Distribution of n -alkanes in the Northern Italy aerosols: Data handling of gc-ms signals for homologous series characterization

Abstract

The paper describes the characterization of n-alkane homologous series present in PM samples performed by Gas Chromatography-Mass Spectrometry analysis. The PM samples were collected in three locations in northern Italy: Milan, a large urban area, Oasi Bine, a rural site far from big city centers, and Alpe San Colombano, a remote, high altitude site in the Alps. They represent different particle sizes (PM1 , PM2.5 , PM1 ) and seasons (summer, fall and winter). The analyzed samples were characterized in terms of PM total mass, total concentration of C20-C32 n-alkanes and carbon preference index, CPI , to quantify the relative abundance of odd versus even n-alkanes. 34 As alternative to the conventional method based on peak integration, a chemometric approach based on Autocovariance Function ( EACVF ) computation was found reliable to characterize the homologous series. In particular two parameters have proven useful chemical markers for tracking the biogenic and anthropogenic origins of n-alkanes: CPIEACVF and series%, estimating the % n-alkanes abundance relative to total alkane concentration. The investigated samples display a large variation in the n-alkanes relative abundance: the lowest values ( series% = 1-14%) were found in summer and the highest ( series% =24-48%) in winter. In addition, a considerable seasonal variation of EACVF 4 CPI values can be identified for all the samplingsites: the CPI values are close to 1 (CPI 0.8-1.2) in the cold seasons, revealing a strong contribution from anthropogenic emissions, while spreader values (CPI 0.9-3) were found in the warm season, i.e reflecting a variable contribution from biogenic sources in combination with anthropogenic emissions