Measurement of nonvolatile particle number size distribution

[摘要] An experimental methodology was developed to measure the nonvolatileparticle number concentration using a thermodenuder (TD). The TD was coupledwith a high-resolution time-of-flight aerosol mass spectrometer, measuringthe chemical composition and mass size distribution of the submicrometeraerosol and a scanning mobility particle sizer (SMPS) that provided thenumber size distribution of the aerosol in the range from 10 to 500 nm. Themethod was evaluated with a set of smog chamber experiments and achievedalmost complete evaporation (> 98 %) of secondary organic as well asfreshly nucleated particles, using a TD temperature of 400 °C anda centerline residence time of 15 s.

This experimental approach was applied in a winter field campaign in Athensand provided a direct measurement of number concentration and sizedistribution for particles emitted from major pollution sources. Duringperiods in which the contribution of biomass burning sources was dominant,more than 80 % of particle number concentration remained after passingthrough the thermodenuder, suggesting that nearly all biomass burningparticles had a nonvolatile core. These remaining particles consistedmostly of black carbon (60 % mass contribution) and organic aerosol(OA; 40 %). Organics that had not evaporated through the TD were mostlybiomass burning OA (BBOA) and oxygenated OA (OOA) as determined from AMSsource apportionment analysis. For periods during which traffic contributionwas dominant 50–60 % of the particles had a nonvolatile core whilethe rest evaporated at 400 °C. The remaining particle massconsisted mostly of black carbon with an 80 % contribution, while OAwas responsible for another 15–20 %. Organics were mostlyhydrocarbon-like OA (HOA) and OOA. These results suggest that even at 400 °C some fraction of the OA does not evaporate from particlesemitted from common combustion processes, such as biomass burning and carengines, indicating that a fraction of this type of OA is of extremely lowvolatility.

[学科分类] 几何与拓扑