Simulation of Wintertime High Ozone Concentrations in Southwestern Wyoming Using the CALMET CALGRID Modeling System
As summarized in Reed et. al. (2009), the Upper Green River Basin (UGRB), which is located in Sublette County, Wyoming, is bounded by the Wind River Range to the east, the Wyoming Range to the west, the Gros Ventre Range to the north, and bounded by the Uinta Range to the south. These surrounding, significant terrain features effectively create a bowl-like basin that greatly influences the local meteorology relative to the rest of the area. The UGRB is roughly 1,000 meters to 2,000 meters lower than the terrain features to the east and west (WDEQ-AQD 2009).
Within the UGRB, significant development of oil and gas fields has occurred recently. This development has resulted in the release of significant quantities of NOx and VOC emissions, which are both known ozone precursors. Recent monitoring data has indicated elevated ozone concentrations in the late winter that exceed the current National Ambient Air Quality Standards (NAAQS) for 8-hour ozone. As a result of these high concentrations, the WDEQ initiated the Upper Green River Winter Ozone Study (UGWOS) to understand and characterize observed phenomenon.
The 2008 UGWOS final report (ENVIRON 2008) documents the monitoring network and field operations during Intensive Operating Periods (IOPs) that were part of the study during February and March, 2008. The UGWOS field study produced a high quality database of observations for several meteorological parameters as well as ambient measurements of air quality concentrations of ozone precursors in several areas within the Basin. The formulation of the CALMET database has been discussed fully in prior documents (Reed 2009, TRC 2009).
The CALGRID photochemical grid model was run with the above CALMET meteorological database and oil and gas operator-supplied emissions in an effort to replicate the high winter-time ozone concentrations observed at three Federal Reference (FR) ozone-monitoring sites in Sublette Co., WY in February and March 2008. The sites are Daniel, Boulder and Jonah – each within the county and more specifically, the Upper Green River Basin. The ozone monitoring sites are also located close to (Daniel, Boulder) or within (Jonah) active oil and gas field developments, i.e., the Pinedale and Jonah fields. Five full-scale CALGRID runs for the period of February 18-24, 2008, along with several sensitivity and diagnostic analyses, were conducted. The results of this modeling indicate the most sensitivity to VOC speciation and total mass.Read more...
Recent, winter-season high ozone concentrations in the Upper Green River Basin (UGRB) led to the Upper Green River Winter Ozone Study (UGWOS) during late-winter 2008, sponsored by the Wyoming Department of Environmental Quality (WYDEQ). Under the right seasonal conditions, the UGRB’s unique natural and anthropogenic factors make rapid winter-time ozone formation possible. Recent development of oil and gas fields Basin-wide has increased the amount of ozone precursors (VOC and NOx) within the airshed. The Basin itself has surrounding mountain ranges that block airflow from entering or exiting during certain synoptic conditions, such as anomalously low wind speeds associated with strong high pressure systems. Finally, snow cover increases the available radiation for photochemistry as well as the atmospheric stability of the Basin.
Given the known-importance of meteorology during these events, the UGWOS field study produced a comprehensive, Basin-wide meteorological database during the 2008 high ozone events. The resulting, quality-controlled meteorological database contains high resolution observations during intensive operation periods as well as hourly observations. Hourly observations include: a 19-station surface-based mesonet and a multi-level SODAR. High resolution measurements of vertical wind data and temperature from rawinsondes are also available during the intensive operation periods.
Nearly the entire UGWOS database was integrated into the CALMET wind field development for a 7-day period in February 2008, using a 1-km resolution to assess the extent of atmospheric conditions associated with ozone formation. The CALMET simulations blended three-dimensional hourly RUC analysis fields, observational data and 1-km resolution snow cover data retrieved from the National Hydrologic Remote Sensing Center. Use of accurate snow cover data allowed CALMET to better simulate/replicate the observed mixing heights and vertical temperature profiles, both of which are very important in characterizing the observed meteorological conditions associated with winter ozone formation. This paper will discuss the development of the CALMET database and results of the CALMET model performance in terms of simulating observed meteorological conditions in a complex terrain environment, while employing enhanced geophysical inputs and a high resolution meteorological dataset.Read more...