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The errors inherent in the fitting and integration of the pseudo-Gaussian ionpeaks in Aerodyne high-resolution aerosol mass spectrometers (HR-AMSs) havenot been previously addressed as a source of imprecision for these orsimilar instruments. This manuscript evaluates the significance of thisimprecision and proposes a method for their estimation in routine dataanalysis. In the first part of this work, it is shown that peak-integration errors areexpected to scale linearly with peak height for the constrained-peak-shapefits performed in the HR-AMS. An empirical analysis is undertaken toinvestigate the most complex source of peak-integration imprecision: theimprecision in fitted peak height, σh. It is shown that the majorcontributors to σh are the imprecision and bias inherent in them/z calibration, both of which may arise due to statistical and physicalnon-idealities of the instrument. A quantitative estimation of thesem/z-calibration imprecisions and biases show that they may vary from ion toion, even for ions of similar m/z. In the second part of this work, the empirical analysis is used to constraina Monte Carlo approach for the estimation of σh and thus thepeak-integration imprecision. The estimated σh for selectedwell-separated peaks (for which m/z-calibration imprecision and bias couldbe quantitatively estimated) scaled linearly with peak height as expected(i.e. as n1). In combination with the imprecision in peak-widthquantification (which may be easily and directly estimated duringquantification), peak-fitting imprecisions therefore dominate countingimprecisions (which scale as n0.5) at high signals. The previous HR-AMSuncertainty model therefore underestimates the overall fitting imprecisioneven for well-resolved peaks. We illustrate the importance of this conclusionby performing positive matrix factorization on a synthetic HR-AMS dataset both with and without its inclusion. In the third part of this work, the Monte Carlo approach is extended to thecase of an arbitrary number of overlapping peaks. Here, a modification to theempirically constrained approach was needed, because the ion-specificm/z-calibration bias and imprecision can generally only be estimated forwell-resolved peaks. The modification is to simply overestimate them/z-calibration imprecision in all cases. This overestimation results inonly a slight overestimate of σh, while significantly reducing thesensitivity of σh to the unknown, ion-specific m/z-calibrationbiases. Thus, with only the measured data and an approximate estimate of theorder of magnitude of m/z-calibration biases as input, conservative andunbiased estimates of peak-integration imprecisions may be obtained for eachpeak in any ensemble of overlapping peaks

Peak-fitting and integration imprecision in the Aerodyne aerosol mass spectrometer: effects of mass accuracy on location-constrained fits