Absorption at San Antonio with 3-Wavelength Photo Acoustic Soot Spectrometer, Tricolor Absorption Photometer (ASAPT) Field Campaign Report
Fine particulate matter (PM2.5; particulate matter with an aerodynamic diameter of 2.5μm and smaller) samples were collected at the University of Texas, San Antonio (UTSA) campus (29.57901, -98.62889) from May 15-30. An additional measurement at the UTSA site included aerosol absorption coefficient of PM1 (particulate matter with an aerodynamic diameter of 1.0μm and smaller) using a tricolor absorption photometer (TAP) (Brechtel Mfg. Inc., Hayward, California). The sampling site is approximately 15 miles northwest of downtown San Antonio and in close proximity to major highway 10 and is just south of a forested area. The setup of the sampler and TAP and collection of PM2.5 samples were completed by Baylor University’s graduate student, Subin Yoon. Three three-wavelength photoacoustic soot spectrometers (PASS-3s) were shipped to San Antonio for testing and possible data collection. R. Subramanian went to San Antonio to lead this effort with assistance from Yoon. Each instrument had a critical flaw that inhibited its use for this campaign. Two instruments had low laser power for each wavelength; in addition, there were power and overheating issues with the one instrument that was installed on a test basis. The third instrument had computer issues that impeded any testing. In short, these three instruments would require a major overhaul in terms of lasers and computer systems to be brought back to field capability. As a result, the filter-based optical measurements were added to the campaign as an alternate measurement that would provide mass absorption efficiency at a single wavelength, but no scattering measurement. The TAP instrument was successfully installed and collected data for San Antonio, but full use of the data would have required a co-located scattering measurement. This campaign was co-located with a Texas Commission on Environmental Quality (TCEQ) ozone field study. That TCEQ field study was a collaboration of the University of Houston (PI James Flynn), Rice University (Co-PI Robert Griffen), and Baylor University (Co-PIs Rebecca Sheesley and Sascha Usenko).