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A micro-gas analysis system (μGAS) was developed for mobile monitoring and continuous measurements of atmospheric HCHO. HCHO gas was trapped into an absorbing/reaction solution continuously using a microchannel scrubber in which the microchannels were patterned in a honeycomb structure to form a wide absorbing area with a thin absorbing solution layer. Fluorescence was monitored after reaction of the collected HCHO with 2,4-pentanedione (PD) in the presence of acetic acid/ammonium acetate. The system was portable, battery-driven, highly sensitive (limit of detection = 0.01 ppbv) and had good time resolution (response time 50 s). The results revealed that the PD chemistry was subject to interference from O(3). The mechanism of this interference was investigated and the problem was addressed by incorporating a wet denuder. Mobile monitoring was performed along traffic roads, and elevated HCHO levels in a street canyon were evident upon mapping of the obtained data. The system was also applied to stationary monitoring in a forest in which HCHO formed naturally via reaction of biogenic compounds with oxidants. Concentrations of a few ppbv-HCHO and several-tens of ppbv of O(3) were then simultaneously monitored with the μGAS in forest air monitoring campaigns. The obtained 1 h average data were compared with those obtained by 1 h impinger collection and offsite GC-MS analysis after derivatization with o-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine (PFBOA). From the obtained data in the forest, daily variations of chemical HCHO production and loss are discussed.

本研究では，簡易でかつ時間分解能の比較的高いイソプレンの分析装置を開発し，森林大気のオンサイト分析に応用した．測定では4分間の大気サンプリングに続いて，加熱脱着によって化学発光セルに導入した．本装置によりppbvレベルのイソプレンを10分ごとに測定することが可能になり，検出限界は0.15 ppbvであった．植物をチャンバー内に設置したラボ実験では，チャンバー内イソプレン濃度は光照射とともに増大し消灯とともに減少した．この結果は加熱脱着－ガスクロマトグラフ－質量分析による結果とよい一致を示した．森林内測定においては有意な日内変化がみられ，日中イソプレン濃度が増大し夜間はほとんど見られなかった．これに対し同じ植物起源のα-ピネンは夜間濃度のほうが高く，α-ピネン放出の常時性と日中の高い分解速度に起因していると考えられる．このほかホルムアルデヒド，オゾン，窒素酸化物，有機・無機酸についても測定を行い，日内変化の追跡や季節変動の考察を行った．また，発生・消失のモデル構築を行い，日内変動よりイソプレンやα-ピネンの森林内発生のシミュレーションを行った．さらに実大気におけるイソプレンの発生とオゾン増幅の関係について考察を行った．