Quasi-Seasonal Neutralization of Acid Rain in Tuscany: Can Saharan Dust be Responsible?

Rainwater is often acidic (pH in the range 4–4.5 in many cases) in coastal, inland and mountain zones of Tuscany (central Italy). Neutralized rainfalls, i. e. exhibiting pH > 5.6, usually occur in spring and autumn; sometimes Saharan dust is visibly evident, in which cases a pH > 7 is generally found. When the contribution from Saharan dust is not evident, the neutralization (pH 5.6–7) appears to be due to local atmospheric dust or, in samples collected near to the shoreline, to marine aerosol. Collection of single rainfall, or fractions of single events, is recommended to distinguish among the various contributions to the neutralization.