Application of chemometrics to the identification of trends in polynuclear aromatic hydrocarbons and alkanes in air samples from Oporto

A sampling system for collecting airborne particulate matter was installed at Oporto Town Hall, Sampling was carried out every seven days and took place from June 1995 to June 1996. A total of 56 samples were collected and analysed for 16 PAHs and 23 alkanes by GC-MS, and organic and elemental carbon by thermal oxidation and detection of CO2 by infra-red. In addition meteorological data (precipitation, mind speed and direction, maximum and minimum temperature) were also obtained, Both cluster and principal component analysis mere used for detecting patterns and trends in the data set. Cluster analysis detected a seasonal effect from the data on polynuclear aromatic hydrocarbons (PAHs), Two clusters mere identified: one from June to September 1995 and January to June 1996 and another from September 1995 to January 1996. These clusters could be related to changes in both maximum and minimum temperatures as well as precipitation during these periods of time. Principal component analysis identified two factors: the first factor (36.4% variance) contained nine PAHs characteristic of urban areas while the second factor (22.7% variance) contained four alkanes also characteristic of biological contribution in urban areas.