Temperature Dependence of Gas-Particle Partitioning of Primary Organic Aerosol Emissions from a Small Diesel Engine

摘要

A new experimental technique has been developed to study the gas-particle partitioning behavior of primary organic aerosol (POA) emissions from combustion sources at atmospherically relevant concentrations. The technique involves slowly filling a Teflon chamber with a constant emission source. As aerosol concentrations increase inside the chamber, the gas-particle partitioning of semivolatile organics shifts to the particle phase, thus increasing the fuel-based POA emission factor. The technique allows characterization of partitioning under isothermal conditions and atmospherically relevant concentrations. The technique was evaluated using emissions from a small diesel engine; the measured changes in gas-particle partitioning agreed well with previously published data for this engine measured with a dilution sampler. The temperature dependence of the gas-particle partitioning was investigated by conducting experiments at three different temperatures (15°C, 26°C, and 33°C). Increasing organic aerosol concentration and decreasing temperature increased the fuel-based POA emission factor. The gas-particle partitioning data were fit using absorptive partitioning theory to determine the volatility distribution and enthalpy of vaporization (ΔH _v) of the emissions. We have derived two fits; one using the volatility basis set approach and a second using a two-product model. Both fits are suitable for use in chemical transport models. These fits were tested using previously published thermodenuder data. Partitioning calculations predict that the gas-particle partitioning from POA emissions from this engine vary by about a factor of 4 across the atmospherically relevant range of temperature and organic aerosol concentrations. This underscores the semivolatile nature of POA emissions.