Determination of the particle counting efficiency and chemical sensitivities of an aerosol time of flight mass spectrometer under ambient sampling conditions

Recently developed aerosol time-of-flight mass spectrometer (ATOFMS) instruments are capable of determining the size and chemical composition of single particles (Noble and Prather, 1996, Gard et al., 1997). These instruments provide convenient determination of atmospheric aerosol composition on a single particle basis in real time. To date, data from these instruments have been used qualitatively to study both the sources of ambient aerosols (Liu et al., 1997) and the atmospheric transformation of particles (Gard et al., 1998). However, quantitative reconstruction of a continuous time series of the actual size distribution and chemical composition of atmospheric aerosols requires that the absolute counting efficiency and chemical sensitivities of these instruments be known.