Source Identification of Size-Segregated Aerosol in Munster, Germany, by Factor Analysis

Sources of size-segregated PM10, as collected with a five stage Berner type impactor during six intensive measurement campaigns between January 2006 and August 2007 in Munster, NW Germany, were studied by applying factor analysis. PM samples were collected twice a day, each with a sampling duration of 5 to 7.5 hours. Samples were analyzed for water soluble ions, Ca2+, Cl-, Mg2+, Na+, NH4+, NO3-, SO42-, and elemental and organic carbon. Positive matrix factorization (PMF) was used for source apportionment where each size class accounted for a single variable. Five factors were identified of which at least four could be found during each season. Traffic, ammonium nitrate, and long distance transport showed a weekly cycle, whereas the factor representing power generation and industrial products seemed to be relatively stable through the week. Sea salt particles were independent of the day of week. The five factors do not only have a similar composition, but also a similar size distribution, throughout all seasons of the year. Particles from long-distance transport were identified in the accumulation mode while PM originating from power generation were characterized by a larger diameter. Sea salt aerosol consisted mainly of coarse particles, ammonium nitrate is mainly found in the largest size fraction. Even without a detailed chemical trace elements analysis, precise PM source apportionment was accomplished.