LDTR Measurements of PSAP Particle-Laden Filters from the Biomass Burning Observation Project (BBOP) Field Campaign
Cary Presser, Ashot Nazarian, Joseph M. Conny, Duli Chand, Arthur Sedlacek
Absorptivity measurements in the infrared with the laser-driven thermal reactor (LDTR) at ambient conditions were carried out with particle-laden filters from a three-wavelength (visible) particle/soot absorption photometer (PSAP) obtained during the Biomass Burning Observation Project (BBOP) field campaign. The focus of this study was to validate whether the LDTR approach could provide results for particle absorption coefficient that are consistent with other commercially available instrumentation (in this case with the PSAP which has been compared with numerous other optical techniques). The technique measures material absorption directly, provides information on filter optical properties, and considers for the presence of the filter material and its effect of particle absorption (e.g., filter material and volatile organics effects on absorption enhancement', and particle loading effects leading to 'shadowing'). For measurements carried out under ambient conditions (as with the PSAP), only a thermocouple placed flush with the filter back surface and the laser probe beam impinging normal to the filter front particle-laden surface are required to ascertain particle absorptivity. Thus, in principle one can carried simultaneously both the transmission and absorption measurements (at different discrete wavelengths) with a simple arrangement to determine particle absorption coefficient. For this investigation, LDTR measurements were carried out with PSAP filters (pairs with both blank and exposed filters) from eight different days during the campaign, having different relatively light particle loadings. The observed particles coating the filters were thought to consist of soot (having broadband absorption characteristics) and viscous organic material (probably absorbing at shorter wavelengths). The LDTR analysis compared well with the PSAP results when compared to wavelength dependent results from an ultraviolet/visible spectrometer.