Colloquium Thursday, 30 Nov., 3pm, EN6085A

Wintertime Surface Ozone Production in the Jonah/Pinedale, Wyoming Gas Field

The 30,000 acre Jonah gas field, 30 miles south of Pinedale, Wyoming, produces about 15% of the natural gas in Wyoming.  Gas well density is one well per 40 acres but this will soon increase to one per 10 acres.  Presently there are about 800 wells in the field. The field is estimated to hold about 10 trillion cubic feet of gas and produces enough gas to serve 3,000,000 U.S.homes per year. The value of the natural gas to be extracted from the Jonah field over its lifetime is calculated to be in the region of $40 billion (2005 prices).

In late 2004, air quality monitors were installed in the field to measure meteorology, solar radiation, NO_x, NO, NO₂, and O_3.   In January and February of 2005 and 2006, hourly average O₃ concentrations of up to 120 ppb were observed on a number of occasions and concentration of 75 ppb were observed on about 40% of the days at all three of the air quality stations in the gas field.  NO_x values of up to 100 ppb were measured on many nights prior to elevated ozone levels the following afternoons.  The elevated ozone levels could put the gas field into EPA non-compliance if they become a regular occurrence.

The Global Monitoring Division of NOAA was asked to study the high ozone events to determine if they were caused by stratospheric fold events bringing elevated ozone to the surface as suggested by the gas field operators.  By studying the ozone and NO_x cycle in relation to local meteorology, solar radiation, radiosonde soundings, satellite measurements of stratospheric vorticity and air trajectories, it was determined that the ozone was being produced locally on days when there was a cold, high pressure air mass covering Wyoming.  This meteorological situation produced strong, low-level temperature inversions, low winds and cloudless skies. The ozone production had a strong diurnal cycle peaking at one hour after solar noon at which times the high NO_x levels of the prior nocturnal accumulation were reduce to negligible levels.  The presence of snow cover appeared to enhance ozone production. From satellite and balloonborne ozonesonde measurements there was no evidence of stratospheric intrusions bringing ozone into the region.  The sources of the ozone precursors has not been fully determined, but are probably related to leaks in the gas production process and the large number of gasoline and diesel engines operating in the field.