Development of aerosol chemical ionization mass spectrometry for the study of organic particles
Hearn, John Daniel
MetadataShow full item record
An aerosol chemical ionization mass spectrometer (A-CIMS) has been developed for the study of organic particles. The low degree of fragmentation from this soft ionization technique enables detection of intact molecular ions which simplifies quantification and identification, especially in complex mixtures. Chemical ionization also allows flexible ionization which allows organic functional groups to be selectively ionized. For example, alkanes are not detectable with proton transfer ionization from +protonated water clusters, but NO will ionize them. The instrument has been calibrated and it is sensitive to organics near its calculated detection limit, and efforts have been made to reduce this limit further through off-line or on-line particle concentration. As examples of the utility of A-CIMS, heterogeneous reactions involving ozone, OH, or Cl attack on organic particles have been investigated as a function of particle phase and morphology. Accurate measurements of heterogeneous kinetics with A-CIMS have reconciled discrepancies among other published results. Products from these reactions have also been detected, and since A-CIMS is sensitive to both gas and condensed phases, it gives a more complete picture of particle evolution. The implications of the results of these heterogeneous reaction studies are discussed in the context of atmospheric chemistry.