Evaluating Quantification Capabilities of a New Higher-Resolution Aerosol Chemical Speciation Monitor for Long-Term Measurements of Non-Refractory Aerosol

BENJAMIN A. NAULT, Manjula Canagaratna, Philip Croteau, Edward Fortner, Andrew Lambe, Harald Stark, Donna Sueper, Leah Williams, Douglas Worsnop, John Jayne, Aerodyne Research, Inc.

     Abstract Number: 355
     Working Group: Instrumentation and Methods

Abstract
Long-term measurements of the composition and mass concentration of particulate matter (PM) are essential for source apportionment, epidemiological studies, and air quality trends. The Aerosol Chemical Speciation Monitor (ACSM) has been widely used for in-situ, high time resolution measurements. However, current ACSMs have near unit mass resolution (UMR). UMR impacts detection limits and separation and identification of ions, limiting source apportionment. Further, uncertainty in organic aerosol (OA) relative ionization efficiency (RIE) in both ACSM and aerosol mass spectrometer (AMS) measurements can impact quantification. Here, we present a new instrument, the Time-of-Flight ACSM eXtended (TOF-ACSM-X) with updated analysis software (Tofware), to allow for high-resolution peak fitting. The TOF-ACSM-X has a mass resolution of ~2000 m/Δm, which is approximately an order of magnitude increase compared to the other current versions of ACSMs. This enhanced resolution improves ammonium detection limits by approximately 2-orders of magnitude, from ~0.10 μg m^-3 to ~0.004 μg m^-3 (TOF-ACSM versus TOF-ACSM-X, respectively), for 15-minute integration times. Intercomparisons of the TOF-ACSM-X with other measurements show improved performance in source apportionment and elemental analysis. The combined effects of thermal decomposition, ionization, and ion transmission efficiency on OA RIE values measured for the TOF-ACSM-X are discussed and compared with those measured for other ACSM and AMS instruments. The use of different OA RIEs for different sources and instruments will be discussed.