Pinonaldehyde and some other organics in rain and snow in central Japan

Solvent-extractable organic compounds in the rain and snow collected at local cities in the mountainous region in central Japan, were analyzed by GC/MS and GC. Pinonaldehyde (2,2-dimethyl-3-acetyl-cyclobutyl-ethanal), an atmospheric reaction product of alpha-pinene, was detected in the rain and snow for the first time, and n-alkanes (C17-C33), fatty acids (C8-C23), and benzoic acid were also detected as major organic components. Concentrations of pinonaldehyde, C17-C33 n-alkanes, C8-C11 fatty acids, C12-C23 fatty acids and benzoic acid ranged between <0.02-13, 0.10-35, 0.55-5.7, 4.2-19 and <0.02-6.0 microg/l, respectively. Their composition showed some difference in summer and winter. In summer, fatty acids and benzoic acid were more abundant, while pinonaldehyde and n-alkanes were much less. Higher photochemical reactivity and higher bioactivity in summer could explain these seasonal changes except for pinonaldehyde, which would suffer from further oxidation in the atmosphere after its photochemical production from alpha-pinene. Predominance of pinonaldehyde and C12-C23 fatty acids in the rain and snow showed a remarkable contrast to n-alkanes in aerosol phase, which were the most abundant components. It indicated that oxygenated products from biogenic compounds might be important as cloud condensation nuclei in forest areas.