Aerosol source apportionment from 1 year measurements at the CESAR tower at Cabauw, NL.

Intensive measurements of submicron aerosol particles and their chemical composition were performed with an Aerosol Chemical Speciation Monitor (ACSM) at the Cabauw Experimental Site for Atmospheric Research (CESAR) in Cabauw, NL. The campaign lasted nearly one year from July 2012 to June 2013 as part of the ACTRIS project. Including black carbon data an average particulate mass concentration of 9.50 μg m^-3 was obtained during the whole campaign with dominant contributions from ammonium nitrate (45%), organic aerosol (OA, 29%), and ammonium sulfate (19%). 12 exceedances of the World Health Organization (WHO) PM_2.5 daily mean limit (25 μg m^-3) were observed at this rural site using PM1 instrumentation only. Ammonium nitrate and OA represented the largest contributors to total particulate matter during periods of exceedance. Source apportionment of OA was performed season-wise by Positive Matrix Factorization (PMF) using the Multilinear Engine 2 (ME-2) controlled via the source finder (SoFi). Primary organic aerosols were attributed mainly to traffic (8-16% contribution to total OA, averaged season-wise) and biomass burning (0-23%). Secondary organic aerosols (SOA, 61-84%) dominated the organic fraction during the whole campaign, particularly on days with high mass loadings. A SOA factor which is attributed to humic-like substances (HULIS) was identified as a highly oxidized background aerosol in Cabauw. This shows the importance of atmospheric ageing processes for aerosol concentration at this rural site. Due to the large secondary fraction, the reduction of particulate mass at this rural site is challenging on a local scale. [ABSTRACT FROM AUTHOR]