北日本における亜硝酸ガス濃度と窒素酸化物由来成分の挙動 Atmospheric Behavior of Nitrous Acid and Nitrogen Dioxide in Northern Japan

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フィルターパック法または拡散デニューダ法を用いて札幌(都市地域),母子里(田園地域),利尻(遠隔地域,海岸部)および天塩(遠隔地域,山間部)において亜硝酸ガス(HONO)を含む各酸化態窒素の大気濃度を測定し,その挙動について考察した。HONO濃度は都市地域である札幌で最も高く,年平均濃度では他の地域の11~31倍を示した。HONO濃度は,都市地域では冬に,遠隔地域では夏に高く,田園地域では両方の特徴を示した。また環境大気中のHONO/NO<SUB>x</SUB>比はKurtenbach et al. (2001)による直接発生源のそれより大きく,大気中のHONOの生成には大気中粒子表面や地表面におけるNO<SUB>2</SUB>と水の不均一反応による二次生成の寄与が大きいと考えられた。地表面での不均一反応の場合,NO<SUB>2</SUB>の沈着により,HONOが放出されるため,HONOとNO<SUB>2</SUB>の濃度勾配には負の相関関係が見られるはずであるが,天塩ではHONOとNO<SUB>2</SUB>の高度別濃度差(30および10m)に正の相関関係が見られた。また利尻のHONOとPM<SUB>10</SUB>に有意な相関が認められ,また利尻および母子里のHONO/NO<SUB>2</SUB>と絶対湿度に有意な相関が認められた。このことから,NO<SUB>2</SUB>濃度が比較的低い田園および遠隔地域では大気中の粒子表面での不均一反応の寄与が大きいと考えられた。一方,都市部である札幌では地表面における二次生成の寄与は,特にNO<SUB>2</SUB>濃度の高い冬期に無視できない寄与があると考えられた。さらに冬期の札幌ではHONOおよびNOとHNO<SUB>3</SUB>およびO<SUB>3</SUB>は負の相関関係を示した。これはNO濃度が高い冬期の都市部ではO<SUB>3</SUB>濃度が低くなり,NO<SUB>2</SUB>からHNO<SUB>3</SUB>および粒子状硝酸塩への変換が進まないためと考えられた。このように,大気中のHONOの挙動は,大気中粒子表面や地表面におけるNO<SUB>2</SUB>と水の不均一反応による二次生成に支配されており,NO<SUB>2</SUB>濃度,大気中水分,O<SUB>3</SUB>濃度は,この不均一反応に大きな影響を及ぼすと考えられた。

The atmospheric behavior of nitrous acid, HONO, was discussed on the basis of field measurements by an annular-denuder or a filter-pack method at four different nature sites in northern Japan, Sapporo (urban), Moshiri (rural), Rishiri (coastal remote) and Teshio (mountainous remote), in terms of their atmospheric chemistry parameters including nitrogen oxides, nitric acid, nitrate aerosol and ozone. The annual mean concentrations of HONO in Sapporo ranged from 36 to 41 nmol m<SUP>-3</SUP> where the concentration level was 11 to 31 times higher than those for the other sites. A different seasonality of the HONO concentration was detected at the different nature site: the urban site showed a maximum in the winter, the remote in the summer, and the rural in the winter and the summer. A heterogeneous reaction between NO<SUB>2</SUB> and H<SUB>2</SUB>O on the surface of airborne particles and the ground surface is likely to play a significant role in the nitrous acid formation because the HONO/NOx ratio in ambient air is higher than those by direct emission as reported by Kurtenbach et al. (2001). In the case of the ground-surface heterogeneous reaction, the concentration gradient of HONO is expected to negative correlate with that of NO<SUB>2</SUB> because the deposition of NO<SUB>2</SUB> would induce emissions of HONO into the atmosphere. Actually, in Teshio, the difference between the concentrations of HONO at the heights of 30 m and 10 m positive correlated with that for NO<SUB>2</SUB>. Furthermore, the Rishiri measurements showed a significant correlation between the concentrations of HONO and PM<SUB>10</SUB>. In addition, Rishiri and Moshiri measurements showed significant correlations between the concentration ratio, HONO/NO<SUB>2</SUB>, and absolute humidity. These results strongly support the view that the heterogeneous reactions on the airborne particles prevails in the formation of HONO in the rural and remote areas with considerably low concentrations of NO<SUB>2</SUB>. On the other hand, the heterogeneous reaction on the ground-surface reaction plays a significant role in Sapporo, especially in the winter with high NO<SUB>2</SUB> concentrations. In Sapporo, negative correlations were detected in the winter between the concentrations of HONO and NO, and between of HNO<SUB>3</SUB> and O<SUB>3</SUB>, which would be attributable to the insufficient conversion of NO<SUB>2</SUB> to HNO<SUB>3</SUB>, and further to nitrate species, under urban conditions because of the low concentration of ozone along with high concentrations of NO. These field measurements would indicate that the behavior of nitrous acid is controlled by the chemical reactions of NO<SUB>2</SUB> with H<SUB>2</SUB>O, and that this heterogeneous reaction was affected by the NO<SUB>2</SUB> concentration, absolute humidity and O<SUB>3</SUB> concentration.

収録刊行物

  • 大気環境学会誌 = Journal of Japan Society for Atmospheric Environment

    大気環境学会誌 = Journal of Japan Society for Atmospheric Environment 45(4), 153-165, 2010-07-10

    Japan Society for Atmospheric Environment

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各種コード

  • NII論文ID(NAID)
    10030703210
  • NII書誌ID(NCID)
    AN10512108
  • 本文言語コード
    JPN
  • 資料種別
    ART
  • ISSN
    13414178
  • NDL 記事登録ID
    10773039
  • NDL 雑誌分類
    ZN5(科学技術--建設工学・建設業--都市工学・衛生工学)
  • NDL 請求記号
    Z16-490
  • データ提供元
    CJP書誌  CJP引用  NDL  J-STAGE 
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