{"created":"2021-03-01T06:14:37.407674+00:00","id":7939,"links":{},"metadata":{"_buckets":{"deposit":"35aca9f0-0b57-4474-babb-9f417916b3a8"},"_deposit":{"id":"7939","owners":[],"pid":{"revision_id":0,"type":"depid","value":"7939"},"status":"published"},"_oai":{"id":"oai:nagoya.repo.nii.ac.jp:00007939","sets":["488:641:642"]},"author_link":["22668","22669"],"item_12_alternative_title_19":{"attribute_name":"その他のタイトル","attribute_value_mlt":[{"subitem_alternative_title":"乗鞍岳で観測されたサブミクロンエアロゾル粒子の個数粒径分布の変化の要因","subitem_alternative_title_language":"ja"}]},"item_12_biblio_info_6":{"attribute_name":"書誌情報","attribute_value_mlt":[{"bibliographicIssueDates":{"bibliographicIssueDate":"2008-03-25","bibliographicIssueDateType":"Issued"}}]},"item_12_date_granted_64":{"attribute_name":"学位授与年月日","attribute_value_mlt":[{"subitem_dategranted":"2008-03-25"}]},"item_12_degree_grantor_62":{"attribute_name":"学位授与機関","attribute_value_mlt":[{"subitem_degreegrantor":[{"subitem_degreegrantor_language":"ja","subitem_degreegrantor_name":"名古屋大学"},{"subitem_degreegrantor_language":"en","subitem_degreegrantor_name":"Nagoya University"}],"subitem_degreegrantor_identifier":[{"subitem_degreegrantor_identifier_name":"13901","subitem_degreegrantor_identifier_scheme":"kakenhi"}]}]},"item_12_degree_name_61":{"attribute_name":"学位名","attribute_value_mlt":[{"subitem_degreename":"博士(理学)","subitem_degreename_language":"ja"}]},"item_12_description_4":{"attribute_name":"抄録","attribute_value_mlt":[{"subitem_description":"大気エアロゾル粒子の個数粒径分布は、大気エアロゾルを記述する重要な要素であり、大気放射に対するエアロゾルの影響を見積もるためにも不可欠な測定項目である。大気エアロゾル粒子のなかでも、直径約100 nm 以下の粒子は、大気の放射収支にほとんど影響しない。しかし、大気放射に直接関与する直径約100 nm 以上のエアロゾル粒子の個数粒径分布の変化を予測するためには、直径数nm から100 nm の粒径のエアロゾル粒子の、大気中における生成・成長・消滅の過程を理解することが必要である。しかし、これらの過程について十分な理解は得られていない。例えば、降水によるエアロゾル粒子の除去過程については、モデル計算や室内実験によって定量的な研究が行なわれているが、大気観測によってそれらの研究結果を確認した例は少ない。また、均一核生成とそれに続く粒子成長によって直径数ナノメートルのエアロゾル粒子が生成される過程 (新粒子生成) については、その過程の複雑さや測定技術の限界などにより、解明されていない点が多い。1990 年代以降、測定技術の進歩により、大気中の様々な場所で、直径100 nm 以下の粒径範囲を含むエアロゾル粒子の個数粒径分布の観測が行なわれている。しかし、これまで、東アジア・西太平洋域上空の自由対流圏において観測を行なった例は少ない。本研究は、東アジア・西太平洋域上空の自由対流圏におけるサブミクロンエアロゾル粒子の個数粒径分布と、その時間変化の要因を明らかにすることを目的とし、2001 年9 月と2002 年8–9月(全観測日数48 日)に、飛騨山脈・乗鞍岳山頂近く (標高2770 m) において、直径9–300 nm のエアロゾル粒子の個数粒径分布の時系列観測を行なった。乗鞍岳で観測される自由対流圏のエアロゾルは、エアロゾル粒子やその前駆気体について観測地近くの発生源の影響をほとんど受けないため、降水による除去過程の影響を調べるのに適している。そこで、本研究では、乗鞍岳における観測結果から、降水によるエアロゾル粒子の除去係数を見積ることを試みた。一方、乗鞍岳山頂付近では、日中に吹く斜面上昇風 (谷風) により、自由対流圏のエアロゾルだけではなく、境界層に由来するエアロゾルも観測される。自由対流圏のエアロゾルと境界層のエアロゾルとでは、新粒子生成に関係する種々の要因が異なると予想される。そこで、本研究は、この両者の比較から、大気中における新粒子生成に関する新たな知見の獲得を試みた。気塊の後方流跡線上の客観解析データより、過去24 時間に気塊が経験した降水量(蓄積降水量)を見積もり、見積もられた蓄積降水量と乗鞍岳で観測された自由対流圏のエアロゾル粒子の個数粒径分布との関係を調べた。蓄積降水量が0 mm から20 mm に増加すると、直径 9 nmから100 nmの粒子の総粒子数濃度は約半分に減少し、直径100 nm から300 nm の粒子の総粒子数濃度は約一桁減少するような関係が見られた。これらの結果から、乗鞍岳の自由対流圏のエアロゾル粒子の個数粒径分布の変化の要因として、蓄積降水量が重要であることが示された。さらに、蓄積降水量と粒子数濃度から、エアロゾル粒子の除去係数を見積もり、モデル計算による先行研究の結果と比較した。観測結果から見積もられた除去係数は、雲底下で雨滴と衝突すること (雲底下洗浄)による除去係数よりも約二桁高かった。しかし、雲内で雲核として作用することを経て雨滴と衝突すること(雲内洗浄) による除去係数とは、ほぼ一致していた。これらのことから、エアロゾル粒子を除去する過程として、雲内洗浄が重要であると考えられる。気塊の後方流跡線にもとづいて、観測された気塊を太平洋から輸送された気塊とアジア大陸から輸送されてきた気塊に分類し、これらの気塊で観測された自由対流圏のエアロゾル粒子の個数粒径分布を比較した。降水の影響の少ない場合には、太平洋上空から輸送された気塊中の蓄積モード粒子 (モード直径、約100 nm) の個数濃度は、アジア大陸上空から輸送された気塊中の蓄積モード粒子の個数濃度とほとんど同じだった (中央値で約400 cm-3)。しかし、エイトケンモード粒子 (モード直径、約50 nm) の個数濃度は、アジア大陸上空から輸送された気塊 (中央値で約 230cm-3) よりも、太平洋上空から輸送された気塊 (中央値で約890 cm-3) で高かった。このことから、乗鞍岳の自由対流圏エアロゾル中のエイトケンモード粒子の個数濃度の変化の要因として、気塊の輸送経路が重要であることがわかった。エアロゾル粒子の個数粒径分布に核生成モード (直径20 nm に現れる峰) が観測された日 (ここではイベント日と呼ぶ) は、晴天日23 日のうち4 日あった。核生成モードの出現は、その気塊で数時間から半日以内に新粒子生成が起きたことを示す。核生成モード粒子は、自由対流圏のエアロゾル中では観測されず、谷風によって境界層より観測地へ輸送されたエアロゾル中でのみ観測された。観測された核生成モード粒子は、境界層内で生成され、谷風によって観測地へ輸送されたものと考えられる。新粒子生成に関する要因について検討するために、イベント日と非イベント日の谷風条件時に観測されたSO2 やNH3、既存粒子の濃度の比較を行なった。H2SO4 やNH3 が、新粒子生成の前駆気体として重要であるならば、SO2 やNH3 の濃度が高いほど新粒子生成に有利であると考えられる。しかし、非イベント日に比べてイベント日のSO2 やNH3 の濃度は低かった (平均で、非イベント日の約半分)。一方、既存粒子は、新粒子生成に寄与する低揮発性気体成分や、生成されたばかりの粒子のシンクとして働くため、既存粒子の濃度が低いほど新粒子生成に有利であると考えられる。観測結果によれば、非イベント日に比べてイベント日の既存粒子の濃度は低かった (平均で、非イベント日の約半分)。このことから、乗鞍岳において核生成モード粒子が観測されるための条件として、境界層で既存粒子濃度が低いことが重要であると考えられる。本研究は、乗鞍岳山頂付近で大気観測を行なうことにより、これまで観測例の少なかった東アジア・西太平洋域上空の自由対流圏におけるサブミクロンエアロゾル粒子の個数粒径分布、および、その変化の要因について明らかにした。本研究で得られた知見を総合することにより、大気中におけるエアロゾル粒子の個数粒径分布の変化について、エアロゾル粒子の生成・成長・除去過程を介した循環様式を提示し、降水による除去過程が、エアロゾル粒子の個数粒径分布の循環を駆動する重要な過程であることを示唆した。","subitem_description_language":"ja","subitem_description_type":"Abstract"},{"subitem_description":"Particle number-size distribution is an important element describing atmospheric aerosol and a crucial topic to evaluate aerosol effects on the Earth's radiation balance. Although aerosol particles with sizes smaller than about 100-nm diameter are less effective for radiative forcing, the knowledge of formation, growth and removal processes of aerosol particles from nanometer sizes upward is important to predict temporal evolution of number-size distribution of atmospheric aerosol particles. Wet deposition is the dominant removal process especially for submicron aerosol particles. Scavenging coefficient of aerosol particles by precipitation scavenging have been studied mainly by model simulations and laboratory experiments, but the results of these studies have not been fully examined by atmospheric observations. New particle formation from gas-to-particle conversion processes, including homogenous nucleation and subsequent particle growth, is an important source process to increase number concentration of aerosol particles with nanometer sizes. Nevertheless, the mechanism of new particle formation in the atmosphere has not been fully elucidated because of the complexity of the process and technical limitations of measurements. Number-size distributions of aerosol particles covering the size range below 100 nm diameter have been measured at various locations in the atmosphere since the development of new instruments during the 1990s. However, observations have seldom been made in the free troposphere over the East Asia and western Pacific area. In this study, number-size distributions of aerosol particles of 9-300 nm diameters were observed at Mt. Norikura in central Japan during September 2001 and August-September 2002 (48 days in total). Two distinct air-masses transported from over the Pacific Ocean and continental Asia were observed during the observation periods. Discussion was focused on factors controlling variation of number-size distribution of free tropospheric aerosol particles observed at Mt. Norikura. Moreover, utilizing advantages of atmospheric conditions at Mt. Norikura, the observed size distributions were analyzed in terms of effects of precipitation scavenging and favorable conditions for new particle formation. Observed number-size distributions of free tropospheric aerosol particles were compared with total precipitation amount in the air-masses for the last 24 hours (cumulative precipitation amounts). Cumulative precipitation amounts were estimated from the objective analysis data along air-mass backward trajectories. When cumulative precipitation amount increased from 0 to 20 mm, particle concentration of the Aitken mode range (9-100 nm in diameter) decreased by about half, and particle concentration of the accumulation mode range (100-300 nm in diameter) decreased by an order of magnitude. The cumulative precipitation amount is suggested as an important factor to modify the size distribution of free tropospheric aerosol at Mt. Norikura by decreasing particle concentration. From the relation between cumulative precipitation amount and particle concentration, the time constant of precipitation scavenging for the particles in the accumulation-mode size range was estimated at the order of hours. The value estimated in this study agrees well with the time constant of in-cloud scavenging process estimated by model studies in literature, while the value estimated in this study is smaller than that of below-cloud scavenging process estimated by the model studies in literature by about two orders. These results suggest that in-cloud scavenging is important as a process controlling number-size distribution of free tropospheric aerosol particles at Mt. Norirkua According to air-mass backward trajectories, observed air masses were classified into two types: the air mass transported from over the Pacific Ocean and the air mass transported from over continental Asia. Considering data for the air masses transported without precipitation, concentrations of accumulation mode particles (modal diameter about 100 nm) were almost identical (approximately 400 cm-3 as a median value) in the air masses transported from over the Pacific Ocean and continental Asia. Concentration of Aitken mode particles (modal diameter about 50 nm) in the air masses subsiding from over subtropical Pacific Ocean (890 cm-3 as a median value) was higher than that in the air masses transported from over continental Asia (230 cm-3 as a median value). Air-mass transportation pathway was found to be an important controlling factor for Aitken mode particle concentration in the free troposphere at Mt. Norikura. Nucleation mode (a mode that first appears in the size range below 20-nm diameter) was observed on 4 days (called new particle formation (NPF) event days in this study) of 23 clear-sky days during the observation periods of this study. Occurrence of nucleation mode suggests new particle formation event occurred recently (in about a half day) in the observed air mass. Nucleation mode particles were observed in the mixed layer air transported by up-slope valley winds, but never in the free tropospheric air, suggesting that new particle formation event occurred in the air masses transported from the mixed layer. SO2, NH3, and pre-existing particle concentrations observed in up-slope valley wind condition on NPF event days were compared with those on non-event sunny days. If H2SO4 or NH3 were major precursors initiating homogenous nucleation and subsequent particle growth, high SO2 or NH3 concentration would be a favorable condition for new particle formation. However, this study found no positive correlation between an NPF event and SO2 or NH3 concentrations. On the other hand, homogenous nucleation competes with condensation onto pre-existing particles for low-volatile precursor gases; coagulation to pre-existing particles is a strong sink for freshly nucleated particles. Therefore, low pre-existing particle concentration is favorable condition for new particle formation. Based on the results of the observation at Mt. Norikura, pre-existing particle concentration on NPF event days was significantly lower than that on non-event sunny days. The average pre-existing particle concentration on NPF event days was about 50 % of that on non-event sunny days. This result suggests that low pre-existing particle concentration in the mixed layer is important for initiating a new particle formation event at Mt. Norikura. This study investigated number-size distributions of submicron aerosol particles and factors controlling its temporal variation in the free troposphere over the East Asia and western Pacific area, where observation data have seldomly been obtained. Based on the results of the observation at Mt. Norikura, this study suggested a conceptual scheme of a cycle of number-size distribution of aerosol particles, relating to particle formation, growth, or removal processes in a Lagrangian perspective. Precipitation scavenging might be a key process for driving the cycle of size distribution of atmospheric aerosol particles.","subitem_description_language":"en","subitem_description_type":"Abstract"}]},"item_12_description_5":{"attribute_name":"内容記述","attribute_value_mlt":[{"subitem_description":"名古屋大学博士学位論文 学位の種類 博士（理学）（論文）","subitem_description_language":"ja","subitem_description_type":"Other"}]},"item_12_dissertation_number_65":{"attribute_name":"学位授与番号","attribute_value_mlt":[{"subitem_dissertationnumber":"乙第6750号"}]},"item_12_identifier_60":{"attribute_name":"URI","attribute_value_mlt":[{"subitem_identifier_type":"HDL","subitem_identifier_uri":"http://hdl.handle.net/2237/9672"}]},"item_12_select_15":{"attribute_name":"著者版フラグ","attribute_value_mlt":[{"subitem_select_item":"publisher"}]},"item_12_text_14":{"attribute_name":"フォーマット","attribute_value_mlt":[{"subitem_text_value":"application/pdf"}]},"item_12_text_63":{"attribute_name":"学位授与年度","attribute_value_mlt":[{"subitem_text_value":"2007"}]},"item_access_right":{"attribute_name":"アクセス権","attribute_value_mlt":[{"subitem_access_right":"open access","subitem_access_right_uri":"http://purl.org/coar/access_right/c_abf2"}]},"item_creator":{"attribute_name":"著者","attribute_type":"creator","attribute_value_mlt":[{"creatorNames":[{"creatorName":"西田, 千春","creatorNameLang":"ja"}],"nameIdentifiers":[{"nameIdentifier":"22668","nameIdentifierScheme":"WEKO"}]},{"creatorNames":[{"creatorName":"NISHITA, Chiharu","creatorNameLang":"en"}],"nameIdentifiers":[{"nameIdentifier":"22669","nameIdentifierScheme":"WEKO"}]}]},"item_files":{"attribute_name":"ファイル情報","attribute_type":"file","attribute_value_mlt":[{"accessrole":"open_date","date":[{"dateType":"Available","dateValue":"2018-02-19"}],"displaytype":"detail","filename":"o6750_thesis.pdf","filesize":[{"value":"7.1 MB"}],"format":"application/pdf","licensetype":"license_note","mimetype":"application/pdf","url":{"label":"o6750_thesis.pdf","objectType":"fulltext","url":"https://nagoya.repo.nii.ac.jp/record/7939/files/o6750_thesis.pdf"},"version_id":"8904df6e-b3bd-4786-8293-bceba22da16e"}]},"item_language":{"attribute_name":"言語","attribute_value_mlt":[{"subitem_language":"eng"}]},"item_resource_type":{"attribute_name":"資源タイプ","attribute_value_mlt":[{"resourcetype":"doctoral thesis","resourceuri":"http://purl.org/coar/resource_type/c_db06"}]},"item_title":"Factors controlling variation of number-size distribution of　submicron aerosol particles observed at Mt. Norikura","item_titles":{"attribute_name":"タイトル","attribute_value_mlt":[{"subitem_title":"Factors controlling variation of number-size distribution of　submicron aerosol particles observed at Mt. Norikura","subitem_title_language":"en"}]},"item_type_id":"12","owner":"1","path":["642"],"pubdate":{"attribute_name":"PubDate","attribute_value":"2008-04-15"},"publish_date":"2008-04-15","publish_status":"0","recid":"7939","relation_version_is_last":true,"title":["Factors controlling variation of number-size distribution of　submicron aerosol particles observed at Mt. Norikura"],"weko_creator_id":"1","weko_shared_id":-1},"updated":"2023-01-16T03:53:29.110043+00:00"}