Author Response to Letter to the Editor
Dear Dr. Rao,
I would like to thank you for the opportunity to respond to comments by the Texas Commission on Environmental Quality (TCEQ) on my article entitled, “The potential near-source ozone impacts of upstream oil and gas industry emissions” (CitationOlaguer, 2012a).
Flare Emissions
The TCEQ objected to the inclusion of propylene in the flare emissions assumed in my paper. These emissions, however, were based on the USEPA AP-42 flare emissions factor, as recommended by the Canadian Association of Petroleum Producers. The absence of officially accepted emission factors for pure natural gas flares made this necessary, especially since recent data collected by the TCEQ for flares other than propylene-natural gas mixtures were published only after my paper was submitted.
Dr. James CitationSeebold (2011), a flare expert, stated: “Burn even a fuel as simple as laboratory-grade methane pure as the drifted snow, get in the plume traces of virtually all of the approximately 100 hydrocarbon intermediates.” So there is propylene even in pure natural gas flares. The Texas Pipeline Association, in a review of my paper published on October 5, 2012 in Powell Shale Digest, made comments similar to those by the TCEQ, and suggested that data for propane-air and steam-assisted mixtures from the TCEQ Flare Study be used in place of the AP-42 emission factor. An examination of Table 3 in CitationKnighton et al. (2012) shows that the highly reactive VOCs, ethylene and propylene, are indeed present in emissions from these types of flares.
Besides flares, there are other possible sources of highly reactive VOCs at oil and gas sites. The recent TCEQ-funded monitoring study in the Barnett Shale conducted under the auspices of the University of Texas Air Quality Research Program (AQRP) measured flashing emissions of ethylene from a condensate storage tank of 2 kg/hr (CitationJohansson et al., 2011). Therefore the existence of potentially significant emissions of highly reactive VOCs from oil and gas sites is confirmed by research funded by the TCEQ.
Modeling
The TCEQ states that my paper “offers no comparison to actual observations or other performance evaluation to determine the adequacy of this relatively unknown model.” My paper, however, referenced Supplemental Materials in which the model chemical mechanism was tested against real world observations during the TexAQS II Radical and Aerosol Measurement Project (TRAMP). The paper also referenced a companion article (CitationOlaguer, 2012b), in which the model predictions were successfully tested against monitoring observations downwind of historical flares in the Houston Ship Channel. The fact that my model is relatively unknown is not a reason to object to my paper, since it is thus far the only 3D Eulerian model that can tractably compute very high resolution ozone impacts near industrial sources. It was designed precisely to fill a gap in the current suite of available air quality models. The Journal of the Air and Waste Management Association, being a peer-reviewed research journal, was intended to facilitate the production of new policy-relevant research, including the design of new air quality models.
It was not my purpose to retrospectively analyze a historical ozone episode, which would indeed require very high resolution emission inventories and model episodes far longer than 2 hours. Sufficient observational data are still lacking to construct high resolution inventories in the Barnett Shale. The results of my paper, limited though they are in spatial and temporal scope, are sufficiently suggestive of impacts that are worth investigating further with a more comprehensive approach premised on the collection of the appropriate high resolution data.
TCEQ Regulations
The TCEQ should be commended for its current suite of oil and gas regulations. My paper, however, was not intended to focus exclusively on issues in Texas, but rather to highlight the Barnett Shale as an indicator of air quality problems that may occur wherever oil and gas drilling is prevalent, including areas where regulations may not be quite as advanced as in Texas, especially with regard to emission event reporting. Moreover, the existence of regulations does not lessen the value of conservative assumptions in assessing the air quality impacts of oil and gas site emissions, as real operational circumstances may often fall short of the ideal even when regulatory controls are implemented.
Sincerely,
Eduardo P. Olaguer
Director, Air Quality Research
Houston Advanced Research Center
References
- Johansson, J. et al., 2011. Quantification of industrial emissions of VOCs, NO2 and SO2 by SOF and mobile DOAS. AQRP Project 10-006 Final Report, University of Texas at Austin. Available at http://aqrp.ceer.utexas.edu/projectinfo/10-006/10-006%20Final%20Report.pdf (http://aqrp.ceer.utexas.edu/projectinfo/10-006/10-006%20Final%20Report.pdf)
- Knighton , W. B. 2012 . Direct measurement of volatile organic compound emissions from industrial flares using real-time online techniques: Proton Transfer Reaction Mass Spectrometry and Tunable Infrared Laser Differential Absorption Spectroscopy . Ind. Eng. Chem. Res , 51 : 12674 – 12684 . doi: 10.1021/ie202695v
- Olaguer , E. P. 2012a . The potential near-source ozone impacts of upstream oil and gas industry emissions . J. Air and Waste Manage. Assoc , 62 : 966 – 977 . doi: 10.1080/10962247.2012.688923
- Olaguer , E. P. 2012b . Near-source air quality impacts of large olefin flares . J. Air and Waste Manage. Assoc , 62 : 978 – 988 . doi: 10.1080/10962247.2012.693054
- Seebold, J. G., 2011. Comments on 2010 TCEQ Flare Study project final report. Available at http://www.tceq.texas.gov/assets/public/implementation/air/rules/Flare/06012011/James_Seebold.pdf (http://www.tceq.texas.gov/assets/public/implementation/air/rules/Flare/06012011/James_Seebold.pdf)