Measurement report: Size-resolved seasonal study of inorganic ions and isotopic carbon signatures of aerosol particles at the Wadden Sea

Measurements of aerosol size-resolved chemical composition and source contribution of carbonaceous aerosols provide a unique opportunity to characterize continental outflow over the sea. Studies at coastal sites usually show an interesting mix of continental and marine aerosol sources. However, few data exist on the size dependence of the aerosol chemical composition and isotopic source apportionment of organic carbon (OC). This study investigates differences in aerosol composition among size-dependent samples collected in different seasons and wind sectors. It also highlights isotope measurements as a tool to study sources and atmospheric processing of OC. Size-resolved measurements of inorganic ions, levoglucosan, and total carbon (TC) were combined with 13 C and 14 C analysis of OC at different desorption temperatures, which allows to investigate subgroups like secondary organic aerosol (SOA) and aged organic aerosol. The land-sector samples are dominated by nitrate, ammonium, and TC, while sulfate and TC dominated the single sea-sector sample set. Sulfate reached 0.5 µg m −3 in both sea-sector and land-sector samples, indicating a possible contribution from ship-emissions. Fossil OC fractions were highest in particles <250 nm, characteristic for combustion-related traffic emissions. 13C/12C-ratios of ambient OC deviate strongly from expected signatures of primary sources and indicate SOA contribution to more volatile carbon and smaller particles. The 13C/12C-ratios of less volatile OC at larger sizes are consistent with a significant influence of photochemical processing. The results indicate shipping emissions as a possible important contributor to sulfate aerosols in sea-influenced samples and demonstrate the highly processed nature of OC in the European continental outflow.