A study in early 2009 by SMU professor Al Armendariz contends that natural gas production contributes more to air pollution in North Texas than all the major airports and cars in the DFW area combined.

Our research has found that Armendariz' conclusions were based on an inaccurate and flawed interpretation of the facts.

If the SMU study's conclusions were correct, then the Dallas-Fort Worth region would have seen a dramatic rise in ozone levels over the past several years during the time that the number of gas wells has grown exponentially in the Barnett Shale. The chart below, using ozone data from the North Central Texas Council of Governments, shows that the opposite is true.

Clearly, as more and more Barnett Shale wells have been drilled, ozone levels in the nine-county DFW area have actually declined. That is not surprising given the emissions reductions in the Barnett Shale region promoted by the North Texas Clean Air Coalition. The data shows that there is no clear relationship between Barnett Shale natural gas production activities and the highest average ozone levels in the DFW area.

The SMU study estimates emissions from Barnett Shale activity in a 21-county region of nitrogen oxides (NOx), volatile organic compounds (VOC), hazardous air pollutants (HAPs), and the greenhouse gases methane (CH4) and carbon dioxide (CO2). The pollutants NOx and VOC , in particular, contribute to ozone levels in certain types of weather. High ozone levels in the DFW region have caused it to be considered a "non-attainment" area by the U.S. Environmental Protection Agency.

After 35 pages of analysis, the study concludes:

"Emissions of ozone and fine particle smog forming compounds (NOx and VOC) will be approximately 191 tons per day on an annual average basis in 2009. During the summer, VOC emissions will increase, raising the NOx + VOC total to 307 tons per day, greater than the combined emissions from the major airports and on-road motor vehicles in the DFW metropolitan area."

The study asserts that all natural gas production activity in the Barnett Shale contributes to VOC emissions, but the largest source is condensate tank vents.

So why is there no clear relationship between the number of natural gas wells and highest average ozone levels, contrary to the Armendariz study?

There are several reasons.

First, most of the natural gas produced in and around the nine-county DFW area is very "dry" gas. According to geophysicists, this part of the Barnett Shale is "thermally mature," meaning that natural gas wells in this area produce very little associated oil or other liquids. This in turn means most of the wells do not require condensate storage tanks. Indeed, little or no VOC is emitted from these gas wells. The following map shows the approximate boundary areas of "dry" gas (pink), "richer" gas with condensate production (yellow), and even "richer" gas with oil production (green) in the Barnett Shale.

Individual well data from the Railroad Commission of Texas shown in the table below also demonstrates this fact.

The results are the same if we look at all oil and gas wells in the Barnett Shale area. The table below shows that 82.9 percent of all oil and gas wells in the nine-county DFW non-attainment area produce zero condensate.

In fact, approximately 65 percent of the condensate produced across the entire 21-county Barnett Shale region is produced in counties west of DFW.

Second, a basic flaw in the SMU study is that it assumes that the wells in the 21- county Barnett Shale area that do produce condensate all have the same amount of VOC emissions per barrel of condensate, regardless of the wells' production pressure or other site-specific variables.

From an engineering standpoint, it is simply wrong to apply one VOC emissions factor to all condensate storage tanks located across 21 counties and expect a reliable estimate. This is because well-producing pressure greatly affects potential VOC emissions. The study also assumes that summertime VOC emissions from condensate storage tanks are 4.8 times higher than those during the rest of the year. This assumption is not even close to reality based on thermodynamic principals.

Third, wind rose data from the DFW Airport (shown below for the month of July) demonstrates that during the summer months the wind blows from the west or northwest only about 4% of the time. Therefore, during the summer months, any VOC emissions actually emitted from condensate production tanks in counties west or northwest of the DFW NAA, and even in western Denton and Parker counties, is blown away from the DFW metroplex the vast majority of the time. The probability of any actual VOC emissions from these western areas significantly impacting high average 8-hour ozone values in the DFW NAA is likely near zero.

It is important to know that the Texas Commission on Environmental Quality (TCEQ) is responsible for evaluating pollutant emissions and their impact on ozone formation in the DFW non-attainment area. Based on EPA guidance, Texas developed a State Implementation Plan (SIP) in 2007 to address emissions challenges. The agency considers emissions of NOx a much more important precursor to ozone formation in the DFW non-attainment area than VOC based on sensitivity air modeling studies. That is why most major emissions control efforts in the DFW area aim to significantly reduce NOx emissions. TCEQ data indicates that 38 percent of NOx emissions in the DFW area come from on-road vehicles such as cars and trucks. Non-road mobile sources, such as planes, trains, and construction equipment (and some natural gas production activities) contribute to 32 percent of NOx emissions. Emissions from area sources, including most of the oil and gas industry emissions and residential gas use, come in significantly lower at nine percent.

We all share in the challenge to reduce emissions and improve air quality in our region – the natural gas industry is no exception. As part of Texas 2007 SIP, compressor engines over 50 HP are now required to meet NOx emissions standards that, depending on the type of engine, are three to four times stricter than current EPA standards. The natural gas industry will spend more than $100 million to install emissions control equipment on compressor engines and monitoring to meet these federal and state standards and demonstrate future compliance.

Citizens can be assured that the natural gas industry will continue to work cooperatively with TCEQ to achieve an accurate assessment of emissions in the DFW area and will do its part to achieve the new EPA ozone standard of 75 parts per billion.

In summary, it is clear that the data in the SMU study does not support the conclusion that Barnett Shale activities contribute more to ozone levels in the DFW region than vehicle emissions – not even close. On the contrary, natural gas offers a way to help clean up the air. Natural gas is the cleanest burning hydrocarbon and is considered to be the bridge fuel to a future of more renewable and cleaner fuels. Natural gas will be the fuel of choice for decades to come for electric power generation and for fleet vehicles while other clean energy technologies grow and expand in use. The Barnett Shale region will continue to play an important role in producing this important bridge fuel to the future.