil processes involved in the production, consumption and accumulation of volatile organic compounds (VOCs) makes hard to access the overall dynamics of VOCs in the soil. In this study, the field soil, applied with inorganic (CF), organic (OF) and inorganic-organic mixed (CFOF) fertilizers for ten years was evaluated for the emission of VOCs at different temperature and moisture levels. We identified 30–50 soil emitted VOCs representing the most common soil VOCs groups by using the solid-phase microextraction (SPME) fiber and gas chromatography-mass spectroscopy. The highest total emission of VOCs was found in OF treatment, but it was non-significantly different with CF treatment. The emission of VOCs was significantly increased with the decrease in moisture contents and increase in the temperature of the soil. Among different fertilizer treatments, the emission of VOCs was significantly higher in OF treatment at 5% moisture, and in CF and OF treatments at 35°C. Further, the VOCs emitted from soil treated with CFOF showed the highest increase in plant growth while CF and OF treatments showed similar results. The VOCs were also extracted from the soil using methanol to better understand the dynamics of VOCs. The abundance of VOCs extracted from the soil was 44–61%, while the richness was 65–70% higher than the VOCs emitted from the soil in different treatments. Taken together the results of emitted and extracted VOCs from the soil, we conclude that the fertilizers are able to discriminate among the VOC patterns of soil. In addition, most of the VOCs are retained in the soil and the emission of VOCs from soil depends on the type of VOCs, soil properties and environmental conditions; however, more research is required to find out better soil VOCs analysis methods.

Allelopathic effects of volatile organic compounds from Eucalyptus grandis rhizosphere soil on Eisenia fetida assessed using avoidance bioassays, enzyme activity, and comet assays

Allelopathy has been identified as an underlying mechanism of detrimental environmental impacts within commercial plantations. Eucalyptus spp. are known to generate huge amounts of volatile organic compounds (VOCs) that can function as phytotoxins and thus inhibit other plants. In the present study, biochemical markers, including activities of acetylcholinesterase (AChE) and oxidative stress enzymes, such as superoxide dismutase (SOD) and glutathione S-transferase (GST), were assayed to assess changes in Eisenia fetida at the physiological level induced by different doses of VOCs as part of an acute toxicity test over 7 and 14-day exposures. In addition, the toxicities of VOCs were investigated using a soil avoidance test and comet assay. The results revealed that E. fetida exhibited significant avoidance behavior towards the highest concentrations of undecane, decane, 2,4-dimethyl heptane, and 2,2,4,6,6-pentametyl heptane. The tail DNA percentages were significantly increased for all experimental treatments relative to control. However, under the treatments of VOCs, Olive tail moment content and comet tail length also display an obvious increase compared to control, except for that of octane, undecane and decane treatments. As VOC concentrations and durations increased in the soil, activities of AChE, SOD, and GST were either stimulated or inhibited. Among the VOCs, decane, 2,4-dimethyl heptane, 2,2,4,6,6-pentamethyl heptane, and 2,4-di tert buyl phenol exerted stronger effects on enzymatic activities. In summary, VOCs in rhizosphere soils of E. grandis might exert a toxic impact on E. fetida, among which 2,4-dimethyl heptane, 2,2,4,6,6-pentamethyl heptane, and 2,4-di tert buyl phenol have the strongest effects.

Limited recovery of soil microbial activity after transient exposure to gasoline vapors

During gasoline spills complex mixtures of toxic volatile organic compounds (VOCs) are released to terrestrial environments. Gasoline VOCs exert baseline toxicity (narcosis) and may thus broadly affect soil biota. We assessed the functional resilience (i.e. resistance and recovery of microbial functions) in soil microbial communities transiently exposed to gasoline vapors by passive dosing via headspace for 40 days followed by a recovery phase of 84 days. Chemical exposure was characterized with GC-MS, whereas microbial activity was monitored as soil respiration (CO2 release) and soil bacterial growth ([3H]leucine incorporation). Microbial activity was strongly stimulated and inhibited at low and high exposure levels, respectively. Microbial growth efficiency decreased with increasing exposure, but rebounded during the recovery phase for low-dose treatments. Although benzene, toluene, ethylbenzene and xylene (BTEX) concentrations decreased by 83–97% during the recovery phase, microbial activity in high-dose treatments did not recover and numbers of viable bacteria were 3–4 orders of magnitude lower than in control soil. Re-inoculation with active soil microorganisms failed to restore microbial activity indicating residual soil toxicity, which could not be attributed to BTEX, but rather to mixture toxicity of more persistent gasoline constituents or degradation products. Our results indicate a limited potential for functional recovery of soil microbial communities after transient exposure to high, but environmentally relevant, levels of gasoline VOCs which therefore may compromise ecosystem services provided by microorganisms even after extensive soil VOC dissipation.

Soil volatile analysis by proton transfer reaction-time of flight mass spectrometry (PTR-TOF-MS)

We analyzed the volatile organic compounds (VOCs) emitted from different soils by using the PTR-MS-TOF technique under laboratory conditions and compared them with soil chemical biochemical activities. The emitted VOCs were related to soil microbial biomass, soil respiration and some soil enzyme activities so as to evaluate if size and activity of soil microbial communities influenced the soil VOCs profiles. Our results showed that the emitted VOCs discriminated between soils with different properties and management, and differences in the VOCs emission profiles were likely related to the active metabolic pathways in the microbial communities of the three studied soil. Our results also showed that some soil enzyme activities such as β-glucosidase and arylsulfatase were possibly involved in the release of compounds fueling microbial metabolic pathways leading to the production of specific VOCs. It was concluded that the PTR-MS-TOF technique is suitable for analyze VOCs emission from soil and that studies comparing soil enzyme activities and soil volatile profiles can reveal the origin of VOCs and give further insights on microbial activity and soil functionality.

Human Health Risk Assessment of a landfill based on volatile organic compounds emission, immission and soil gas concentration measurements

A Human Health Risk Assessment (HHRA) was required for a closed landfill located in Cerdanyola del Vallès (Barcelona, Spain). The HHRA had two objectives, to evaluate the present risk of the identified receptors in the area and to safely develop the future urban planning of the area, therefore 3 scenarios for the current situation and 4 for the future situation were developed.After reviewing the existing data and exploring the needs of information, the assessment in this study was focused on the measurement of volatile organic compounds (VOCs) fluxes from the subsoil (emission from the landfill at 5 points), concentrations of VOCs in the air (immission in 4 urban sites) and concentration of VOCs in soil–gas (measurements at 5m below ground surface outside the landfill at 8 sites). Around 70 VOCs were analyzed by using multi-sorbent tubes and Thermal Desorption Gas Chromatography (TD–GC–MS). The VOCs that were detected and quantified include alkanes, aromatic hydrocarbons, alcohols, ketones, halocarbons, aldehydes, esters, terpenoids, ethers and some nitrogenated and sulfur compounds, furans and carboxylic acids. Specific mercury flux measurements were performed in a hot spot by using carulite tubes, that were also analyzed by using Thermal Decomposition, Amalgamation, and Atomic Absorption Spectrophotometry.Results showed average values of volatile emission fluxes ranging from non-detected to 331μgm−2day−1 (dichlorodifluoromethane). In the case of immission, the concentration of VOCs measured in the air of populated area surrounding the landfill ranged values from non-detected to 42.0μgm−3 (acetic acid). The soil–gas measurements in piezometers around the landfill showed individual VOC values with a maximum 830μgm−3 for dichlorodifluoromethane.With the obtained fluxes and concentrations in air and soil–gas, USEPA methodology and modeling was used to evaluate equivalent concentration in the scenarios considered. Toxicity values from IRIS database were used to finally obtain chemical risk indicators. Admissible risk indicators were obtained in all scenarios. The VOCs that contributed more to risk indexes in RH2 were trichloroethylene, trimethylbenzene, chloroform, 1,2-dichloroethane and carbon tetrachloride. The carcinogenic risk in RH7 was linked to the presence of benzene and chloroform. The comparison of the measurements of the present work with other landfills evidence that HHRA in ambient air would be needed in order to perform a correct landfill management.

Changes in biogeochemistry and carbon fluxes in a boreal forest after the clear-cutting and partial burning of slash

We quantified the changes in the soil properties and fluxes of soil CO2, CH4 and volatile organic compound (VOC) fluxes following a clear-cut (CC) and prescribed burning of slash (BCC) over a three year time period in a mature spruce forest. Clear-cutting increased soil moisture, soil temperature, pH as well as NH4–N and NO3–N concentrations in the soil. PH and soil temperature in the BCC site were even higher than in the CC site.Probably due to decreased tree root respiration, the soil CO2 efflux decreased only slightly in the first growing season following the clear-cut. During the following two years, the CO2 efflux at the CC site was significantly higher than in the mature control forest due to increased decomposition, which was stimulated by higher soil moisture and temperature. The temperature dependencies of the CO2 efflux did not differ between these sites. The clear-cut and burning of slash, however, decreased the CO2 efflux and its temperature response in BCC for two years but in the third year, the differences between control and BCC were no longer significant.Soil was a sink for CH4 in all treatments. After the clear-cutting and burning of slash, the net CH4 uptake was immediately decreased, but one year later the uptake was comparable to that of the mature control forest. The CC treatment decreased the soil CH4 uptake, however, it did not significantly differ from that of the control.The soil VOC emissions measured at the BCC site were 100-fold compared to those measured before clear-cutting, but the emissions decreased rapidly during the three months following the burning.Although the CO2 effluxes from the BCC site were lower for more than 2.5 years compared to the CC site, the total amount of carbon released from prescribed burning was higher due to the immediate carbon losses. Moreover, the clear-cut and burning of slash temporarily decreased the ability of the forest to bind atmospheric CH4 and increased the VOC emissions significantly.

Modeling volatilization of residual VOCs in unsaturated zones: A moving boundary problem

It is of practical interest to investigate the natural evaporation of volatile organic compounds (VOCs) after the removal of a leaking tank situated on the top of the soil. This study aims to develop a mathematical model to predict mole fraction distributions and migration of evaporation front for two VOCs emanating from residual non-aqueous phase liquid (NAPL) due to the leak from the tank in a homogeneous soil. Considering the location of the front and the regions above and below the front, a numerical model for the diffusive transport of VOCs in unsaturated soils was developed using the finite difference method with a moving grid approach. The model was further simplified to the case of single VOC and solved analytically by Boltzmann's transformation with a moving boundary. Analytical expressions for the depth and moving speed of the front for a single VOC were then obtained for practical use. Finally, the developed model was used to predict the concentration distributions of VOCs below the land surface and examine the factors affecting the location and moving speed of the evaporation front.

Determination of Volatile Organic Compound Emissions and Ozone Formation from Spraying Solvent‐based Pesticides

Large-scale agricultural activities have come under scrutiny for possible contributions to the emission of ozone precursors. The San Joaquin Valley (SJV) of California is an area with intense agricultural activity that exceeds the federal ozone standards for more than 30 to 40 d yr(-1) and the more stringent state standards for more than 100 d yr(-1). Pesticides are used widely in both agricultural and residential subregions of the SJV, but the largest use, by weight of "active ingredient," is in agriculture. The objective of the study was to determine the role of pesticide application on airborne volatile organic compounds (VOC) concentrations and ozone formation in the SJV. The ozone formation from the pesticide formulation sprayed on commercial orchards was studied using two transportable smog chambers at four application sites during the summers of 2007 and 2008. In addition to the direct measurements of ozone formation, airborne VOC concentrations were measured before and after pesticide spraying using canister and sorbent tube sampling techniques. Soil VOC concentrations were also measured to understand the distribution of VOCs between different environmental compartments. Numerous VOCs were detected in the air and soil samples throughout the experiment but higher molecular weight aromatic hydrocarbons were the primary compounds observed in elevated concentrations immediately after pesticide spraying. Measurements indicate that the ozone concentration formed by VOC downwind of the orchard may increase up to 15 ppb after pesticide application, with a return back to prespray levels after 1 to 2 d.

Simulating and Characterizing Agricultural Ground Applications for Soil VOC Deposition Studies

Abstract Reactive volatile organic compounds (VOCs) play a major role in the formation of photochemical oxidants in the atmosphere by reacting with oxides of nitrogen and solar ultraviolet energy producing ozone, which is a criteria pollutant regulated under the National Ambient Air Quality Standards. The United States is one of the most agriculturally productive countries in the world due in part to the use of chemical pesticides that consist of active ingredients that are typically non-volatile or semi-VOCs and inert ingredients such as solvents, emulsifiers, and diluents that may also be volatile. Presently, the VOC determination of emission factors from agricultural pesticide applications assumes that all of the inert VOC ingredients volatilize. This research focuses on the development of a laboratory methodology for applying agricultural spray formulations in accurate and measurable levels to support VOC deposition onto and loss from soil surfaces. Adapting a laboratory spray table system with a modified spray and deposition sampling scheme resulted in repeatable spray applications, with the deposition pattern being mapped across the treatment area. These mapped deposition values allow for measurements from soil samples to be correlated with actual spray deposition. This methodology provides for a rapid and repeatable means for surveying VOC deposition and losses from a variety of spray formulations under varying spray rates and spray droplet sizes.