Pinonaldehyde and some other organics in rain and snow in central Japan
Introduction
A number of organic compounds have been detected in the atmospheric aerosols and shown to attain one-third in total weight occasionally. In such aerosols, in addition to the primary anthropogenic/biogenic compounds, their photochemical reaction products are also widely distributed (Appel et al., 1980; Yokouchi and Ambe, 1986; Satsumabayashi et al., 1990). Since the aerosols are mostly removed from the atmosphere by the precipitation process (rain or snow), the composition of organic compounds in the aerosols might be reflected in rain and snow. Several studies have shown that compositions in rain and the aerosols are similar (Sempere and Kawamura, 1994; Imai and Kawamura, 2000).
Reaction products of monoterpenes, major biogenic volatile organic compounds, are known to contribute to particulate organics in forest areas and could be important for cloud-condensation-nuclei formation (Went, 1960; Kavouras et al., 1998, Kavouras et al., 1999). Among them, pinonaldehyde, which is produced through photochemical reaction of α-pinene (Yokouchi and Ambe, 1985; Hatakeyama et al., 1991), has been detected in aerosols in considerable amounts, typically in several tens of ng/m3 (Yokouchi and Ambe, 1985; Satsumabayashi et al., 1990, Satsumabayashi et al., 1991; Kavouras et al., 1998, Kavouras et al., 1999; Yu et al., 1999). Therefore, it has been our great concern as to how much pinonaldehyde is present in the precipitation.
In this paper, we will report the organic composition including pinonaldehyde in the rain and snow samples collected at local cities in the mountainous region in central Japan, focusing on its seasonal change and its difference from the composition in the aerosols.
Section snippets
Experimental
Rain and snow samples were collected at two local sites, Nagano (360 m altitude) and Okaya (790 m altitude) in the central Japan having population of 360 000 and 60 000, respectively. Sampling was made in December 1986 and January 1987 at Nagano and from June to September 1989 and from November 1989 to January 1990 at Okaya (see the first column of Table 1).
Rain and snow samples were collected in a stainless steel vessel (220 × 380 mm2) which had been washed with pure water and acetone before use.
Organics in rain and snow samples
Table 1 shows the concentrations of pinonaldehyde, n-alkanes, fatty acids (short and long chains) and benzoic acid in the rain and snow samples collected at Nagano and Okaya. Pinonaldehyde was detected in all the samples except for the rain sample collected on 5–6 August 1989, and its concentration ranged from 0.16 to 13 μg/l, which often exceeded total n-alkanes or total short-chain fatty acids. Such a detection of pinonaldehyde in rain or snow is considered to be the first as far as we know.
n
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