Measured Emission Rates Research Articles

When is Enough? Minimum Sample Sizes for On-Road Measurements of Car Emissions.

The power of remote vehicle emission sensing stems from the big sample size obtained and its related statistical representativeness for the measured emission rates. But how many records are needed for a representative measurement and when does the information gain per record become insignificant? We use Monte Carlo simulations to determine the relationship between the sample size and the accuracy of the sample mean and variance. We take the example of NO emissions from diesel cars measured by remote emission monitors between 2011 and 2018 at various locations in Europe. We find that no more than 200 remote sensing records are sufficient to approximate the mean emission rate for Euro 4, 5, and 6a/b diesel cars with 80% certainty within a ±1 g NO per kg fuel tolerance margin (∼±50 mg NO per km). Between 300 and 800 remote sensing records are needed to approximate also the variance of the mean NO emission rates for those diesel car technologies. This translates to only 2 and up to 9 measurement days to characterize the means and their variance for a car fleet typical in Europe.

Long-term volatile organic compound emission rates in a new electric vehicle: Influence of temperature and vehicle age

To investigate the long-term emission characteristics of volatile organic compounds (VOCs) in vehicles, field measurements of the VOC emission rates in a new electric vehicle were conducted for 21 months. During the measuring period, the car was privately used for daily commuting under a natural environment. Detailed in-cabin VOC concentrations, temperature, relative humidity, and air exchange rates were obtained monthly while the car was parked and all windows and doors closed. The influence of in-cabin temperature and car age on the VOC emission rates was explored. For total VOCs, the emission rate was positively associated with the in-cabin temperature and decreased with an increase in vehicle age. For certain VOC species, such as 2-ethyl-1-hexanol, 5-methylundecane, and 3,8-dimethyldecane, the emission rates during the summer were 71–182 times higher than those during the winter. The influence of vehicle age on the VOC species emission rate depended on the compound properties and emission source characteristics. For aromatics, the decay of the emission rate over time was relatively significant; for alkanes and alkenes, the decay of the emission rate over time was relatively minor; and for ketones and aldehydes and esters and alcohols the emission rate was not necessarily negatively associated with vehicle age. These results aid in understanding vehicle cabin air quality and its possible influential factors.

Distribution of transient formaldehyde concentration in confined small glass desiccators and its impact on emission rate measurement

The headspace method is used frequently for measuring the emissions rates of chemical compounds from building materials when operating labeling systems for these materials. A numerical investigation of transient formaldehyde concentration distribution in confined small glass desiccators was conducted in this study. To clarify the impact of the desiccator geometry on the formaldehyde emission and diffusion characteristics, three-dimensional (3D) laser-based measurement was first conducted to define the detailed inner geometries of the different commercial desiccators. A petri dish containing water was used as the sorbent for test specimens of formaldehyde emission sources produced inside the desiccators. Fundamental experiments concerning formaldehyde emission rates and sorption onto the sorbent were next performed using high- and low-emission types of building materials in the desiccators. Transient and steady numerical analyses were conducted for formaldehyde emissions from the building materials, molecular diffusion, and sorption onto the water sorbent. Transient analysis of the formaldehyde diffusion field over 24 h revealed that the total amount of dissolution of formaldehyde in the water was not significantly affected by the desiccator geometry in the building material of the inner diffusion control type. For evaporative/external diffusion emission-type, however, the formaldehyde emission rate was strongly affected by the desiccator shape. To obtain reproducible emission rate measurements in desiccators with different geometrical shapes, substantial adjustment is needed for the relative positions of the emission source and the sorbent in terms of the equivalent diffusion length, Ld.

Applications of quantitative thermal infrared hyperspectral imaging (8–14 μm): measuring volcanic SO2 mass flux and determining plume transport velocity using a single sensor

Remote measurements of sulfur dioxide (SO2) path-concentration and emission rate (mass flux), released by passive volcanic degassing, are a key diagnostic of volcanic behavior. SO2 gas concentrations are also important for public health. Despite the significance of measuring SO2 mass flux at active volcanoes, an accurate method is still very difficult to obtain due largely to uncertainties of plume transport velocities and radiative transfer calculations. Here, we present a new infrared imaging method for deriving SO2 flux at active volcanoes with less than 20% plume transport velocity and radiative transfer uncertainties. The thermal hyperspectral imager (THI) was used for this study. THI is an uncooled remote sensing long-wave thermal infrared (TIR) imaging hyperspectral sensor that can obtain ~ 50 wavelength samples between 8 and 14 μm. Measurements of SO2 at the summit of Kīlauea volcano, collected using THI, are presented, where we obtained (for the periods of July 24–26, 2017, and February 5–6, 2018) a SO2 flux raging between 0 and 20 kg/s with occasional peaks higher than 40 kg/s. The spatial distribution of SO2 path-concentrations was obtained from the THI images by processing them using a newly developed SO2 retrieval algorithm, the SO2 amenable lookup table algorithm (SO2-ALTA). The sampling rate (30 Hz) of the microbolometer camera within THI means raw frames can be used for wind velocity derivation. Volcanic plume motion can be thus inferred by tracking plume features in sequential frames using spatial correlation techniques and knowing the camera angular orientation. Volcanic SO2 flux was estimated from the spatial distribution of SO2 and wind velocity. We evaluated temporal trends of the SO2 flux during the day and the night at the summit of Kīlauea volcano under both clear sky weather with northeasterly trade winds and cloudy sky conditions with low variable wind. These tests showed that the camera and techniques described in this paper provide an effective tool for monitoring SO2 fluxes remotely with less than 20% plume transport velocity and radiative transfer uncertainties and under a variety of background conditions (clear and cloudy sky, cold and hot backgrounds).

Measuring ammonia emissions from vegetable greenhouses with an inverse dispersion technique

China’s greenhouse vegetable production is considered an important contributor to the national ammonia (NH3) inventory because of the excess nitrogen (N) application rate (normally over 1000 N kg ha−1 yr−1) and large N consumption (approximately 10% of the N fertilizer in China). However, the previously measured emission rates are still in question because of the inherent limits of the commonly used techniques (e.g., non-flow-through chamber technique) and the exclusion of the impact of the greenhouse opening/enclosing scheme on NH3 loss from greenhouse soil to the atmosphere over a growing season. This study examines the ability of an inverse dispersion technique, in combination with an open-path laser system, for measuring NH3 emissions from vegetable greenhouses. The NH3 concentrations over the greenhouse areas greatly exceeded the laser’s detectable limit and showed a clear diel variation pattern. Determination of the area and height of the greenhouse sources are critical to emission estimates, while removing the periods with inaccurate wind simulations has minimal effect on the daily and total emission estimations since the omitted periods mainly occurred during nighttime (low emission periods). With the application of our findings, the observed diel NH3 emission patterns are found in good agreement with the air temperature. The NH3-N losses during the measurements in terms of proportions to the N fertilization (40.02% in spring, 7.83% in summer) are generally comparable to those of previous studies. Overall, the inverse dispersion technique can be used to provide good NH3 emission estimates as well as to assess NH3 emission factors along the opening/enclosing scheme across a growing season of greenhouse vegetables in the future.

Effects of flux chamber configuration on the sampling of odorous gases emissions

Flux chambers are commonly used to measure emission rates of odorous compounds at passive liquid surfaces in wastewater treatment plants. Different flux chambers configurations are found in the literature and the main concern regards to the mixing inside the chamber, which is linked to impact on the overall mass transfer between emitting surface and headspace, and the sampling recovery efficiency. However, aspects related to the airflow and mass transfer inside the chambers influence the measured emission rates. The mass transfer coefficients in the liquid and gas phases are functions of the friction velocity on the liquid surface. This work investigates the airflow and odorous compounds transport (with different Henry’s law constants) inside a flux chamber using Computational Fluid Dynamics, to determine the influence of inlet airflow rate (2, 5 and 10 L min−1), inlet configurations (4, 6 and 8 inlet holes) and the inclusion of internal fans on the surface friction velocity and emission rate. The results showed a complex flow inside the chambers and a concentration field that reaches steady state after 6 residence times. The use of an internal fan promoting downward flow increased turbulence and produced values of friction velocity at the liquid interface closer to those found in the near surface flow in the boundary layer, whereas all other configurations tested showed much lower values of friction velocity. Therefore, the use of a fan is recommended.

Measuring SO2 Emission Rates at Kīlauea Volcano, Hawaii, Using an Array of Upward-Looking UV Spectrometers, 2014–2017

The Hawaiian Volcano Observatory uses an array of ten fixed, upward-looking ultraviolet spectrometer systems to measure SO2 emission rates at 10-second sample intervals from the Kīlauea summit. We present Kīlauea SO2 emission rates from the volcano’s summit and Middle East Rift Zone during 2014-2017 and discuss the major sources of error for these measurements. Due to the wide range of SO2 emissions encountered at the summit vent, we used a variable wavelength spectral analysis range to accurately quantify both high and low SO2 column densities. We present case studies comparing the measured emission rates from the fixed spectrometer array to independent road and helicopter-based traverse measurements and evaluate the magnitudes and sources of uncertainties for each method. To address the challenge of obtaining accurate plume speed measurements, we examine ground-based wind-speed, plume speed tracking via spectrometer, and SO2 camera derived plume speeds. Our analysis shows that 1) the summit array column densities calculated using a dual fit window, are within -6 to +22% of results obtained with a variety of other conventional and experimental retrieval methods 2) emission rates calculated from the summit array located ~3 km downwind of the Overlook vent provide the best, practical estimate of summit SO2 release under normal trade wind conditions 3) ground-based anemometer wind speeds are 22% less than plume speeds determined by cross-correlation of plume features 4) our best estimate of average Kīlauea SO2 release for 2014-2017 is 5100 t/d, which is comparable to the space-based OMI emissions of 5518 t/d 5) short-term variability of SO2 emissions reflect Kīlauea lava lake dynamics.

Open cut black coal mining: Empirical verification of PM2.5 air emission estimation techniques

There is a paucity of empirical data relating to PM2.5 emissions from open cut coal mines. Availability of high quality emission data is fundamental to the completion of robust analyses of the potential future impacts of particulate emissions from open cut coal mining operations. This study presents PM2.5 emission rates determined on the basis of empirical data from open cut coal mining operations located in two regions of Australia. These data are used to validate the currently adopted PM2.5 emission estimation methodologies, which are based on total suspended particulate measurements adjusted for PM2.5 size fraction. The emission rates determined in this study demonstrate that regional differences between emission rates may be significant for specific activities. Measured average PM2.5 emission rates are compared to rates calculated using existing available emissions estimation methodologies. This reveals that for dragline operation and coal dumping there are significant differences between the measured emission rates and emission rates calculated using currently available methodologies. This study identifies that the existing adopted US EPA and Australian emissions estimation methods for PM2.5 emissions from coal haul routes, which are one of the most significant sources of PM2.5 emissions at open cut mines, are reliable if the surface moisture content and dust control watering regimes are appropriately accounted for. The Australian estimation method is also considered reliable for overburden haul routes, however the US EPA method over predicts the measured PM2.5 emission rate by a factor of 3.Further, the study highlights that there is a high degree of inherent uncertainty in empirically derived emissions estimates for fugitive dust sources of this type. This uncertainty should be considered when completing emissions calculations, particular where these estimations are subsequently the basis for impact assessment and health risk analysis.

A Critical Evaluation of the Influence of Different Panel Composition in the Measurement of Odour Concentration by Dynamic Olfactometry

Odour concentration expressed in terms of OUE/m3 by using the dynamic olfactometry analysis, standardized by the European Norm (EN) 13725 are by now the most commonly and worldwide accepted method to measure odours. The EN, first edition published in the year 2003, is actually under review process by the WG2 of the CEN/TC246 and the end of the revision work is expected for the year 2018. Related to the odour panel the standard fixes some parameters (e.g: panel size). Nothing is, however, performed about the composition of the panel members in terms of their gender, the age of the involved persons and their origin and nationality. Also the current literature is limited to discussing how the measurement of emission rates derived from the same odour source could be related to the panel composition.The scope of this study is to investigate the influence on the determination of odour concentration with dynamic olfactometry, according to EN 13725 standards, applying different panel conditions, with the objective to define the optimal criteria to evaluate the odour concentration and obtain the highest repeatability and accuracy of the sensorial measure.A critical evaluation was carried out in relation to the same odour source with the comparison of the different panel composition (in terms of gender, age and nationality) to measure the odour concentration. In the experimental studies the measurements were conducted within 5 h after sampling to reduce the variability of the mixture and increase the reliability. All assessors who participate in odour measurements were qualified and tested according the quality criteria assurance foreseen by the EN13725. Studies were taken considering real environmental odour emissions collected at a wastewater treatment plant (WWTP).The results obtained show a not significantly influence of the investigated characteristics of the single panel member in the repeatability assurance of the measure of the odour concentration by dynamic olfactometry. While a variation of the results in terms of OU/m3 is demonstrated related to the different nationality and biological factors (age and gender) of the assessors. There is therefore the need to consider these factors in the current odour determination practices, for example in calculating the uncertainty factor of the measurement.

Empirical values of branching ratios in the three-body recombination reaction for O(1S) and O2(0,0) airglow chemistry

The branching ratios ε and α in the three-body recombination reaction for O(1S) greenline and O2(0,0) atmospheric band airglow chemistry represent the fraction of O2 that branch into the b1∑g+ and c1∑u- electronic states, respectively. In the present work, the empirical values of these branching ratios have been deduced using a numerical optimization approach. They were obtained using the optimization scheme known as the Covariance Matrix Adaptation Evolution Strategy (CMA-ES) with our MACD-00 model and simultaneous volume emission rate (VER) measurements of the O(1S) greenline and O2(0,0) atmospheric band emissions. The CMA-ES was employed as the optimization algorithm that would match the O(1S) and O2(0,0) VER profiles simulated by the MACD-00 model to observations made by OXYGEN/S35, S310.10, NASA Flight 4.339, ETON flights P229H and P230H, OASIS, SOAP/WINE, MULTIFOT, and WINDII. We found that most of the values deduced for ε were in the [0.1, 0.3] range, while most of the values of α were in the [0.01, 0.03] range. Excluding the outliers, the average branching ratio values involving the production of O2(b1∑g+) and O2(c1∑u-) were determined to be ε = 0.15 ± 0.02 and α = 0.018 ± 0.004, respectively. Overall, the simulations showed good agreement with the observations albeit with some discrepancies in the peak altitudes and shape of the profiles, possibly due to small perturbations in the observed VER profiles that are not considered in our simulations.

(Invited) Physical Modeling of Performance, Membrane and Catalyst Degradation in PEMFC

High cost and performance degradation are still the main issues which hinder the commercialization of low temperature fuel cells on a grand scale [1]. Both of these issues are closely related to the catalyst which accounts for up to 40% of the PEMFC stack cost [2] while the loss of electrochemically active surface area (ECSA) poses a major contribution to the overall performance degradation. Furthermore, chemical membrane degradation is another main issue as membrane thinning and pinhole formation are limiting the lifetime of the cells. Detailed physical models provide a better understanding of the underlying mechanisms leading to these degradation mechanisms and therefore can help in developing strategies to increase the durability of the cells. Here we present a two-step approach to achieve this goal. First we develop a transient, two-dimensional single cell model, which includes all relevant mechanisms to describe the cell performance, i.e., electrochemistry, two-phase multi-component transport in the porous layers, charge and heat transport as well as water and gas permeation through the membrane. This model is implemented in our in-house code NEOPARD-X which is based on the open-source framework DuMux [3]. It provides important insights on the local conditions within the cell which are often not accessible in experiments but determine the local degradation rates. In particular we discuss the water management and how simulations of electrochemical impedance spectra (EIS) can be used for process identification. In the second step we discuss detailed physical models for the degradation mechanisms. A multi-step chemical membrane degradation model is presented which incorporates the formation and decomposition of hydrogen peroxide, iron ion redox cycle, radical formation and degradation via “unzipping” and “side chain scission” mechanism. The model provides insights on the local degradation rates depending on the operating conditions. Strongest degradation is obtained at the anode side during OCV while at higher current densities the degradation is strongly reduced and shifts to the cathode side (left figure). The model is validated with fluoride emission rate (FER) measurements under various operating conditions. Finally, a catalyst degradation model due to platinum dissolution and particle growth is discussed. Since the dissolution kinetics strongly depends on the platinum oxide coverage, a platinum oxide model has been developed and validated with dedicated CV experiments. This model is able to describe the experimentally observed logarithmic growth of the oxide coverage. This coverage affects the surface energy of the particles and thus influences the platinum dissolution. Therefore, taking into account the kinetics of the oxide formation is crucial for describing the catalyst degradation under dynamic operating conditions such as fast potential cycling which is typically used as an AST for the catalyst. By coupling the degradation model to the single cell model we investigate the catalyst degradation in AST and long-term degradation tests. The degradation model is validated with experimental data for the ECSA loss during these tests as well as with particle size distributions (PSD) obtained with TEM (right figure). The occurrence of heterogeneities in the catalyst degradation is discussed. Figure: simulated local FER (mol m-3 s-1) due to chemical membrane degradation at various cell voltages (a); comparison between simulated and measured catalyst PSD evolution (b). Figure 1

Top‐Down Estimates of NOx and CO Emissions From Washington, D.C.‐Baltimore During the WINTER Campaign

AbstractAirborne mass balance experiments were conducted around the Washington, D.C.‐Baltimore area using research aircraft from Purdue University and the University of Maryland to quantify emissions of nitrogen oxides (NOx = NO + NO2) and carbon monoxide (CO). The airborne mass balance experiments supported the Wintertime INvestigation of Transport, Emissions, and Reactivity (WINTER) campaign, an intensive airborne study of anthropogenic emissions along the Northeastern United States in February–March 2015, and the Fluxes of Atmospheric Greenhouse Gases in Maryland project which seeks to provide best estimates of anthropogenic emissions from the Washington, D.C.‐Baltimore area. Top‐down emission rates of NOx and CO estimated from the mass balance flights are compared with the Environmental Protection Agency's 2011 and 2014 National Emissions Inventory (NEI‐11 and NEI‐14). Inventory and observation‐derived NOx emission rates are consistent within the measurement uncertainty. Observed CO emission rates are a factor of 2 lower than reported by the NEI. The NEI's accuracy has been evaluated for decades by studies of anthropogenic emissions, yet despite continuous inventory updates, observation‐inventory discrepancies persist. WINTER NOx/CO2 enhancement ratios are consistent with inventories, but WINTER CO/NOx and CO/CO2 enhancement ratios are lower than those reported by other urban summertime studies, suggesting a strong influence of CO seasonal trends and/or nationwide CO reductions. There is a need for reliable observation‐based criterion pollutant emission rate measurements independent of the NEI. Such determinations could be supplied by the community's reporting of sector‐specific criteria pollutant/CO2 enhancement ratios and subsequent multiplication with currently available and forthcoming high‐resolution CO2 inventories.

Analysis of the number of flux chamber samples and study area size on the accuracy of emission rate measurements

ABSTRACTMonte Carlo simulations were conducted on a set of flux chamber measurements at a landfill to estimate the relationship between the number of flux chamber samples and study area size on the emission rate measurement accuracy. The spatial variability of flux was addressed in the study by utilizing an existing flux chamber measurement data set that is one of the most dense flux chamber sampling arrays published to date for a landfill. At a probability of 95%, the Monte Carlo simulations indicated that achieving an accuracy within 10% with the flux chamber method is highly unlikely. An accuracy within 20% was achieved for small areas of less than about 0.2 hectares using 220 flux chamber measurements, but achieving this level of accuracy for area emission sources, of similar or greater variability, that are larger than this is highly unlikely. An accuracy within 30% was achieved up to the Full Area of about 0.4 hectares if more than approximately 120 samples were obtained. Even for an accuracy within 50%, at least 40 flux chamber measurements were needed for the Full Area of about 0.4 hectares. Available methods of estimating the number of samples required were compared to the Monte Carlo simulation results. The Monte Carlo simulations indicate that, in general, more samples are required than determined from an existing statistical method, which is a function of the mean and standard deviation of the population. Specifying the number of samples based on a regulatory method results in very poor accuracy. A modification to the statistical method for estimating the number of samples, or for estimating an accuracy for a given probability and number of samples, is proposed.Implications: The flux chamber method is the most widely used method of measuring fugitive emission rates from area sources. However, extrapolation of a set of individual flux chamber samples to a larger area results in area flux measurement values of unknown accuracy. Quantification of the accuracy of the extrapolation of a set of flux chamber measurements would be beneficial for understanding the confidence that can be placed on the measurement results. Guidance as to the appropriate number of flux chamber measurements to achieve a desired level of accuracy would benefit flux chamber method practitioners.

Characterization of methane emissions from five cold heavy oil production with sands (CHOPS) facilities

ABSTRACTCold heavy oil production with sands (CHOPS) is a common oil extraction method in the Canadian provinces of Alberta and Saskatchewan that can result in significant methane emissions due to annular venting. Little is known about the magnitude of these emissions, nor their contributions to the regional methane budget. Here the authors present the results of field measurements of methane emissions from CHOPS wells and compare them with self-reported venting rates. The tracer ratio method was used not only to analyze total site emissions but at one site it was also used to locate primary emission sources and quantify their contributions to the facility-wide emission rate, revealing the annular vent to be a dominant source. Emissions measured from five different CHOPS sites in Alberta showed large discrepancies between the measured and reported rates, with emissions being mainly underreported. These methane emission rates are placed in the context of current reporting procedures and the role that gas-oil ratio (GOR) measurements play in vented volume estimates. In addition to methane, emissions of higher hydrocarbons were also measured; a chemical “fingerprint” associated with CHOPS wells in this region reveals very low emission ratios of ethane, propane, and aromatics versus methane. The results of this study may inform future studies of CHOPS sites and aid in developing policy to mitigate regional methane emissions.Implications: Methane measurements from cold heavy oil production with sand (CHOPS) sites identify annular venting to be a potentially major source of emissions at these facilities. The measured emission rates are generally larger than reported by operators, with uncertainty in the gas-oil ratio (GOR) possibly playing a large role in this discrepancy. These results have potential policy implications for reducing methane emissions in Alberta in order to achieve the Canadian government’s goal of reducing methane emissions by 40–45% below 2012 levels within 8 yr.

Wind tunnel experiments on dust emissions from different landform types

The measurement and assessment of dust emissions from different landforms are important to understand the atmospheric loading of PM10 (particulate matter ≤10 μm aerodynamic diameter) and to assess natural sources of dust; however, the methodology and technique for determining the dust still present significant research challenges. In the past, specialized field observation and field wind tunnel studies have been used to understand the dust emission. A series of wind tunnel tests were carried out to identify natural sources of dust and measure the magnitudes of dust emissions from different landforms. The method used in this study allowed the measurement of the PM10 emission rate using a laboratory based environmental boundary layer wind tunnel. Results indicated that PM10 emissions demonstrated strong temporal variation and were primarily driven by aerodynamic entrainment. Sand dunes, playa, and alluvial fans had the largest dust emission rates (0.8–5.4 mg/(m2•s)) while sandy gravel, Gobi desert and abandoned lands had the lowest emission rates (0.003–0.126 mg/(m2•s)). Dust emissions were heavily dependent on the surface conditions, especially the availability of loose surface dust. High dust emissions were a result of the availability of dustparticle materials for entrainment while low dust emissions were a result of surface crusts and gravel cover. Soil surface property (surface crusts and gravel cover) plays an important role in controlling the availability of dust-sized particles for entrainment. The dust emission rate depended not only on the surface conditions but also on the friction velocity. The emission rate of PM10 varies as a power function of the friction velocity. Although dynamic abrasion processes have a strong influence on the amount of dust entrainment, aerodynamic entrainment may provide an important mechanism for dust emissions. Large volumes of dust entrained by aerodynamic entrainment cannot only occur at low shear velocity without saltation, but may dominate the entrainment process in many arid and semi-arid environments. So it may also be responsible for large magnitude dust storms. Playa and alluvial fan landforms, prior to developing a surface crust, may be the main sources of dust storms in Qinghai Province.

Fast Ion Confinement Study by Neutron Emission Rate Measurement after Short Pulse NB Injection in the Large Helical Device

Fast Ion Confinement Study by Neutron Emission Rate Measurement after Short Pulse NB Injection in the Large Helical Device

Measurement and interpretation of emission rate and loading rate of air pollutants from the non-point source of naturally ventilated dairy farm

Measurement and interpretation of emission rate and loading rate of air pollutants from the non-point source of naturally ventilated dairy farm

Measuring methane emissions from a UK landfill using the tracer dispersion method and the influence of operational and environmental factors

The methane emissions from a landfill in south-east, UK were successfully quantified during a six-day measurement campaign using the tracer dispersion method. The fair weather conditions made it necessary to perform measurements in the late afternoon and in the evening when the lower solar flux resulted in a more stable troposphere with a lower inversion layer. This caused a slower mixing of the gasses, but allowed plume measurements up to 6700 m downwind from the landfill. The average methane emission varied between 217 ± 14 and 410 ± 18 kg h−1 within the individual measurement days, but the measured emission rates were higher on the first three days (333 ± 27, 371 ± 42 and 410 ± 18 kg h−1) compared to the last three days (217 ± 14, 249 ± 20 and 263 ± 22 kg h−1). It was not possible to completely isolate the extent to which these variations were a consequence of measuring artefacts, such as wind/measurement direction and measurement distance, or from an actual change in the fugitive emission. Such emission change is known to occur with changes in the atmospheric pressure. The higher emissions measured during the first three days of the campaign were measured during a period with an overall decrease in atmospheric pressure (from approximately 1014 mbar on day 1 to 987 mbar on day 6). The lower emissions measured during the last three days of the campaign were carried out during a period with an initial pressure increase followed by a period of slowly reducing pressure. The average daily methane recovery flow varied between 633 and 679 kg h−1 at STP (1 atm, 0 °C). The methane emitted to the atmosphere accounted for approximately 31% of the total methane generated, assuming that the methane generated is the sum of the methane recovered and the methane emitted to the atmosphere, thus not including a potential methane oxidation in the landfill cover soil.

Measurement of methane emissions from abandoned oil and gas wells in Hillman State Park, Pennsylvania

ABSTRACTAbandoned oil and gas wells, improperly plugged or unplugged, present a risk to current and future oil and gas development because they provide a potential pathway for unwanted gas and fluid migration to the surface. The appropriate emission factor for gaseous emissions from these wells is uncertain, as a limited number of studies have reported abandoned wells as a methane emissions source. A helicopter-based survey that mapped methane concentration and located wells by detecting magnetic anomalies was conducted in Hillman State Park in southwestern Pennsylvania. Although well finding via aerial survey was successful, elevated methane concentrations due to emissions from wells in the survey area were not detected by helicopter as abandoned wells were likely too small a source of methane to detect from elevations that helicopters fly at (tens of meters). Measurement of methane emission rates from 31 wells were collected using several techniques that are compared and evaluated for their effectiveness: Hi Flow sampler, field-portable flame ionization detector, infrared camera, dynamic flux chamber and bag sampling. Nine of the 31 wells were buried; average methane flux for these wells was not statistically different from the background. Mass flow rate from the remaining 22 wells ranged from non-detection (less than 0.09 kg CH4/day) to 4.18 kg CH4/day with a mean of 0.70 kg/well/day (median of 0.24 kg CH4/day/well) and a sample standard of error of 0.21 kg CH4/well/day. This emission factor, while not intended for exclusive use in developing a methane emissions inventory for abandoned oil and gas wells, contributes to the growing amount of methane emissions data for this source category. The results from the aerial survey, ground-based well location verification and emissions measurements, and the evaluation of measurement approaches described here, provide a comprehensive characterization of abandoned wells in one field that can inform future measurement studies.

Calibration experiment and the neutronics analyses on the LHD neutron flux monitors for the deuterium plasma experiment

Prior to the deuterium experiments of the Large Helical Device (LHD), an in situ neutron calibration experiment was carried out by using an 800 MBq 252Cf neutron source in November 2016, where a neutron flux monitor, a neutron activation system and a vertical neutron camera are calibrated. This paper concentrates on the in situ calibration for the neutron flux monitor. The neutron flux monitor based on 235U fission chambers and 10B and 3He proportional counters are positioned at three locations outside the LHD cryostat. The counts are measured during continuous rotation of the 252Cf neutron source on the typical magnetic axis of the plasma by a toy train, where the neutron source can be regarded as a ring neutron source. Detection efficiencies for the 252Cf ring source are derived by (total counts)/(total emitted neutron number) in the continuous rotation of the neutron source. Detection efficiencies for the real plasma neutron source are obtained from the measured detection efficiencies with the correction factor taking account of the deference between the 252Cf ring source and the real plasma neutron source evaluated by MCNP calculations with the three-dimensional model of the LHD. Finally, the uncertainty of the total neutron emission rate measurement is discussed.