Regional Air Quality Impacts of Increased Natural Gas Production and Use in Texas

Abstract

Natural gas use in electricity generation in Texas was estimated, for gas prices ranging from $1.89 to $7.74 per MMBTU, using an optimal power flow model. Hourly estimates of electricity generation, for individual electricity generation units, from the model were used to estimate spatially resolved hourly emissions from electricity generation. Emissions from natural gas production activities in the Barnett Shale region were also estimated, with emissions scaled up or down to match demand in electricity generation as natural gas prices changed. As natural gas use increased, emissions decreased from electricity generation and increased from natural gas production. Overall, NOx and SO2 emissions decreased, while VOC emissions increased as natural gas use increased. To assess the effects of these changes in emissions on ozone and particulate matter concentrations, spatially and temporally resolved emissions were used in a month-long photochemical modeling episode. Over the month-long photochemical modeling episode, decreases in natural gas prices typical of those experienced from 2006 to 2012 led to net regional decreases in ozone (0.2-0.7 ppb) and fine particulate matter (PM) (0.1-0.7 μg/m(3)). Changes in PM were predominantly due to changes in regional PM sulfate formation. Changes in regional PM and ozone formation are primarily due to decreases in emissions from electricity generation. Increases in emissions from increased natural gas production were offset by decreasing emissions from electricity generation for all the scenarios considered.

Emissions from oil and gas operations in the United States and their air quality implications

“…In contrast, emissions in the Barnett Shale in North Central Texas occur in a region in which the background reactivity of the atmosphere is relatively low. Direct emissions from oil and gas operations in this region produce relatively low quantities of ozone (Pacsi et al, 2013).…”

“…In ERCOT, natural gas-fired units generally have lower air pollutant emissions per kilowatt hour of generation, relative to the coal plants, so when lower natural gas prices drive shifts from coal-based generation to natural gas-based generation, emissions of NO x , particulate matter (PM), sulfur oxides (SO x ), and carbon dioxide decrease (Alhajeri et al, 2011). Pacsi et al (2013 have modeled the electricity generation shifts, from coal to natural gas, that would be expected in ERCOT as natural gas prices change from $7.74 per million BTU (a representative price from 2006 to 2008), to $3.87 per million BTU, $2.88 per million BTU (an average price in late 2012) and $1.89 per million BTU (the price in late 2015, and a price equivalent to coal on an energy basis). Changes in emissions of NO x , VOCs, CO, SO x , and PM from these changes in electricity generation were estimated and compared with emissions due to added natural gas production in the Barnett Shale and Eagle Ford natural gas production regions that would be required to fuel the switch from coal to natural gas.…”

“…(b) Increases in summer month average daily maximum 8-hr ozone concentration due to increases in Eagle Ford production sufficient to supply the natural gas for the increased natural gas consumption in electricity generation. Figure 14. (a) Locations of coal-fired and natural gas-fired power generation, relative to oil and gas production regions in Texas; (b) distribution of electricity generation at high natural gas prices (sizes of dots representing power plants is proportional to extent of generation); (c) distribution of electricity generation at low natural gas prices (sizes of dots proportional to extent of generation) (Pacsi et al, 2013.…”

“…Among the environmental consequences of increased oil and gas production are impacts on land use, impacts on water use (Nicot and Scanlon, 2012), water contamination (U.S. Environmental Protection Agency [EPA], 2012;Osborn et al, 2011;Vidic et al, 2013;Rahm and Riha, 2012), criteria air pollutant and air toxics releases (McKenzie et al, 2012;Litovitz et al, 2013;Pacsi et al, 2013, and greenhouse gas emissions (Laurenzi et al, 2013;Miller et al, 2013;Brandt et al, 2014;Balcombe et al, 2015). Given the potential scope and magnitude of the economic and industrial transformations that increased oil and gas production can lead to, it is important to understand, as thoroughly as possible, the environmental implications of the transformations.…”

Emissions from oil and gas operations in the United States

“…Environmental impacts associated with increased natural gas production and fracking have been controversial, and several reports have raised questions about the overall effect of natural gas usage on total U.S. greenhouse gas emissions and whether or not the impact of emissions associated with oil and gas production is effectively offset by reduced emissions from replacing less cleanly burning fuels with natural gas in domestic automotive, industrial, and power generation applications (Pacsi et al, 2013). Widely varying assumptions concerning the potential emissions of methane during extraction and production processes make it highly uncertain much methane is released into the atmosphere during these processes, largely because the availability of measured data is limited and because drilling processes continue to evolve.…”