AAAR 34th Annual Conference
October 12 - October 16, 2015
Hyatt Regency
Minneapolis, Minnesota, USA
Abstract View
Seasonal Variations in the Carbonaceous Composition of Size-Resolved Particles Collected in Tempe, Arizona
DENISE NAPOLITANO, Pierre Herckes, Arizona State University
Abstract Number: 678 Working Group: Carbonaceous Aerosols in the Atmosphere
Abstract Atmospheric processing (chemical and physical) and variations in aerosol sources both affect the composition of particles in different size fractions. However, few studies exist that examine individual organic compounds in size-resolved aerosol samples, and fewer still characterize these types of samples using isotopic analysis. In this study, total carbon (TC) and individual n-alkanes were quantified and analyzed for stable carbon isotopic composition to determine variations in particle composition among different seasons and different size fractions.
Aerosol samples were collected on the Tempe campus of Arizona State University in January, April, June, and October of 2014. High-volume samplers were equipped with five cascade impactor stages to collect particle size fractions with cutoff diameters of 7.2, 3, 1.5, 0.95, and 0.49 microns, and a backup filter to collect particles smaller than 0.49 microns. Samples were analyzed by thermal optical transmittance for TC concentration, and isotopic analysis of TC was performed using elemental analysis – isotope ratio mass spectrometry. n-alkanes were quantified by GC/MS, and compound-specific isotope analysis was performed by gas chromatography-combustion-isotope ratio mass spectrometry.
Samples collected in January were found to be more concentrated and lighter in total isotopic composition by 0.5-1.7 per mil, indicating a dominant emission source in the winter that is less significant in warmer months. Changes in isotopic composition with particle size during a single sampling period were observed for bulk carbon and n-alkanes in all seasons, signifying varying source contributions with particle size. The carbon preference index (CPI) of long-chain n-alkanes in April, June, and October, as well as the depletion of carbon-13 in odd-chain n-alkanes during the spring and summer months, indicate dominance of biogenic sources during these sampling times, while a CPI < 2 in January suggests a dominance of anthropogenic emissions.