Differentiation of Natural and Anthropogenic Organic Compounds on Atmospheric Particles by Molecular and Stable Isotope Composition - Pacific 2001, Lower Fraser Valley Air Shed Study

This component of the CFCAS Pacific 2001 study examined the character of specific non-volatile organic compounds (nVOCs) extracted from filtered total suspended particulates at the Pacific 2001 sites in the Lower Fraser Valley (LFV), Vancouver, BC region. The objective is to identify or fingerprint spatial and temporal variations in both molecular and stable isotope composition of these organic compounds with the goal of understanding their sources or to provide insights into transport and/or atmospheric chemistry processes. This will provide critical information to help assess the potential type and magnitude of exposure that humans receive from nVOCs in such urban settings, and the associated health risks. Aerosol samples were collected over 24hr to 7-day period on HiVol filters in the LFV at Slocan Park, Golden Ears Park, Langley HS, Sumas Mt., and Cassiar Tunnel (2hr). nVOCs s were solvent-extracted from filters, then separated into different compound classes by silica-gel chromatography. Selected fractions are analysed for their individual compound molecular compositions by Gas Chromatography-Mass Spectrometry (GC/MS) and by Continuous Flow-Isotope Ratio Mass Spectrometry (CF-IRMS) for their stable carbon ratio. Significant variations in nVOC composition are observed for the 5 LFV sites. These are related to a combination of natural and anthropogenic urban activities. The most striking discovery is the strong odd-even carbon number predominance (OEP) observed for BOTH molecular and carbon isotope data. Recent natural release of hydrocarbons from plants have a clear predominance for the odd-carbon numbered n-alkanes. These C23 - C31 compounds are also systematically depleted in 13-C. The carbon isotope range between the odd and even compounds is up to 10 permil for the plant signatures. Anthropogenic and "aged" hydrocarbons have substantially lower molecular and isotope OEPs. This novel biogeochemical approach has good potential for estimating broad source apportionment and process control of nVOCs in rural and urban air masses.