Variation patterns of nitric oxide in Catalonia during the period from 2001 to 2006 using multivariate data analysis methods.

Multivariate data analysis methods are applied to study of the geographical and temporal distribution of nitric oxide (NO) in Catalonia (North-East Spain), measured during the period 2001-2006 in 50 sampling stations. Principal component analysis (PCA) and Multivariate Curve Resolution Alternating Least Squares (MCR-ALS) were applied for that purpose. The simultaneous analysis of NO data from sampling stations showed that its geographical distribution was rather uniform during the period considered. When three individual sampling stations were considered (two urban sites and one rural location), three different temporal patterns were resolved, with marked daily-night changes mainly attributed to traffic and also, important winter-summer seasonal variations. A decreasing trend in the levels of NO has been also observed in recent years. Comparison with nitrogen dioxide (NO(2)) profiles shows that the daily variation is quite similar to the NO variation, however NO(2) displays very little oscillations along the seasons and no reduction of its concentration was observed in the last years, contrasting with NO tendencies. The use of MCR-ALS is confirmed to be a useful method to improve interpretability in atmospheric contamination studies. The use of non-negativity and trilinearity constraints is shown to provide improved interpretations of the different contamination patterns in environmental terms.