Sampling, storage, and analysis of C2–C7 non-methane hydrocarbons from the US National Oceanic and Atmospheric Administration Cooperative Air Sampling Network glass flasks

Impact of U.S. Oil and Natural Gas Emission Increases on Surface Ozone Is Most Pronounced in the Central United States

Observations of volatile organic compounds (VOCs) from a surface sampling network and simulation results from the EMAC (ECHAM5/MESSy for Atmospheric Chemistry) model were analyzed to assess the impact of increased emissions of VOCs and nitrogen oxides from U.S. oil and natural gas (O&NG) sources on air quality. In the first step, the VOC observations were used to optimize the magnitude and distribution of atmospheric ethane and higher-alkane VOC emissions in the model inventory for the base year 2009. Observation-based increases of the emissions of VOCs and NO_x stemming from U.S. oil and natural gas (O&NG) sources during 2009-2014 were then added to the model, and a set of sensitivity runs was conducted for assessing the influence of the increased emissions on summer surface ozone levels. For the year 2014, the added O&NG emissions are predicted to affect surface ozone across a large geographical scale in the United States. These emissions are responsible for an increased number of days when the averaged 8-h ozone values exceed 70 ppb, with the highest sensitivity being in the central and midwestern United States, where most of the O&NG growth has occurred. These findings demonstrate that O&NG emissions significantly affect the air quality across most of the United States, can regionally offset reductions of ozone precursor emissions made in other sectors, and can have a determining influence on a region's ability to meet National Ambient Air Quality Standard (NAAQS) obligations for ozone.

International comparison of a hydrocarbon gas standard at the picomol per mol level

Studies of climate change increasingly recognize the diverse influences of hydrocarbons in the atmosphere, including roles in particulates and ozone formation. Measurements of key nonmethane hydrocarbons (NMHCs) suggest atmospheric mole fractions ranging from low picomoles per mol (ppt) to nanomoles per mol (ppb), depending on location and compound. To accurately establish mole fraction trends and to relate measurement records from many laboratories and researchers, it is essential to have accurate, stable, calibration standards. In February of 2008, the National Institute of Standards and Technology (NIST) developed and reported on picomoles per mol standards containing 18 nonmethane hydrocarbon compounds covering the mole fraction range of 60 picomoles per mol to 230 picomoles per mol. The stability of these gas mixtures was only characterized over a short time period (2 to 3 months). NIST recently prepared a suite of primary standard gas mixtures by gravimetric dilution to ascertain the stability of the 2008 picomoles per mol NMHC standards suite. The data from this recent chromatographic intercomparison of the 2008 to the 2011 suites confirm a much longer stability of almost 5 years for 15 of the 18 hydrocarbons; the double-bonded alkenes of propene, isobutene, and 1-pentene showed instability, in line with previous publications. The agreement between the gravimetric values from preparation and the analytical mole fractions determined from regression illustrate the internal consistency of the suite within ±2 pmol/mol. However, results for several of the compounds reflect stability problems for the three double-bonded hydrocarbons. An international intercomparison on one of the 2008 standards has also been completed. Participants included National Metrology Institutes, United States government laboratories, and academic laboratories. In general, results for this intercomparison agree to within about ±5% with the gravimetric mole fractions of the hydrocarbons.

Invited article: A materials investigation of a phase-change micro-valve for greenhouse gas collection and other potential applications

The deleterious consequences of climate change are well documented. Future climate treaties might mandate greenhouse gas (GHG) emissions measurement from signatories in order to verify compliance. The acquisition of atmospheric chemistry would benefit from low cost, small size/weight/power of microsystems. In this paper, we investigated several key materials science aspects of a phase-change microvalve (PCμV) technology with low power/size/weight/cost for ubiquitous GHG sampling. The novel design, based on phase-change material low-melting-point eutectic metal alloys (indium-bismuth, InBi and tin-lead, SnPb), could be actuated at temperatures as low as 72 °C. Valve manufacturing was based on standard thick and thin-film processes and solder technologies that are commonly used in industry, enabling low-cost, high-volume fabrication. Aging studies showed that it was feasible to batch fabricate the PCμVs and store them for future use, especially in the case of SnPb alloys. Hermetic sealing of the valve prototypes was demonstrated through helium leak testing, and Mil spec leak rates less than 1 × 10(-9) atm cm(3)/s were achieved. This confirms that the sample capture and analysis interval can be greatly expanded, easing the logistical burdens of ubiquitous GHG monitoring. Highly conservative and hypothetical CO(2) bias due to valve actuation at altitude in 1 cm(3) microsamplers would be significantly below 1.0 and 2.2 ppmv for heat-treated InBi and SnPb solders, respectively. The CO(2) bias from the PCμV scales well, as a doubling of sampler volume halved the bias. We estimated the shelf life of the SnPb PCμVs to be at least 2.8 years. These efforts will enable the development of low cost, low dead volume, small size/weight microsystems for monitoring GHGs and volatile organic compounds.