Sampling Atmospheric Carbonaceous Aerosols Using an Integrated Organic Gas and Particle Sampler

Abstract

Measurement of particle-bound organic carbon (OC) may be complicated by sampling artifacts such as adsorption of gas-phase species onto particles or filters or evaporation of semivolatile compounds off the particles. 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 is designed to first remove gas-phase chemicals via sorption to the XAD-coated denuder, and subsequently particles are trapped on a quartz filter. A backup sorbent system consisting of sorbent- (XAD-4 resin) impregnated filters (SIFs) was used to capture the semivolatile OC that evaporates from the particles accumulated on the upstream quartz filter. A traditional filter pack (FP) air sampler, which uses a single quartz filter to collect the particles, was employed for comparison in this study. Elemental and organic carbon were determined from filter punches by a thermal optical transmittance aerosol carbon analyzer. Field measurements show that there was no significant difference between the elemental carbon concentrations determined by the FP and IOGAPS, indicating that particle loss during the transit through the denuder tube was negligible. Compared with the OC determined by FP (3.9-12.6 microg of C/m3), the lower OC observed on the quartz filter in the IOGAPS (2.2-6.0 microg of C/m3) was expected because of the removal of gas-phase organics by the denuder. Higher semivolatile organic carbon (SVOC) on the backup SIFs during the night (1.24-8.43 microg of C/m3) suggests that more SVOC, emitted from primary sources or formed as secondary organic compounds, partitions onto the particles during the night because of the decreased ambient temperature. These data illustrate the utility of an IOGAPS system to more accurately determine the particle-bound OC in comparison to FP-based systems.

Methods to Assess Carbonaceous Aerosol Sampling Artifacts for IMPROVE and Other Long-Term Networks

“…Denuder Approach OC denuders [31][32][33][34][35][36][37][38][39][40][41][42] allow organic vapors to diffuse to an absorbing surface while permitting small particles to pass through the filter. Baked quartz fiber filter strips, 33 XAD resin, 35 and activated carbon impregnated filter strips 14,43 have been used as absorbents.…”

Evaluation of an annular denuder system for carbonaceous aerosol sampling of diesel engine emissions

“…The annular denuder is an XAD-coated glass tube with one to eight annular channels with annuli spacing of 1.0, 1.0, 1.2, 1.0, 1.0, 1.0, 1.4, and 1.2 mm (from center outward) and is available in two lengths, 28 and 60 cm (URG, Inc., Chapel Hill, NC) (Fan et al, 2003). The annular XAD denuder is coupled with a cyclone and multistage filterpack as the integrated organic gas and particle sampler (IOGAPS), which has been applied to examine artifacts associated with OC measurement in the urban atmosphere (Fan et al, 2003;Fan et al, 2004b). The honeycomb denuder consists of cells separated by disks and has also been applied in ambient carbonaceous aerosol sampling (Mader et al, 2001).…”

“…But the activated carbon can become loose and shed, thus introducing additional OC and EC onto the filter downstream of the denuder (Subramanian et al, 2004;Viana et al, 2006). Overall, XAD is a sorbent with reasonably high collection efficiency (Fan et al, 2004a;Fan et al, 2003) and has the advantage that the organic compounds adsorbed by XAD can be extracted with solvents for further analysis.…”

“…XAD-coated filters (Fan et al, 2003;Fan et al, 2004a;Fan et al, 2004b) and carbonimpregnated filters (Subramanian et al, 2004;Eatough et al, 1999;Eatough et al, 2003;Cheng et al, 2010) are the main kinds of backup filters that are used. XAD-coated quartz filters are able to withstand a higher temperature (350 C) than carbonimpregnated glass-fiber filters (200 C) (Cheng et al, 2010), which allows more SVOC to be desorbed and detected.…”

“…Detailed information on the IOGAPS used for this work has been published elsewhere (Fan et al, 2003;Fan et al, 2004a;Fan et al, 2004b) and is briefly summarized here. The IOGAPS is a multicomponent air sampler consisting of a cyclone (URG, Chapel Hill, NC, USA) and a 60-cm-long, eight-channel XAD-4-coated annular glass denuder (Gundel et al, 2001).…”