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Transgenic American chestnut trees expressing a wheat gene for oxalate oxidase (OxO) can tolerate chestnut blight, but as with any new restoration material, they should be carefully evaluated before being released into the environment. Native pollinators such as bumble bees are of particular interest: Bombus impatiens use pollen for both a source of nutrition and a hive building material. Bees are regular visitors to American chestnut flowers and likely contribute to their pollination, so depending on transgene expression in chestnut pollen, they could be exposed to this novel source of OxO during potential restoration efforts. To evaluate the potential risk to bees from OxO exposure, queenless microcolonies of bumble bees were supplied with American chestnut pollen containing one of two concentrations of OxO, or a no-OxO control. Bees in microcolonies exposed to a conservatively estimated field-realistic concentration of OxO in pollen performed similarly to no-OxO controls; there were no significant differences in survival, bee size, pollen use, hive construction activity, or reproduction. A ten-fold increase in OxO concentration resulted in noticeable but non-significant decreases in some measures of pollen usage and reproduction compared to the no-OxO control. These effects are similar to what is often seen when naturally produced secondary metabolites are supplied to bees at unrealistically high concentrations. Along with the presence of OxO in many other environmental sources, these data collectively suggest that oxalate oxidase at field-realistic concentrations in American chestnut pollen is unlikely to present substantial risk to bumble bees. Supplementary Information The online version contains supplementary material available at 10.1007/s11248-021-00263-w.

As part of the MILAGRO 2006 field campaign, the exchange of atmospheric aerosols with the urban landscape was measured from a tall tower erected in a heavily populated neighborhood of Mexico City. Urban submicron aerosol fluxes were measured using an eddy covariance method with a quadrupole aerosol mass spectrometer during a two week period in March, 2006. Nitrate and ammonium aerosol concentrations were elevated at this location near the city center compared to measurements at other urban sites. Significant downward fluxes of nitrate aerosol, averaging −0.2 μg m−2 s−1, were measured during daytime. The urban surface was not a significant source of sulfate aerosols. The measurements also showed that primary organic aerosol fluxes, approximated by hydrocarbon-like organic aerosols (HOA), displayed diurnal patterns similar to CO2 fluxes and anthropogenic urban activities. Overall, 47% of submicron organic aerosol emissions were HOA, 35% were oxygenated (OOA) and 18% were associated with biomass burning (BBOA). Organic aerosol fluxes were bi-directional, but on average HOA fluxes were 0.1 μg m−2 s−1, OOA fluxes were −0.03 μg m−2 s−1, and BBOA fluxes were −0.03 μg m−2 s−1. After accounting for size differences (PM1 vs PM2.5) and using an estimate of the black carbon component, comparison of the flux measurements with the 2006 gridded emissions inventory of Mexico City, showed that the daily-averaged total PM emission rates were essentially identical for the emission inventory and the flux measurements. However, the emission inventory included dust and metal particulate contributions, which were not included in the flux measurements. As a result, it appears that the inventory underestimates overall PM emissions for this location.

The parameterization of the energy balance from a residential and commercial neighborhood of Mexico City was investigated using direct measurements of radiative and heat fluxes carried out during the MILAGRO/MCMA-2006 field campaign as a reference. The measured fluxes were used to evaluate different models of the energy balance based on parameterizations that require standard meteorological observations: ambient temperature, relative humidity, atmospheric pressure and cloudiness. It was found that these models reproduce with reasonable accuracy the diurnal features of the radiative and heat fluxes. The largest differences between modeled and observed fluxes correspond to the incoming longwave radiation, mainly due to errors in the cloudiness data. This paper contributes to the understanding of the energy partitioning in (sub)tropical urban environments, particularly in the developing world, where energy balance models have not been evaluated.

A significant fraction of Earth consists of mountainous terrain. However, the question of how to monitor the surface–atmosphere carbon exchange over complex terrain has not been fully explored. This article reports on studies by a team of investigators from U.S. universities and research institutes who carried out a multiscale and multidisciplinary field and modeling investigation of the CO2 exchange between ecosystems and the atmosphere and of CO2 transport over complex mountainous terrain in the Rocky Mountain region of Colorado. The goals of the field campaign, which included ground and airborne in situ and remote-sensing measurements, were to characterize unique features of the local CO2 exchange and to find effective methods to measure regional ecosystem–atmosphere CO2 exchange over complex terrain. The modeling effort included atmospheric and ecological numerical modeling and data assimilation to investigate regional CO2 transport and biological processes involved in ecosystem–atmosphere carbon exch...

Synthetic pheromones and other behavioral chemicals are used by land managers to prevent insect-caused tree mortality or crop failure in forest and agricultural systems. Currently, no method exists to continuously measure pheromone concentration or movement in real-time. To improve our understanding of pheromone fate and transport under different forest canopies, results from a set of surrogate pheromone (sulfur hexafluoride tracer) experimental trials were used to evaluate a simple, instantaneous, three-dimensional Lagrangian dispersion model. The model was designed to predict both instantaneous and time-averaged pheromone concentrations. Overall, the results from the model show simulated time-averaged arc maximum concentrations within a factor of two of the observed data. The model correctly matched the sharp peaks and narrow widths of the meandering plumes observed in the instantaneous data, however the magnitude of the instantaneous peaks was often under-estimated. This model and evaluation provide the basis for a tool that can be used to guide deployment of synthetic pheromones or other semiochemicals for monitoring, mass trapping, or disruption of mating or aggregation.

An atmospheric tracer dispersion study known as Joint Urban 2003 was conducted in Oklahoma City, Oklahoma, during July of 2003. As part of this field program, vertical concentration profiles were measured at approximately 1 km from the downtown ground-level tracer gas release locations. These profiles showed that the urban landscape was very effective in mixing the plume vertically. In general, the lowest concentration measured along the profile was within 50% of the highest concentration in any given 5-min measurement period. The general slope of the concentration profiles was bounded by a Gaussian distribution with Briggs’s urban equations (stability classes D and E/F) for vertical dispersion. However, measured concentration maxima occurred at levels above the surface, which would not be predicted by Gaussian formulations. Variations in tracer concentration observed in the time series between different release periods were related to changes in wind direction as opposed to changes in turbulence. This was demonstrated using data from mobile analyzers that captured the width of the plume by traveling east to west along nearby streets. These mobile-van-analyzer data were also used to compute plume widths. Plume widths increased for wind directions at larger angles to the street grid, and a simple model comprising adjusted open-country dispersion coefficients and a street channeling component, were used to describe the measured widths. This dispersion dataset is a valuable asset not only for developing advanced tools for emergency-response situations in the event of a toxic release but also for refining air-quality models.

Our objectives were to: characterize spatial and temporal variation in wind speed, direction and air temperature within a steeply sloping 96 ha forested watershed in the Oregon Cascade Mountains; assess the area contributing to advection in cold air drainage; identify appropriate conditions for sampling advected gases representative of the entire watershed; estimate ecosystem respiration from mass balance estimates. The flow dynamics could be categorized into four periods: daytime flows, evening transition, nighttime conditions (formation of a cold air pool) and morning transition. On summer days, the wind above the canopy flowed upvalley whereas the wind direction below the canopy was often down-valley. During the evening transition, the below-canopy cold air drainage becamewellmixedafter theverticaltemperature profileatthetower became isothermal, and sodarand tethersonde data revealed that a second drainage flow developed above the canopy. Between 20:00 and 24:00 h (PST), a cold air pool formed within thevalley;cold air drainage continued, butwind speed decreased as the night progressed. After sunrise, CO2in air passing the tower remained well mixed, but its concentration decreased. After the base of thewatershed began to receive direct solar radiation, the incanopy vertical CO2 concentration profile became stratified and the cold air drainage ceased or was confined below the canopy. After the cold air pool formed, the entire watershed supplied the respired CO2 that advected past the tower. During this period, the potential temperature profilewithin thewatershed indicated a strong inversion within thewatershed. Because the air passing the tower was well mixed and the cold air pool encompassed the entire watershed, it is probable that air samples collected during this period could provide the best estimate of watershed-scale respiration and carbon isotope composition of respired CO2 (Keeling plot analysis). However, sampling prior to the formation of the cold air pool may confound interpretations as the area contributing to the tower is likely changing. Mass balance calculations using an inert tracer (SF6) released below the canopy demonstrated that data from a single vertical profile could provide plausible estimates of ecosystem respiration at the watershed scale. # 2007 Elsevier B.V. All rights reserved.

Data from a recent field campaign in Mexico City are used to evaluate the performance of the EPA Federal Reference Method for monitoring the ambient concentrations of NO2. Measurements of NO2 from standard chemiluminescence monitors equipped with molybdenum oxide converters are compared with those from Tunable Infrared Laser Differential Absorption Spectroscopy (TILDAS) and Differential Optical Absorption Spectroscopy (DOAS) instruments. A significant interference in the chemiluminescence measurement is shown to account for up to 50% of ambient NO2 concentration during afternoon hours. As expected, this interference correlates well with non-NOx reactive nitrogen species (NOz) as well as with ambient O3 concentrations, indicating a photochemical source for the interfering species. A combination of ambient gas phase nitric acid and alkyl and multifunctional alkyl nitrates is deduced to be the primary cause of the interference. Observations at four locations at varying proximities to emission sources indicate that the percentage contribution of HNO3 to the interference decreases with time as the air parcel ages. Alkyl and multifunctional alkyl nitrate concentrations are calculated to reach concentrations as high as several ppb inside the city, on par with the highest values previously observed in other urban locations. Averaged over the MCMA-2003 field campaign, the chemiluminescence monitor interference resulted in an average measured NO2 concentration up to 22% greater than that from co-located spectroscopic measurements. Thus, this interference has the potential to initiate regulatory action in areas that are close to non-attainment and may mislead atmospheric photochemical models used to assess control strategies for photochemical oxidants.

A wide array of volatile organic compound (VOC) measurements was conducted in the Valley of Mexico during the MCMA-2002 and 2003 field campaigns. Study sites included locations in the urban core, in a heavily industrial area and at boundary sites in rural landscapes. In addition, a novel mobile-laboratory-based conditional sampling method was used to collect samples dominated by fresh on-road vehicle exhaust to identify those VOCs whose ambient concentrations were primarily due to vehicle emissions. Four distinct analytical techniques were used: whole air canister samples with Gas Chromatography/Flame Ionization Detection (GC-FID), on-line chemical ionization using a Proton Transfer Reaction Mass Spectrometer (PTR-MS), continuous real-time detection of olefins using a Fast Olefin Sensor (FOS), and long path measurements using UV Differential Optical Absorption Spectrometers (DOAS). The simultaneous use of these techniques provided a wide range of individual VOC measurements with different spatial and temporal scales. The VOC data were analyzed to understand concentration and spatial distributions, diurnal patterns, origin and reactivity in the atmosphere of Mexico City. The VOC burden (in ppbC) was dominated by alkanes (60%), followed by aromatics (15%) and olefins (5%). The remaining 20% was a mix of alkynes, halogenated hydrocarbons, oxygenated species (esters, ethers, etc.) and other unidentified VOCs. However, in terms of ozone production, olefins were the most relevant hydrocarbons. Elevated levels of toxic hydrocarbons, such as 1,3-butadiene, benzene, toluene and xylenes, were also observed. Results from these various analytical techniques showed that vehicle exhaust is the main source of VOCs in Mexico City and that diurnal patterns depend on vehicular traffic in addition to meteorological processes. Finally, examination of the VOC data in terms of lumped modeling VOC classes and its comparison to the VOC lumped emissions reported in other photochemical air quality modeling studies suggests that some alkanes are underestimated in the emissions inventory, while some olefins and aromatics are overestimated.

The new generation of gravitational waves detectors require unprecedented levels of isolation from seismic noise. This article reviews the seismic isolation strategy and instrumentation developed for the Advanced LIGO observatories. It summarizes over a decade of research on active inertial isolation and shows the performance recently achieved at the Advanced LIGO observatories. The paper emphasizes the scientific and technical challenges of this endeavor and how they have been addressed. An overview of the isolation strategy is given. It combines multiple layers of passive and active inertial isolation to provide suitable rejection of seismic noise at all frequencies. A detailed presentation of the three active platforms that have been developed is given. They are the hydraulic pre-isolator, the single-stage internal isolator and the two-stage internal isolator. The architecture, instrumentation, control scheme and isolation results are presented for each of the three systems. Results show that the seismic isolation sub-system meets Advanced LIGO's stringent requirements and robustly supports the operation of the two detectors., Laser Interferometer Gravitational-Wave Observatory, National Science Foundation (U.S.)

New generations of gravity wave detectors require unprecedented levels of vibration isolation. This paper presents the final design of the vibration isolation and positioning platform used in Advanced LIGO to support the interferometer's core optics. This five-ton two-and-half-m wide system operating in ultra-high vacuum. It features two stages of isolation mounted in series. The stages are imbricated to reduce the overall height. Each stage provides isolation in all directions of translation and rotation. The system is instrumented with a unique combination of low noise relative and inertial sensors. The active control provides isolation from 0.1 Hz to 30 Hz. It brings the platform motion down to 10^(−11) m/√Hz at 1 Hz. Active and passive isolation combine to bring the platform motion below 10^(−12) m/√Hz at 10 Hz. The passive isolation lowers the motion below 10^(−13) m/√Hz at 100 Hz. The paper describes how the platform has been engineered not only to meet the isolation requirements, but also to permit the construction, testing, and commissioning process of the fifteen units needed for Advanced LIGO observatories.

This paper presents the results of the past seven years of experimental investigation and testing done on the two-stage twelve-axis vibration isolation platform for Advanced LIGO gravity waves observatories. This five-ton two-and-half-meter wide system supports more than a 1000 kg of very sensitive equipment. It provides positioning capability and seismic isolation in all directions of translation and rotation. To meet the very stringent requirements of Advanced LIGO, the system must provide more than three orders of magnitude of isolation over a very large bandwidth. It must bring the motion below 10^(−11) m/√Hz at 1 Hz and 10^(−12) m/√Hz at 10 Hz. A prototype of this system has been built in 2006. It has been extensively tested and analyzed during the following two years. This paper shows how the experimental results obtained with the prototype were used to engineer the final design. It highlights how the engineering solutions implemented not only improved the isolation performance but also greatly simplified the assembly, testing, and commissioning process. During the past two years, five units have been constructed, tested, installed and commissioned at each of the two LIGO observatories. Five other units are being built for an upcoming third observatory. The test results presented show that the system meets the motion requirements, and reach the sensor noise in the control bandwidth.

The performance of the EPA Federal Equivalent Method (FEM) technique for monitoring ambient concentrations of O3 via ultraviolet absorption (UV) has been evaluated using data from the Mexico City Metropolitan Area field campaign (MCMA-2003). Comparisons of UV O3 monitors with open path Differential Optical Absorption Spectroscopy (DOAS) and open path Fourier Transform Infrared (FTIR) spectroscopy instruments in two locations revealed average discrepancies in the measured concentrations between +13% to −18%. Good agreement of two separate open path DOAS measurements at one location indicated that spatial and temporal inhomogeneities were not substantially influencing comparisons of the point sampling and open path instruments. The poor agreement between the UV O3 monitors and the open path instruments was attributed to incorrect calibration factors for the UV monitors, although interferences could not be completely ruled out. Applying a linear correction to these calibration factors results in excellent agreement of the UV O3 monitors with the co-located open path measurements; regression slopes of 0.94 to 1.04 and associated R2 values of >0.89. A third UV O3 monitor suffered from large spurious interferences, which were attributed to extinction of UV radiation within the monitor by fine particles (

A proton transfer reaction mass spectrometer (PTR-MS) was redesigned and deployed to monitor selected hydrocarbon emissions from in-use vehicles as part of the Mexico City Metropolitan Area (MCMA) 2003 field campaign. This modified PTR-MS instrument provides the necessary time response (

In a densely populated section of Mexico City, an eddy covariance (EC) flux system was deployed on a tall urban tower to obtain direct measurements of CO 2 emissions from an urban neighborhood located in a subtropical megacity. The measured fluxes and boundary layer conditions satisfy EC assumptions of stationarity, and cospectral analyses of the turbulence measurements exhibit the required boundary layer patterns for acceptable flux measurements. Results from a field experiment conducted during April 2003 show that the urban surface is a net source of CO 2 . The CO 2 flux measurements showed a clear diurnal pattern, with the highest emissions during the morning (up to 1.60 mg m −2 s −1 ), and the lowest emissions during nighttime. The measured fluxes were closely correlated to traffic patterns in the area. The mean daily flux was 0.41 mg m −2 s −1 , which is similar to that observed in European and US cities.

Atmospheric tracer release techniques have been used to quantify low-level fugitive methane emissions from components and facilities in all sectors of the natural gas system in the United States. The emission data are collected as part of a program to extrapolate the emissions from the entire U.S. natural gas industry and thus reduce uncertainties in the environmental impact of increased natural gas use. In these experiments, the total methane emission from a site is measured by releasing a tracer gas (SF6) at the natural gas facility to simulate the source. Both methane and tracer levels are measured with real-time instruments deployed in a mobile laboratory downwind of the site. A large range of emission levels for the different sectors of the entire system was determined. Within any one group of a particular facility type there is also much variability in the emission rates. The exact nature and number of gas system components in a facility are important factors in determining its emission level.

In this work, stationary and mobile point source tracer release techniques have been used to determine PM10 emission rates from four-lane commercial/residential paved roads under sanded and unsanded conditions, and from unpaved roads relative to site-specific vehicular and ambient parameters. Measured street (4 + lanes; ⩾ 10,000 vehicles per day) emission factors for unsanded and sanded roads were 40 and 20% lower, respectively, than the EPA approved reference value. The sanded road emission factor was approximately 40% higher than that for the unsanded road. These results indicate a consistent relationship between PM10 and relative humidity under unsanded conditions. There is some evidence to suggest that street sweeping has a measurable effect on PM,, emission reduction during periods of low relative humidity (i.e. ⩽ 30%). Within the constraints imposed by the variable experimental conditions, the emission factors determined for unpaved roads agreed reasonably well with the unpaved road empirical formula. Limited correlations were observed with ambient meteorological parameters. The capability of the “upwind-dowiawind” concentration modeling method to predict accurate emission was tested using a Gaussian dispersion model (SIMFLUX). Predictions agreed well with the experimentally determined emission factors.

During the summer of 1992, isoprene emissions were measured in a mixed deciduous forest near Oak Ridge, Tennessee. Measurements were aimed at the experimental scale-up of emissions from the leaf level to the forest canopy to the mixed layer. Results from the scale-up study are compared to different canopy models for determining the leaf microclimate as input to isoprene emission algorithms. These include (1) no canopy effects, (2) a simple vertical scaling canopy model with a leaf energy balance, and (3) a numerical canopy model which accounts for leaf-sun geometries, photosynthesis, respiration, transpiration, and gas transport in the canopy. Initial evaluation of the models was based upon a standard emission rate factor of 90 μgC g-1 hr-1 (0.42 nmol g-1 s-1) taken from leaf cuvette measurements and a biomass density factor of 203 g m-2 taken from biomass surveys and a flux footprint analysis. The results indicated that predicted fluxes were consistent among the models to within approximately ±20%, but that the models overestimated the mean flux by about a factor of 2 and overestimated the maximum observed flux by 30 to 50%. Adjusting the standard emission factor and biomass density each downward by 20% yielded predicted means approximately 20% greater than the observed means and predicted maxima approximately 25% less than the observed maxima. Accounting for changes in biomass density as a function of direction upwind of the tower improved the overall model performance.

Methane (CH4) emissions were measured from the Nashua, New Hampshire municipal landfill using static enclosure and atmospheric tracer methods. The spatial variability of emissions was also examined using geostatistical methods. One hundred and thirty nine enclosure measurements were performed on a regular grid pattern over the emitting surface of the landfill resulting in an estimate of whole landfill emissions of 15,800 L CH4 min−1. Omnidirectional variograms displayed spatial correlation among CH4 fluxes below a separation distance of 7 m. Eleven tracer tests, using sulfur hexafluoride (SF6) as a tracer gas, resulted in a mean emissions estimate of 17,750 L CH4 min−1. The favorable agreement between the emission estimates was further refined using the observed relationship between atmospheric pressure and CH4 flux. This resulted in a pressure-corrected tracer flux estimate of whole landfill emissions of 16,740 L CH4 min−1.

We have investigated methane emissions from urban sources in the former East Germany using innovative measurement techniques including a mobile real-time methane instrument and tracer release experiments. Anthropogenic and biogenic sources were studied with the emphasis on methane emissions from gas system sources, including urban distribution facilities and a production plant. Methane fluxes from pressure regulating stations ranged from 0.006 to 24. l/min. Emissions from diffuse sources in urban areas were also measured with concentration maps and whole city flux experiments. The area fluxes of the two towns studied were 0.37 and 1.9 μg/m2/s. The emissions from individual gas system stations and total town emissions of this study are comparable to results of similar sites examined in the United States.

Field measurements of methane emissions from landfills are essential if one is to accurately constrain uncertainties in current estimates of global methane emissions from landfills and document emissions reductions realized by currently available control technology. Two experimental techniques for the measurement of methane flux from landfills, flux chamber measurements and tracer flux techniques, have been evaluated at a 24 hectare landfill site in New England. Agreement between the two techniques was quite good, with the flux chamber technique giving a landfill wide methane flux of 16.4 m 3 CH 4 min -1 while a series of seven tracer flux tests resulted in a mean flux of 17.8 m 3 CH 4 min -1 . Model estimates suggest that the installation of gas recovery measures at the five largest landfill sites in the state of New Hampshire and the ten largest sites in Massachusetts would reduce landfill emissions in each state by approximately 75%, resulting in a total emissions reduction of 65 x 10 9 g CH 4 /yr.

Isoprene emission rates from Engelmann ( Picea engelmannii ), red ( Picea rubens ), and black ( Picea mariana ) spruce were measured from groups of seedlings in a controlled environmental chamber. Standard isoprene emission rate factors, obtained from measurements over an array of light and temperature conditions, ranged from 1 to 16 μgCg −1 h −1 at 30°C and 1000 μmolm −2 s −1 photosynthetically active radiation. Emission measurements were also collected using a dynamic enclosure technique from branches of a mature white spruce ( Picea glauca ) through a complete growing season. These data indicate that isoprene emissions, normalized to standard conditions, are moderate in spring and fall (∼ 7 μgC g −1 h −1 at 30°C, 1000 μmol m −2 s −1 ) with a maximum in mid-summer (∼ 12 μgCg −1 h −1 at 30°C, 1000 μmolm −2 s −1 ) Isoprene from white spruce represented more than 90% of the total identified hydrocarbons. Branch enclosure measurements from limited survey samples for blue spruce ( Picea pungens ) yielded a standard emission rate of 12 μgC g −1 h −1 while samples for Norway spruce ( Picea abies ) indicated very little isoprene emitted ( −1 h −1 ). The wide range of isoprene emissions from these different spruce species suggest that improvements in hydrocarbon emission inventories may require detailed species distribution data. On a regional basis, this may be especially true in Europe where 22% of isoprene emissions are estimated to be from spruce and in boreal regions where spruce is a dominant part of the ecosystem.

The Canopy Horizontal Array Turbulence Study (CHATS) took place in spring 2007 and is the third in the series of Horizontal Array Turbulence Study (HATS) experiments. The HATS experiments have been instrumental in testing and developing subfilterscale (SFS) models for large-eddy simulation (LES) of planetary boundary layer (PBL) turbulence. The CHATS campaign took place in a deciduous walnut orchard near Dixon, California, and was designed to examine the impacts of vegetation on SFS turbulence. Measurements were collected both prior to and following leafout to capture the impact of leaves on the turbulence, stratification, and scalar source/sink distribution. CHATS utilized crosswind arrays of fast-response instrumentation to investigate the impact of the canopy-imposed distribution of momentum extraction and scalar sources on SFS transport of momentum, energy, and three scalars. To directly test and link with PBL parameterizations of canopy-modified turbulent exchange, CHATS also included a 30-m profile tower instrumented with turbulence instrumentation, fast and slow chemical sensors, aerosol samplers, and radiation instrumentation. A highresolution scanning backscatter lidar characterized the turbulence structure above and within the canopy; a scanning Doppler lidar, mini sodar/radio acoustic sounding system (RASS), and a new helicopter-observing platform provided details of the PBL-scale flow. Ultimately, the CHATS dataset will lead to improved parameterizations of energy and scalar transport to and from vegetation, which are a critical component of global and regional land, atmosphere, and chemical models. This manuscript presents an overview of the experiment, documents the regime sampled, and highlights some preliminary key findings.

Eddy covariance (EC) flux measurements of the atmosphere/surface exchange of gases over an urban area are a direct way to improve and evaluate emissions inventories, and, in turn, to better understand urban atmospheric chemistry and the role that cities play in regional and global chemical cycles. As part of the MCMA-2003 study, we demonstrated the feasibility of using eddy covariance techniques to measure fluxes of selected volatile organic compounds (VOCs) and CO2 [CO subscript 2] from a residential district of Mexico City (Velasco et al., 2005a, b). During the MILAGRO/MCMA-2006 field campaign, a second flux measurement study was conducted in a different district of Mexico City to corroborate the 2003 flux measurements, to expand the number of species measured, and to obtain additional data for evaluation of the local emissions inventory. Fluxes of CO2 [CO subscript 2] and olefins were measured by the conventional EC technique using an open path CO2 [CO subscript 2] sensor and a Fast Isoprene Sensor calibrated with a propylene standard. In addition, fluxes of toluene, benzene, methanol and C2-benzenes [C subscript 2 - benzenes] were measured using a virtual disjunct EC method with a Proton Transfer Reaction Mass Spectrometer. The flux measurements were analyzed in terms of diurnal patterns and vehicular activity and were compared with the most recent gridded emissions inventory. In both studies, the results showed that the urban surface of Mexico City is a net source of CO2 [CO subscript 2] and VOCs with significant contributions from vehicular traffic. Evaporative emissions from commercial and other anthropogenic activities were significant sources of toluene and methanol. The data show that the emissions inventory is in reasonable agreement with measured olefin and CO2 [CO subscript 2] fluxes, while C2-benzenes [C subscript 2 - benzenes] and toluene emissions from evaporative sources are overestimated in the inventory. It appears that methanol emissions from mobile sources occur, but are not present in the mobile emissions inventory., National Science Foundation (U.S.) (Grant ATM-0528227), United States. Dept. of Energy (Award DE-FG02-05ER63980), Mexico. Comisión Ambiental Metropolitana, Molina Center for Energy and the Environment

The concept of disjunct eddy sampling (DES) for use in measuring ecosystem-level micrometeorological fluxes is re-examined. The governing equations are discussed as well as other practical considerations and guidelines concerning this sampling method as it is applied to either the disjunct eddy covariance (DEC) or disjunct eddy accumulation (DEA) techniques. A disjunct eddy sampling system was constructed that could either be combined with relatively slow sensors (response time of 2 to 40 s) to measure fluxes using DEC, or could also be used to accumulate samples in stable reservoirs for later laboratory analysis (DEA technique). Both the DEC and DEA modes of this sampler were tested against conventional eddy covariance (EC) for fluxes of either CO2 (DEC) or isoprene (DEA). Good agreement in both modes was observed relative to the EC systems. However, the uncertainty in a single DEA flux measurement was considerable (~40%) due to both the reduced statistical sampling and the analytical precision of the concentration difference measurements. We have also re-investigated the effects of nonzero mean vertical wind velocity on accumulation techniques as it relates to our DEA measurements. Despite the higher uncertainty, disjunct eddy sampling can provide an alternative technique to eddy covariance for determining ecosystem-level fluxes for species where fast sensors do not currently exist.

Ambient concentrations of isoprene and several of its atmospheric oxidation productsmethacrolein, methylvinyl ketone, formaldehyde, formic acid, acetic acid, and pyruvic acid-were measured in a central Pennsylvania deciduous forest during the summer of 1988. Isoprene concentrations ranged from near zero at night to levels in excess of 30 ppbv during daylight hours. During fair weather periods, midday isoprene levels normally fell in the 5–10 ppbv range. Methacrolein and methylvinyl ketone levels ranged from less than 0.5 ppbv to greater than 3 ppbv with average midday concentrations in the 1 to 2 ppbv range. The diurnal behavior of formaldehyde paralleled that of isoprene with ambient concentrations lowest (∼1 ppbv) in the predawn hours and highest (>9.0 ppbv) during the afternoon. The organic acids peaked during the midday period with average ambient concentration of 2.5, 2.0, and 0.05 ppbv for formic, acetic, and pyruvic acid, respectively. These data indicate that oxygenated organics comprise a large fraction of the total volatile organic carbon containing species present in rural, forested regions of the eastern United States. Consequently, these compounds need to be included in photochemical models that attempt to simulate oxidant behavior and/or atmospheric acidity in these forested regions.

An infrared video camera and recording system were used to record near source plume rise from a low turbine stack at an oil gathering center at Prudhoe Bay, AK. The system provided real-time, continuous visualization of the plume using a color monitor while the images were recorded with a standard video tape recorder. Following the field study, single frame images were digitized using a micro-computer video system. As part of the digitization, the plume centerline was determined as well as an isotherm of the plume outline. In this application, one frame from each 2-rain period in the record was digitized. The results were used to calculate the variability in plume centerline during each hour. During strong winds with blowing snow, the mean plume rise for the hour at 15 m downwind was 6 + 2 m. The observed plume rise from the turbine stack was greater than that calculated using momentum-only or buoyancy-only plume rise models and only slightly larger than that estimated from combined momentum-buoyancy plume rise models.

Measurements of velocity and tracer plume concentrations during stable atmospheric conditions were obtained in the Boise River Valley as part of the EPA Integrated Air Cancer Project during December, 1986. Wind speed, temperature, and wind direction were measured at two levels on a 30 m tower. Spectral and autocorrelation analyses of the velocity component data clearly indicate the occurrence of wave-like oscillations in the flow and the almost complete lack of turbulent energy. The predominate wave-like motion had an oscillation period of about 1000 s. Halogenated atmospheric tracers were released from as many as four houses during the night-time drainage conditions. Hourly averaged horizontal dispersion coefficients were very large compared to the Pasquill-Gifford curves and the urban McElroy-Pooler dispersion curves. The time-averaged dispersion coefficients formed an upper bound on very short-term dispersion coefficients obtained from mobile traverses of the tracer plume with a continuous SF 6 analyzer. These results agree with the concept of a narrow instantaneous plume with a broad meander driven by the observed 1000 s oscillation. Vertical dispersion rates were slightly smaller than the Pasquill-Gifford class F curve. Results from a single tracer release from a side canyon near the neighborhood showed that drainage flow from the tributary impacted the main residential sampling site at Elm Grove Park and represented a significant fraction of the upstream air flow at Elm Grove Park. For sources with equal emission rates, a source in the tributary adds about 10% to the mean of the concentration caused by a neighborhood source.

[1] Direct measurements of volatile organic compound (VOC) emissions that include all sources in urban areas are a missing requirement to evaluate emission inventories and constrain current photochemical modelling practices. Here we demonstrate the use of micrometeorological techniques coupled with fast-response sensors to measure urban VOC fluxes from a neighbourhood of Mexico City, where the spatial variability of surface cover and roughness is high. Fluxes of olefins, methanol, acetone, toluene and C2-benzenes were measured and compared with the local gridded emissions inventory. VOC fluxes exhibited a clear diurnal pattern with a strong relationship to vehicular traffic. Recent photochemical modelling results suggest that VOC emissions are significantly underestimated in Mexico City, but for the olefin class, toluene, C2-benzenes, and acetone fluxes measured in this work, the results show general agreement with the gridded emissions inventory. While these measurements do not address the full suite of VOC emissions, the comparison with the inventory suggests that other explanations may be needed to explain the photochemical modelling results.

Measurements of natural hydrocarbon emission rates are reported for an old-growth Pacific Northwest coniferous forest. The emission data were collected for the two dominant species Douglas-fir (Pseudotsuga menziesii) and western hemlock (Tsuga heterophylla) during the growing season in 1997 and 1998 using branch enclosure techniques. Samples were collected at different heights from 13 to 51 m within the canopy using the Wind River Canopy Crane facility. The standard emission factor at a temperature of 30°C and the temperature coefficient for Douglas-fir is Es=0.39±0.14 μg C g−1 h−1 and β=0.14±0.05°C−1 and for western hemlock Es=0.95±0.17 μg C g−1 h−1 and β=0.06±0.02°C−1. There was considerable variability among all the emission factors due to seasonal and branch-to-branch variations. Within season emission factors appear to decline from May to September for the Douglas-fir, although there was no corresponding decrease for the western hemlock. There was no significant difference in standard emission factors (Es) or temperature coefficients as a function of sunlit versus shady growth environment (different heights) for Douglas-fir, but western hemlock emission samples collected low in the canopy showed no exponential correlation with temperature. Applying the standard emission factors from this study to a Pacific Northwest domain and comparing the modified emission inventory to the current regulatory-based emission inventory yielded a net decrease of 19% in the domain wide monoterpene emissions. The relatively small difference in biogenic emissions is slightly misleading, as the difference in standard emission rates between this study and current regulatory rates is quite significant, and they offset each other when combined in this domain. When this inventory was input into a regional photochemical air quality simulation using the MM5/CMAQ system, the reduction in biogenic emissions resulted in an insignificant decrease of O3 and a significant decrease in the secondary organic aerosol (domain wide −20%). The emission measurements reported here represent one of the first extensive data sets for an old-growth forest, where sampling conditions are limited to in situ enclosure techniques within the tall, elevated canopy.

Landfills are the largest source of anthropogenic methane (CH4) emissions to the atmosphere in the United States. However, few measurements of whole landfill CH4 emissions have been reported. Here, we present the results of a multi-season study of whole landfill CH4 emissions using atmospheric tracer methods at the Nashua, New Hampshire Municipal landfill in the northeastern United States. The measurement data include 12 individual emission tests, each test consisting of 5-8 plume measurements. Measured emissions were negatively correlated with surface atmospheric pressure and ranged from 7.3 to 26.5 m3 CH4 min(-1). A simple regression model of our results was used to calculate an annual emission rate of 8.4 x 10(6) m3 CH4 year(-1). These data, along with CH4 oxidation estimates based on emitted landfill gas isotopic characteristics and gas collection data, were used to estimate annual CH4 generation at this landfill. A reported gas collection rate of 7.1 x 10(6) m3 CH4 year(-1) and an estimated annual rate of CH4 oxidation by cover soils of 1.2 x 10(6) m3 CH4 year(-1) resulted in a calculated annual CH4 generation rate of 16.7 x 10(6) m3 CH4 year(-1). These results underscore the necessity of understanding a landfill's dynamic environment before assessing long-term emissions potential.

Isoprene fluxes were estimated using eight different measurement techniques at a forested site near Oak Ridge, Tennessee, during July and August 1992. Fluxes from individual leaves and entire branches were estimated with four enclosure systems, including one system that controls leaf temperature and light. Variations in isoprene emission with changes in light, temperature, and canopy depth were investigated with leaf enclosure measurements. Representative emission rates for the dominant vegetation in the region were determined with branch enclosure measurements. Species from six tree genera had negligible isoprene emissions, while significant emissions were observed for Quercus, Liquidambar, and Nyssa species. Above-canopy isoprene fluxes were estimated with surface layer gradients and relaxed eddy accumulation measurements from a 44-m tower. Midday net emission fluxes from the canopy were typically 3 to 5 mg C m−2 h−1, although net isoprene deposition fluxes of −0.2 to −2 mg C m−2 h−1 were occasionally observed in early morning and late afternoon. Above-canopy CO2 fluxes estimated by eddy correlation using either an open path sensor or a closed path sensor agreed within ±5%. Relaxed eddy accumulation estimates of CO2 fluxes were within 15% of the eddy correlation estimates. Daytime isoprene mixing ratios in the mixed layer were investigated with a tethered balloon sampling system and ranged from 0.2 to 5 ppbv, averaging 0.8 ppbv. The isoprene mixing ratios in the mixed layer above the forested landscape were used to estimate isoprene fluxes of 2 to 8 mg C m−2 h−1 with mixed layer gradient and mixed layer mass balance techniques. Total foliar density and dominant tree species composition for an approximately 8100 km2 region were estimated using high-resolution (30 m) satellite data with classifications supervised by ground measurements. A biogenic isoprene emission model used to compare flux measurements, ranging from leaf scale (10 cm2) to landscape scale (102 km2), indicated agreement to within ±25%, the uncertainty associated with these measurement techniques. Existing biogenic emission models use isoprene emission rate capacities that range from 14.7 to 70 μg C g−1 h−1 (leaf temperature of 30°C and photosynthetically active radiation of 1000 μmol m−2 s−1) for oak foliage. An isoprene emission rate capacity of 100 μg C g−1 h−1 for oaks in this region is more realistic and is recommended, based on these measurements.

Environ. Sci. Techno/. 1995, 29, 1468-1 479 Introduction Tracer -Methods To Measure Downloaded by UNIV OF CALIFORNIA IRVINE on August 26, 2015 | http://pubs.acs.org Publication Date: June 1, 1995 | doi: 10.1021/es00006a007 Gas Faciliies and U h n Areas BRIAN K. LAMB,*,’ J. BARRY MCMANUS,* JOANNE H. SHORTER,* CHARLES E . KOLB,* BYARD MOSHER,$ R O B E R T C . HARRISS,§ EUGENE ALLWINE,’ DENISE BLAHA,$ T O U C H E H O W A R D , ” A L E X GUENTHER,l ROBERT A. LOTT,A ROBERT SIVERSON,’ HAL WESTBERG,’ AND PAT ZIMMERMAN- Laboratory for Atmospheric Research, Department of Civil & Environmental Engineering, Washington State University, Pullman, WA 99164-2910, Center for Chemical and Environmental Physics, Aerodyne Research, Inc., Billerica, Massachusetts 01821, Institute for the Study of Earth, Oceans and Space, University of New Hampshire, Durham, New Hampshire 03824, Indaco Air Quality Services, Inc., Pullman, Washington 99163, National Center for Atmospheric Research, Boulder, Colorado 80303, and Gas Research Institute, Chicago, Illinois 60631 -3562 A new, integrated methodologyto locate and measure methane emissions from natural gas systems has been developed. Atmospheric methane sources are identified by elevated ambient CH4 concentrations measured with a mobile laser-based methane analyzer. The total methane emission rate from a source is obtained by simulating the source with a sulfur hexafluoride (SFS) tracer gas release and by measuring methane and tracer concentrations along downwind sampling paths using mobile, real-time analyzers. Combustion sources of methane are dis- tinguished from noncombustion sources by concur- rent ambient carbon dioxide measurements. Three variations on the tracer ratio method are described for application to (1) small underground vaults, (2) above- ground natural gas facilities, and (3) diffuse methane emissions from an entire town. Results from controlled releases and from replicate tests demonstrate thatthe tracer ratio approach can yield total emission rates to within approximately &15%. The estimated accuracy of emission estimates for urban areas with a variety of diffuse emissions is &50%. Methane (CH4) has been a contributor to the increasing burden of greenhouse gases in the earth’s atmosphere for more than a century (1). Faced with significant risks identified in scenarios of increasing greenhouse gas con- centrations, many countries are developing plans to reduce emissions. However, uncertainties in specific source emission rates for CH4 and other non-COz greenhouse gases currently limit the quantitative risk-benefit analysis needed to answer key policy questions related to the socioeconomic impacts of large-scale mitigation actions (2, 3 ) . Initial attempts to estimate CH4 losses to the atmosphere from natural gas production and use assumed that emis- sions could be approximated by industry reports of “unac- counted for” gas (e.g., ref 4). Unaccounted for gas, defined as the difference between the amount of natural gas metered into a system and the amount of gas metered out of a system, does not account for gas losses from wells to the processing plant, gas used as fuel in facilities, theft of gas, meter inaccuracies, and differences in accounting procedures between companies (4,5). Thus, the unaccounted for gas estimates cannot unambiguously be considered an upper or lower bound on emissions (5). Extrapolation of engi- neering estimates or data obtained from component by component sniffing methods also leads to large uncertain- ties in estimated emissions. In the United Kingdom, the British Gas Company estimates CH4 emissions from gas distribution system components to be less than 1% of throughput, while others estimate losses as high as 11% of gas throughput (6). A recent estimate of CH4 leakage from the natural gas system in the former Soviet Union, which was characterized as “tentative and highly conditional” suggested a range of total losses from 3.3% to 7% of gas production ( 7 ) . The U.S. Environmental Protection Agency (EPA) and the Gas Research Institute (GRI) have recently sponsored an integrated field measurement and analysis program to better define methane emissions from the U.S. natural gas system. Drawing on initial measurements using some of the techniques reported here as weil as engineering estimates, GRI has developed a preliminary estimate of methane emissions from the gas industry that equals approximately 1.5 i 0.5% of annual throughput (8). In the case of CH4 emissions due to the use of natural gas, there is an added motivation for correctly prescribing the methane source strength. Since natural gas typically produces 32-45% less COz per unit of thermal output compared to coal and 30% less compared to fuel oil, switching from coal and fuel oil to natural gas has the potential to reduce carbon dioxide emissions and reduce global warming (5). However, CH4 is a more potent greenhouse gas than CO2 on a molecule for molecule basis (9- 1 I). As a result, increasing the usage of natural gas may * To whom correspondence should be addressed: e-mail address: blamb@wsu.edu. + Washington State University. Aerodyne Research, Inc. 5 University of New Hampshire. I’ Indaco Air Quality Services, Inc. National Center for Atmospheric Research. A Gas Research Institute. 1468 ENVIRONMENTAL SCIENCE &TECHNOLOGY / VOL. 29, NO. 6, 1995 0013-936)(/95/0929-1468$09.00/0 @ 1995 American Chemical Society

We recently have conducted measurements of distributions and fluxes of methane in several small towns in the U.S. These measurements are made with a real-time methane instrument recently developed at Aerodyne Research. This instrument is based on absorption of infrared light from a Zeeman-broadened HeNe laser operating at 3.39 micrometers . A non-uniform magnetic field applied to the laser plasma results in a nearly flat gain profile, which allows piezoelectric tuning of the laser on and off a methane line. Long path (47 m) absorption occurs in a multipass cell. The instrument has a noise level of 5 ppbv (rms, 1 sec.) and a gas sampling time of 6 sec. The instrument is mounted in a van with a suite of other real-time instruments (CO2 and SF6) which can function while moving at roadway speeds. We map the methane distribution in towns, identify the primary methane sources, and measure fluxes with tracer methods. The simultaneous measurement of CO2 with a commercially available NDIR device is useful in identifying some sources of methane. An SF6 instrument (electron capture) allows precise location and measurement of tracer plumes during flux measurement experiments.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

AtlftOspheric Environment Vol. 24A, No. 9, pp. 2329- 2347, 1990. Printed in -Great Britain. Pergamon Press pie BUILDING WAKE DISPERSION AT AN ARCTIC INDUSTRIAL SITE: FIELD TRACER OBSERVATIONS AND PLUME MODEL EVALUATIONS ALEX GUENTHER, BRIAN LAMB* and EUGENE ALLWINE Laboratory for Atmospheric R~search, Department of Civil & Environmental Engineering, Washington State University, Pullman, WA 99164-2910, U.S.A. (First received 8 June 1989 and in final form 21 February 1990) Abstract-Ten multi-hour atmospheric dispersion SF 6 tracer experiments were conducted during October and November of 1987 near a large oil gathering facility in the Prudhoe Bay, Alaska, oilfield reservation. The purpose of this study was to investigate dispersion under arctic conditions and in situations where building- generated airflow disturbances dominate downwind distributions of ground level pollutant concentrations. This was accomplished with a network of micrometeorological instruments, portable syringe tracer samplers, continuous tracer analyzers, and infrared visualization of near source plume behavior. Atmospheric stability and wind speed profiles at this arctic site are influenced by the smooth (surface roughness=0.03 cm), snow covered tundra surface which receives negligible levels of solar isolation in winter. The dispersion of pollutants emitted from sources within the oil gathering facility, however, is dominated by the influence of nearby buildings when high winds generate elevated ground level concentrations. An order of magnitude increase in maximum ground level concentration was observed as wind speeds increased from 5 to 8 ms - 1 and another order of magnitude increase was observed as winds increased from 8 to 16ms - 1 . Variation in maximum concentrations was also observed with changes in wind direction. Vertical plume diffusion (a,) near the buildings was a factor of 2-3 greater than that observed in open terrain and was dependent on both wind speed and the projected building width and location of nearby buildings. Wind tunnel tracer distributions for east winds agree with field observations but also indicate that a significant increase in plume downwash occurs with other wind directions. Concentration distributions were calculated using several versions of the Industrial Source Complex (ISC) model. Model estimates of ground level concentrations were within a factor of three depending on wind direction. The model predictions are extremely sensitive to the ratio of plume height to vertical plume diffusion which is significantly influenced by a complex aerodynamic wake in the field. Key word index : Arctic, dispersion, tracer, downwash, buildings, plume rise, ISC. 1. INTRODUCTION The development and evaluation of air quality modeling techniques have greatly benefited from transport and diffusion field studies. These include early experiments using smoke visualization techni- ques (Richardson, 1920); the classical large scale, open terrain diffusion experiments such as Project Prairie Grass (Haugen, 1959) which provide the empirical basis for the Pasquill-Gifford (PG) curves used in current regulatory air quality models; and more recent investigations of sites and conditions which deviate from the relatively simple dispersion environment of earlier experiments. In this paper we present the results of a field tracer investigation of plume trans- port and diffusion near the clustered and intercon- nected buildings of an arctic industrial complex. The natural gas compressor turbine which was the focus of this field study is typical of the major NOx sources in the Prudhoe Bay, Alaska, oilfields. Accurate simu- *To whom correspondence should be addressed. lation of pollutant dispersion from existing sources will aid in determining the present air quality within this tundra ecosystem and is needed for predicting the impacts of future development within potential oil- fields along the Alaska coast. We have previously analyzed open terrain micro- meteorological and tracer data collected at Prudhoe Bay to provide a description of the Arctic atmospheric boundary layer (Guenther and Lamb, 1990). Near the oil gathering facilities, building-generated disturban- ces to the flow field around the exhaust stacks signific- antly change dispersion patterns by altering mean airflow streamlines and by increasing turbulence lev- els. Maximum concentrations can increase signific- antly as high winds generate downwash conditions around the low turbine and heater stacks typical of an arctic industrial complex. Field observations of plume behavior from a 35 MHP turbine are described and compared to our analysis of a wind tunnel simulation of the same source and surrounding buildings (Guen- ther et al., 1989). Building downwash, diffusion, and plume rise algorithms in existing Gaussian plume models and cavity wake models are evaluated in this

We explore the variability in monoterpene emissions from ponderosa pine beyond that which can be explained by temperature alone. Specifically, we examine the roles that photosynthesis and needle monoterpene concentrations play in controlling emissions. We measure monoterpene concentrations and emissions, photosynthesis, temperature, and light availability in the late spring and late summer in a ponderosa pine forest in central Oregon. We use a combination of measurements from cuvettes and Teflon bag enclosures to show that photosynthesis is not correlated with emissions in the short term. We also show that needle monoterpene concentrations are highly correlated with emissions for two compounds, alpha-pinene and beta-pinene, but that Delta-carene concentrations are not correlated with emissions. We suggest that direct effects of light and photosynthesis do not need to be included in emission algorithms. Our results indicate that the role of needle concentration bears further investigation; our results for alpha-pinene and beta-pinene are explainable by a Raoult's law relationship, but we cannot yet explain the cause of our results with Delta-carene.