LIGHT ABSORBING AEROSOLS: CALIBRATION, MEASUREMENTS, AND EMISSIONS FOR NEW YORK CITY
Grimes, Courtney Deejounette
Dickerson, Russell R.
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Light absorbing aerosols such as black carbon (BC) impact weather, climate, and human health. Several instruments have been developed to measure light absorbing aerosols. Filter-based techniques, due to the simplicity of operation, are used on airborne platforms and ground sites across the globe. One such instruments, the Aethalometer, determines the attenuation of light passing through a filter but is known to have inherent errors that need to be corrected. One part of this dissertation focuses on characterizing BC instruments in the laboratory using a well-studied BC surrogate and other atmospherically relevant aerosols. The second part focus on measurements of light absorbing, ambient aerosols to evaluate emissions inventories.I characterize BC instrumentation using a commercially available BC surrogate, Cab-O-Jet 200. This BC surrogate was first size selected at 300 nm mobility diameter, and then the particle mass, mp, was determined with an aerosol particle mass analyzer (APM). A condensation particle counter (CPC) served as a reference method for measurement of number concentration, Np; when multiplied by mp, Np gives the mass concentration. I evaluated an Aethalometer (Model AE31) as a function of particle loading, size, wavelength, and coating. Uncertainty in filter-based BC measurements increases substantially for BC particles coated with minimally absorbing ammonium sulfate or with brown carbon (BrC). A Thermal optical absorbance (TOA) instrument was also characterized with a binary, aqueous mixture consisting of the same BC surrogate plus sucrose to test separation of elemental carbon (EC) from organic carbon (OC). A Model AE33 Aethalometer was also successfully evaluated with particles from the BC surrogate, and it performed with good accuracy when compared to in-situ laboratory measurements. Ambient measurements of light absorbing aerosols from campaigns in Xingtai, China were used to determine the mass absorption cross section (MAC) – critical to understanding radiative forcing and climate. Relatively high ambient MAC values in Xingtai, China were found by using airborne data from the single particle soot photometer (SP2) and the particle soot absorption photometer (PSAP). Particles from Xingtai were also collected on filters and classified using Scanning electron microscopy and energy dispersive X-Ray (SEM-EDX); both BC and mineral dust were found. Using a well characterized Aethalometer for BC mass concentration, total BC emissions from the NYC region were calculated from ambient BC/CO ratios and emission inventories of CO. Results indicate BC emissions are somewhat underestimated in existing inventories, suggesting issues of environmental health and justice.