Wednesday, 16 January 2002
Measurements of photochemical species at La Porte Airport during TEXAQS-2000
Measurements of NO, NO2, NOy, O3, CO, SO2, and surface meteorological variables were made from the top of a 10 meter tower at the La Porte Municipal Airport from mid-August to mid-September, 2000. This site was set-up with an extensive suite of aerosol, gas-phase, and remote sensing instrumentation as a part of the larger TEXAQS 2000 study in an effort to characterize the urban air chemistry of the Houston metropolitan area. Surface wind data were consistent with a regular offshore-onshore flow pattern. Evidence for a wide variety of emission sources in the region around the La Porte Airport was seen. Elevated levels of NOy and CO from 0500 to 0900 CST were highly correlated with a measured ratio of CO to NOy of approximately 8 that was consistent with the ratio estimated from mobile source emission inventory data. Plumes of short duration (~1 hour) from nearby point sources with levels of NOy in excess of 90 ppbv were typically observed around midnight. Occasionally, these plumes had elevated SO2 or elevated CO, indicative of different types of power plant emissions or of emissions from industrial sources. Ozone levels varied widely. With wind from the southeast through the southwest sector, peak O3 levels could be as low as 50 ppbv. However, episodes of highly elevated O3 (>200 ppbv) were also observed. These episodes appeared to be related to air that had originally passed over the industrialized ship channel area to the north of the site and then transported over the northern part of Galveston Bay where high levels of O3 were photochemically produced. Changing regional airflow then brought the polluted air over the La Porte measurements site. Over the four weeks of the study, a wide range of air pollution episodes was seen at the site, as determined by the relationship of O3 to 1-NOx/NOy (i.e., the fraction of NOx oxidized). The principal features of the data set will be examined with respect to the sources around the site, the meteorology that transports and mixes the emissions from these sources, and the resulting levels of photochemical oxidants produced.
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