Atmospheric carbonaceous aerosols: Sampling, analysis, and characterization.

摘要

A denuder-based integrated organic gas and particle sampler (IOGAPS), specifically designed to minimize sampling artifacts, has been developed to sample atmospheric carbonaceous aerosols. IOGAPS first removes gas-phase chemicals via sorption to the XAD coated denuder, then traps particles on a quartz filter placed downstream of the denuder. A backup system consisting of sorbent (XAD-4 resin) impregnated quartz filters (SIFs) was used to capture the semivolatile organic carbon (SVOC) that evaporates from the upstream particle-laden filter. Elemental and organic carbon (EC and OC) were determined from filter punches by a thermal optical transmittance (TOT) aerosol carbon analyzer. Systematic evaluation of the performance of the IOGAPS showed that the IOGAPS system is able to determine the particle-bound OC more accurately in comparison to filter-pack (FP) based systems. Field sampling was conducted in July 2001 and March 2003 in downtown Toronto, ON and August 2001 in Vancouver, BC. Both IOGAPS and FP samples (i.e., PM2.5) were collected separately during the day and night so that diurnal variations of OC and SVOC could be investigated. The OC determined by the IOGAPS was usually higher during the night. This could be explained by the partitioning of the gas phase SVOC onto the pre-existing aerosols due to decreased ambient temperatures during the night. Such SVOC is often lost during FP sampling, but can be captured by the IOGAPS.; The temperature-dependent subcooled liquid vapor pressures (PL) and enthalpies of vaporization (DeltavapH) at 25°C for 10 oxygenated polycyclic aromatic hydrocarbons (OPAHs) were determined by a gas chromatography (GC) method. The vapor pressures of OPAHs were found to be significantly lower than their corresponding PAHs. It was estimated by the Junge-Pankow model that OPAHs with vapor pressures lower than 10-4 Pascal would predominately reside in the particle phase in the atmosphere. This could help explain the field measurements of four detected OPAHs (i.e., 9-fluorenone, anthraquinone, benzanthrone, and benz[a]anthracene-7,12-dione) in total suspended particle (TSP) samples collected in downtown Toronto during the summer of 2003. Their average particle-bound concentrations (ranges in parentheses) were 40 (10--70), 130 (50--270), 220 (110--360), and 270 (170--390) pg/m3, respectively.