Assessment of sea salt and mineral dust contributions to PM10 in NW Germany using tracer models and positive matrix factorization

In order to assess the contribution of natural sources (sea salt and mineral dust) to PM10 levels in North-West Germany, a one year measurement project was conducted at two sites between April 2008 and March 2009. The sites were located in an urban and a regional background area. A Positive Matrix Factorization (PMF) based source apportionment study was carried out using chemical composition data of PM10 and PM1 filter samples from 79 selected days in a pooled dataset yielding eight source related factors. High to moderate urban versus regional correlations are obtained for factors denoted as aged marine aerosol, aged mineral dust, secondary sulfate and fossil fuel combustion. The factors identified as secondary nitrate, biomass combustion, re-suspended road dust and industry do not correlate significantly. Since the PMF factors do not represent the natural sources in the meaning of the EU air quality directive, tracer methods based on sodium, chloride and calcium are proposed to infer the PM10 concentrations of natural sea salt, mineral dust background, and the impact of long-range dust intrusions on PM10 concentrations, respectively. These tracer methods are viewed suitable for application in routine source apportionment within the air quality monitoring network.