Quantitative Analysis of Aerosol Time-of-Flight Mass Spectrometry Data using YAADA

Quantitative Analysis of Aerosol Time-of-Flight Mass Spectrometry Data using YAADA Aerosol Time-of-Flight Mass Spectrometry (ATOFMS) instruments have been used to measure the size and composition of single aerosol particles in California. ATOFMS data are not direct quantitative measurements of aerosol composition because the instruments exhibit non-linear response to aerosol concentration, particle size, and particle composition. The goal of this work is to quantitatively compare ATOFMS and reference sampler data in order to both understand ATOFMS instrument operation, and to develop procedures to transform ATOFMS data to semi-quantitative aerosol compositions. Ambient measurements from the Bakersfield Instrument Intercomparison Study were analyzed. ATOFMS instrument busy time (the time required to save acquired data) was found using a statistical comparison of the number of particles detected to that expected for a Poisson process modified to include busy time. The fraction of busy time was highly variable and in the range 0.05 to 0.95; thus busy time cannot be ignored for accurate quantitative comparison of ATOFMS data with reference sampler data. The sensitivities of the ATOFMS instrument to aerosol mass, organic carbon (OC), and elemental carbon (EC) were determined by a selecting single particle response function for each analyte. ATOFMS response to mass, OC and EC fit well to a power law in particle size; these responses are similar to those found previously for aerosol mass and inorganic ions. Using the recommended response functions, ATOFMS data were scaled for comparison with independent aerosol measurements. Comparison of scaled aerosol mass with that measured using Beta Attenuation Monitors (BAMs) showed semiquantitative agreement, i.e., scaled ATOFMS data agreed within a factor of three with the BAMs data. ATOFMS data scaled for OC and EC concentrations were systematically lower than from collocated filter-based measurements because the scaled ATOFMS data propagated the systematic difference between short-term impactor measurements and the filter-based measurements. The novel data analysis methods developed here will be included in the next public release of YAADA, a software toolkit to analyze single particle mass spectral data.