Seasonal variation of ~(210)Pb activity concentration in outdoor air of Milan (Italy)

摘要

Weekly measurements of ~(210)Pb activity concentration on aerosol particles were performed at ground level in outdoor air in Milan (Italy) during the years 2000-2001. The experimental method was based on the delayed alpha spectrometry of in-grown ~(210)Po activity detected on airborne particles collected on a filter support. On the same filter the ~(214)Pb activity concentration was also measured during the sampling. ~(210)Pb weekly concentration values showed a great variability and the average monthly values exhibited a seasonal pattern characterised by maxima in winter and minima in spring-summer. The same seasonal trend was also observed in ~(214)Pb concentration values. ~(210)Pb average yearly values were 0.70 and 0.82 mBq/m~3 in 2000 and 2001, respectively, in good agreement with literature data registered at continental sites of similar latitude and longitude. The activity ratio ~(210)Pb/~(214)Pb was used to evaluate the residence time of fine aerosols in the urban air of Milan, which was 1-2 days.