Formaldehyde in the rainwater in the eastern Mediterranean: occurrence, deposition and contribution to organic carbon budget

Formaldehyde (HCHO) concentrations have been measured in 66 rain samples during the rainy season (September 1999–May 2000) at Heraklion (25°07′E, 35°20′N; Crete) a coastal urban location in the eastern Mediterranean. HCHO concentrations vary between 0.42 and 11.14 μM, in the range of HCHO levels reported at other locations worldwide. The annual volume-weighted mean (VWM) rainwater HCHO concentration is 3.05 μM and comprised 3% of the dissolved organic carbon. Formaldehyde levels in rainwater depend on the air mass origin. The per event deposition of HCHO when air masses originate from NW Europe, Balkans or Turkey is 2–4 times higher than that from Africa or from marine sectors indicating strong influence from anthropogenic sources. The significant correlation of formaldehyde with non-sea-salt sulfate, nitrate and ammonium also indicates a significant anthropogenic component in HCHO levels. Formaldehyde is found to correlate significantly with formate and acetate with a ratio of formate to formaldehyde close to 1. According to our measurements rainwater HCHO and TOC could significantly contribute to the productivity of the eastern Mediterranean seawater. In particular, the rainwater can be an important supplier of the HCHO reservoir in the seawater. In addition the rainwater TOC levels can provide to phytoplankton species up to 32% of the organic carbon needed for new production.