Isoprene and its degradation products methyl vinyl ketone, methacrolein and formaldehyde in a eucalyptus forest during the FIELDVOC'94 campaign in Portugal

During FIELDVOC'94, isoprene and its main degradation products, methyl vinyl ketone (MVK), methacrolein (MAC) and formaldehyde (HCHO) were measured in a Portuguese eucalyptus forest. All compounds were analyzed by two or three different techniques. Isoprene mixing ratios were highest on sunny days (8 to 12 ppbv) correlating with temperature, and lowest at night (<0.02 ppbv). MVK and MAC reached on daytime ∼1 and ∼0.5 ppbv, respectively, and minimum values at night, for both species, comprised between 0.1 and 0.2 ppbv. Formaldehyde varied between 1 ppbv (night) and 9 ppbv (sunny day). Ambient mixing ratios of all compounds were highly variable due to changeable meteorological conditions. The MVK/MAC ratio between 1.5 and 2.5 is indicative of OH-oxidation as the primary isoprene degradation process during the day.