Real-time chemical analysis of organic aerosols using a thermal desorption particle beam mass spectrometer

An instrument has been developed for real time, quantitative chemical analysis of organic particles in laboratory environments, In this apparatus, which we call a Thermal Desorption Particle Beam Mass Spectrometer (TDPBMS), particles are sampled into a differentially-pumped vacuum chamber, focused into a narrow, low-divergence particle beam using aerodynamic lenses, and then transported into a high-vacuum region where they impact on a heated surface, evaporate, and the vapor is mass analyzed in a quadrupole mass spectrometer, The average composition of a continuous stream of particles is thus measured in real Lime, and size-dependent composition can be obtained by passing the incoming aerosol through a differential mobility analyzer, The TDPBMS can analyze multicomponent organic particles in the similar to 0.02-0.5 mu m size range for compound concentrations > similar to 0.1-1 mu g/m(3) without particle matrix effects, By using careful calibration techniques that account for particle shape and transport efficiency, the particulate organic components can be quantified with an estimated uncertainty of similar to 20%. The utility of TDPBMS for laboratory studies of aerosol chemistry is demonstrated by monitoring the tridecanoic acid concentration in secondary organic aerosol formed during a smog chamber reaction of 1-tetradecene and ozone.