Group Publications
59 Publications
2025
Lemay, Amélie C, Desirée L Plata, and Mark A Zondlo. “Observational Evidence of the Impact of Electric Vehicles on Local Air Quality in the United States.” Environ. Sci. Process. Impacts (2025): n. pag. Print.
Abstract
Replacement of internal combustion engine vehicles with battery electric vehicles (EVs) is expected to impact air quality. Previous projections, often relying on emissions inventories of precursors with high uncertainties, have yielded results that vary by model parameters and assumptions. There remains little empirical investigation of the real-world effects, particularly for the low yet growing levels of electrification in the United States. Here county-level vehicle registrations and measurements from ground-level air monitors from 2018 through 2023 were used to investigate the impacts of EV penetration on annual and seasonal concentrations of criteria air pollutants in the United States. Fixed effects regression analysis revealed that rising EV penetration was associated with reductions in mean annual concentrations of nitrogen oxides (NOx as the sum of NO2 and NO), carbon monoxide (CO), and fine particulate matter (PM2.5) and in mean summer season concentrations of ozone (O3). By contrast, there was a potential increase in sulfur dioxide (SO2). The findings demonstrate empirical improvements in air quality associated with EV adoption yet highlight the risk of a continued reliance on fossil fuels. Strategic policies that support enhanced EV adoption must support commensurate expansion of renewable energy access in order to maximize the air quality benefits of the technology.
Moore, Daniel P et al. “Comprehensive Assessment of the Contribution of Wastewater Treatment to Urban Greenhouse Gas and Ammonia Emissions.” Nature Water (2025): n. pag.
Abstract
Population growth and urbanization are driving the demand for centralized wastewater treatment, a primary source of N2O and CH4 emissions. We have conducted the first comprehensive assessment of CH4, N2O and NH3 emissions across diurnal, day-to-day and seasonal scales at 96 US water resource recovery facilities (WRRFs) that collectively treat 9% of US centralized wastewater. Facility-level emissions were scaled to the national level using a probabilistic approach. Here we show that the measured emissions were 1.9 times higher for N2O (95% confidence interval (CI): 1.3–2.6) and 2.4 times higher for CH4 (CI: 1.9–2.9) than current US inventories. Considering the cumulative climate impacts of CH4 and N2O, the top 10% of emitters contributed 74% of the carbon footprint, with the top half contributing 98%, highlighting priorities for mitigation. Although detected at only a small fraction of facilities, measurements of NH3 emissions (86 kt yr−1 in the USA) suggest WRRFs are an overlooked source of urban NH3. Finally, the contribution of centralized wastewater treatment to global greenhouse gas emissions will increase 2- to 17-fold by 2100 under future scenarios. Overall, greater consideration of wastewater treatment emissions is needed to reach sustainability targets.
2024
Allouche, M. et al. “Estimating Scalar Turbulent Fluxes With Slow-Response Sensors in the Stable Atmospheric Boundary Layer.” Atmospheric Chemistry and Physics 24 (2024): 9697–9711.
Cady-Pereira, K. E. et al. “Validation of MUSES NH$_3$ Observations from AIRS and CrIS Against Aircraft Measurements from DISCOVER-AQ and a Surface Network in the Magic Valley.” Atmospheric Measurement Techniques 17 (2024): 15–36.
Gerges, Firas et al. “Weather and the City: Machine Learning for Predicting and Attributing Fine Scale Air Quality to Meteorological and Urban Determinants.” Environmental Science & Technology 58 (2024): 6313–6325.
Pan, Da et al. “Regime Shift in Secondary Inorganic Aerosol Formation and Nitrogen Deposition in the Rural United States..” Nature Geoscience 17.7 (2024): 617–623.
Abstract
Secondary inorganic aerosols play an important role in air pollution and climate change, and their formation modulates the atmospheric deposition of reactive nitrogen (including oxidized and reduced nitrogen), thus impacting the nitrogen cycle. Large-scale and long-term analyses of secondary inorganic aerosol formation based on model simulations have substantial uncertainties. Here we improve constraints on secondary inorganic aerosol formation using decade-long in situ observations of aerosol composition and gaseous precursors from multiple monitoring networks across the United States. We reveal a shift in the secondary inorganic aerosol formation regime in the rural United States between 2011 and 2020, making rural areas less sensitive to changes in ammonia concentrations and shortening the effective atmospheric lifetime of reduced forms of reactive nitrogen. This leads to potential increases in reactive nitrogen deposition near ammonia emission hotspots, with ecosystem impacts warranting further investigation. Ammonia (NH), a critical but not directly regulated precursor of fine particulate matter in the United States, has been increasingly scrutinized to improve air quality. Our findings, however, show that controlling NH became significantly less effective for mitigating fine particulate matter in the rural United States. We highlight the need for more collocated aerosol and precursor observations for better characterization of secondary inorganic aerosols formation in urban areas.
Song, Cuihong et al. “Oversimplication and Misrepresentation of Nitrous Oxide Emissions from Wastewater Treatment Plants.” Nature Sustainability (2024): 1348–1358.
Abstract
Wastewater treatment is a major source of anthropogenic nitrous oxide (N2O) emissions. However, the current emission estimations rely on a uniform emission factor (EF) proposed by the Intergovernmental Panel on Climate Change based on a limited database suffering from large uncertainties and inaccuracies. To address this limitation, this study expands the database 12-fold and develops a tier-based approach. Our method considers emission variations across spatial scales, treatment processes and monitoring techniques, enabling more-precise estimations. Here, applying this approach to the US database, we highlight the limitations of current estimations based on uniform EFs and quantified the mean wastewater N2O emission in the United States to be 11.6 MMT CO2-eq. The results also reveal the diverse nature of wastewater N2O emissions and underscore the need for a customized approach to inform facility-level N2O emission estimation as well as inform national- and sector-wide greenhouse gases inventories with emphasis on site-specific considerations. Overall, this study provides a tool to recalibrate the estimations of wastewater N2O emissions, which form the foundation of carbon footprint reduction in wastewater treatment.
2023
Bertagni, Matteo B. et al. “Minimizing the Impacts of the Ammonia Economy on the Nitrogen Cycle and Climate.” Proceedings of the National Academy of Sciences 120 (2023): e2311728120.
Abstract
The global transition to low-carbon energy necessitates exploring alternatives to fossil fuels. Hydrogen has emerged as a promising option; however, hydrogen storage and transportation challenges have led to considering ammonia as a hydrogen carrier and fuel. This study investigates the potential environmental risks associated with ammonia use in the energy sector. Our findings demonstrate that reactive nitrogen compounds released throughout the ammonia value chain can harm air quality, human health, ecosystems, and climate, and lead to stratospheric ozone depletion. However, we also show that optimal engineering practices and management strategies can effectively mitigate these concerns. Our research contributes to informed decision-making and the development of environmentally responsible ammonia energy systems. Ammonia (NH3) is an attractive low-carbon fuel and hydrogen carrier. However, losses and inefficiencies across the value chain could result in reactive nitrogen emissions (NH3, NOx, and N2O), negatively impacting air quality, the environment, human health, and climate. A relatively robust ammonia economy (30 EJ/y) could perturb the global nitrogen cycle by up to 65 Mt/y with a 5% nitrogen loss rate, equivalent to 50% of the current global perturbation caused by fertilizers. Moreover, the emission rate of nitrous oxide (N2O), a potent greenhouse gas and ozone-depleting molecule, determines whether ammonia combustion has a greenhouse footprint comparable to renewable energy sources or higher than coal (100 to 1,400 gCO2e/kWh). The success of the ammonia economy hence hinges on adopting optimal practices and technologies that minimize reactive nitrogen emissions. We discuss how this constraint should be included in the ongoing broad engineering research to reduce environmental concerns and prevent the lock-in of high-leakage practices.
Moore, Daniel et al. “Underestimation of Sector-Wide Methane Emissions from United States Wastewater Treatment..” Environmental science & technology 57.10 (2023): 4082–4090.
Abstract
An increasing percentage of US waste methane (CH) emissions come from wastewater treatment (10% in 1990 to 14% in 2019), although there are limited measurements across the sector, leading to large uncertainties in current inventories. We conducted the largest study of CH emissions from US wastewater treatment, measuring 63 plants with average daily flows ranging from 4.2 × 10 to 8.5 m s (<0.1 to 193 MGD), totaling 2% of the 62.5 billion gallons treated, nationally. We employed Bayesian inference to quantify facility-integrated emission rates with a mobile laboratory approach (1165 cross-plume transects). The median plant-averaged emission rate was 1.1 g CH s (0.1-21.6 g CH s; 10th/90th percentiles; mean 7.9 g CH s), and the median emission factor was 3.4 × 10 g CH (g influent 5 day biochemical oxygen demand; BOD) [0.6-9.9 × 10 g CH (g BOD); 10th/90th percentiles; mean 5.7 × 10 g CH (g BOD)]. Using a Monte Carlo-based scaling of measured emission factors, emissions from US centrally treated domestic wastewater are 1.9 (95% CI: 1.5-2.4) times greater than the current US EPA inventory (bias of 5.4 MMT CO-eq). With increasing urbanization and centralized treatment, efforts to identify and mitigate CH emissions are needed.
Song, Cuihong et al. “Methane Emissions from Municipal Wastewater Collection and Treatment Systems.” Environmental Science & Technology 57 (2023): 2248–2261.
Soskind, Michael G. et al. “Stationary and Drone-Assisted Methane Plume Localization With Dispersion Spectroscopy.” Remote Sensing of Environment 289 (2023): 113513.
Abstract
This work presents stationary and mobile retroreflector-based remote sensing techniques for methane leak localization and quantification using chirped laser dispersion spectroscopy equipped with a custom laser transceiver capable of continuous tracking of a flying drone and coupled with inverse atmospheric gas dispersion modeling. The techniques demonstrate the ability to localize leaks as low as 0.13 g CH4·s−1, which are up to 25 times smaller than those typically observed at natural gas facilities, as well as actively track a moving retroreflector mounted on a lightweight (∼250 g) drone to enable spatial plume reconstruction. This system exhibited a 2.3 ppm-m sensitivity over pathlengths of 40–150 m. Source localization to within ±7 m is demonstrated using a modified horizontal radial plume mapping technique with a stationary retroreflector grid. Meanwhile, the mobile system utilizing a drone-mounted retroreflector is able to localize a controlled release within ±1 m of its source location and estimate leak rates using inversion techniques assuming type B Gaussian plume stability class within ±30% error with respect to the actual low flow rate releases.
Wang, R. et al. “Bridging the Spatial Gaps of the Ammonia Monitoring Network Using Satellite Ammonia Measurements.” Atmospheric Chemistry and Physics 23 (2023): 13217–13234.
2022
Beale, Christopher A et al. “Large Sub-Regional Differences of Ammonia Seasonal Patterns over India Reveal Inventory Discrepancies.” Environmental Research Letters 17 (2022): 104006.
Abstract
Ammonia (NH3) is a key precursor of haze particles and fine particulate matter (PM2.5) and its spatiotemporal variabilities are poorly constrained. In this study, we present measurements of NH3 over the Indian subcontinent region from the Infrared Atmospheric Sounder Interferometer (IASI) and Cross-track Infrared Sounder (CrIS) satellite instruments. This region exhibits a complex emission profile due to the number of varied sources, including crop burning, fossil fuel combustion, fertilizer application, livestock and industrial sources. Observations from the CrIS and IASI instruments are oversampled to a resolution of 0.02° × 0.02°. Five regions with distinct spatiotemporal NH3 profiles are determined using k-means clustering. Maximum NH3 columns are seen in July over the western India with column densities of 6.2 × 1017 mol cm−2 and 7.2 × 1017 mol cm−2 respectively for IASI and CrIS. The seasonality of measured NH3 columns show annual maxima occurring in spring in Eastern India and Bangladesh and in mid-summer for the western Indo-Gangetic plain. Our observational constraints suggest that the impact of local farming practices on NH3 emissions is not well captured in emission inventories such as Coupled Model Intercomparison Project Phase 6 (CMIP6), which exhibits peaks in the late spring and autumn. The spatial variability in the seasonal patterns of NH3 is also not captured by the single emissions profile used in CMIP6 for India. The high-resolution maps obtained from these measurements can be used to improve NH3 emission inventories in order to understand its sources for more accurate predictions of air quality in the Indian subcontinent. Our study points to the need for regionally specific emissions inventories for short-lived species such as NH3 that have heterogeneous emissions profiles due to specific agricultural practices and other emission source characteristics.
Guo, Xuehui et al. “Spatial Heterogeneity of Ammonia Fluxes in a Deciduous Forest and Adjacent Grassland.” Agricultural and Forest Meteorology 326 (2022): 109128.
Abstract
Gas-phase ammonia (NH3), emitted primarily from agriculture, contributes significantly to reactive nitrogen (Nr) deposition. Excess deposition of Nr to the environment causes acidification, eutrophication, and loss of biodiversity. The exchange of NH3 between land and atmosphere is bidirectional and can be highly heterogenous when underlying vegetation and soil characteristics differ. Direct measurements that assess the spatial heterogeneity of NH3 fluxes are lacking. To this end, we developed and deployed two fast-response, quantum cascade laser-based open-path NH3 sensors to quantify NH3 fluxes at a deciduous forest and an adjacent grassland separated by 700 m in North Carolina, United States from August to November, 2017. The sensors achieved 10 Hz precisions of 0.17 ppbv and 0.23 ppbv in the field, respectively. Eddy covariance calculations showed net deposition of NH3 (-7.3 ng NH3-N m−2 s−1) to the forest canopy and emission (3.2 ng NH3-N m−2 s−1) from the grassland. NH3 fluxes at both locations displayed diurnal patterns with absolute magnitudes largest midday and with smaller peaks in the afternoons. Concurrent biogeochemistry data showed over an order of magnitude higher NH3 emission potentials from green vegetation at the grassland compared to the forest, suggesting a possible explanation for the observed flux differences. Back trajectories originating from the site identified the upwind urban area as the main source region of NH3. Our work highlights the fact that adjacent natural ecosystems sharing the same airshed but different vegetation and biogeochemical conditions may differ remarkably in NH3 exchange. Such heterogeneities should be considered when upscaling point measurements, downscaling modeled fluxes, and evaluating Nr deposition for different natural land use types in the same landscape. Additional in-situ flux measurements accompanied by comprehensive biogeochemical and micrometeorological records over longer periods are needed to fully characterize the temporal variabilities and trends of NH3 fluxes and identify the underlying driving factors.
Pan, Da et al. “A New Open-Path Eddy Covariance Method for Nitrous Oxide and Other Trace Gases That Minimizes Temperature Corrections.” Global Change Biology 28 (2022): 1446–1457.
Abstract
Abstract Low-power, open-path gas sensors enable eddy covariance (EC) flux measurements in remote areas without line power. However, open-path flux measurements are sensitive to fluctuations in air temperature, pressure, and humidity. Laser-based, open-path sensors with the needed sensitivity for trace gases like methane (CH4) and nitrous oxide (N2O) are impacted by additional spectroscopic effects. Corrections for these effects, especially those related to temperature fluctuations, often exceed the flux of gases, leading to large uncertainties in the associated fluxes. For example, the density and spectroscopic corrections arising from temperature fluctuations can be one or two orders of magnitude greater than background N2O fluxes. Consequently, measuring background fluxes with laser-based, open-path sensors is extremely challenging, particularly for N2O and gases with similar high-precision requirements. We demonstrate a new laser-based, open-path N2O sensor and a general approach applicable to other gases that minimizes temperature-related corrections for EC flux measurements. The method identifies absorption lines with spectroscopic effects in the opposite direction of density effects from temperature and, thus, density and spectroscopic effects nearly cancel one another. The new open-path N2O sensor was tested at a corn (Zea mays L.) field in Southwestern Michigan, United States. The sensor had an optimal precision of 0.1 ppbv at 10 Hz and power consumption of 50 W. Field trials showed that temperature-related corrections were 6% of density corrections, reducing EC random errors by 20-fold compared to previously examined lines. Measured open-path N2O EC fluxes showed excellent agreement with those made with static chambers (m = 1.0 ± 0.3; r2 = .96). More generally, we identified absorption lines for CO2 and CH4 flux measurements that can reduce the temperature-related corrections by 10–100 times compared to existing open-path sensors. The proposed method provides a new direction for future open-path sensors, facilitating the expansion of accurate EC flux measurements.
2021
Guo, Xuehui et al. “Validation of IASI Satellite Ammonia Observations at the Pixel Scale Using In Situ Vertical Profiles.” Journal of Geophysical Research: Atmospheres 126 (2021): n. pag.
Li, Nathan et al. “Methane Detection Using an Interband-Cascade LED Coupled to a Hollow-Core Fiber.” Optics Express 29 (2021): 7221.
Abstract
Midwave infrared interband-cascade light-emitting devices (ICLEDs) have the potential to improve the selectivity, stability, and sensitivity of low-cost gas sensors. We demonstrate a broadband direct absorption CH 4 sensor with an ICLED coupled to a plastic hollow-core fiber (1 m length, 1500 µm inner diameter). The sensor achieves a 1σ noise equivalent absorption of approximately 0.2 ppmv CH 4 at 1 Hz, while operating at a low drive power of 0.5 mW. A low-cost sub-ppmv CH 4 sensor would make monitoring emissions more affordable and more accessible for many relevant industries, such as the petroleum, agriculture, and waste industries.
Pan, Da et al. “Ammonia Dry Deposition in an Alpine Ecosystem Traced to Agricultural Emission Hotpots.” Environmental Science & Technology 55 (2021): 7776–7785.
Wang, Rui et al. “Monthly Patterns of Ammonia Over the Contiguous United States at 2‐km Resolution.” Geophysical Research Letters 48 (2021): n. pag.
2020
Golston, Levi M. et al. “Variability of Ammonia and Methane Emissions from Animal Feeding Operations in Northeastern Colorado.” Environmental Science & Technology 54 (2020): 11015–11024.
Guo, Yixin et al. “Air Quality, Nitrogen Use Efficiency and Food Security in China Are Improved by Cost-Effective Agricultural Nitrogen Management.” Nature Food 1 (2020): 648–658.
Pan, Da et al. “Methane Emissions from Natural Gas Vehicles in China.” Nature Communications 11 (2020): 4588.
Abstract
Abstract Natural gas vehicles (NGVs) have been promoted in China to mitigate air pollution, yet our measurements and analyses show that NGV growth in China may have significant negative impacts on climate change. We conducted real-world vehicle emission measurements in China and found high methane emissions from heavy-duty NGVs (90% higher than current emission limits). These emissions have been ignored in previous emission estimates, leading to biased results. Applying our observations to life-cycle analyses, we found that switching to NGVs from conventional vehicles in China has led to a net increase in greenhouse gas (GHG) emissions since 2000. With scenario analyses, we also show that the next decade will be critical for China to reverse the trend with the upcoming China VI standard for heavy-duty vehicles. Implementing and enforcing the China VI standard is challenging, and the method demonstrated here can provide critical information regarding the fleet-level CH 4 emissions from NGVs.
2019
Caulton, Dana R. et al. “Importance of Superemitter Natural Gas Well Pads in the Marcellus Shale.” Environmental Science & Technology 53 (2019): 4747–4754.
2018
Caulton, Dana R. et al. “Quantifying Uncertainties from Mobile-Laboratory-Derived Emissions of Well Pads Using Inverse Gaussian Methods.” Atmospheric Chemistry and Physics 18 (2018): 15145–15168.
Abstract
Abstract. Mobile laboratory measurements provide information on the distribution of CH4 emissions from point sources such as oil and gas wells, but uncertainties are poorly constrained or justified. Sources of uncertainty and bias in ground-based Gaussian-derived emissions estimates from a mobile platform were analyzed in a combined field and modeling study. In a field campaign where 1009 natural gas sites in Pennsylvania were sampled, a hierarchical measurement strategy was implemented with increasing complexity. Of these sites, ∼ 93 % were sampled with an average of 2 transects in < 5 min (standard sampling), ∼ 5 % were sampled with an average of 10 transects in < 15 min (replicate sampling) and ∼ 2 % were sampled with an average of 20 transects in 15–60 min. For sites sampled with 20 transects, a tower was simultaneously deployed to measure high-frequency meteorological data (intensive sampling). Five of the intensive sampling sites were modeled using large eddy simulation (LES) to reproduce CH4 concentrations in a turbulent environment. The LES output and LES-derived emission estimates were used to compare with the results of a standard Gaussian approach. The LES and Gaussian-derived emission rates agreed within a factor of 2 in all except one case; the average difference was 25 %. A controlled release was also used to investigate sources of bias in either technique. The Gaussian method agreed with the release rate more closely than the LES, underlining the importance of inputs as sources of uncertainty for the LES. The LES was also used as a virtual experiment to determine an optimum number of repeat transects and spacing needed to produce representative statistics. Approximately 10 repeat transects spaced at least 1 min apart are required to produce statistics similar to the observed variability over the entire LES simulation period of 30 min. Sources of uncertainty from source location, wind speed, background concentration and atmospheric stability were also analyzed. The largest contribution to the total uncertainty was from atmospheric variability; this is caused by insufficient averaging of turbulent variables in the atmosphere (also known as random errors). Atmospheric variability was quantified by repeat measurements at individual sites under relatively constant conditions. Accurate quantification of atmospheric variability provides a reasonable estimate of the lower bound for emission uncertainty. The uncertainty bounds calculated for this work for sites with > 50 ppb enhancements were 0.05–6.5q (where q is the emission rate) for single-transect sites and 0.5–2.7q for sites with 10+ transects. More transects allow a mean emission rate to be calculated with better precision. It is recommended that future mobile monitoring schemes quantify atmospheric variability, and attempt to minimize it, under representative conditions to accurately estimate emission uncertainty. These recommendations are general to mobile-laboratory-derived emissions from other sources that can be treated as point sources.
Golston, Levi et al. “Natural Gas Fugitive Leak Detection Using an Unmanned Aerial Vehicle: Localization and Quantification of Emission Rate.” Atmosphere 9 (2018): 333.
Abstract
We describe a set of methods for locating and quantifying natural gas leaks using a small unmanned aerial system equipped with a path-integrated methane sensor. The algorithms are developed as part of a system to enable the continuous monitoring of methane, supported by a series of over 200 methane release trials covering 51 release location and flow rate combinations. The system was found throughout the trials to reliably distinguish between cases with and without a methane release down to 2 standard cubic feet per hour (0.011 g/s). Among several methods evaluated for horizontal localization, the location corresponding to the maximum path-integrated methane reading performed best with a mean absolute error of 1.2 m if the results from several flights are spatially averaged. Additionally, a method of rotating the data around the estimated leak location according to the wind is developed, with the leak magnitude calculated from the average crosswind integrated flux in the region near the source location. The system is initially applied at the well pad scale (100–1000 m2 area). Validation of these methods is presented including tests with unknown leak locations. Sources of error, including GPS uncertainty, meteorological variables, data averaging, and flight pattern coverage, are discussed. The techniques described here are important for surveys of small facilities where the scales for dispersion-based approaches are not readily applicable.
Kelly, James T. et al. “Modeling NH $_\textrm4$ NO $_\textrm3$ Over the San Joaquin Valley During the 2013 DISCOVER‐AQ Campaign.” Journal of Geophysical Research: Atmospheres 123 (2018): 4727–4745.
Sun, Kang et al. “A Physics-Based Approach to Oversample Multi-Satellite, Multispecies Observations to a Common Grid.” Atmospheric Measurement Techniques 11 (2018): 6679–6701.
Abstract
Abstract. Satellite remote sensing of the Earth s atmospheric composition usually samples irregularly in space and time, and many applications require spatially and temporally averaging the satellite observations (level 2) to a regular grid (level 3). When averaging level 2 data over a long period to a target level 3 grid that is significantly finer than the sizes of level 2 pixels, this process is referred to as “oversampling”. An agile, physics-based oversampling approach is developed to represent each satellite observation as a sensitivity distribution on the ground, instead of a point or a polygon as assumed in previous methods. This sensitivity distribution can be determined by the spatial response function of each satellite sensor. A generalized 2-D super Gaussian function is proposed to characterize the spatial response functions of both imaging grating spectrometers (e.g., OMI, OMPS, and TROPOMI) and scanning Fourier transform spectrometers (e.g., GOSAT, IASI, and CrIS). Synthetic OMI and IASI observations were generated to compare the errors due to simplifying satellite fields of view (FOVs) as polygons (tessellation error) and the errors due to discretizing the smooth spatial response function on a finite grid (discretization error). The balance between these two error sources depends on the target grid size, the ground size of the FOV, and the smoothness of spatial response functions. Explicit consideration of the spatial response function is favorable for fine-grid oversampling and smoother spatial response. For OMI, it is beneficial to oversample using the spatial response functions for grids finer than ∼16 km. The generalized 2-D super Gaussian function also enables smoothing of the level 3 results by decreasing the shape-determining exponents, which is useful for a high noise level or sparse satellite datasets. This physical oversampling approach is especially advantageous during smaller temporal windows and shows substantially improved visualization of trace gas distribution and local gradients when applied to OMI NO2 products and IASI NH3 products. There is no appreciable difference in the computational time when using the physical oversampling versus other oversampling methods.
Yang, Shuting et al. “Natural Gas Fugitive Leak Detection Using an Unmanned Aerial Vehicle: Measurement System Description and Mass Balance Approach.” Atmosphere 9 (2018): 383.
Abstract
Natural gas is an abundant resource across the United States, of which methane (CH4) is the main component. About 2% of extracted CH4 is lost through leaks. The Remote Methane Leak Detector (RMLD)-Unmanned Aerial Vehicle (UAV) system was developed to investigate natural gas fugitive leaks in this study. The system is composed of three major technologies: miniaturized RMLD (mini-RMLD) based on Backscatter Tunable Diode Laser Absorption Spectroscopy (TDLAS), an autonomous quadrotor UAV and simplified quantification and localization algorithms. With a miniaturized, downward-facing RMLD on a small UAV, the system measures the column-integrated CH4 mixing ratio and can semi-autonomously monitor CH4 leakage from sites associated with natural gas production, providing an advanced capability in detecting leaks at hard-to-access sites compared to traditional manual methods. Automated leak characterization algorithms combined with a wireless data link implement real-time leak quantification and reporting. This study placed particular emphasis on the RMLD-UAV system description and the quantification algorithm development based on a mass balance approach. Early data were gathered to test the prototype system and to evaluate the algorithm performance. The quantification algorithm derived in this study tended to underestimate the gas leak rates and yielded unreliable estimations in detecting leaks under 7 × 10 − 6 m3/s (\textasciitilde1 Standard Cubic Feet per Hour (SCFH)). Zero-leak cases can be ascertained via a skewness indicator, which is unique and promising. The influence of the systematic error was investigated by introducing simulated noises, of which Global Positioning System (GPS) noise presented the greatest impact on leak rate errors. The correlation between estimated leak rates and wind conditions were investigated, and steady winds with higher wind speeds were preferred to get better leak rate estimations, which was accurate to approximately 50% during several field trials. High precision coordinate information from the GPS, accurate wind measurements and preferred wind conditions, appropriate flight strategy and the relative steady survey height of the system are the crucial factors to optimize the leak rate estimations.
2017
Alessandro, John J. D et al. “Dynamical Conditions of Ice Supersaturation and Ice Nucleation in Convective Systems: A Comparative Analysis Between in Situ Aircraft Observations and WRF Simulations: Ice Supersaturation in Convective System.” Journal of Geophysical Research: Atmospheres 122 (2017): 2844–2866.
Clark, Sydney C. et al. “Effluent Gas Flux Characterization During Pyrolysis of Chicken Manure.” ACS Sustainable Chemistry & Engineering 5 (2017): 7568–7575.
Golston, Levi M. et al. “Lightweight Mid-Infrared Methane Sensor for Unmanned Aerial Systems.” Applied Physics B 123 (2017): 170.
Sun, Kang et al. “Vehicle Emissions As an Important Urban Ammonia Source in the United States and China.” Environmental Science & Technology 51 (2017): 2472–2481.
2016
Whitburn, S. et al. “A Flexible and Robust Neural Network IASI‐NH $_\textrm3$ Retrieval Algorithm.” Journal of Geophysical Research: Atmospheres 121 (2016): 6581–6599.
2015
Miller, David J. et al. “Ammonia and Methane Dairy Emission Plumes in the San Joaquin Valley of California from Individual Feedlot to Regional Scales.” Journal of Geophysical Research: Atmospheres 120 (2015): 9718–9738.
Nathan, Brian J. et al. “Near-Field Characterization of Methane Emission Variability from a Compressor Station Using a Model Aircraft.” Environmental Science & Technology 49 (2015): 7896–7903.
Sun, Kang et al. “Validation of TES Ammonia Observations at the Single Pixel Scale in the San Joaquin Valley During DISCOVER-AQ: VALIDATION OF TES AMMONIA IN SJV.” Journal of Geophysical Research: Atmospheres 120 (2015): 5140–5154.
Sun, Kang et al. “Quantifying the Influence of Random Errors in Turbulence Measurements on Scalar Similarity in the Atmospheric Surface Layer.” Boundary-Layer Meteorology 157 (2015): 61–80.
Sun, Kang et al. “Open-Path Eddy Covariance Measurements of Ammonia Fluxes from a Beef Cattle Feedlot.” Agricultural and Forest Meteorology 213 (2015): 193–202.
Tao, Lei et al. “Low-Power, Open-Path Mobile Sensing Platform for High-Resolution Measurements of Greenhouse Gases and Air Pollutants.” Applied Physics B 119 (2015): 153–164.
Wang, Siyuan et al. “Active and Widespread Halogen Chemistry in the Tropical and Subtropical Free Troposphere.” Proceedings of the National Academy of Sciences 112 (2015): 9281–9286.
Abstract
Significance Our measurements show that tropospheric halogen chemistry has a larger capacity to destroy O 3 and oxidize atmospheric mercury than previously recognized. Halogen chemistry is currently missing in most global and climate models, and is effective at removing O 3 at altitudes where intercontinental O 3 transport occurs. It further helps explain the low O 3 levels in preindustrial times. Public health concerns arise from bioaccumulation of the neurotoxin mercury in fish. Our results emphasize that bromine chemistry in the free troposphere oxidizes mercury at a faster rate, and makes water-soluble mercury available for scavenging by thunderstorms. Naturally occurring bromine in air aloft illustrates global interconnectedness between energy choices affecting mercury emissions in developing nations and mercury deposition in, e.g., Nevada, or the southeastern United States. , Halogens in the troposphere are increasingly recognized as playing an important role for atmospheric chemistry, and possibly climate. Bromine and iodine react catalytically to destroy ozone (O 3 ), oxidize mercury, and modify oxidative capacity that is relevant for the lifetime of greenhouse gases. Most of the tropospheric O 3 and methane (CH 4 ) loss occurs at tropical latitudes. Here we report simultaneous measurements of vertical profiles of bromine oxide (BrO) and iodine oxide (IO) in the tropical and subtropical free troposphere (10°N to 40°S), and show that these halogens are responsible for 34% of the column-integrated loss of tropospheric O 3 . The observed BrO concentrations increase strongly with altitude (∼3.4 pptv at 13.5 km), and are 2–4 times higher than predicted in the tropical free troposphere. BrO resembles model predictions more closely in stratospheric air. The largest model low bias is observed in the lower tropical transition layer (TTL) over the tropical eastern Pacific Ocean, and may reflect a missing inorganic bromine source supplying an additional 2.5–6.4 pptv total inorganic bromine (Br y ), or model overestimated Br y wet scavenging. Our results highlight the importance of heterogeneous chemistry on ice clouds, and imply an additional Br y source from the debromination of sea salt residue in the lower TTL. The observed levels of bromine oxidize mercury up to 3.5 times faster than models predict, possibly increasing mercury deposition to the ocean. The halogen-catalyzed loss of tropospheric O 3 needs to be considered when estimating past and future ozone radiative effects.
2014
Diao, Minghui et al. “Hemispheric Comparison of Cirrus Cloud Evolution Using in Situ Measurements in HIAPER Pole-to-Pole Observations: Zondlo et Al.: Cirrus Evolution Between Hemispheres.” Geophysical Research Letters 41 (2014): 4090–4099.
Diao, M. et al. “Cloud-Scale Ice-Supersaturated Regions Spatially Correlate With High Water Vapor Heterogeneities.” Atmospheric Chemistry and Physics 14 (2014): 2639–2656.
Abstract
Abstract. Cirrus clouds have large yet uncertain impacts on Earth s climate. Ice supersaturation (ISS) – where the relative humidity with respect to ice (RHi) is greater than 100% – is the prerequisite condition of ice nucleation. Here we use 1 Hz (\textasciitilde230 m) in situ, aircraft-based observations from 87° N to 67° S to analyze the spatial characteristics of ice-supersaturated regions (ISSRs). The median length of 1-D horizontal ISSR segments is found to be very small (\textasciitilde1 km), which is 2 orders of magnitude smaller than previously reported. To understand the conditions of these small-scale ISSRs, we compare individual ISSRs with their horizontally adjacent subsaturated surroundings and show that 99% and 73% of the ISSRs are moister and colder, respectively. When quantifying the contributions of water vapor (H2O) and temperature (T) individually, the magnitudes of the differences between the maximum RHi values inside ISSRs (RHimax) and the RHi in subsaturated surroundings are largely derived from the H2O spatial variabilities (by 88%) than from those of T (by 9%). These features hold for both ISSRs with and without ice crystals present. Similar analyses for all RHi horizontal variabilities (including ISS and non-ISS) show strong contributions from H2O variabilities at various T, H2O, pressure (P) and various horizontal scales (\textasciitilde1–100 km). Our results provide a new observational constraint on ISSRs on the microscale (\textasciitilde100 m) and point to the importance of understanding how these fine-scale features originate and impact cirrus cloud formation and the RHi field in the upper troposphere (UT).
Homeyer, Cameron R. et al. “Convective Transport of Water Vapor into the Lower Stratosphere Observed During Double-Tropopause Events.” Journal of Geophysical Research: Atmospheres 119 (2014): 10,941–.
Miller, D. J. et al. “Open-Path, Quantum Cascade-Laser-Based Sensor for High-Resolution Atmospheric Ammonia Measurements.” Atmospheric Measurement Techniques 7 (2014): 81–93.
Abstract
Abstract. We demonstrate a compact, open-path, quantum cascade-laser-based atmospheric ammonia sensor operating at 9.06 μm for high-sensitivity, high temporal resolution, ground-based measurements. Atmospheric ammonia (NH3) is a gas-phase precursor to fine particulate matter, with implications for air quality and climate change. Currently, NH3 sensing challenges have led to a lack of widespread in situ measurements. Our open-path sensor configuration minimizes sampling artifacts associated with NH3 surface adsorption onto inlet tubing and reduced pressure sampling cells, as well as condensed-phase partitioning ambiguities. Multi-harmonic wavelength modulation spectroscopy allows for selective and sensitive detection of atmospheric pressure-broadened absorption features. An in-line ethylene reference cell provides real-time calibration (±20% accuracy) and normalization for instrument drift under rapidly changing field conditions. The sensor has a sensitivity and noise-equivalent limit (1σ) of 0.15 ppbv NH3 at 10 Hz, a mass of \textasciitilde 5 kg and consumes \textasciitilde 50 W of electrical power. The total uncertainty in NH3 measurements is 0.20 ppbv NH3 ± 10%, based on a spectroscopic calibration method. Field performance of this open-path NH3 sensor is demonstrated, with 10 Hz time resolution and a large dynamic response for in situ NH3 measurements. This sensor provides the capabilities for improved in situ gas-phase NH3 sensing relevant for emission source characterization and flux measurements.
Sun, Kang et al. “On-Road Ammonia Emissions Characterized by Mobile, Open-Path Measurements.” Environmental Science & Technology 48 (2014): 3943–3950.
2013
Cziczo, Daniel J. et al. “Clarifying the Dominant Sources and Mechanisms of Cirrus Cloud Formation.” Science 340 (2013): 1320–1324.
Abstract
Dusty Origins The formation of cirrus clouds begins with the production of ice nuclei, on which water vapor then condenses. Cziczo et al. (p. 1320 , published online 9 May) determined the kinds of particles on which cirrus ice crystals form by sublimating samples collected by research aircraft and analyzing the chemical and physical properties of the residual seeds. Most of the seed particles were either mineral dust or metallic. , Mineral dust and metallic particles initiate most ice nucleus condensation during cirrus cloud formation. , Formation of cirrus clouds depends on the availability of ice nuclei to begin condensation of atmospheric water vapor. Although it is known that only a small fraction of atmospheric aerosols are efficient ice nuclei, the critical ingredients that make those aerosols so effective have not been established. We have determined in situ the composition of the residual particles within cirrus crystals after the ice was sublimated. Our results demonstrate that mineral dust and metallic particles are the dominant source of residual particles, whereas sulfate and organic particles are underrepresented, and elemental carbon and biological materials are essentially absent. Further, composition analysis combined with relative humidity measurements suggests that heterogeneous freezing was the dominant formation mechanism of these clouds.
Diao, Minghui et al. “Validation of AIRS AMSU-A Water Vapor and Temperature Data With in Situ Aircraft Observations from the Surface to UT LS from 87°N-67°S: GLOBAL AIRS AMSU-A H $_\textrm2$ O AND T VALATIONS.” Journal of Geophysical Research: Atmospheres 118 (2013): 6816–6836.
Diao, Minghui et al. “Evolution of Ice Crystal Regions on the Microscale Based on in Situ Observations.” Geophysical Research Letters 40 (2013): 3473–3478.
Sun, Kang et al. “Inline Multi-Harmonic Calibration Method for Open-Path Atmospheric Ammonia Measurements.” Applied Physics B 110 (2013): 213–222.
2012
Khan, Amir et al. “Low Power Greenhouse Gas Sensors for Unmanned Aerial Vehicles.” Remote Sensing 4 (2012): 1355–1368.