3-D DISTRIBUTION OF OZONE DURING THE MAJOR POLLUTION EVENT OF 30 AUGUST 2000 DURING TEXAQS 2000

摘要

Air pollution in the Houston, Texas area is a product of strong emissions and specialized meteorological conditions. The emissions are from the Houston urban area, from power plants, and, to the east and southeast of the city, from the many refineries and petrochemical plants along the Ship Channel and the western shore of Galveston Bay. The specialized meteorology consists of interactions of the local sea-breeze circulations with larger-scale geostrophic or gradient flows. During the Texas Air Quality Study (TexAQS) from mid August to mid September 2000, many days had onshore or weak ambient flow, and the sea breeze, generated by the temperature contrast between the land and the Gulf of Mexico, moved inland by early afternoon. However, conditions where the larger-scale flow was offshore and opposed the sea breeze (Fig. 1) were especially conducive to pollution events, because the sea-breeze front stalled over the sources, and the pollutants remained in the area and accumulated. Stalled synoptic fronts have also previously been identified as preferred locations for high-pollution episodes (McNider et al., 1995). One especially dramatic example of these processes was 30 August 2000 during the Houston air quality experiment (TexAQS 2000). 30 August was a day when the bay and gulf breezes did not begin along the western shore of Galveston Bay until late in the afternoon, as a result of large-scale offshore flow in the atmospheric boundary layer (ABL). In the following study we present a detailed analysis of this event, emphasizing how the chemistry and airborne ozone lidar profile measurements provide insight into the meteorological processes beyond that available from the meteorological instrumentation alone, which included rawinsondes, tethersondes, surface flux sites, surface mesonets, and radar wind profilers.