Carbon and nitrogen isotopic ratio of the water-insoluble fraction in air filter particulate matter

Particulate matter samples were collected during two episodes of thermal inversion (14.01-2.3.2006) and at four different air monitoring stations in Krakow (Agri: urban background site, Indu: industrial site at Nowa Huta, Poly: domestic coal heating district, Traffic: traffic site) and from the Zakopane sub-urban mountain site (Zakopane), dominated by domestic coal heating. The carbon and nitrogen isotopic compositions of aerosol particles collected in the city of Krakow were measured in 2006 as part of the JRC-IES Krakow project, for which the samples were taken. A total of 42 samples (including 24 source samples) was analysed by Isotope Ratio Mass Spectrometry (IRMS) for isotopic ratios of N and C. The results for samples from different locations show clear grouping of related samples. The leftover of samples provided within the Krakow project were stored in the refrigerator. After one year of cool storage the EA-IRMS measurement was repeated and water extraction was applied. The aim of this experiment was to get more isotopic data for source apportionment. The results showed that the isotopic values of some source samples obtained in 2007 are different from these measured in 2006. However, these differences were not observed for ambient air samples. The possible explanation could be improper storage conditions causing continued reactions between products adsorbed on the filter during storage in the refrigerator. The water extraction removed water soluble inorganic and organic nitrogen-containing compounds and caused the changes in δ15NAir. In this study it is difficult to make a link between sources and ambient air samples after application of water extraction because of the problem with instability of isotopic compositions of the original source samples.