Regional and local background ozone in Houston during Texas AirQuality Study 2006

摘要

Principal Component Analysis (PCA) is used to isolate the common modes ofbehavior in the daily maximum 8-h average ozone mixing ratios measured at 30Continuous Ambient Monitoring Stations in the Houston-Galveston-Brazoria areaduring the Second Texas Air Quality Study field intensive (1 August to 15 October 2006).Three principal components suffice to explain 93% of the total variance. Nearly 84%is explained by the first component, which is attributed to changes in the "regionalbackground" determined primarily by the large-scale winds. The second component (6%)is attributed to changes in the "local background," that is, ozone photochemicallyproduced in the Houston area and spatially and temporally averaged by local circulations.Finally, the third component (3.5%) is attributed to short-lived plumes containing highozone originating from industrial areas along Galveston Bay and the Houston ShipChannel. Regional background ozone concentrations derived using the first componentcompare well with mean ozone concentrations measured above the Gulf of Mexico by thetunable profiler for aerosols and ozone lidar aboard the NOAA Twin Otter. The PCAregional background values also agree well with background values derived using thelowest daily 8-h maximum method of Nielsen-Gammon et al. (2005), provided theGalveston Airport data (C34) are omitted from that analysis. The differences found whenGalveston is included are caused by the sea breeze, which depresses ozone at Galvestonrelative to sites further inland. PCA removes the effects of this and other local circulationsto obtain a regional background value representative of the greater Houston area.