加熱脱着-GC/MSによるPM_(2.5)中多環芳香族炭化水素類の直接分析と熊本における日内変動•季節変動や野焼きの解析

摘要

PM_(2.5)中の多環芳香族炭化水素(polycyclic aromatic hydrocarbons:PAHs)を簡便かつ高感度に分析を行うため，従来の溶媒抽出(solvent extraction:SE)に代わり，加熱脱着法によるガスクロマトグラフィー質量分析(thermal desorption-gas chromatography/mass spectrometry:TD-GC/MS)について検討した.本研究では，フィルター捕集したPM_(2.5)中のPAHsについてTDの条件検討を行うとともに，TD法とSE法の比較検討を行った.その結果，煩雑で時間のかかるSE法に比べTD法では溶媒を用いる前処理が不要なばかりか.同じフィルタ一を処理した場合桁違いに高感度なことが示された.簡便かっ高感度なため.比較的短いサンプリング(1〜3日)を長期間続けることができ.PM_(2.5)中PAHsの詳細な季節変動の追跡が達成された.PM_(2.5)濃度は四季を通じて大きな推移を示さない一方，PM_(2.5)中のPAHsは冬から春に高く.逆に夏にはほとんど観測されなかった.これは冬場の中国大陸におけるPAHsの放出とその移流が主な原因と考えられる.さらに，本法の高感度な特性を生かし，短時間のサンプリングによるPAHsの変動をみることができた.例えば4時間ごとにサンプリングを行い.日内でPAHs濃度が推移する様子を捉えることができた.また.阿蘇山の草原を20km程度自家用車で走行し，野焼きで発生したPAHsの組成を調べることができた.野焼きの際に得られたPAHsは，季節変動の調査で得られたPAHsに比べて3〜4環の低分子量のPAHsが多く.巿内で1〜3日採取したPM_(2.5)中のPAHsと組成が異なった.以上のようにTD-GC/MSによるフィルターに捕集したPM中PAHsの分析条件を確立し，特徴ある分析結果を示して本法の有用性を示した.%In order to establish a simple and highly sensitive analytical method, thermal desorption followed by gas chromatography/mass spectrometry (TD-GC/MS) was investigated for polycyclic aromatic hydrocarbons (PAHs) in PM_(2.5). In this work, the TD condition was optimized for PAHs in filter samples, and the performance was compared with those by the solvent extraction method (SE). Even the TD method was much simpler, sensitivity is much higher compared to that of the SE method. TD-GC/MS was highly sensitive and PAHs could be detected with shorter sampling time. Accordingly, detailed seasonal variations were obtained with relatively shorter sampling time (1-3 days) for the long term. While the PM_(2.5) concentration changed in small ratio in different seasons, the PAH concentrations were much higher in the winter and spring when PAHs were largely emitted on the Chinese continent and transferred to Japan. The TD-GC/MS is highly sensitive, and a daily variation was obtained with a 4 h resolution. Furthermore the PAHs compositions emitted in the field burning could be determined just by sampling the air by driving a car for a half an hour through the burning grass field. The ratio of low molecular PAHs (3-4 rings) was higher in the field burning sample compared to those in PM_(2.5) sampled in Kumamoto-city for days. The TD-GC/ MS is superior in both analytical cost and performance, and is expected to be used for many applications in atmospheric analysis and air monitoring.