Critique of Well Activity Proxy Uses Inadequate Data and Statistics.

The recent publication, "Assessing Agreement in Exposure Classification between Proximity-Based Metrics and Air Monitoring Data in Epidemiology Studies of Unconventional Resource Development" by Hess et al [...].

Flaring in two Texas shale areas: Comparison of bottom-up with top-down volume estimates for 2012 to 2015.

Since advances in horizontal drilling and hydraulic fracturing technologies have opened oil and gas development in previously unreachable areas, air pollution emissions have increased from the burning (i.e., flaring) or releasing (i.e., venting) of natural gas at oil and gas extraction sites. While venting and flaring is a growing concern, accounting of how much gas is vented and flared, and where this occurs, remains limited. The purpose of this paper is to describe two methods for estimating venting and flaring volumes - self-reports required by state law and satellite imagery radiant heat measurements - and to compare these methods using the case of Texas Eagle Ford and Permian Basin venting and flaring practices from 2012 to 2015. First, we used data self-reported by companies to the Texas Railroad Commission (TxRRC), and National Oceanic and Atmospheric Administration (NOAA) data captured by satellite-based Visible Infrared Imaging Radiometer Suite sensors, to estimate the annual total volumes of gas vented and flared in the Eagle Ford and Permian Basin from 2012 to 2015. Next, we developed a method using a geographic information system to link and compare TxRRC and NOAA county-based and point-based volume estimates. Finally, we conducted case studies of two oil and gas fields to better understand how TxRRC and NOAA venting and flaring volumes differ. We find both TxRRC and NOAA estimated venting and/or flaring volumes steadily increased from 2012 to 2015. Additionally, TxRRC reports captured about half the volumes estimated by NOAA. This suggests that self-reported volumes significantly underestimate the volume of gas being vented or flared. However, this research is limited by the data currently available. As such, future research and policy should further develop methods to systemically capture the extent to which oil and gas extraction facilities vent and flare natural gas.

Anthropogenic and Biogenic Features of Long-Term Measured CO Flux in North Downtown Houston, Texas.

Long-term urban carbon cycle studies remain rare despite the importance of carbon for energy, air quality, and climate change. To study spatial and temporal variations of energy and carbon fluxes in a subtropical urban environment, eddy covariance flux measurements were conducted north of downtown Houston, TX, using a tall radio-tower installation. The results of the first 2 yr of measurements show that both concentrations and fluxes of CO display typical seasonal and diurnal variations in urban areas. The seasonal variation of net CO flux is driven by steady anthropogenic emissions dominated by car traffic and human respiration, moderated by the local deciduous tree foliage. Weekday-weekend differences were observed in carbon fluxes, but not concentrations, while diurnal changes were dominated by rush-hour peaks from traffic and vegetation influences. Interestingly, CO and CO concentrations, but not CO flux, exhibited long-term declines, especially comparing pre- and post-Hurricane Ike periods. A directional analysis of CO fluxes revealed that the highest fluxes typically occurred from northwest directions, most likely due to emissions from small industrial sources. Car traffic as carbon source was revealed via correlations of CO with CO during the morning rush hours, and of CO flux with traffic counts during winter time. The influence of urban vegetation on net CO fluxes was identified via correlations with daytime photosynthetically active radiation due to photosynthesis, and with nighttime temperatures due to ecosystem respiration. The study site is a net source of CO throughout all seasons.

Photosynthesis and isoprene emission from trees along an urban-rural gradient in Texas.

Isoprene emission is an important mechanism for improving the thermotolerance of plant photosystems as temperatures increase. In this study, we measured photosynthesis and isoprene emission in trees along an urban-rural gradient that serves as a proxy for climate change, to understand daily and seasonal responses to changes in temperature and other environmental variables. Leaf-level gas exchange and basal isoprene emission of post oak (Quercus stellata) and sweet gum (Liquidambar styraciflua) were recorded at regular intervals over an entire growing season at urban, suburban, and rural sites in eastern Texas. In addition, the temperature and atmospheric carbon dioxide concentration experienced by leaves were experimentally manipulated in spring, early summer, and late summer. We found that trees experienced lower stomatal conductance and photosynthesis and higher isoprene emission, at the urban and suburban sites compared to the rural site. Path analysis indicated a daily positive effect of isoprene emission on photosynthesis, but unexpectedly, higher isoprene emission from urban trees was not associated with improved photosynthesis as temperatures increased during the growing season. Furthermore, urban trees experienced relatively higher isoprene emission at high CO2 concentrations, while isoprene emission was suppressed at the other sites. These results suggest that isoprene emission may be less beneficial in urban, and potentially future, environmental conditions, particularly if higher temperatures override the suppressive effects of high CO2 on isoprene emission. These are important considerations for modeling future biosphere-atmosphere interactions and for understanding tree physiological responses to climate change.

Organosulfates as tracers for secondary organic aerosol (SOA) formation from 2-methyl-3-buten-2-ol (MBO) in the atmosphere.

2-Methyl-3-buten-2-ol (MBO) is an important biogenic volatile organic compound (BVOC) emitted by pine trees and a potential precursor of atmospheric secondary organic aerosol (SOA) in forested regions. In the present study, hydroxyl radical (OH)-initiated oxidation of MBO was examined in smog chambers under varied initial nitric oxide (NO) and aerosol acidity levels. Results indicate measurable SOA from MBO under low-NO conditions. Moreover, increasing aerosol acidity was found to enhance MBO SOA. Chemical characterization of laboratory-generated MBO SOA reveals that an organosulfate species (C(5)H(12)O(6)S, MW 200) formed and was substantially enhanced with elevated aerosol acidity. Ambient fine aerosol (PM(2.5)) samples collected from the BEARPEX campaign during 2007 and 2009, as well as from the BEACHON-RoMBAS campaign during 2011, were also analyzed. The MBO-derived organosulfate characterized from laboratory-generated aerosol was observed in PM(2.5) collected from these campaigns, demonstrating that it is a molecular tracer for MBO-initiated SOA in the atmosphere. Furthermore, mass concentrations of the MBO-derived organosulfate are well correlated with MBO mixing ratio, temperature, and acidity in the field campaigns. Importantly, this compound accounted for an average of 0.25% and as high as 1% of the total organic aerosol mass during BEARPEX 2009. An epoxide intermediate generated under low-NO conditions is tentatively proposed to produce MBO SOA.

Rural southeast Texas air quality measurements during the 2006 Texas Air Quality Study.

The authors conducted air quality measurements of the criteria pollutants carbon monoxide, nitrogen oxides, and ozone together with meteorological measurements at a park site southeast of College Station, TX, during the 2006 Texas Air Quality Study II (TexAQS). Ozone, a primary focus of the measurements, was above 80 ppb during 3 days and above 75 ppb during additional 8 days in summer 2006, suggestive of possible violations of the ozone National Ambient Air Quality Standard (NAAQS) in this area. In concordance with other air quality measurements during the TexAQS II, elevated ozone mixing ratios coincided with northerly flows during days after cold front passages. Ozone background during these days was as high as 80 ppb, whereas southerly air flows generally provided for an ozone background lower than 40 ppb. Back trajectory analysis shows that local ozone mixing ratios can also be strongly affected by the Houston urban pollution plume, leading to late afternoon ozone increases of as high as 50 ppb above background under favorable transport conditions. The trajectory analysis also shows that ozone background increases steadily the longer a southern air mass resides over Texas after entering from the Gulf of Mexico. In light of these and other TexAQS findings, it appears that ozone air quality is affected throughout east Texas by both long-range and regional ozone transport, and that improvements therefore will require at least a regionally oriented instead of the current locally oriented ozone precursor reduction policies.

Abundances and flux estimates of volatile organic compounds from a dairy cowshed in Germany.

Animal husbandry and manure treatment have been specifically documented as significant sources of methane, ammonia, nitrous oxide, and particulate matter. Although volatile organic compounds (VOCs) are also produced, much less information exists concerning their impact. We report on chemical ionization mass spectrometry and photo-acoustic spectroscopy measurements of mixing ratios of VOCs over a 2-wk measurement period in a large cowshed at the Federal Agricultural Research Centre (FAL) in Mariensee, Germany. The high time resolution of these measurements enables insight into the sources of the emissions in a typical livestock management setting. During feeding hours and solid manure removal, large mixing ratio spikes of several VOCs were observed and correlated with simultaneous methane, carbon dioxide, and ammonia level enhancements. The subsequent decay of cowshed concentration due to passive cowshed ventilation was used to model emission rates, which were dominated by ethanol and acetic acid, followed by methanol. Correlations of VOC mixing ratios with methane or ammonia were also used to calculate cowshed emission factors and to estimate potential nationwide VOC emissions from dairy cows. The results ranged from around 0.1 Gg carbon per year (1 Gg = 10(9) g) for nonanal and dimethylsulfide, several Gg carbon per year for volatile fatty acids and methanol, to over 10 Gg carbon per year of emitted ethanol. While some estimates were not consistent between the two extrapolation methods, the results indicate that animal husbandry VOC emissions are dominated by oxygenated compounds and may be a nationally but not globally significant emission to the atmosphere.

Atmospheric methyl tertiary butyl ether (MTBE) at a rural mountain site in California.

Methyl tertiary butyl ether (MTBE) was measured in air samples collected at hourly intervals near Blodgett Forest Research Station on the western slope of the Sierra Nevada, California, in July 1997, October 1998, and June through September 1999. Mixing ratios ranged from below the detection limit (< approximately 0.01 ppbv) to 0.5 ppbv, but were generally less than 0.3 ppbv. At these mixing ratios partitioning of MTBE into surface waters would lead to MTBE concentrations of less than 0.2 microg L(-1). As expected, MTBE mixing ratios were highly correlated with other anthropogenically emitted hydrocarbons. Based on the observed diurnal cycle of MTBE and its ratio to 2-methyl-butane (isopentane), we estimated the average regional daytime oxidant concentration to be (9 to 13) x 10(6) OH radicals per cubic centimeter, consistent with our earlier estimates for this region. Furthermore, MTBE ratios to toluene, another ubiquitous anthropogenic hydrocarbon, were generally consistent with regional transport and dilution, as well as atmospheric oxidation. Exceptions, pertaining to MTBE mixing ratios below or close to the detection limit, were associated with the influence of marine air masses that did not experience anthropogenic hydrocarbon input from California. With all these constraints in place, evidence for an additional atmospheric loss process, such as nonreversible deposition of MTBE, could not be established, and we conclude that any deposition is slow compared with removal from the atmosphere by the OH radical.