PROTON TRANSFER REACTION ION TRAP MASS SPECTROMETER (PTR-ITMS): NEXT GENERATION AIRCRAFT INSTRUMENTATION FOR GAS PHASE ORGANIC ANALYSIS M. Lizabeth Alexander Pacific Northwest National Laboratory P.O. Box 999/K8-93 Richland, WA 99352 email: lizabeth.alexander@pnl.gov Knowledge of the impacts of volatile organic compounds (VOCs) on aerosol formation and evolution in the troposphere is limited by our ability to make selective, high time resolution measurements of key species from airborne platforms. Current technologies lack the sensitivity to measure boundary layer concentrations of these species (<10 ppt at one second time resolution) and their oxidation products from aircraft platforms. Real-time measurements of key volatile organic species are a critical component in understanding gas-particle partitioning and the interaction of primary and secondary aerosols (POA and SOA) with organic species and their oxidation products. Recent evidence shows that VOCs play an important role in the nucleation process where new aerosols are formed. New climate models will require improved measurements of the gas-phase organic species correlated with real-time measurements of aerosol size distributions, composition, and optical properties. Proton transfer reaction mass spectrometry (PTR-MS) is a chemical ionization (CI) method that has been successfully deployed on aircraft with a demonstrated sensitivity of close to 100 ppt for a single species with 1 second time resolution. Current PTR-MS instruments are limited in both time resolution and sensitivity by the use of a linear, sequential scanning quadrupole mass spectrometer. The use of proton transfer from H3O+ as a CI reagent also has limitations that result from ions of the same mass but different identity (isobaric interferences). We propose to develop a more sensitive and selective direct sampling mass spectrometer by coupling the H3O+ ionization source to an ion trap mass spectrometer (ITMS). This PTR-ITMS instrument will allow simultaneous, multiple ion detection with the time resolution and sensitivity required for the new aircraft studies. The use of an ITMS will also allow resolution of isobaric interferences using real-time MS-MS analysis. Finally, the PTR-ITMS will incorporate the use of CI agents other than H3O+ to further increase selectivity for key organic species. [back to ASP ST Membership]