Monday, 15 January 2007
Spatial, vertical, and temporal variability of aerosol concentration and properties in Houston
Exhibit Hall C (Henry B. Gonzalez Convention Center)
Here we provide a preliminary analysis of data collected during the TexAQS-II study in August and September, 2006, and compare those data with similar measurements made at the surface and from an aircraft in the summer of 2005. The height-dependence of the aerosol was characterized both through the aircraft measurements in 2005 and through simultaneous measurements made from three levels of the 275 m Williams Tower in west Houston in 2006. Those fixed-site measurements were complemented with experiments conducted using a hybrid environmental chamber to examine the temporal evolution of the aerosol. Similar to conventional captured air chambers, the outer walls of this enclosure are made of FEP Teflon. Unlike conventional chambers, the enclosure is divided into two parts by an Expanded PTFE (ePTFE) Teflon sheet. The fibrous structure of the ePTFE acts as a barrier to particulates, while allowing gas molecules to move from one side of the chamber to the other. Ambient air was drawn through a Teflon tube from an adjacent tower and through the lower portion of the chamber. The gas phase composition in the upper portion of the chamber reflects that in the lower portion, which reflects that of the ambient environment, whereas the particulate populations in the two chamber sections are distinct. The change in size and hygroscopicity of an initially monodisperse single component aerosol was continuously monitored for experimental durations as long as a day. These data help decouple the evolution of an aerosol from changes caused by variability in source region and history prior to sampling.