PM mass concentration and chemical composition in the alpine remote site Bormio-San Colombano (N. Italy, 2,200 m a.s.l.)

A study on PM mass and composition was carried out between April 2004 and March 2006 in the remote site Bormio - San Colombano (2,200 m a.s.l. - 46°27’N; 10°18’E). Annual means of PM2,5 and PM10 were 6 and 7 µg/m3 respectively and the ratio PM2.5/PM10 was 0.9. Both PM2,5 and PM10 mass concentrations presented mean spring-summer values higher than those observed in autumn-winter. From April to October, when the site was included in the mixed layer, PM concentrations in the remote site were correlated to those registered in the sites of the valley floor. In Bormio S.C., BaP concentrations resulted below 0.02 ng/m3 while those of Σ6 IARC (BaP, BaA, BbF, BkF, IcdP, dBahA) were below 0.15 ng/m3. In both size fractions, PAH’s concentrations presented a seasonal pattern with lower values in the warm season. Concentrations of sulphate, chloride and ammonia were similar in PM2.5 and PM10. In the warm season concentrations of sulphate reached their maximum levels while those of nitrate felt to minimum levels. The percentages of these anions with respect to particulate mass were similar in both size fractions. Sulphates were higher in Bormio S.C. with respect to the values observed in PM10 in the urban site of Sondrio. On the contrary, nitrate and ammonia mean percentages in Sondrio were higher than those observed in Bormio S.C. As concerns organic carbon (OC) and elemental carbon (EC), average concentrations in the PM10 fraction were lower in Bormio S.C. than in Sondrio. During spring-summer, OC average values were 2.8 μg/m3 and 2.9 μg/m3 in PM2.5 and PM10, respectively, with a ratio PM2.5/PM10 of 0.9. In both sites organic matter was the most abundant component of PM.