Nguyen Nhu Bao Chinh

称号及び氏名博士（工学）

学位授与の日付

令和 2 年 3 月 31 日論

「Development of Simultaneous and Continuous
Measurements of Formaldehyde in the Atmosphere andRain and Role of Photoproduction and Microorganism for
Formaldehyde Concentration （大気と雨中のホルムアルデヒドの同時連続測定の開発とホルムアルデヒド濃度に対する光生成及び微生物の役割）」

文

論文審査委員

名

主査

竹中

規訓

副査

久本秀明

副査

松岡雅也

論文要旨

Formaldehyde (HCHO) is well-known as an important chemical species in term of atmosphericchemistry and toxicology. It exists in most of medias in the atmosphere, including gaseous phase, aqueousphase and particle phase as the result of oxidation of volatile organic compounds (VOCs). HCHO is an
essential component of the reactivity of the atmosphere, a providing source of radicals that drive
important chemical processes of atmosphere such as ozone formation. Due to its high solu bility in waterand interactions with other, HCHO participates in aqueous chemistry in clouds. The chemistry of HCHO
is an indicator of our overall understanding of atmospheric chemistry. Understanding the production anddecay of HCHO will enable us to consider the effect of technology development and policies on air quality.
Besides, HCHO is a hazardous air pollutant suspected as a carcinogenic risk for human and well -known as
one of sick house gases. Therefore, studying on HCHO in the environment is necessary and brings many
benefits, but the existing barrier is a measuring method. In considering of the role, the importance of goodunderstanding and the lacuna in knowledge of HCHO in atmosphere, this thesis approached issues asfollowing steps:
In Chapter 1, the introduction to the nature of HCHO in the environment, the formation, importantrole, motivation, and difficulty in HCHO research field are summarized.
In Chapter 2, the developed continuous and selective determination method of formaldehyde(HCHO) in gas phase using the chemiluminescence method is described. The concentration of HCHO in
the ambient air is low and the conventional determination method of aldehyde (2, 4 -DNPH-HPLC method)
requires long time for sampling. Furthermore, there are some difficulties to measure HCHO continuouslyand selectively with high time resolution. The chemiluminescence method by using gallic acid and H 2O2
can measure HCHO continuously with high time resolution, but the interference is still a problem. Tosolve these problems, the improved chemiluminescence method was developed. The counter current flow
tube was used to collect and concentrate gaseous formaldehyde. The air sample was passed through the (id6 mm×100 cm length) counter current flow tubes (CCFT) that comprises a 6 mm outer diameter helicalglass wire that was inserted inside a glass tube. The absorption solution containing HCHO was introduced
to the iodoform reaction section to remove the interferences from other aldehydes. Subsequently, thesample was introduced to the sample analysis section by the chemiluminescence. The chemiluminescenceproduced from the reaction of HCHO, gallic acid, H 2O2, and KOH was detected by a photo-diode detector.
The limit of detection (S/N = 3) was 4.5 ppbv (v indicates volume ratio) in the air with a linearity up to6.25 ppmv. The effect of ions and heavy metal ions are negligible in which the effect of ferrous ion wastotally removed. The removal of interference makes this method suitable for measuring in the air andrainwater with good time resolution and reliability. HCHO concentration measured by the present method
showed good agreement with that obtained by the 2,4-Dinitrophenylhydrazine method.
In Chapter 3, the developed method was applied to measure HCHO in the ambient air and rainwater
to investigate the characteristic of HCHO in the environment. In this study, the HCHO in the ambient air
in a residential area (Sakai City, Japan) and polluted area (Ho Chi Minh City, Vietnam) and that inrainwater in Sakai City were investigated. In Sakai City, the measurement of HCHO in the ambient air wasconducted continuously from December 2017 to January 2018. The diurnal average of HCHO
concentration varied within 8 to 23 ppbv. The HCHO concentration in the nighttime was persistent
approximately 12 ppbv and slowly increased to 14 ppbv in the morning (around 9 AM). The variation ofHCHO in Sakai City was reflected by the pattern characterized for clean environment and affected bymeteorological conditions but less affected by stationary emission. In contrast to Sakai City, in Ho Chi

Minh City, HCHO pattern seems to be strongly affected by rush hours, and high peaks were clearlyobserved. The high peak (up to 65 ppbv) appeared in the morning rush hours is the evidence for directemission from the vehicles.
The concentration of HCHO in rainwater, its variation and the processes that might be expected tooccur in rainwater were also investigated. The concentration of HCHO in 20 rain events including
typhoons in 2018 Baiu season in Sakai City, Osaka, Japan, ranged from below detection limit (3σ) of 0.08
μM to 9.91 μM, and the average of each rain event varied from 0.13 to 2.75 μM. The average
concentration observed in this study was lower than the reported in the previous studies and between th erange of the marine value and urban value. The high concentration was mainly observed during thenighttime that contrast with the ambient HCHO that is usually high in day time due to the photoproduction.
Based on observation, the variation patterns of HCHO during rain events were divided into four types. The
concentration and observed patterns could be the result of complex processes relating to sources andprocesses during rainfall. However, no relations were observed for HHO concentration in rainwater w ithrainfall intensity and local HCHO gas phase concentration. That implies the concentration of HCHO in
rainwater might be controlled before falling by aqueous photolysis of dissolved organic compounds(DOCs) and other processes.
Furthermore, the formation and sink of HCHO in rainwater were investigated. Series of irradiation
experiments was carried out to confirm that HCHO was produced by photolysis of DOCs in rainwater. The
samples were exposed under various kinds of light sources including room light, s unlight and UV lamp,
and the results were compared with control samples. The result showed that HCHO concentrations
increased in all irradiated samples. The formation rates were calculated in the range of 0.05 to 2.43 μM h -1
and faster than the decomposition rate by radical in aqueous phase. These results proved thephotoproduction of HCHO. Besides the HCHO formation by photolysis of DOCs, the role ofmicroorganism in rainwater was also investigated. The loss in dark samples indicated the activity ofmicroorganisms in the samples. Microbial activity in the cloud and droplet could be one important factor
to control the concentration of HCHO with digestion rate observed up to 3.2 μM h-1 in normal rainwaterand 0.27 and 0.15 μM h -1 in typhoon rainwater.
In Chapter 4, the sources of HCHO indoor was focused. Incense stick burning is one of casualhousehold activity especially in east and southeast Asian countries, including Vietn am, but the emission
profile carbonyls has not been studied properly. In this study, the target is HCHO and other carbonylcompounds emitted from burned incense stick. Nine incense stick types were collected from Vietnam andinvestigated the carbonyl emission profile. The incense sticks were burned in a chamber, and aldehydes
were collected by 2,4-dinitrophenylhydrazine cartridge (2,4-DNPH) and analyzed by HPLC. The
concentration of HCHO was also measured by the developed chemiluminescence method. The resul t
showed that in ten analyzed carbonyl compounds, propionaldehyde (3-84 %, avg. 32 %), acetaldehyde(8-90 %, avg. 30 %), and acetone (0-38 %, avg. 9 %) were the most abundant in term of total weight
emitted carbonyls, respectively. The fourth abundant aldehyde was HCHO (1-26 %, avg. 8 %). The
concentration of HCHO in released smoke was ranged from 46.65 ± 4.44 to 596.89 ± 279.17 µg/m 3 (38.02± 3.62 to 486.46 ± 242.19 ppb). Tested samples showed HCHO concentrations higher than the value
according to the World Health Organization (WHO) guideline (WHO 2010) and Vietnam National
standard for indoor air quality (QCVN-2009). Therefore, in this chapter, the personal risk assessment ofHCHO inhalation exposure was carried out by the burning simulation in a small unventilated room. Therisk calculation showed the cancer risk is 1.81 x 10 -5 which is 24% higher than the base risk. However, thenumber of the day people burning incense could be more than the estimation. Therefore, the cancer risk
they can get must be much higher, especially for the women who are the most frequently use incense.
In Chapter 5, the obtained results were summarized and discussed future study for aldehydes
especially role of HCHO in the environment.

審査結果の要旨

本論文は、大気中及び雨中のホルムアルデヒド(HCHO)の新規連続測定法の開発と環境測定への応用についてまとめたものである。HCHO は毒性物質、発がん物質、シックハウス症候群の原因物質としても知られており、また、大気環境中での種々の反応により生成したり、種々の反応に関与するなど重要な役割を果たしている。しかし、HCHO の測定には一般には誘導体化して測定する必要があるなど、連続測定が難しい物質の一つである。本研究では、HCHO だけを選択的に高時間分解能で測定する簡易な方法を新たに開発し、環境測定に適応した結果をまとめたもので、次のような興味深い新たな結果を得ている。
(１) 簡易的な連続測定法である化学発光法を改良し、従来は全てのアルデヒドが検知されていた方法を、ヨードホルム反応が HCHO は起こらないが、アセトアルデヒドとアセトンが反応することに着目し、HCHO だけを連続測定できる方法を確立した。気液接触型の向流管を用いることで大気中の HCHO を吸収液に吸収させ、大気の連続測定に用いることができることを明らかにした。本法を堺市及びホーチミンの大気観測に用い、それぞれの都市の大気中

HCHO の濃度変動の違いを示し、その原因を推定した。
(２) 開発した方法を改良し、大気と雨中の HCHO の同時連続測定に応用した。その結果、雨の中 HCHO 濃度は従来考えられていたように大気の濃度に影響を受けているわけではな
く、雨の中の有機物の光化学生成が重要であることを明らかにした。また、微生物による分解も雨中の濃度に影響を与えている可能性を示した。
(３) 線香の燃焼から放出されるアルデヒド類濃度を従来の方法で測定すると同時に開発した測定法で HCHO の連続測定を行い、線香を使用した後の室内の濃度変動を明らかにした。
その結果をもとにシミュレーションを行い、家庭生活で生涯にわたって線香を使用した際のHCHO による健康リスクを評価した。
以上の結果は、従来の測定法では困難であった高時間分解能の HCHO の動態を解明したもので、大気環境分野で非常に貴重な研究結果である。大気化学や室内環境で重要であると認識されている HCHO の濃度及び動態に新たな知見を加え、今後の発展に期待できる結果を示したもので、大気環境の研究領域で多大な貢献がある。また、申請者が自立して研究活動を行うのに必要な能力と学識を有することを示したものである。