Activity: Talk or presentation › Talk at conference or symposium › Science to science
Introduction: Condensation nuclei counters (CNC) are proven metrology devices for particle number (PN) concentration measurements, used in scientific, industrial and environmental applications alike and legally mandated for automotive exhaust characterisation. The condensation of the working fluid on the (nano)particles is known to depend on both, the particles and the working fluid. As presented already at the AAAR annual meeting 2017, the inherent potential of optimising and usefully exploiting fluid - particle matching remains largely untapped. Instead, n-butanol is presently used almost invariably for an undesignated mix of different aerosol particles. Similarly, condensation models assume spherical structures, neglecting the real, often highly complex surface structures of aerosol nanoparticles.
Methods: A correction model of the deviation in the effective CNC cutoff caused by the difference of a fractally shaped condensation nucleus to an ideal sphere was developed. This theory-based approach was backed by analysis of published counting efficiency curves using different nuclei and validated against this data. In a parallel effort, key factors describing particle species – working fluid interaction and resultant counting efficiency – have been compiled and are presently being experimentally examined using a dedicated research CNC with different working fluids and particle species and structures. To examine the dedicated influence of morphology on the nucleation process a study using small angle X-ray scattering (SAXS) on defined particles in a well-known CNC is in progress.
Results: Comparing the developed model with literature data indicates a strong dependency of nucleation efficiency on the respective material properties and furthermore a significant impact of the particle morphology. Both effects are hence significant for a correct determination of PN and a targeted further development of CNC-based aerosol analysers. Yet, the contributions of morphology and material matching to particle activation overlap and cannot be clearly and unambiguously separated experimentally. A test series was designed to settle this point by systematic examination of the nucleation on particles with different morphology but same material. By comparisons of the experimental results with the model, the correction of CNCs is further sharpened for measuring PN in automotive exhaust.