Articles | Volume 8, issue 6
Research article
24 Jun 2015
Research article |  | 24 Jun 2015

ACTRIS ACSM intercomparison – Part 2: Intercomparison of ME-2 organic source apportionment results from 15 individual, co-located aerosol mass spectrometers

R. Fröhlich, V. Crenn, A. Setyan, C. A. Belis, F. Canonaco, O. Favez, V. Riffault, J. G. Slowik, W. Aas, M. Aijälä, A. Alastuey, B. Artiñano, N. Bonnaire, C. Bozzetti, M. Bressi, C. Carbone, E. Coz, P. L. Croteau, M. J. Cubison, J. K. Esser-Gietl, D. C. Green, V. Gros, L. Heikkinen, H. Herrmann, J. T. Jayne, C. R. Lunder, M. C. Minguillón, G. Močnik, C. D. O'Dowd, J. Ovadnevaite, E. Petralia, L. Poulain, M. Priestman, A. Ripoll, R. Sarda-Estève, A. Wiedensohler, U. Baltensperger, J. Sciare, and A. S. H. Prévôt

Abstract. Chemically resolved atmospheric aerosol data sets from the largest intercomparison of the Aerodyne aerosol chemical speciation monitors (ACSMs) performed to date were collected at the French atmospheric supersite SIRTA. In total 13 quadrupole ACSMs (Q-ACSM) from the European ACTRIS ACSM network, one time-of-flight ACSM (ToF-ACSM), and one high-resolution ToF aerosol mass spectrometer (AMS) were operated in parallel for about 3 weeks in November and December~2013. Part 1 of this study reports on the accuracy and precision of the instruments for all the measured species. In this work we report on the intercomparison of organic components and the results from factor analysis source apportionment by positive matrix factorisation (PMF) utilising the multilinear engine 2 (ME-2). Except for the organic contribution of mass-to-charge ratio m/z 44 to the total organics (f44), which varied by factors between 0.6 and 1.3 compared to the mean, the peaks in the organic mass spectra were similar among instruments. The m/z 44 differences in the spectra resulted in a variable f44 in the source profiles extracted by ME-2, but had only a minor influence on the extracted mass contributions of the sources. The presented source apportionment yielded four factors for all 15 instruments: hydrocarbon-like organic aerosol (HOA), cooking-related organic aerosol (COA), biomass burning-related organic aerosol (BBOA) and secondary oxygenated organic aerosol (OOA). ME-2 boundary conditions (profile constraints) were optimised individually by means of correlation to external data in order to achieve equivalent / comparable solutions for all ACSM instruments and the results are discussed together with the investigation of the influence of alternative anchors (reference profiles). A comparison of the ME-2 source apportionment output of all 15 instruments resulted in relative standard deviations (SD) from the mean between 13.7 and 22.7 % of the source's average mass contribution depending on the factors (HOA: 14.3 ± 2.2 %, COA: 15.0 ± 3.4 %, OOA: 41.5 ± 5.7 %, BBOA: 29.3 ± 5.0 %). Factors which tend to be subject to minor factor mixing (in this case COA) have higher relative uncertainties than factors which are recognised more readily like the OOA. Averaged over all factors and instruments the relative first SD from the mean of a source extracted with ME-2 was 17.2 %.

Short summary
Source apportionment (SA) of organic aerosol mass spectrometric data measured with the Aerodyne ACSM using PMF/ME2 is a frequently used technique in the AMS/ACSM community. ME2 uncertainties due to instrument-to-instrument variations are elucidated by performing SA on ambient data from 14 individual, co-located ACSMs, recorded during the first ACTRIS ACSM intercomparison study at SIRTA near Paris (France). The mean uncertainty was 17.2%. Recommendations for future studies using ME2 are provided.