Sheryl H. Ehrman

Production of coal and natural gas is responsible for one third of anthropogenic methane (CH₄) emissions in the United States. Here we examine CH₄ emissions from coal and natural gas production in southwestern Pennsylvania. Using a top‐down methodology combining measurements of CH₄ and ethane, we conclude that while Environmental Protection Agency inventories appear to report emissions from coal accurately, emissions from unconventional natural gas are underreported in the region by a factor of 5 (±3). However, production‐scaled CH₄ emissions from unconventional gas production in the Marcellus remain small compared to other basins due to its large production per well. After normalizing emissions by energy produced, total greenhouse gas emissions from Pennsylvania unconventional natural gas production produce half the carbon footprint compared to regionally produced coal, with carbon dioxide emissions from combustion being the dominant source of greenhouse gas emissions for both sources.

Natural gas production in the United States has increased rapidly over the past decade, along with concerns about methane (CH₄) fugitive emissions and its climate impacts. Quantification of CH₄ emissions from oil and natural gas (O&NG) operations is important for establishing scientifically sound policies for mitigating greenhouse gases. We use the aircraft mass balance approach for three flight experiments in August and September 2015 to estimate CH₄ emissions from O&NG operations over the southwestern Marcellus Shale. We estimate a mean CH₄ emission rate as 21.2 kg/s with 28% coming from O&NG operations. The mean CH₄ emission rate from O&NG operations was estimated to be 1.1% of total NG production. The individual best‐estimate emission rates from the three flight experiments ranged from 0.78 to 1.5%, with overall limits of 0% and 3.5%. These emission rates are at the low end of other top‐down studies, but consistent with the few observational studies in the Marcellus Shale region as well as the U.S. Environmental Protection Agency CH₄ inventory. A substantial source of CH₄ (~70% of observed CH₄ emissions) was found to contain little ethane, possibly due to coalbed CH₄ emitted either directly from coal mines or from wells drilled through coalbed layers in O&NG operations. Recent regulations requiring capture of gas from the completion‐venting step of hydraulic fracturing appear to have reduced the atmospheric release of CH₄. Our study suggests that for a 20‐year time scale, energy derived from the combustion of natural gas extracted from this region likely exerts a net climate benefit compared to coal.

Urban areas are responsible for a substantial fraction of anthropogenic emissions of greenhouse gases (GHGs) including methane (CH₄), with the second largest anthropogenic direct radiative forcing relative to carbon dioxide (CO₂). Quantification of urban CH₄ emissions is important for establishing GHG mitigation policies. Comparison of observation‐based and inventory‐based urban CH₄ emissions suggests possible improvements in estimating CH₄ source emissions in urban environments. In this study, we quantify CH₄ emissions from the Baltimore‐Washington area based on the mass balance aircraft flight experiments conducted in Winters 2015 and 2016. The field measurement‐based mean winter CH₄ emission rates from this area were 8.66 ± 4.17 kg/s in 2015 and 9.14 ± 4.49 kg/s in 2016, which are 2.8 times the 2012 average U.S. GHG Inventory‐based emission rate. The observed emission rate is 1.7 times that given in a population‐apportioned state of Maryland inventory. Methane emission rates inferred from carbon monoxide (CO) and CO₂ emission inventories and observed CH₄/CO and CH₄/CO₂ enhancement ratios are similar to those from the mass balance approach. The observed ethane‐to‐methane ratios, with a mean value of 3.3% in Winter 2015 and 4.3% in Winter 2016, indicate that the urban natural gas system could be responsible for ~40–60% of total CH₄ emissions from this area. Landfills also appear to be a major contributor, providing 25 ± 15% of the total emissions for the region. Our study suggests there are grounds to reexamine the CH₄ emissions estimates for the Baltimore‐Washington area and to conduct flights in other seasons.

Copper is an inexpensive replacement for silver in electronic applications such as solar cell metallization, electromagnetic interference packaging, and printable electronics. However, copper has a characteristically low reduction potential under ambient conditions, favoring formation of non-conducting copper oxides. Here, a spray pyrolysis method of producing oxidation resistant copper particles with surfaces rich in zinc, without need for post-fabrication modifications is described. The effects of precursor and reactor parameters on the particle surface composition with respect to the bulk composition are explored. At reactor temperature conditions of 1000 °C with a precursor containing 90 at% copper–10 at% zinc, the formation of desired morphologies was achieved, smooth dense particles with surfaces enriched in zinc. Increasing the concentration of zinc in the precursor did not improve enrichment, and instead led to the formation of a zinc diamine chloride [Zn(NH₃)₂Cl₂] byproduct. © 2018 American Association for Aerosol Research

Artificial photosynthesis uses a catalyst to convert CO₂ into valuable hydrocarbon products by cleaving the C=O bond. However, this technology is strongly limited by two issues, namely insufficient catalytic efficiency and complicated catalyst-fabrication processes. Herein, we report the development of a novel spray-drying photocatalyst-engineering process that addresses these two issues. Through one-step spray drying, with a residence time of 1.5 s, nanocomposites composed of tin oxide (SnO₂) nanoparticles and edge-oxidized graphene oxide (eo-GO) sheets were fabricated without post-treatment. These nanocomposites exhibited 28-fold and five-fold enhancements in photocatalytic efficiency during CO₂ reduction compared to SnO₂ and commercialized TiO₂ (P25), respectively, after irradiation with simulated sunlight for 4 h. This scalable approach, based on short residence times and facile equipment setup, promotes the practical application of artificial photosynthesis through the potential mass production of efficient photocatalysts. Open image in new window

Little is known about the amount and infectiousness of influenza virus shed into exhaled breath. This contributes to uncertainty about the importance of airborne influenza transmission. We screened 355 symptomatic volunteers with acute respiratory illness and report 142 cases with confirmed influenza infection who provided 218 paired nasopharyngeal (NP) and 30-minute breath samples (coarse >5 μm and fine 4 /30-min fine, 1.2×10 ⁴ /30-min coarse aerosol sample, and 8.2×10 ⁸ per NP swab. Fine and coarse aerosol viral RNA was positively associated with body mass index (fine p<0.05, coarse p<0.10) and number of coughs (fine p<0.001, coarse p<0.01) and negatively associated with increasing days since symptom onset (fine p<0.05 to p<0.01, coarse p<0.10) in adjusted models. Fine aerosol viral RNA was also positively associated with having influenza vaccination for both the current and prior season (p<0.01). NP swab viral RNA was positively associated with upper respiratory symptoms (p<0.01) and negatively associated with age (p<0.01) but was not significantly associated with fine or coarse aerosol viral RNA or their predictors. Sneezing was rare, and sneezing and coughing were not necessary for infectious aerosol generation. Our observations suggest that influenza infection in the upper and lower airways are compartmentalized and independent. Significance: Lack of human data on influenza virus aerosol shedding fuels debate over the importance of airborne transmission. We provide overwhelming evidence that humans generate infectious aerosols and quantitative data to improve mathematical models of transmission and public health interventions. We show that sneezing is rare and not important for, and that coughing is not required for influenza virus aerosolization. Our findings, that upper and lower airway infection are independent and that fine particle exhaled aerosols reflect infection in the lung, open a new pathway for understanding the human biology of influenza infection and transmission. Our observation of an association between repeated vaccination and increased viral aerosol generation demonstrated the power of our method, but needs confirmation.

Cu-Sn powders are promising alternatives to Ag and Au in applications including printed electronics because of their low cost and high oxidation-resistance. Further development requires the knowledge of the conductivity of their corresponding one-dimensional and two-dimensional structures. Herein, CuSn_y (y=atom ratio of Sn/Cu) wires and films were produced by direct printing. In-situ measurements of structural resistivities while varying the temperature from 2 K to 400 K in oxygen-free conditions revealed that CuSn_0.1 wires have comparable resistivities to Cu wires. Furthermore, CuSn0.1 films exhibited significantly lower resistivity increase after being heated at 573 K in ambient air, compared with Cu films.