Comparison of methods for measuring gas-particle partitioning of semivolatile compounds

This work demonstrates several difficulties associated with sampling semivolatile aerosols. Gas-particle partition coefficients (Kp=[F/TSP]/A) of semivolatile PAHs and alkanes were estimated from chamber tests using four different sampling methods: filter-adsorbent (FA), filter–filter-adsorbent (FFA), Denuder–filter-adsorbent (DFA), and electrostatic precipitator-Adsorbent (EA). The FA, FFA, and EA sampling methods estimated Kp accurately for high concentrations of PAHs in diesel engine exhaust aerosol. The FA sampler, which used a Teflon Zeflour filter, was biased by filter adsorption of alkane gases sampled at lower concentrations, whereas the FFA sampler, which used a Teflon coated glass fiber filter, was biased by particle evaporation during the same tests. The EA sampler introduced small biases at low concentrations due to chemical artifacts from the corona, non-ideal particle collection, and evaporative loss of collected particles. The DFA sampler was biased by particle losses in the denuder for PAHs in diesel exhaust aerosol, but gave accurate estimates of Kp for alkanes measured at lower concentrations. Results from this research show that none of the methods tested was able to measure gas-particle partition coefficients accurately for each series of compounds under all sampling situations.