Doctoral Thesis

Photochemical generation of OH radical in water-extractof aerosol and aqueous solution of water-soluble gases in
the air

Sonia Naomi Nomi

Graduate School of Biosphere Science
Hiroshima University

March 2012

Doctoral Thesis

Photochemical generation of OH radical in water-extractof aerosol and aqueous solution of water-soluble gases in
the air

Sonia Naomi Nomi
Environmental Management and Dynamics
Graduate School of Biosphere Science
Hiroshima University

March 2012

Contents
Acknoledgements.........
Abstract (English) .........
Abstract (Japanese) .........
1.

................................................................
..............................................................
...........................................................

Chapter One

.
.i
.v

...........................................................................

.....1................................. .....................

.......2

Outlines of this study…………………………………………….………….

..5

References…

….6

General introduction.........

……………………………………………… ……………...

2. Chapter Two - Photoformation rate of OH radical in water-extracts of atmosphericaerosols and aqueous solution of water-soluble gases collected
Higashi-Hiroshima, Japan…

3.

…………………………...

…………..

9

Introduction………….………………………………………………………..

10

Experimental……….…………………………………………………………

10

Results and Discussions

16……………………………………………………

Conclusions………………….……………………………………………

20

References……………………………………………………………….…

…21

Chapter Three - Photochemical formation of OH radical formation in marine
aerosols collected in Seto Inland Sea, Japan……

4.

in..……..……...

35

Introduction…………………………………………………………..…

…….36

Experimental………………………………………………………….

………. 37

Results and Discussions………………………………………………..………

41

Conclusions…………………………………………………………….……..

46

References… ……………………….…………………………...……..

.. …….. 47

Chapter Four ……….…………………………………………………

…… 69

General Discussion.…………

………….………………………………… …..70

Conclusions..……………………………………………………………

…….72

Further research…………………………………………………………

…….72

References…...………………………………………………………...

……...73

Abstract
This thesis focuses on the oxidation capacity of ●OH photogenerated in water-extract ofaerosol and aqueous solution of water-soluble gases fraction collected at Hiroshima
University and in the Seto Inland Sea. The aqueous phase photoreactions involving ●OH
is known to play important roles in the troposphere by affecting regional and global
climate in various atmospheric photochemical processes and determining the fates ofsome air pollutants. The aqueous solution of water-soluble gases in ambient air may
contain various ●OH source compounds such as nitric acid (HNO 3 ), HONO, H 2 O 2 ,oxalic acid and other water-soluble organic matter. After transferring to the atmosphericaqueous phase these compounds could generate●

OH photochemically. Thus,

investigation on sources and sinks of ●OH generation is the first step to understanding
the capacity and strength of ●OH formation in atmospheric aqueous phase and to clarify
their influences on photochemical reactions occurring in the air.
The overall structure of the thesis includes 4 chapters. Chapter 1 introduces the basic
concepts of the atmospheric aerosol and the photochemical mechanisms of ●OHgeneration occurring in aqueous phase. The role and significance of ●OH in theatmosphere and past results obtained by other investigators and the contributions to thisfield of research are shown.
iThe following Chapter 2 reports the collection of ambient aerosol at Higashi-Hiroshima
campus using a coupled sampler for simultaneous collection of both phases,
water-extracts of aerosols (WEA) and aqueous solution of water-soluble gas fraction(WSG) during June/2008 to June 2010. The ●OH photoformation rate (R OH ) andchemical composition of both fractions were determined. Among the major anions
present in the WSG and WEA samples, the SO 4 2- concentration was highest followed by
NO 3 - and Cl-. The mean concentration of SO 4 2- was 9.4±4.0 nmol m-3 in the WSG and
81±33 nmol.m-3 for the WEA. The R OH determined and normalized based on the
air-volume, which revealed values of 1.4 and 0.5 nmol h-1 m-3 for the WEA and WSG,
respectively. The contribution of NO 3 -, NO 2 - and H 2 O 2 as the main sources of ●OH via
photolysis were 4.5, 0.7 and 1.2%, respectively, for the WSG fraction, while in the
WEA fraction, NO 3 -, NO 2 - and H 2 O 2 contributed 8.9, 1.2 and 2.5%, respectively. DOC,
which was determined only for WSG samples, ranged from 0.1 to 5.3 mg C m-3 with amean of 2.9±2.6 mg C m-3. To find potential sources of ●OH in the atmospheric aqueous
phase, known amount (excess) of iron (III) was added into the solution of the WSG
fraction and then the R OH of photo-Fenton reaction was determined. The photo-Fenton
reaction contributed 42% of the total ●OH formation in the WSG fraction, while
unknown sources that might have been humic-like substances (HULIS) accounted forii

the remaining 52%. The results showed high contribution from unknown sources andfluorescent properties very similar to those existing in natural waters and water-extractof aerosol.
Chapter 3 follows similar methodologies used in the previous chapter, however using ahigh volume sampler for the sampling, reports the photochemistry of the ●OH inwater-extract of marine aerosol collected in the Seto Inland Sea during a research cruisein summer of 2010. Unlike the ambient aerosols collected on land, the chemicalcomposition showed large influence of the sea-salt ions such as Na+ and Cl- and theoxidation capacity of the ●OH much lower compared to aerosols collected on land,
indicating minor influence of anthropogenic activities on the photochemical generationof ●OH. The mean concentration of Cl- and Na+ were 36.3±51 nmol m-3 and 47.7±34nmol m-3 respectively. Cl- represents 47.6% and Na+ represents 52.6% of the total ions
measured. Low percentages of SO 4 2- (32.1%) and NO 3 - (20.5%) are good indicators formarine aerosol. NO 2 - was present in only 2 of the total 16 samples (mean of 1.39 nmolm-3). The mean concentration of DOC was 7.0±6.6 mg C m-3 and the mean pH was
6.18±0.114.
The ●OH photoformation rate ranged from 0.019-0.014 with the mean of 0.06±0.03
nmol h-1 m-3.Among the major sources of ●OH, NO 3 - accounted for 18.6% while theiiiunknown sources contributed for about 74%. The occurrence of unknown sources,
possibly HULIS, as the main and important contributor of ●OH generation in marine
aerosol samples. Formation mechanism involving the photolysis of DOM such as
HULIS, which have been suggested to be the major source of ●OH formation in theriver and sea waters.
In the Chapter 4 a general discussion on the obtained results and the suggestion offurther research are made. Sources and sinks of ●OH in the WEA fractions from land
and marine aerosols are almost same to those in the WSG fractions. In addition,mechanism of ●OH generations occurring in atmospheric aqueous phase, in which
HULIS is involved, are probably same/identical to those in natural waters. Therefore, in
the analogue of photoformed ●OH in natural waters, ●OH in the WEA and WSG
fractions in the atmosphere may significantly control for the aerosol and gas phasechemistry, especially degradation rates of several organic matter.

iv

論文題目：大気中エアロゾルの水抽出画分およびガスの水溶性画分におけるヒドロキシルラジカ
ルの光化学的生成速度に関する研究

広島大学大学院生物圏科学研究科 環境循環系制御学 専攻
Nomi Sonia Naomi
本研究では、大気中エアロゾル（微細粒子）中で光化学的に生成するヒドロキシルラジカル（OH ラジカル）の生成過程に関して研究を行った。大気試料は、東広島市及び瀬戸内海海上において採取した。大気エアロゾル中の OH ラジカルの主な生成源として、大気気相（ガス）中の水溶性成分が考えられるので、大気気相中の水溶性成分も同時に採取し、比較検討した。
第 1 章は序論であり、大気エアロゾルの大気汚染、酸性雨、地球温暖化・冷却化に及ぼす作用について紹介し、大気エアロゾル中で OH ラジカルの存在状態や役割に関して考察した後、本研究の意義や目的を述べている。
第 2 章では、東広島において 2008 年から 2010 年にかけて月 1 回合計 24 回大気試料を採取し、エアロゾルの水抽出画分およびガスの水溶性画分をそれぞれ分離して OH ラジカルの光化学的発生速度を求めた。その結果、大気エアロゾルの水抽出画分およびガス水溶性画分中 OH
ラジカルの平均発生速度はそれぞれ 1.4 および 0.5 nmol h-1 m-3であり、硝酸イオン、亜硝酸イオン、過酸化水素の光分解からの発生寄与率は水抽出画分でそれぞれ 8.9、1.2、2.5%、水溶性画分で 4.5、0.7、1.2%であった。その他成分からの発生寄与率はガス水溶性画分で光フェント
ン反応から 42％、溶存有機物（おそらく腐植様物質）から 52％であった。OH ラジカルの生成速度の月毎の変動を解析したところ、季節変化は見られないものの、黄砂飛来時にはエアロゾル
水抽出画分の OH ラジカルの生成速度が増加する傾向があることが確認された。黄砂時の OH
ラジカル生成速度の増加は、黄砂粒子中に含まれる硝酸塩や水溶性有機物の光分解に原因すると推察した。
第 3 章では、瀬戸内海海上大気中のエアロゾル中 OH ラジカルの生成過程を調べた。2010 年
夏の広島大学生物生産学部実習船豊潮丸の瀬戸内海航海において、海上大気中エアロゾルを船首デッキで採取した。エアロゾルの水抽出画分中 OH ラジカルの平均発生速度は 0.06 nmol h-1 m-3であり、硝酸イオンからの発生寄与率は 19%であった。その他成分からの発生寄与率は 74％であった。また、その他成分は腐植様物質の可能性が高いことが 3 次元蛍光分析から示唆された。
第 4 章は総合討論、結論、今後の課題を述べている。本研究により、大気エアロゾル中でのOH ラジカルの発生過程には硝酸イオンなどの無機物以外に、腐植様物質のような有機物が関与することが示唆された。また、大気ガスの水溶性画分からも OH ラジカルが発生することから、エアロゾル中 OH ラジカルの発生物質の一部は大気ガスから移行してきたものであることが推察された。光化学的に発生した OH ラジカルは、エアロゾル液相中で多くの化学物質の酸化還元反応に関与することで、それらの大気中での寿命や動態を決定すると考えられる。したがって、
OH ラジカルの消失過程に関する研究が今後の課題といえる。

v

Chapter 1-1-

Chapter 1
1-1-General Introduction
Historically, the field of atmospheric chemistry has focused on gas-phase oxidations as
the primary fate-determining processes of chemical substances in the troposphere. However,
there

is

increasing

evidence

demonstratingthat

aqueous-phase

photochemicaltransformations in atmospheric water drops (cloud, fog, and rain drops, and aqueous
aerosols) can significantly affect the chemical composition of the troposphere (FinlaysonPitts and Pitts, 2000).
Aerosols, defined as suspensions of solid or liquid particles in a gas, are currently ofinterest for a number of reasons. Their potential to offset global warming, the opticalproperties of aerosols mean that they are efficient scatters of light, aerosols have thepotential to both heat and cool the surface of the earth (Seinfeld and Pandis, 1998;
Finlayson-Pitts and Pitts, 2000; Ramanathan et al., 2001). Aerosol particles present surface
area to reactive gaseous species that can provide new pathways for atmospheric chemical
reactions and/or serves as sinks for reactive species such as free radicals. Aerosol particles
serve as cloud condensation nuclei thereby altering the composition of cloud water andinfluencing the course of aqueous reactions in clouds. Through scattering and absorption ofradiation in the solar spectrum aerosol particles influence the rate of primary photochemical
reactions (Heintzenberg et al., 2003). They control the visibility in the air, the intensity ofsolar radiation reaching the surface of our planet, as well as electric and radioactive
properties of the atmospheric environment (Bizjak et al., 1999)
Reactions taking place in the atmosphere are extremely important because theysignificantly influence the lifetime of many atmospheric components and yieldintermediates that often play a key role in atmospheric chemistry (Vione et al., 2006). The-2-

fate of numerous organic and inorganic compounds in the atmosphere is controlled byphotochemically produced oxidants (Calvert et al., 1966; Finlayson-Pitts and Pitts, 2000;
Warneck, 1988).
The chemical transformations occurring in the atmosphere are best characterized asoxidation processes. Solar radiation influences the chemical processes in the atmosphere byinteracting with molecules that act as photo acceptors (Boubel et al., 1973).
Reactive oxygen species (ROS) have been defined according to their own name, toderive and present higher reactivity due of unpaired electrons than molecular oxygen with
redox activity (Pardini, 1995; Murrant and Reid, 2001). It includes families of oxygencentered or related free radicals, ions, and molecules. The free radical family includes
superoxide (●O 2 -), hydroxyl (●OH), hydroperoxyl (●O 2 H) and organic peroxy radicals.
Non-radicals such as hydrogen peroxide (H 2 O 2 ), singlet oxygen (1O 2 ), hypochlorous acid
(HOCl) (Fink, 2002) and organic and inorganic peroxides also come under the umbrella of‘Reactive Oxygen Species’ (Figure 1).

Figure 1. Reactive Oxygen Species-3-1-2-Atmospheric Hydroxyl Radical●

OH is the most powerful daytime oxidant among ROS generated as short-lived

intermediates in tropospheric chemistry (second-order rate constants of 107 to 1010 M-1 s-1).
Occurring in aqueous phase at very slow steady-state concentrations, this is difficult tomonitor directly by spectroscopy methods (Buxton et al., 1988). Due to its high oxidation
potential for the removal of air pollutants, ●OH is referred to as the “detergent” or “vacuum
cleaner” of the atmosphere (Thompson, 1992). The oxidation capacity of most organic
substances has attracted many researchers focus on the role of the ●OH as an oxidant in theenvironment (Zepp et al., 1992).
In the atmospheric gas phase, ●OH is generated by photochemical mechanisms such as
photolysis of ozone (O 3 ), nitrous acid (HONO), hydrogen peroxide (H 2 O 2 ), methylhydroperoxide (CH 3 OOH), and carbonyl compounds (mainly aldehydes and ketones)(Atkinson, 2000; Moortgat, 2001).
In the atmospheric aqueous phase, ●OH is generated by the photolysis of nitrate ions
(NO 3 -) (reaction 1), nitrite ions (NO 2 -/HNO 2 ) (reactions 2 and 3) and hydrogen peroxide(H 2 O 2 ) (reaction 4). Moreover, in the Fenton reaction, ●OH is produced by the reaction
between reduced iron, Fe2+, and H 2 O 2 (reaction 5) (Zellner et al. 1990). Iron (III), which
may exist in the form of complexes with natural dissolved organic matter (DOM) such as
oxalic acid and humic-like substances (HULIS) in the aqueous phase, is photochemicallyreduced to Fe2+ through a ligand-to-metal charge transfer. The Fe2+ subsequently reacts
with H 2 O 2 (reactions 6 to 8) (Voelker et al. 1997). Furthermore, direct photolysis reactionsof DOM such as p-benzoquinone and HULIS may act as sources of ●OH in the atmosphericaqueous phase, through mechanisms similar to those that occur in natural water chemistry-4-

(Alegría et al. 1997; Vaughan and Blough, 1998). However, the generation mechanisms of●OH have not been fully characterized to date.

NO 3 - + H 2 O + hν  ●OH + OH- + NO 2

(1)

NO 2 - + H 2 O + hν  ●OH + OH- + NO

(2)

HONO + hν  ●OH + NO

(3)

H 2 O 2 + hν  2 ●OH(4)

Fe2+ + H 2 O 2 +H+  Fe3+ + ●OH + H 2 O(5)

Fe3+ + C 2 O 4 2-  [Fe3+ (C 2 O 4 )] +(6)

[Fe3+ (C 2 O 4 )]+ + hν  [Fe2+ (C 2 O 4 )] +(7)

[Fe2+ (C 2 O 4 )] + + O 2  Fe2+ + O 2 - + 2CO 2(8)

Even though studies of ●OH photoformation in cloud droplets, fog, dew and rain havebeen conducted (Faust and Allen, 1993; Faust et al., 1993; Arakaki and Faust, 1998,
Arakaki et al., 1998, Anastasio et al., 1994; Nakatani et al., 2007), only a few studies haveinvestigated the water-extract of atmospheric aerosols (Arakaki et al., 2006, Kondo et al.,2009); therefore, sources and sinks of ●OH have not been clarified.
Moreover, no studies that have been conducted to date have focused on photoformationof ●OH in aqueous solutions of water-soluble gases in the atmosphere, even though anunderstanding of this process may be useful for evaluation of the oxidation capacities ofambient air. Therefore, this study was conducted to determine the ●OH photoformation rate,
as well as its sources and contributions in both the water-extract of aerosol and aqueous
solution of water-soluble gas in air samples.
-5-1-3-Outlines of this study
The overall structure of the thesis includes 4 chapters. It consists of two main parts:
first part is about the study of the ●OH generation capacity in the water-extracts of aerosols(WEA) and aqueous solution of water-soluble gas (WSG) fractions collected at Hiroshima
University. Chemical composition, the main sources and source strengths of ●OHgeneration in ambient aerosol and aqueous soluble gases were investigated (Chapter 2).
The air sampling system used for the collection of both gas and particle fractions was set up
to collect relatively low-volume air samples.
The second part deals with water-extracts of marine aerosols collected from the Seto
Inland Sea region using a high-volume air sampler for determination of the oxidative
capacity of ●OH (Chapter 3).
The research concerns of this thesis are:1) To acquire information about the oxidation capacity of ●OH in the water-extracts ofaerosols and aqueous solution of water-soluble gas fractions in atmospheric ambient landair (Chapter 2).
2) To identify the main sources, source intensities and mechanisms for the ●OH formationof the ambient air of Higashi-Hiroshima, Japan (Chapter 2).
3) To determine the ●OH formation rate (R OH ), the chemical composition and contribution
from the major sources of ●OH in water-extracts of marine aerosols collected from the Seto
Inland Sea region, in western Japan (Chapter 3).

-6-

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quinones. Production of water-derived spin adduct. Photochemistry and Photobiology
66(4), 436-442.
Anastasio, C., Faust, B.C., and Allen, J.M., 1994. Aqueous phase photochemical formationof hydrogen peroxide in authentic cloud waters. Journal of Geophysical Research 99(D4), 8231-8248.
Arakaki, T., Miyake, T., Shibata, M. and Sakugawa, H., 1998. Measurement ofphotochemically formed hydroxyl radical in rain and dew waters. The Chemical
Society of Japan, 9, 619-625 (in Japanese).
Arakaki, T. and Faust, B.C., 1998. Sources, sinks, and mechanisms of hydroxyl radical(OH) photoproduction and consumption in authentic acidic continental cloud watersfrom Whiteface in Mountain, New York: the role of the Fe(r) (r =II, III)

photochemical cycle. Journal of Geophysical Research 103 (D3), 3487-3504.
Arakaki, T., Kuroki, Y., Okada, K., Nakama, Y., Ikota, H., Kinjo, M., Higuchi, T., Uehara,
M.; Tanahara, A., 2006. Chemical composition and photochemical formation ofhydroxyl radicals in aqueous extracts of aerosol particles collected in Okinawa, Japan.
Atmospheric Environment 40, 4767-4774.
Atkinson, R., 2000. Atmospheric chemistry of VOCs and NO x . Atmospheric Environment
34, 2063-2101.
Bizjak, M., Grgié, Hudnik, V., 1999. The role of aerosol composition in the chemical
processes in the atmosphere. Chemosphere, Vol. 38, no. 6, 1233-1240.

-7-Boubel, R.W., Fox, D.L., Turner, D.B., and Stern, A.C., 1973. Fundamentals of air
pollution, 3rd edition – Academic Press USA, page 165.
Buxton, G. V., Greenstok, C. L., Helman, W.P., Ross, A. B., 1988. Critical review of rate
constants for reactions of hydrated electron, hydrogen atoms and hydroxyl radicals(OH/O−) in aqueous solution. Journal of Physical Chemistry. Ref. Data 17, 513.
Calvert, J.G., Pitts, J.N. Jr, 1966. Photochemistry. Wiley, New York, 899.
Faust, B.C. and Allen, J.M., 1993. Aqueous-phase photochemical formation of hydroxyl
radical in authentic cloudwaters and fogwaters. Environmental Science andTechnology 27, 1221-1224.
Faust, B.C., Anastasio, C., Allen, J.M., Arakaki, T., 1993. Aqueous-phase photochemical
formation of peroxides in authentic cloud and fog waters. Science 260, 73-75.
Fink, M.P., 2002. Role of reactive oxygen and nitrogen species in acute respiratory distresssyndrome. Curr Opin Crit Care, 8:6–11.
Finlayson-Pitts, B. J. and Pitts, J. N. J., 2000. Chemistry of the Upper and Lower
Atmosphere, Academic Press, San Diego, California.
Heintzenberg, J., Raes, F., Schwartz, S. E., 2003. Atmospheric Chemistry in a Changing
World – an Integration and Synthesis of a Decade of Tropospheric Chemistry Research.
Eds., Springer, Berlin, pp. 125-156. (Chapter 4 available online)
Kondo, H., Chiwa, M., Sakugawa, H., 2009. Photochemical formation and scavenging
mechanisms of hydroxyl radical in water-extracts of atmospheric aerosol collected in
Higashi-Hiroshima, Japan. Geochemical Chemistry 43, 15-25 (in Japanese)-8-

Moortgat, G.K., 2001. Important photochemical processes in the atmosphere. Pure andApplied Chemistry, 73 (3), 487-490.
Murrant, C.L. and Reid, M.B., 2001. Detection of reactive oxygen and reactive nitrogenspecies in skeletal muscle. Microscopy Research and Technique, 55:236– 48.
Nakatani, N., Ueda, M., Shindo, H., Takeda, K., and Sakugawa, H., 2007. Contribution of
the Photo-Fenton reaction to hydroxyl radical formation rates in river and rain water
samples. Analytical Sciences, 23, 1137-1142.
Pardini, R.S., 1995. Toxicity of oxygen from naturally occurring redox-active pro-oxidants.
Arch Insect Biochem Physiol, 29:101–18.
Ramanathan, V. et al., 2001. Indian Ocean Experiment: An integrated analysis of theclimate forcing and effects of the great Indo-Asian haze. Journal of GeophysicalResearch 106: 28371–28399, doi: 10.1029/2001JD900133.
Seinfeld, J.H. and Pandis, S.N., 1998. Atmospheric Chemistry and Physics: From Air
pollution to climate Change. 1st edition, J. Wiley, New York.
Thompson, A.M., 1992. The oxidizing capacity of the earth’s atmosphere: Probable pastand future changes. Science 256, 1157-1165.
Vaughan, P.P. and Blough, N.V., 1998. Photochemical formation of hydroxyl radical byconstituents of natural waters. Environmental Science and Technology 32, 2947-2953.
Vione, D., Maurino, V., Minero, C., Pelizzetti, E., Harrison, M.A.J., Olariu, R., and Arsene,C., 2006. Photochemical reactions in the tropospheric aqueous phase and on particulatematter. Chemical Society Review, 35, 441-453.

-9-

Voelker, B.M., Morel, F.M.M. and Sulzberger, B., 1997. Iron redox cycling in surface
waters: Effects of humic substances and light. Environmental Science and Technology
31, 1004-1011.
Warneck, P., 1988. Chemistry of the Natural Atmosphere 41, Academic press: San Diego
International Geophysics Series.
Zellner, R., Exner, M. and Herrmann, H., 1990. Absolute OH quantum yields in the laser
photolysis of nitrate and dissolved H 2 O 2 at 308 and 351 nm in the temperature range
278-353 K. Journal of Atmospheric Chemistry, 10, 411-425.
Zepp, R.G.; Faust, B.C. and Hoigné, J., 1992. Hydroxyl radical formation in aqueous
reactions (pH 3-8) in iron (II) with hydrogen peroxide: The photo-Fenton reaction.
Environmental Science and Technology 26, 313-319.

-10-

Chapter 2-11-

Chapter 2
Photoformation of OH radical in water-extracts of atmospheric aerosols and aqueous
solution of water-soluble gases collected in Higashi-Hiroshima, Japan
2-1-Introduction
It is widely accepted that hydroxyl radicals (●OH) play an important role in theoxidation of various organic and inorganic compounds in not only atmospheric gas phase
but also atmospheric aqueous systems (i.e. aerosols, cloud fog, dew and rain) (FinlaysonPitts and Pitts, 1986). ●OH is the most powerful daytime oxidant among reactive oxygen
species (ROS) generated as short-lived intermediates in tropospheric chemistry (FinlaysonPitts and Pitts, 1986). ●OH can be formed via photochemical reactions in sunlightilluminated aqueous phase through a variety of mechanisms as previously detailed in the
Chapter 1.
Even though studies of ●OH photoformation in cloud droplets, fog, dew and rain havebeen reported (Faust et al., 1993; Arakaki and Faust, 1998, Arakaki et al., 1998, Anastasio
et al., 1994), only a few studies were made for water extract of atmospheric aerosol
particles (Arakaki, et al., 2006, Kondo et al., 2009), and thus sources and sink of ●OH are
still not yet clarified. Moreover no studies to date have focused on photoformation of ●OHin the water-soluble gaseous fraction of the atmosphere, which may be useful for evaluationof oxidation capacities of ambient air.
Therefore, this study was conducted to determine the ●OH photoformation rate, its
sources and contribution in both the water-extract of aerosol and water-soluble gaseous
fractions of ambient air samples collected in Higashi-Hiroshima.

-12-2-2- Experimental
2-2-1- Sampling site
Higashihiroshima is a university town of Hiroshima University. As the central cityof Hiroshima Central Technopolis, high-tech industry is growing. Higashihiroshima isadjacent to Hiroshima city, so it is also a commuter town of Hiroshima. Atmosphericaerosol particle and gas fraction samples were collected monthly on the roof of the Facultyof Integrated Arts and Sciences building of Hiroshima University (about 30 m above
ground level) at the Higashi-Hiroshima campus (34°24’N, 132°42’E, altitude 242 meters)(Figure 2-1), Japan, from June 2008 to June 2010 (n= 24). As of June 2011, HigashiHiroshima had an estimated population of 183,834 in a total area of 635, 32 km².
2-2-2- Reagents
All chemicals and solvents were of reagent grade and were used as received without
further treatment. All reagent solutions were prepared using ultrapure water (Milli-Q, ≥18
MΩ cm, Millipore Japan).
2-2-3- Air sampling
An air filtering unit combined with two sequential scrubber vessels (impingers) wasused to collect samples (Figure 2-2). A silica fiber filter (QR-100, ϕ= 47 mm, 0.3 μm poresize) was attached to the system input to collect aerosol particles. The collection system
was also connected to two sequential gas scrubbers containing 500 ml of Milli-Q water as
an absorption solution for collection of atmospheric aqueous solution of water-soluble gas(WSG). The flow rate was maintained at 1.5-2.0 L min-1 using an air pump (AP-032Z
Model, Iwaki Air Pump APN-215 NV-1) for approximately 2-7 days, during which time
8.3 to 29 m3 of ambient air were collected.
-13-

A blank control filter was analyzed in the same manner as the aerosol filters, after being
kept in a clean room for one week without being connected to the pump. Additionally,
Milli-Q water (500 ml) was kept in the impinger for one week and used as a blank control
solution for the WSG fraction. The Milli-Q water was analyzed for inorganic ions andmetal species to check for possible contamination from the impinger and other instrumentsin the collection device and, if found contaminants were found, the WSG fraction wascorrected (Figure 2-3).
The aerosol collected on the fiber filters and the blank control filter were stored inpolyethylene plastic bags and the absorption solutions were stored in polyethylene plastic
bottles under refrigeration until further extraction and analytical measurements wereconducted.
2-2-4- Extraction procedure and analytical methods
The sampled aerosol filter (WEA fraction) was soaked in 20 mL of Milli-Q water for
three hours shaking at 120 rpm using a multishaker (MMS-310, EYELA). The sample wasthen filtered using a syringe filter with a 0.45 µm pore size (Pall, Akrodisc 25mm) before
being subjected to photochemical experiments and chemical analyses.
2-2-5- Chemical analysis of water-soluble fractions
The concentrations of the major inorganic ions, dissolved organic carbon (DOC) andH 2 O 2 were measured using ion chromatography (ICS –1600, Dionex), a TOC analyzer(TOC-5000A, Shimadzu) and isocratic HPLC (LC-10Ai, Shimadzu), respectively. The total
dissolved iron and other heavy metals were determined using inductively coupled plasma
atomic emission spectrometry (Optima 3000, Perkin Elmer).

-14-

The initial concentration of H 2 O 2 was determined according to the method described by
Olasehinde et al. (2008) based on the reduction of H 2 O 2 by ferrous iron (Fe2+) in acidsolution to yield ●OH which is scavenged by benzene to produce phenol and analyzed byisocratic HPLC (LC-10Ai, Shimadzu) with fluorescence detector (Ex= 270nm and Em=298nm) (reactions 9 and 10).
Fe2+ + H 2 O 2  Fe3+ + ●OH + OH-

(9)

●

(10)

OH + C 6 H 6  C 6 H 5 OH

The amount of phenol produced is directly proportional to the original amount of H 2 O 2
present in the sample.
2-2-6- Photochemical Experiments: OH radical measurement●

OH formation rate (R OH ) from the photo-Fenton reaction and total R OH were

determined by HPLC-fluorescence detection (RF-10A, Shimadzu) following irradiation of
the extracted sample using a solar simulator (Model 81160-100, Oriel Corp.) unit equippedwith a 300 W Xenon lamp (ozone free, model 6258, Oriel Corp.). During photolysis,
sample solutions were stirred by a magnetic stirrer covered with Teflon and maintained at aconstant temperature of 20 °C using a circulator (RTE-111, NESLAB) and a chemical trapof photoformed ●OH with benzene probe (1.2 mM) according to the methodology describedby Faust and Allen (1993) (Fig.2-4). This simple methodology has been used for thedetermination of ●OH formation rate in rain, dew and cloud water (Arakaki and Faust,
1998; Arakaki et al., 1998).
Benzene is a suitable compound for this investigation because it undergoes fast reaction
with OH (rate constant 7.8 x 109 M-1 s-1, Buxton et al., 1988) does not absorb lamp
radiation and does not alter either the pH or the buffer capacity of the solutions.
-15-

Therefore, R OH was then determined using the following equation 11:
R OH = (R p /F b-OH Y p )(11)

where R p is the photochemical formation rate of phenol obtained experimentally, F b-OH is
the fraction of ●OH that react with benzene, as opposed to with other competing ●OH
scavengers, and Y p is the chemical yield of phenol from the reaction of ●OH with the added
benzene. Y p was reported to be 0.75. F b-OH for cloud water, reported by Arakaki and Faust(1998), was at least 0.94 with 1.2 mM added benzene, suggesting that most of the ●OHformed photochemically in cloud water reacted with benzene.
The initial concentration of the added benzene in the WSF solution was 20 mM. Phenol
was measured using isocratic HPLC with a pump (LC 10 Ai; Shimadzu), a C-18 column(LC-18 5 µm 4.6 mm i.d. x 250mm, Supelco or RP-18 GP 5µm 4.6 mm i.d. x 150 mm
length, Kanto Kagaku) was used for separation and a ﬂuorescence detector (λ Ex 270/λ Em
298 nm; RF-10A, Shimadzu). The mobile phase was acetonitrile and Milli-Q water[CH 3 CN:H 2 O 60:40] (v/v) and the ﬂow rate 1.0 mL min–1.
The concentrations of phenol were determined based on calibration curves made with
Milli-Q water on the day of the illumination experiments. The initial formation rate ofphenol (R p , M min-1) during an illumination experiment was determined from the plot of
phenol concentrations versus illumination time using a linear regression analysis.
The light intensity of the solar simulator was controlled measuring the photochemicaldegradation rate of 2-nitrobenzaldehyde (2-NB) (chemical actinometer) by isocratic HPLC
with UV detection of the absorbance wavelength set at 260 nm. The mobile phase and theflow rate were the same as for the determination of ●OH. The degradation rate of 8µm 2NB (J 2-NB ) solution was normalized against a degradation rate of J 2-NB = 0.00923 s-1, which-16-was determined at noon under clear sky conditions in Higashi-Hiroshima city (34ºN) on 1
May of 1998 (Arakaki et al., 1998).
The contribution of the photo-Fenton reaction was determined based on the difference
between the ●OH formation rates with and without the addition of deferoxamine mesylate(DFOM) (Sigma Aldrich, Japan). The addition of DFOM produces a stable and strong
complex with Fe (III) that results in suppression of the photo-Fenton reaction (Nakatani etal. 2007). Next, 1 μM potassium trioxalate ferrate (III) is added to the solution of the WSG
fraction with 0.5 μM H 2 O 2 with and without 10 μM DFOM to determine the potential for
generation of ●OH from the photo-Fenton reaction (reactions 12 to 14).
Fe (III)-(DOM) m + light  Fe (II)-DOM m-1 + DOM ox +(12)

Fe (OH) 2+ + light  Fe (II) + ●OH(13)

Fe (II) + H 2 O 2  Fe (III) + ●OH + OH-(14)

The initial concentration of H 2 O 2 was determined according to the method described by
Olasehinde et al. (2008) based on the reduction of H 2 O 2 by ferrous iron in acid solution toyield ●OH which is scavenged by benzene to produce phenol and analyzed by HPLC withfluorescence detector (reactions 15 and 16).
Fe2+ + H 2 O 2  Fe3+ + ●OH + OH-

(15)

●

(16)

OH + C 6 H 6  C 6 H 5 OH

The amount of phenol produced is directly proportional to the original amount of H 2 O 2
present in the sample. The total dissolved iron was determined using inductively coupledplasma atomic emission spectrometry (Optima 7300-DV, Perkin Elmer).

-17-

2-2-7- Contribution of major sources of ●OH (%)
The contributions of various sources to ●OH photoproduction were estimated. The
percent contributions (fi) from well-known ●OH sources, such as NO 3 -, NO 2 - and H 2 O 2 tototal ●OH formation (fi (I=NO 3 -, NO 2 - and H 2 O 2 )) can be calculated by the following
equation 17:
fi =ki[Ci ]x100(%)
Rtotal(i=NO 3 -, NO 2 - and H 2 O 2 )(17)

where ki is the rate of ●OH formation from nitrate (k NO3- = 2.43 x 10-7 s-1), nitrite (k NO2- =2.81 x10-5 s-1) and hydrogen peroxide (k H2O2 = 3.52 x 10-6 s-1), [C i ] is the concentration ofeach species and R OHtotal is the ●OH photoproduction rate determined experimentally for the
sample (Arakaki et al., 1998; Nakatani et al., 2001).
2-2-8- Fluorescence Properties
To estimate the unknown sources of ●OH, the fluorescence matter (FM) wasinvestigated based on the 3D-excitation emission matrix (EEM) spectrum obtained using afluorescence spectrometer (F-4500, Hitachi, Ltd.). The samples were scanned at excitation
wavelengths of 225-400 nm and emission wavelengths of 250-500 nm at intervals of 5 nm
and a scanning speed of 1200 nm.min-1 to obtain the overall characteristics. The samples
were calibrated using 2.8 µg L-1 of quinine sulfate dehydrated solution (Nacalai Tesque) asa standard for fluorescence intensity (FI), which corresponds to 25 fluorescence units (flu).
2-2-9- Air mass backward trajectory analysis
Air mass backward trajectories were analyzed using the North American simulator
HYSPLIT model (Hybrid Single-Particle Lagrangian Integrated Trajectory) from the Air
Resources

Laboratory(ARL)of National-18-

Oceanic

andAtmosphericAdministration (NOAA, 2010), available online. Using a mathematical dispersion model,
simple to complex windy trajectories can be simulated (Draxler, 1998). Setting up theparameters such as trajectory direction (backward), start time (day and time), total run time
(total sampling duration) and new trajectory frequency (represents the color trajectories
traced every 6 hours totalizing 24 trajectories), the wind backward can be traced andinvestigated. The occurrence of the Yellow Sand event was monitored by the Japan
Meteorology Agency (2010).
2-3- Results and Discussion
2-3-1- Chemical composition of WSG and WEA fractions
Among the major anions present in the WSG and WEA samples, SO 4 2- was the mostabundant. The mean concentration of SO 4 2- was 9.4±4.0 nmol m-3 in the WSG and 81±33nmol.m-3 for the WEA. This was followed by NO 3 -, which was present at mean
concentrations of 9.3±4.1 nmol m-3 for the WSG and 47±32 nmol m-3 for the WEA fraction.
The NH 4 + concentration was the highest among the measured cations, being present at amean concentration of 8.4±9.4 nmol m-3 in the WSG and 84±42 nmol m-3 in the WEA
samples. The total concentrations of anions found in the WEA fraction were about fivetimes higher than those found in the WSG fraction. The WSG fraction showed that metal
species such as Na+, K+, Ca2+, and Mg2+ were contaminated from the impinger and other
instruments in the collection device, resulting in apparent presence of those metals in the
WSG fraction. Therefore the data of metal species in the WSG fraction was omitted fromour results. Iron and other heavy metals were not detected in the WSG fraction. The mean
initial concentration of H 2 O 2 was 0.2±0.3 nmol m-3 in the WSG and 0.9±2.3 nmol m-3 inthe WEA fraction. DOC, which was determined for WSG fraction only, due to the scarce-19-

volume of WEA sample, ranged from 0.1 to 5.3 mg C m-3 with a mean of 2.9±2.6 mg C m-3(Table 2-1).
2-3-2- ●OH photoformation rate (R OH )●OH was detected in all 24 samples and was found to increase linearly with increasingillumination time in both fractions (WEA and WSG) (Figure 2-5). These findings show thesame photochemistry occurring in both fractions on ●OH generation in the aqueous phase.
The ●OH photoformation rate was found to range from 0.04 to 2.5 nmol h-1 m-3 with amean of 0.5 nmol h-1 m-3 for the WSG fraction and from 0.1 to 8.4 nmol h-1 m-3 with a meanof 1.4 nmol.h-1m-3 for the WEA sample. The ●OH photoformation rates in the WSG
fractions collected during this study are summarized in Table 2-2 and compared with thoseof other studies. Analyses in the other studies were conducted using the same conditions toirradiate samples (simulated sunlight), except for the Okinawa and Canada studies, inwhich a monochromatic light adjusted to 313 nm was used.
The ●OH photoformation rate determined in this study revealed that the WEA
photoformation rate was about three times higher than that of the WSG fraction, and wasmuch higher (more than one magnitude) than previously reported R OH values for the WEA
fraction. The ●OH formation rate of the WSG fraction was even higher than that of the R OH
in the WEA fraction obtained by other investigators.
Once the mean R OH in the WEA is shown higher than the WSG fraction in this study,
there is a hypothesis that the WEA fraction contains larger source compounds of ●OH thanthe WSG fraction.

-20-

2-3-3- Contribution of major sources of ●OH
In the WSG fraction, the presence of NO 3 -, NO 2 - and H 2 O 2 detected in most of thesamples contributed only a relatively low percentage of the ●OH photoformation whencompared to the unknown sources (Table 2-3). The contributions of the major sources ofOH generation in the WSG fraction were found to be 4.5% for NO 3 -, 0.7% for NO 2 - and●1.2% for H 2 O 2 . Majority of ●OH sources is, therefore, unknown. In this study, an
experiment was carried out to elucidate the sources of ●OH. Photo-Fenton reaction was
examined because this reaction is considered to be a major ●OH source in both atmosphericaqueous phase and natural water (Nakatani et al. 2007). Dissolved iron species are common
to exist in atmospheric aqueous phase (Kim et al. 2001, 2003). If water soluble gases meetwith iron species in the aqueous phase photo-Fenton reaction may occur. To find potential
sources of ●OH in the atmospheric aqueous phase, known amount (excess) of iron (III) was
added into the solution of the WSG fraction and then the R OH of photo-Fenton reaction wasdetermined by the method of Nakatani et al. (2007). The results indicated that the photoFenton reaction contributed up to 42% of the total ●OH photoformation in the WSG
fraction while remaining unknown sources accounted for 52% of the photo-formations(Table 2-3). In a previous study conducted by Kondo et al. (2009), the photo-Fenton
reaction was found to contribute 49% of the ●OH photoformation in the WEA fraction
collected at Higashi-Hiroshima during 2003-2007 (n= 23). Therefore the photo-Fenton
reaction may be a significant contributor of ●OH in the aqueous phase of ambient air, as
well as river and rainwaters, as summarized in Table 2-3.
In the WEA fraction, NO 3 -, NO 2 -, H 2 O 2 and unknown sources accounted for 8.9, 1.2,
2.5 and 87% of the ●OH photoformed, respectively (Table 2-3). However, photo-Fenton
reaction was not analyzed in the WEA fraction due to lack of sufficient amount of air-21-

samples for the analysis and thus the unknown sources are supposed to contain photoFenton reaction.
2-3-4- HULIS as unknown sources of ●OH
Fluorescence properties were higher present in the WEA than the WSG fractions.
Among the 24 samples collected, 24 WEA samples showed fluorescent properties while in
the WSG, 22 samples (91%). For most of these samples, two peaks of fluorescence weredetected. A fluorescence peak was observed at λ Ex/Em =240–250/395–415nm (peak A),
while a second peak was observed at λ Ex/Em = 295–315/395–410 nm (peak B). Previous
studies (Coble et al., 1990; Coble, 1996; Parlanti et al., 2000; Zepp et al., 2004; Graber and
Rudich, 2006) found that HULIS had two distinctive peaks, whose Ex/Em wavelengths are
similar to those of the two peaks found in this study, suggesting the presence of HULIS inboth WEA and WSG fractions (Figure 2-6).
The mean fluorescence intensities of the peak A were 54±122 flu for the WSG and
316±116 flu for the WEA while those of the peak B were72±170 flu for the WSG and
311±136 flu for the WEA fractions. Larger abundance of the two peaks in the WEA
fraction than the WSG fraction was associated with higher photoformation rate of ●OH in
the former fraction than the latter fraction, suggesting that HULIS may be the “unknown
sources” of ●OH. Kondo et al. (2009) suggested that WEA samples collected at same
sampling site as this study contains unidentified compounds which could be fluorescentorganic compounds, such as HULIS. They found liner correlations of the fluorescenceintensities of the peak A and B with the photoformation rate of ●OH from the unknown
sources. Possible presence of HULIS in the WSG fractions leads to the discussion thatsome HULIS perhaps exist as a low molecular size and existed in the WSG fraction.

-22-

Presently no conclusive data of HULIS, other than the 3D-EEM spectra, are available andthus further study needs to confirm it.
2-3-5- Monthly variations in the R OH and other chemical compounds
Figure 2-7a shows the ●OH photoformation rate and the concentrations of SO 4 2-, NH 4 +,NO 3 - and DOC per month in the WSG fraction. The R OH determined for the samples
collected in June, July and September of 2008 revealed increasing rates of ●OH generation
and after that shown to be a decreasing trend. The sample collected in the September, 2008
showed the highest, R OH =2.5 nmol h-1 min-1. Low contributions from NO 2 - (0.17%), NO 3 (0.55%) and H 2 O 2 (0.01%) and high contribution from unknown sources (50.3%) in
September 2008 explained the highest R OH among the 24 samples. During 2009-2010 ●OH
photoformation rate was low (<0.5nmol m-3) and flat. There were no clear relations
between R OH and concentrations of other analytical items.
The R OH variations in the WEA fractions were observed higher in the samples collectedin 11-18 March, 23-30 April and 20-27 May of 2010 (Figure 2-7b). The Yellow Sand
(Asian Aeolian Dust) events were occurred in the sampling date of 11-21 February and 1618 March of 2009, and 13-16 March, 27-30 April and 21-25 May of 2010 (Japan
Meteorological Agency, 2010). Air masses from continental China brought large amountsof yellow Sand and the concentrations of SO 4 2- and NH 4 + appeared to be relatively highduring the event. As Arakaki et al. (2006) reported that a few WEA samples collected in
Okinawa were affected by a Yellow Sand event, which resulted in increased ●OHphotoformation, there is a hypothesis about the possible influence of long-range transportof air masses (from the Asia continent) increasing the ●OH formation rate. In this study,
even though a similar phenomenon was observed as the Arakaki et al. reported, the R OH
was not always following the monthly variations of SO 4 2- and NH 4 +, which suggests that-23-

other factors may also be involved in the photoformation of ●OH in the WEA fraction. Lackof a number of Yellow Sand event observed (5 events) at Higashi-Hiroshima and/or
possible mixing of domestic pollutants in Japan with long-range transported ones may
cause a difficulty in evaluating effects of Yellow Sand event to the R OH (Figure 2-8).
2-4- Conclusions
The ●OH photoformation rate, its generation sources and source strength for the WEA
and WSG fractions in ambient air of Higashi-Hiroshima were studied from June 2008 toJune 2010. To the best of our knowledge, this study reports the first findings regarding ●OH
generation in WSG fractions collected from ambient air. ●OH photoformation rate in WSG
fractions may be useful as an indicative of amount of ●OH generation sources and oxidation
capacities of ambient air. A linear relationship between the ●OH generation and irradiation
time in the photochemical experiments showed that both fractions have the same
photochemistry of ●OH generation. The results also revealed that among the major sourcesof ●OH, the photo-Fenton reaction and unknown sources were the most important sourcesof ●OH. The unknown source may be fluorescent organic matter such as HULIS. However,a further research focusing on organic matter and the relationship with ●OH generation in
the WSG fraction is need and expected to continue.

-24-

References
Anastasio, C., Faust, B. C. and Allen, J. M., 1994. Aqueous-phase photochemical formationof hydrogen-peroxide in authentic cloud waters, Journal of Geophysical ResearchAtmospheres, 99, 8231–8248.
Anastasio, C. and Jordan, A.L., 2004. Photoformation of hydroxyl radical and hydrogen
peroxide in aerosol particle from Alert, Nunavut: implications for aerosol and snowpack
chemistry in the Artic. Atmospheric Environment 38, 1153-1166.
Anastasio, C. and Newberg, J.T., 2007. Sources and sinks of hydroxyl radical in sea-salt
particles. Journal of Geophysical Research 112, D10306, doi:10.1029/2006JD008061.
Arakaki, T. and Faust, B.C., 1998. Sources, sinks, and mechanisms of hydroxyl radical (OH)photoproduction and consumption in authentic acidic continental cloud waters fromWhiteface in Mountain, New York: the role of the Fe(r) (r = II, III) photochemical cycle.
Journal of Geophysical Research 103 (D3), 3487-3504.
Arakaki, T., Miyake, T., Shibata, M. and Sakugawa, H., 1998. Measurement ofphotochemically formed hydroxyl radical in rain and dew waters. The Chemical Societyof Japan, 9, 619-625 (in Japanese).
Arakaki, T., Kuroki, Y., Okada, K., Nakama, Y., Ikota, H., Higuchi, T., Uehara, M., Tanahara,A., 2006. Chemical composition of photochemical formation of hydroxyl radical inaqueous extracts of aerosol particles collected in Okinawa, Japan. Atmospheric
Environment 40, 4764-4774.
Buxton, G.V., Greenstock, C.L., Helman, W.P., Ross, A.B., 1988. Critical review of rate
constants for reactions of hydrated electrons, hydrogen atoms and hydroxyl radicals (●OH/●O-) in aqueous solution. J. Phys. Chem. Ref. Data17, 513-886.
-25-

Coble, P.G.; Green, S.A.; Blough, N.V.; Gagosian, R.B., 1990. Characterization of dissolved
organic matter in the Black Sea by fluorescence spectroscopy. Nature 348 (6300), 432435.
Coble, P.G., 1996. Characterization of marine and terrestrial DOM in sea water using
excitation-emission matrix spectroscopy. Marine Chemistry 51, 325-346.
Draxler, R.R., 1998. An overview of the HYSPLIT_4 Modeling System for Trajectories,
Dispersion, and Deposition. Australian Meteorological Magazine, 45, 295-308.
Faust, B.C. and Allen, J.M., 1993. Aqueous-phase photochemical formation of hydroxyl
radical in authentic cloudwaters and fogwaters. Environmental Science and Technology
27, 1221-1224.
Faust, B.C., Anastasio, C., Allen, J.M., Arakaki, T., 1993. Aqueous-phase photochemical
formation of peroxides in authentic cloud and fog waters. Science 260, 73-75.
Finlayson-Pitts, B. J. and Pitts, James N. Jr., 1986. Tropospheric air pollution: ozone, airborne
toxics, polycyclic aromatic hydrocarbons, and particles. Atmospheric Chemistry, WileyInterscience, New York, 667-724.
Graber, E. R. and Rudich, Y., 2006. Atmospheric HULIS: How humic-like are they? A
comprehensive and critical review. Atmospheric Chemistry and Physics 6, 729-753.
Japan

Meteorological

Agency,2010.

Aeolian

Dust

Information.

http://www.data.kishou.go.jp/obs-env/kosahp/kosa_table_1.html (in Japanese)
Kim, D.H., Takeda, K., Sakugawa, H., Lee, J.S., 2001. The determination of dissolved total
Fe by flow injection analysis in environmental samples.
Technology Vol. 14 (6), 510-515.
-26-

Analytical Science &Kim, D.H., Takeda, K., Sakugawa, H., Lee, J.S., 2003. The photochemical reactions of iron
species in rain and snow in Higashi-Hiroshima, Japan. Analytical Science & Technology
Vol. 16 (6), 466-474.
Kondo, H., Chiwa, M., Sakugawa, H., 2009. Photochemical formation and scavenging
mechanisms of hydroxyl radical in water-extracts of atmospheric aerosol collected in
Higashi-Hiroshima, Japan. Geochemistry 43, 15-25 (in Japanese).
Nakatani, N., Miyake T., Chiwa, M., Hashimoto, N., Arakaki, T. and Sakugawa, H., 2001.
Photochemical formation of OH radicals in dew formed on the pine needles at Mt.
Gokurakuji. Water, Air and Soil Pollution 130: 397-402.
Nakatani, N., Ueda, M., Shindo, H., Takeda, K. and Sakugawa, H., 2007. Contribution of the
Photo-Fenton reaction to hydroxyl radical formation rates in river and rain water samples.
Analytical Sciences, 23, 1137-1142.
National Oceanic and Atmospheric Administration (NOAA), HYSPLIT trajectory model
simulator. http://ready.arl.noaa.gov/HYSPLIT.php
Olasehinde, E.F., Makino, S., Kondo, H., Takeda, K., Sakugawa, H., 2008. Application of
Fenton reaction for nanomolar determination of hydrogen peroxide in seawater. Analytica
Chimica Acta, 627, 270-276.
Parlanti, E., Wörz, K., Geoffroy, L., Lamotte, M., 2000. Dissolved organic matter
fluorescence spectroscopy as a toll to estimate biological activity in a coastal zone
submitted to anthropogenic inputs. Organic Geochemistry 31 (12), 1765-1781.
Zepp, R.G., Sheldon, W.M., Moran, M.A., 2004. Dissolved organic fluorophores insoutheastern US coastal waters: correction method for eliminating Rayleigh and Raman
scattering peaks in excitation-emission matrices. Marine Chemistry 89 (1-4), 15-36.
-27-

Table 2-1. Chemical composition and mean concentration of WEA and WSG fractions
extracted from air samples collected during 2008 - 2010 in Higashi-Hiroshima,Japan
WEA (mean± SD)

Range

WSG (mean± SD)

Range

Cl- (nmol m-3)

25±18

4.2 – 66

9.4±4.0

0.3 - 16

NO 3 - (nmol m-3)

47±32

13 – 1489.3±4.1

2.1 – 19.7

NO 2 -* (nmol m-3)

0.07±0.06

ND-0.140.03±0.016

ND-0.04

SO 4 2- (nmol m-3)

81±33

20 – 150

9.4±4.0

0.2 – 16.6

NH 4 + (nmol m-3)

84±42

31 –2278.4±9.4

ND – 35

Na+ (nmol m-3)

56±30

24 –151

NANA

K+ (nmol m-3)

29±19

7.5– 78

NA

NA

Ca2+ (nmol m-3)

NA

NA

NA

NA

Mg2+ (nmol m-3)

7.6±4.1

2.8– 17NANA

DOC (mg C m-3)NANA

2.9±2.6

0.1 – 5.3

H 2 O 2 (nmol m-3)

0.9±2.3

0.01 - 11

0.2±0.3

0.02– 1.0

Note: NA: not analyzed

ND: not detected

SD: standard deviation-28-

Table 2-2. OH radical photo formation rate in WEA and WSG fractions
R OH,air (nmol h-1 m-3)
Mean

Range

Mean

Range

References

Site

Light b

n

WEA

WEA

WSG

WSG

Higashi-Hiroshima,

Solar

24

1.4a

0.1-8.4

0.5

0.04-2.5

This Study

Solar

41

0.33a

0.02-1.91-c-c

Kondo et al.,Japan
Higashi-Hiroshima,
Japan
Bodega Bay,

2009
Solar

1

0.092

-

-c

-c

California, USA
Alert, Canada

Anastasio andNewberg,2007

313

20.010 0.008-0.013-c-c

Anastasio andJordan, 2004

Okinawa, Japan

313

14

0.11

ND-0.21-c-c

Arakaki et al.,2006

Note: a Normalized to J 2-NB = 0.0093 s-1 b Light used to irradiate sample (simulated light) c no data

-29-

Table 2-3. The contribution of major sources of OH radical to the atmospheric WEA and
WSG fractions, as well as river and rainwater collected in Higashi-Hiroshima,
Japan (n=22)
Contribution, %a
Siten

Higashi-Hiroshima, Japan 24

f NO3 - f NO2 - f H2O2 f Photo-Fenton
4.5

0.7

1.2

8.9

1.2

2.5

12

10

0.4

(42)b

f Unknown

References

52

This study(87)cThis study(WSG)
Higashi-Hiroshima, Japan 24(WEA)
Higashi-Hiroshima, Japan 41

49d

33d

(WEA)
Higashi-Hiroshima, Japan 33

2009
33

31

<1

15

20

(River)Higashi-Hiroshima, Japan 9acNakatani etal., 2007

10

16

37

(Rain)
Notes:

Kondo et al.,f i = [ki[Ci]/R OHtotal ] x 100 (%)
d
f Photo-Fenton + f Unknown
n=23

21

16

Nakatani etal., 2007

Generation potential of ●OH from photo-Fenton reaction

b

-30-

Figure 2-1. Sampling site of atmospheric aerosol particles and aqueous solution of watersoluble gas in Hiroshima prefecture-31-

Figure 2-2. Sampling system of atmospheric aerosol particles and aqueous solution of watersoluble gas fractions (coupled low volume air sampler).

-32-

WEA

WSG
Figure 2-3. Blank control test (without pump connection)

Figure 2-4. Benzene probe reaction to determine the ●OH formation rate

-33-

Figure 2-5. Photoformation rate of phenol in WSG (a) and WEA (b) fractions in the air
sample collected in August, 11 of 2009

-34-

B

B

A
(a)

(b)

A

Figure 2-6. 3-D EEM spectrum of WEA sample collected in August 11, 2009 (a) and of
WSG sample collected in June, 15, 2009 (b)

-35-

(a)

-36-

(b)
Figure 2-7. Variations in the photoformation rates of ●OH and concentrations of inorganic
ions and DOC in the WSG (a) and photoformation rates of ●OH andconcentrations of inorganic ions in WEA (b) samples collected during June 2008
- June 2010.

-37-

Figure 2-8. Wind back trajectory showing the possible influence of Yellow sand event
affecting the oxidation capacity of ●OH (March 18th /2010).

-38-

Chapter 3-39-

Chapter 3
Photochemical formation of OH radical in marine aerosols collected in Seto Inland Sea,
Japan.

3-1-Introduction
Aerosol particles consist of many natural and anthropogenic components, including
mineral dust, soot, organic molecules, sea salt crystals, spores, bacteria, and other microscopic
particles (Duce, 2005).
Given the ocean’s extension, marine aerosol constitutes one of the most important natural
aerosol systems at the global level (O’Dowd et al., 2007). The literature contains a great dealof evidence that large sectors of the marine atmosphere are influenced by continental outflows(natural and anthropogenic) and by ship exhaust emissions (Chen et al., 2005; Huang et al.,2008).
According to Keene et al. (2007), the relative concentrations of inorganic constituents ofnascent marine aerosols are similar to those in bulk seawater but organic matter (OM) is likely
a major source of reactive species including the hydroxyl radicals (●OH) and hydroperoxides.
It’s reported that ●OH are photochemically generated in atmospheric hydrometeors (Faust
et al., 1993; Faust and Allen, 1993; Arakaki et al., 1998; Arakaki and Faust, 1998; Anastasio
et al., 1994; Anastasio and McGregor, 2001; Arakaki et al., 2006 and Kondo et al. 2009), as
well as seawater, river water and lake water (Mopper and Zhou, 1990; Allen et al., 1996;
Vaughan and Blough, 1998; Qian et al., 2001; White et al., 2003; Takeda et al., 2004; Vione
et al., 2006; Nakatani et al., 2007). ●OH can be generated in the aqueous phase throughvarious photochemical reactions as we discussed in the Chapter 2, such as the photolysis ofnitrate (NO 3 -), nitrite (NO 2 - and HNO 2 ), hydrogen peroxide (H 2 O 2 ), and aqueous ironcomplexes in the Fenton and photo-Fenton reaction (Mopper and Zhou, 1990).
-40-

To better assess the impact of marine aerosols on tropospheric chemistry and their overalloxidizing capacity in the troposphere, we need to understand the sources and fates ofphotoformed ●OH in the aerosol. However, only few studies on the ●OH photoformation rate
in aqueous extract of marine aerosols had been conducted (Anastasio and Newberg, 2007) andno study regarding the ●OH photogeneration in the samples collected in the Seto Inland Sea
region has been done. Thus, this study focused on the determination of the ●OHphotoformation rate, chemical composition and the major sources of ●OH in water-extracts ofmarine aerosol particles collected in the Seto Inland Sea region, in Japan.
3-2- Experimental
3-2-1- Sampling Area
Formally named the Seto Inland Sea (or Seto Naikai), the Inland Sea is the body of water
separating Honshū, Shikoku, and Kyūshū, three of the main islands of Japan. It connects to
Osaka Bay and provides a sea transport link to industrial centers in the Kansai region,
including Osaka and Kobe (Figure 3-1). The Seto Inland Sea is well known to be one of themost industrially developed areas in Japan. Its length is about 500 km, its width 5 km to 50
km and its average depth about 30 m (Yanagi and Okaichi, 1997).
3-2-2- Sampling Methods
Marine aerosol particles were collected using a High Volume Sampler (HVS-500-5,
Kimoto Electric Co. LTD, Japan) (Figure 3-2) in the research cruise of the Toyoshio Maru
belonging to Hiroshima University during 13th -16th September 2010. Sixteen aerosol samples
were collected during the cruise (n=16).
The sampler was set up on the front deck (5 m above sea level) of the ship and air filter
used consisted of precombusted silica fiber filter (QR-100 203 x 254 mm, Advantec)
operating at a constant flow rate of approximately 1 m3 min-1. All the samples, of which-41-

average air volume was 113.3 m3 (ranging from 30 to 240 m3), were collected during daylightwhen the ship was running at regular speed (10 nautical mile or 5.38 m min-1) in order toavoid smoke contamination from the ship’s stack.
Each sample corresponds to certain trajectory on the cruise in the Seto Inland Sea,
numbered according to Table 3-1 that describes the day, time, coordinates and correspondingarea. Figure 3-3 illustrates the sampling trajectory during the research cruise.
The sampled filters were covered by aluminum foil and sealed in plastic bags and kept
under refrigeration (≈4°C). A blank control filter was analyzed in the same manner as theaerosol filters. It was left on the non-operating sampler for a few minutes and sealed in plasticbags to avoid light influence.
3-2-3- Extraction Procedure
One quarter (1/4) of sampled filter was soaked into 200 ml of ultrapure water (Milli-Q) in
a 200 mL conical beaker wrapped the beaker with parafilm and aluminum foil keeping it in a
shaker machine (multishaker MMS, EYELA) operating at 120rpm during 3h and filteredthrough syringe filter 0.45 μm PTFE (Akrodisk) and stored at ≈ 4°C until chemical analysis
was performed. The pH was measured by a glass electrode pH meter (HM30S, TOA).
3-2-4- Analytical Methods
The concentrations of the major inorganic ions, dissolved organic carbon (DOC) andH 2 O 2 were measured using ion chromatography (ICS –1600, Dionex), TOC analyzer (TOC5000A, Shimadzu) and isocratic HPLC (LC-10Ai, Shimadzu), respectively. The total
dissolved iron and other heavy metals were determined using inductively coupled plasma
atomic emission spectrometry (Optima 3000, Perkin Elmer).
The initial concentration of H 2 O 2 was determined according to the method described by
Olasehinde et al. (2008) based on the reduction of H 2 O 2 by ferrous iron (Fe2+) in acid-42-

solution to yield ●OH which is scavenged by benzene to produce phenol and analyzed byisocratic HPLC (LC-10Ai, Shimadzu) with fluorescence detector (λ Ex = 270 nm and λEm =298 nm).

3-2-5- OH radical measurement●

OH formation rate (R OH ) from the photo-Fenton reaction and total R OH were determinedby HPLC-fluorescence detection (RF-10A, Shimadzu) following irradiation of the extracted
sample using a solar simulator (Model 81160-100, Oriel Corp.) unit equipped with a 300 W
Xenon lamp (ozone free, model 6258, Oriel Corp.). During photolysis, sample solutions werestirred by a magnetic stirrer covered with Teflon and maintained at a constant temperature of
20 °C using a circulator (RTE-111, NESLAB) and a chemical trap of photoformed ●OH withbenzene probe (1.2 mM) according to the methodology described by Faust and Allen (1993).
Therefore, R OH was then determined using the equation 11:
R OH = (R p /F b-OH Y p )(11)

where R p is the photochemical formation rate of phenol, F b-OH is the fraction of ●OH thatreact with benzene, and Y p is the chemical yield of phenol from the reaction of ●OH with theadded benzene (C 6 H 6 ).
Phenol (C 6 H 5 OH) was measured using isocratic HPLC with a pump (LC-10 Ai;
Shimadzu), a C 18 column (LC-18 5 µm 4.6 mm i.d. x 250mm, Supelco or RP-18 GP 5µm 4.6
mm i.d. x 150 mm length, Kanto Kagaku) was used for separation and a ﬂuorescence detector(λ Ex 270/λ Em 298 nm; RF-10A, Shimadzu). The mobile phase was acetonitrile and Milli-Q
water [CH 3 CN:H 2 O 60:40] (v/v) and the ﬂow rate 1.0 mL min–1.

-43-

The initial formation rate of phenol (R p , M min-1) during an illumination experiment wasdetermined from the plot of phenol concentrations versus illumination time using a linear
regression analysis.
The light intensity of the solar simulator was controlled measuring the photochemicaldegradation rate of 2-nitrobenzaldehyde (2-NB) by isocratic HPLC with UV detection of theabsorbance wavelength set at 260 nm. The mobile phase and the flow rate were the same as
for the determination of ●OH. The degradation rate of 8µm 2-NB (J 2-NB ) solution was
normalized against a degradation rate of J 2-NB = 0.00923 s-1 (Arakaki et al., 1998).
The contribution of the photo-Fenton reaction was determined based on the difference
between the ●OH formation rates with and without the addition of deferoxamine mesylate(DFOM) (Sigma Aldrich, Japan). The addition of DFOM produces a stable and strong
complex with Fe (III) that results in suppression of the photo-Fenton reaction (Nakatani et al.
2007). Next, 1 μM potassium trioxalate ferrate (III) is added to the solution of the WSG
fraction with 0.5 μM H 2 O 2 with and without 10 μM DFOM to determine the potential for
generation of ●OH from the photo-Fenton reaction (reactions 12 to14).
Fe (III)-(DOM) m + light  Fe (II)-DOM m-1 + DOM ox +(12)

Fe (OH) 2+ + light  Fe (II) + ●OH(13)

Fe (II) + H 2 O 2  Fe (III) + ●OH + OH-(14)

The total dissolved iron was determined using inductively coupled plasma (ICP-AES)
atomic emission spectrometry (Optima 7300-DV, Perkin Elmer).

-44-

3-2-6- Contribution of major sources of ●OH (%)
The contributions of various sources to ●OH photoproduction were estimated. The percent
contributions (fi) from well-known ●OH sources, such as NO 3 -, NO 2 - and H 2 O 2 to total ●OHformation (fi (i=NO 3 -, NO 2 - and H 2 O 2 )) were calculated by the equation 17.
fi =ki[Ci ]x100(%)
ROHtotal(i=NO 3 -, NO 2 - and H 2 O 2 )(17)

where ki is the rate of ●OH formation from nitrate (k NO3- = 2.43 x 10-7 s-1), nitrite (k NO2- = 2.81
x10-5 s-1) and hydrogen peroxide (k H2O2 = 3.52 x 10-6 s-1), [C i ] is the concentration of eachspecies and R OHtotal is the ●OH photoproduction rate determined experimentally for the
sample (Arakaki et al., 1998; Nakatani et al., 2001).
3-2-7- Fluorescence Properties
To estimate the unknown sources of ●OH, the fluorescence matter (FM) was investigatedbased on the 3D-excitation emission matrix (EEM) spectrum obtained using a fluorescence
spectrometer (F-4500, Hitachi, Ltd.). The samples were scanned at excitation wavelengths of
225-400 nm and emission wavelengths of 250-500 nm at intervals of 5 nm and a scanningspeed of 1200 nm.min-1 to obtain the overall characteristics. The samples were calibratedusing 2.8 µg L-1 of quinine sulfate dehydrated solution (Nacalai Tesque) as a standard for the
total fluorescence intensity (FI), which corresponds to 25 quinine sulfate units (QSU).
3-2-8- Meteorological data
Meteorological parameters such as temperature (T), solar intensity (SI) and relative
humidity (RH) were monitored by the automatic meteorological data acquisition system with
the Global Positioning System (GPS) installed in the ship.

-45-

3-3- Results and discussion
3-3-1- Chemical composition
Table 3-2 shows the average and range concentration of chemical components in thewater-extract of marine aerosols collected in Seto Inland Sea.
The abundance of chloride (Cl-) and sodium (Na+) was obvious, indicating predominanceof sea salts particles in the aerosol samples collected. The mean concentration of Cl- and Na+
are 36.3±51 nmol m-3 and 47.7±34 nmol m-3 respectively. Cl- represents 47.6% and Na+
52.6% of the total anions and cations respectively. Relatively lower percentages of sulfate(SO 4 2-) (32.1%) and nitrate (NO 3 -) (20.5%) in the present analysis (Table 3-2 and Figure 3-4)
than those collected at Higashi-Hiroshima (Chapter 2) suggest the differences in chemical
nature between the marine and land water-extract of aerosols. Nitrite (NO 2 -) was present in
only 2 of the total 16 samples (mean of 1.4 nmol m-3). The mean concentration of DOC was
7.0±6.6 mg C m-3 and the mean pH was 6.18±0.114.
The sum of anions (Cl-, NO 3 -, SO 4 2-, and NO 2 -) of each sample has been compared withthat of cations (Na+, K+, Ca2+, Mg2+ and NH 4 +) to check the charge balance (Figure 3-5). The
ratio of the sum of anions to that of cations averaged 0.72±0.37 (R=0.83), indicating an
existence of undetermined anions.
The Table 3-3 shows the sea-salts ratios calculated using Na+ as reference element
assuming all Na+ to be of marine origin. The Cl-/Na+ ratios (0.64) determined in our samples
were lower than the Cl-/Na+ ratio for seawater (1.79) reported by Millero (1996) indicating
mixture of surface soil and sea salts (Pio and Lopes, 1998; Arakaki et al., 2006).
The mean SO 4 2-/Na+ ratio was 0.46 and ranged from 0.18 to 1.63 indicating no influenceof soil dust or anthropogenic activities. However, the sample 5 showed higher ratio (1.63)
than sea water (0.25) indicating that samples were possibly affected by anthropogenic-46-

activities (including combustion of fossil fuels from the stack of the ship). The high Ca2+/Na+
ratios indicate the influence of soil dust/mineral aerosol. The good correlation between Ca2+and NO 3 - (R=0.97) suggests its association with mineral aerosols (Müller et al., 2001).
The Figure 3-6 shows individual aerosol composition at each sampling site. For eachsample, we first analyzed the concentration at different sites and correlated the aerosol
concentrations with the characterization of each site. This analysis can provide some insightto the dominant sources on each aerosol.
The moderate correlations between Na+ and Cl- (R=0.61) or between Na+ and other ionslike K+, Ca2+ and Mg2+ (R=0.62, R=0.99 and R=0.96 respectively) show the predominance ofsea-salt aerosols in our samples (Table 3-4). The good correlations observed between NH 4 +and NO 3 - (R=0.95) and between NH 4 + and SO 4 2- (R= 0.90) suggest the existence form ofammonium sulfate, (NH 4 ) 2 SO 4 , and ammonium nitrate, NH 4 NO 3 . The existence of the(NH 4 ) 2 SO 4 or NH 4 NO 3 depends of the stability of the products of these ammonium
compounds and depends on temperature and relative humidity as reported by Seinfeld (1986)
and Parmar et al. (2001). (NH 4 ) 2 SO 4 is most stable in most case while NH 4 NO 3 is volatileand can be formed and remain stable in the particulate phase under high concentrations of
NH 3 and HNO 3 and high humidity and temperature conditions (under RH 70 - 100%,
temperature 30 - 42ºC, formation of NH 4 NO 3 would be favored) (Parmar et al., 2001).
Therefore for our samples, due to lower relative humidity (mean of 66.9%) and temperature(mean of 26ºC) (Table 3-5), (NH 4 ) 2 SO 4 must be the stable form.
3-3-2-●OH photoformation rate (R OH ) and contribution percentage (%)
All 16 samples were irradiated with a solar simulator to determine the ●OHphotoformation rate (R OH ). The concentrations of NO 3 -, NO 2 -, H 2 O 2 , FI, DOC and R OH are-47-

listed in the Table 3.6. The range of the R OH determined in marine aerosol was from 0.019 to
0.14 nmol h-1 m-3 with the mean of 0.06±0.03 nmol h-1m-3(Figure 3-7).
The analysis of the ship speed combined to wind direction during the sample collection
showed winds coming from the land affecting the samples and possibly explaining thevariation of R OH in those some points (Table 3-7).
The Figure 3-8 shows the R OH variation for each aerosol sample. The highest R OH wasobserved in the samples 2, 9 and 11 corresponding to Aki-Nada (R OH = 0.114 nmol h-1 m-3),
Osaka Bay (R OH = 0.096 nmol h-1 m-3) and Harima-Nada (R OH = 0.141 nmol h-1 m-3)
respectively. These 3 samples are located near to the land (Figure 3-3) suggesting theinfluence of anthropogenic pollution as sources of ●OH in those areas.
Specifically the samples 2 and 11 showed high concentrations of NO 3 - and DOC. NO 3 contributes for 23.8% on the ●OH production and the photo-Fenton 10.4% in the sample 2
while for the sample 11, NO 3 - contributes for 12.1% and 7.4% for photo-Fenton. The NO 2 showed 93% of contribution in the sample 11. The unknown sources contribute for 46% and<1% in the samples 2 and 11 respectively. In order to clarify the sources of ●OH, weestimated the contributions of various sources to ●OH photoproduction. The contribution
percentage from well-known ●OH sources were calculated using the equation 1 previously
shown in the Chapter 2. The estimated contribution of NO 3 - photolysis accounted for 9 – 47%(mean of 18.6%) of photochemically formed ●OH in the marine aerosol samples (Table 3-6).
A good correlation between R OHtotal and concentration of NO 3 - (R = 0.63; p<0.01)(Figure 3-9 (a)) suggests NO 3 - as significant source of ●OH generation in marine aerosols.
R OH did not show correlations with concentration of DOC (R=0.27; p<0.01) and FI (sum of
fluorescence intensities of the peaks A+B+C).

-48-

Nevertheless, the analysis of correlation between R OHuknown and the FI of each peakseparately showed some relationship with ●OH generation (discussed further). DOC and FI
seemed to show an unclear correlation (R=0.49; p<0.01) (Figure 3.9c) although R OHunknown
does not appear correlated with DOC concentrations (R= 0.22; p<0.01) (Figure 3.9d). Thus,
due of the presence of organic compounds (DOC) detected in marine aerosol of the Seto
Inland Sea, water-soluble organic compounds leads to the discussion and are thought as animportant source of ●OH. Mopper and Zhou (1990) suggested DOC was the major source of●

OH in sea water.
The Table 3.8 shows the correlations between R OH and major sources of ●OH combined.

Non-correlation between the parameters was observed however some indicatives such as thepresence of fluorescence properties in unknown fraction perhaps are involved to thephotochemical production of ●OH. Some significance in the correlation between R OH and FI(R= 0.26, p<0.01) leads to the discussion that the presence of organic compounds has
involvement as source of ●OH.
In this study, an experiment was carried out to elucidate the sources of ●OH. PhotoFenton reaction was examined because this reaction is considered to be a major ●OH source inboth atmospheric aqueous phase and natural water (Nakatani et al. 2007). Dissolved iron
species are common to exist in atmospheric aqueous phase (Kim et al. 2001, 2003). If watersoluble gases meet with iron species in the aqueous phase photo-Fenton reaction may occur.
To find potential sources of ●OH in the atmospheric aqueous phase, known amount (excess)of iron (III) was added into the solution of the water-extract of marine aerosols and then the
R OH of photo-Fenton reaction was determined by the method of Nakatani et al. (2007).
The Table 3.9 shows a comparison of the average contribution percentage of the major
sources of ●OH generation in WEA of marine aerosol obtained in this study and sea water.

-49-

In marine aerosols, NO 3 - more contributed (18.6%) to the ●OH photoformation thanNO 2 - , H 2 O 2 and photo-Fenton reaction. However, unknown source(s) contribute for about
71%. In the sea water of Seto Inland Sea region, NO 2 - (6.8%) and unknown (92.6%) sources
showed to be most contributor of ●OH generation on surface water as reported by Takeda et al.
(2004). Hydrogen peroxide was a less important source of ●OH. The unknown sources are themost significant contributors of ●OH in WEA of marine aerosol suggesting that the unknown
sources may significantly contribute to photoformation of ●OH as in the sea water.
The Table 3-10 summarizes the R OH obtained in this study and determined previously
by other investigators. The R OH in water-extract of aerosols were found out lower (about 6
times) in this study compared to land aerosol, reported by Kondo et al. (2009); however theoxidation capacity of ●OH in our samples is comparable to coastal area of California and theremote area of Canada.
Alert in Canada is the northernmost permanently inhabited in the world. The low R OH
determined in the snow packs have NO 3 - as the significant source of ●OH generation (Wolff,
1995). However under some circumstances, photochemical reactions of particle-derived
chromophores can be significant sources of ●OH and H 2 O 2 in the Artic (Anastasio and Jordan,
2004). A study carried out in Okinawa presented 2 types of kinetics of the ●OH formation in
the aerosol particles from the coastal area being possibly influenced by the Yellow Sand
events (Arakaki et al., 2006). Since DOM represents one of the largest exchangeable organic
reservoirs at the earth’s surface and it has been pointed as a possible unknown source of ●OHgeneration for surface sea waters (Yamashita and Tanoue 2003).
3-3-3- Fluorescence properties
For most of the samples, two distinct wavelength of fluorescence excitation (λ Ex ) ranges
and emission (λ Em ) ranges have been found (λ Ex 250-260 and λ Em 380-480nm) within the-50-scanned wavelength (λ Ex = 225-400nm and λ Em =250-500nm) which are characteristics ofHumic-Like Substances (HULIS) (Coble et al., 1990; Coble, 1996; Parlanti et al., 2000; Zeppet al. 2004; Graber and Rudich, 2006).
Previous studies found that dissolved organic compounds had three distinctive peaks (A,B and C) in the 3D-EES obtained from sea water samples. In our study case, three peaks offluorescence were observed in the contour plots spectra of marine aerosols (Figure 3.10).
A highest peak was observed at λ Ex/Em =240–270/350–450nm (peak A), with the mean of
43.6±19.7 QSU or flu, the second peak was observed at λ Ex/Em = 305–320/395–420 nm (peakB), with the mean of 27.2±16 QSU indicating the presence of HULIS in the marine aerosols
collected in the Seto Inland Sea (Table 3-11). A third peak, peak C, at λ Ex/Em = 260-285/305345 nm was found in 12 samples with a mean of 23.6±8.6 QSU. Nakajima et al. (2008) also
reported that the presence of those two peaks in the aerosol of Okinawa. Although not exactly
same wavelengths as Nakajima et al., 2008 reported for the samples collected in Okinawa,aromatic amines such as tryptophan and proteins might exist in our samples.
The presence of the peaks A and B were confirmed in 15 aerosol samples and 12 showed
the peak C. No correlations between R OHunknown and FI (A+B+C) were observed however;between R OHunknown and the peaks A and B and C (separately) some relationship was detected(Table 3-8).
The correlations between R OHuknown and FI of the peaks A, B and C were found in thisstudy (R=0.21, R=0.21 and R=0.50; p<0.01 respectively) (Figure 3-11a-c). Although no clear
correlations were observed between the R OHunknown and peaks A and B, the peak C, thepresence of fluorescence properties possibly indicates that organic compounds are perhaps
related with generation of ●OH.
-51-

The results of the fluorescence properties suggested the presence of carbonaceouscompounds and may be related with ●OH generation in the water-extract of marine aerosols.
As Mopper and Zhou (1990), Zhou and Mopper, 1990 and Vaughan and Blough, 1998 had
reported, the photolysis of DOM has been believed to be a source of ●OH formation in natural
waters. However, further researches are needed to better understand the various and complex
mechanisms involving the ●OH formation from the photolysis of DOM in the water-extractsof marine aerosol.
Therefore, the fluorescence technique used for characterization of carbonaceouscompounds in our samples provided information about the possible presence of HULIS
substances and tryptophan. Mostafa et al. (2005) reported in their photo irradiation
experiment the changes (shifts) in the fluorescence peak wavelengths of standard SuwanneeRiver Fulvic Acid (SRFA) with increasing solar simulator irradiation time (30 min) while
fluorescence intensity of SRFA was no change during the irradiation, which phenomena was
explained by low photosensitivity of the SRFA and its high molecular size and complex
structures (Malcom, 1985; Senesi, 1990, Münster et al., 1999).
Reactions involving the photolysis of DOM have been believed as a major source of ●OHformation in natural waters (river and sea waters) (Vaughan and Blough, 1998; Mopper andZhou, 1990; Anastasio and Newberg, 2007). Thus, for this study there is a hypothesis that
DOM may be the most significant source of ●OH production in the marine aerosols.
3-4- Conclusions
This study determined the ●OH photoformation rate, chemical composition, sources andmajor contributors of ●OH in the water-extract of marine aerosols. In the Seto Inland Sea
region, as a coastal sea, sea salts were the major contributing source of aerosol particles. Sea-52-

salts such as Na+ and Cl- were observed most abundant species in the marine aerosol. The
SO 4 2-/Na+ ratio (0.46) indicates that samples were possibly affected by anthropogenic
activities. The low R OH observed in the samples may reflect small amount of ●OH generation
sources and oxidation capacities in coastal atmosphere. NO 3 - accounted for a significant
contribution percentage (18.6%) of ●OH generation in marine aerosols. The results also
revealed that unknown sources were the most important sources of ●OH (74%) suggesting
similar mechanisms of ●OH formation as sea water. The unknown source related to thedissolved organic compounds showed no clear correlation between the FI and DOC
concentrations. However previous studies had reported a mechanism involving the photolysis
of DOM occurring in the natural and sea waters have been suggested to be the major source of●

OH formation in the water-extract of marine aerosols.

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Millero, F.L., 1996. Chemical Oceanography. CRC Press, Boca Raton, Tokyo.
Mopper, K., and Zhou, X., 1990. Hydroxyl radical photoproduction in the sea and its potential
impact on marine processes. Science, 250, 661-664.
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Mostofa, K. M. G., Honda, Y. and Sakugawa, H., 2005. Dynamics and optical nature offluorescent dissolved organic matter in river waters in Hiroshima prefecture, Japan.
Geochem. J. 39, 257–271.
Muller, D., Franke, K., Wagner, F., Althausen, D., Ansmannm A., Heintzenberg, J., 2001.
Vertical profiling over the tropical Indian Ocean with sex-wavelength lidar: 1, seasonal
cycle. Journal of Geophysical Research 106, 28567-28575.
Münster, U., Salonen, K. and Tulonen, T., 1999. Decomposition. Limnology of Humic
Waters (Keskitalo, J. and Eloranta, P., eds.), 225–263, Backhuy Publishers.
Nakajima, H., Okada, K., Kuroki, Y., Nakama, Y., Handa, D., Arakaki, T., Tanahara, A.,
2008. Photochemical formation of peroxides and fluorescence characteristics of thewater-soluble fraction of bulk aerosols collected in Okinawa, Japan. Atmospheric
Environment 42, 3046-3058.
Nakatani, N., Miyake T., Chiwa, M., Hashimoto, N., Arakaki, T. and Sakugawa, H., 2001.
Photochemical formation of OH radicals in dew formed on the pine needles at Mt.
Gokurakuji. Water, Air and Soil Pollution 130: 397-402.
Nakatani, N., Ueda, M., Shindo, H., Takeda, K., and Sakugawa, H., 2007. Contribution of the
Photo-Fenton reaction to hydroxyl radical formation rates in river and rain water samples.
Analytical Sciences, 23, 1137-1142.
O’Dowd, C. D. and de Leeuw, G., 2007. Marine aerosol production: a review of the current
knowledge, Philosophical Transactions of the Royal Society, 365, 2007–2043.
Olasehinde, E.F., Makino, S., Kondo, H., Takeda, K., Sakugawa, H., 2008. Application of
Fenton reaction for nanomolar determination of hydrogen peroxide in seawater. Analytica
Chimica Acta, 627, 270-276.
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Parmar, R.S., Satsangi, G.S., Kumari, M., Lakhani, A., Srivastava, S.S., Prakash, S., 2001.
Study of size distribution of atmospheric aerosol at Agra. Atmospheric Environment 35,
693-702.
Parlanti, E., Worz, K., Geoffroy, L.M., 2000. Dissolved organic matter fluorescence
spectroscopy as a toll to estimate biological activity in a coastal zone submitted toanthropogenic inputs. Organic Geochemistry 31 (12), 1765-1781.
Pio, C.A. and Lopes, D.A., 1998. Chlorine loss from marine aerosol in a coastal atmosphere.
Journal of Geophysical Research 103 (D19), 25263-25272.
Qian, J., Mopper, K., Kieber, D.J., 2001. Photochemical production of the hydroxyl radical in
Antarctic waters. Deep-Sea Res. Pt. I 48, 741-759.
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Senesi, N., 1990 Molecular and quantitative aspects of the chemistry of fulvic acid and its
interactions with metal ions and organic chemicals. Part II. The fluorescence
spectroscopy approach. Anal. Chim. Acta 232, 77–106.
Takeda, K., Tadedoi, H., Yamaji, S., Ohta, K., Sakugawa, H., 2004. Determination ofhydroxyl radical photoproduction rates in natural waters. Analytical Sciences 20, 153-159.
Vaughan, P.P. and Blough, N.V., 1998. Photochemical formation of hydroxyl radicals byconstituents of natural waters. Environmental Science and Technology 32, 2947-2953.
Yamashita, Y., Tanoue, E., 2003. Chemical characterization of protein-like fluorophores in
DOM in relation to aromatic amino acids. Marine chemistry 82, 255-271.

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Yanagi, T. and Okaichi, T., 1997. Seto Inland Sea – Historical background. Sustainable
development in the Seto Inland Sea, Japan – From the viewpoint of fisheries, Eds. T.
Okaichi and T. Yanagi, pp. 9-14.
Zepp, R. G., Sheldon, W.M., Moran, M.A., 2004. Dissolved organic fluorophores insoutheastern US coastal waters; correction method for eliminating Rayleigh and Raman
scattering peaks in excitation-emission matrices. Marine Chemistry 89 (1-4), 15-36.
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between air and seawater and between air and freshwater: Implications for air-sea
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production of hydroxyl radicals and photobleaching of colored dissolved organic matterin a coastal river of the southern United States. Aquatic Science 65, 402-414.
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biogeochemical cycles. Springer, Berlin, 1-3.

-59-

JapanFigure 3-1. Map of sampling area: Seto Inland Sea region, in Japan

Figure 3-2. High Volume Air Sampler set up on the deck of Toyoshio Maru
-60-

Table 3-1. Aerosol sampling schedule: Seto Inland Sea and Osaka Bay
SampleDay

Time

Coordinates

Area

1

2010.9.13

10:00-11:16

34°06.07' N; 132° 38.06' E

Aki Nada2

2010.9.13

11:45-12:15

34°06.43' N; 132° 44.55' E

Aki Nada3

2010.9.13

12:30-14:40

34°08.08' N; 133° 09.94' E

Hiuchi Nada

4

2010.9.13

15:00-16:20

34°12.98' N; 133° 24.96' E

Hiuchi Nada

5

2010.9.13

16:37-19:31

34°25.00' N; 133° 59.95' E

Harima Nada

6

2010.9.14

7:25-9:25

34°36.94' N; 135° 00.82' E

Harima Nada

7

2010.9.14

9:30-11:30

34°27.94' N; 135° 07.77' E

Osaka Bay8

2010.9.14

11:30-13:30

34°37.88' N; 135° 17.05' E

Osaka Bay9

2010.9.14

13:33-15:03

34°38.06’N 135°11.17’E

Osaka Bay10

2010.9.15

8:00-10:30

34°36.64' N; 134° 44.88' E

Osaka Bay11

2010.9.15

10:55-11:32

34°31.23' N; 134° 36.38' E

Harima Nada

12

2010.9.15

11:50-13:00

34°22.96' N; 134° 24.98' E

Harima Nada

13

2010.9.15

13:20-17:20

34°19.08' N; 133° 37.24' E

Harima Nada

14

2010.9.15

17:40-19:25

34°20.26' N; 133° 13.87' E

Hiuchi Nada

15

2010.9.16

8:00-10:00

34°17.63' N; 132° 52.48' E

Hiuchi Nada

16

2010.9.16

10:00-11:50

34°11.66’N; 132°32.24’E

Aki Nada-61-

Figure 3-3. Map of cruise trajectory through the Seto Inland Sea by the Toyoshio-Maru,
September 13th – 16th, 2010-62-

Table 3-2. Chemical composition of water-extract of marine aerosols(mean± SD)

Range

Cl-

36.3±51

0.02 - 160

NO 3 -

11±6.8

5.0 – 32.6

NO 2 -

1.4±0.1

ND-1.5

SO 4 2-18.1±11

7.8 – 48.4

(nss)-SO 4 2-

6.2±7.1

ND – 22.5

NH 4 +

3.9±2.2

1.6 – 10.4Na+47.7±34

16.1 – 157

K+

15.5±21

2.3 – 87Ca2+

13.6±10

4.84–46Mg2+

9.9±6.9

3.2 – 30.9Fe0.15±0.09

ND – 0.321

DOC*

7.05±6.6

0.8 – 29.4

H2O2

0.51±0.6

ND– 0.91

pH

6.18±0.114

5.89-6.32

Note: Mean indicates arithmetic mean.
SD: Standard Deviation
Unit: nmol.m-3*mg C m-3

-63-

ND: not detectable

Figure 3-4. Percentage distribution of major cations and anions.

Figure 3-5. Charge balance of ions in water-extract of marine aerosols-64-Table 3-3. Mass-based ratio of chemical constituents relative to Na+
Sample
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16

Cl-/Na+
1.87
0.53
0.30
1.0
0.18
2.4
0.26
0.36
0.12
0.14
1.84
0.24
0.33
-

SO 4 2-/Na+
0.41
0.31
0.72
0.70
1.63
0.34
0.27
0.29
0.18
0.31
0.24
0.24
0.54
0.30
0.41
0.52

Mg2+/Na+
0.17
0.19
0.19
0.25
0.29
0.20
0.19
0.19
0.20
0.29
0.23
0.30
0.20
0.15
0.14
0.21

Ca2+/Na+
0.25
0.29
0.29
0.28
0.32
0.28
0.32
0.29
0.29
0.29
0.31
0.3
0.3
0.19
0.23
0.27

Mean
STD

0.64
0.76

0.46
0.33

0.21
0.05

0.28
0.03

Sea water

1.79

0.25

0.12

0.04

Note: - : not available-65-Figure 3-6. Concentrations of Cl-, NO 3 -, SO 4 2-, Na+, NH 4 +, K+ and Mg2+ measured in eachmarine aerosol samples.
-66-

Table 3-4. Multi-correlation coefficients (R) involving major ions determined in marine
aerosols
Na+
ClNO 3 SO 4 2-

Na+
1
0.61
0.97
0.82

K+
0.62
0.67
0.60
0.71

Ca2+
0.99
0.65
0.96
0.74

Mg2+
0.96
0.61
0.95
0.69

NH 4 +
0.93
0.66
0.94
0.93

Table 3-5. Temperature, relative humidity and solar intensity during the cruise (Feb. 13th16th , 2010
SampleTemperature, ᵒC

Relative Humidity, %

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
Mean

25
24.3
25.9
27.8
27.1
26.1
26.4
27.7
27.1
26
26.3
26.1
26.5
25.96
23.1
25
26.02

74.8
78
65.5
60.3
69.6
65.6
64
60.6
62
63.6
65.7
66.8
63.1
69.6
74.5
67.5
66.95

-67-

Solar intensity,
MJ/m2
11.6
20.8
22.4
27.1
3.61
26
35.5
17.1
11.2
21
16
20.5
4.6
0.08
34.2
49.2
20.06

Table 3-6. The contribution of major sources of ●OH to the marine aerosols collected in the
Seto Inland Sea, Japan.
Concentration, nmol m-3

Contributiona, %n

R OH *

NO 2 -

NO 3 - H 2 O 2FI*****DOCf NO2 -

f NO3 -

f H2O2

1

0.05

1.5

27.6

0.4

48.1

12.3

ND

27.6

9.75

4.22

-

-

2

0.12

ND

23.8

1.36

19.8

0.8

ND

24

14.3

10.4

45.9

0.055

3

0.02

ND

26.6

ND

55.4

5.2

ND

26.6

ND

1.19

65.6

0.016

4

0.04

ND

20.7

ND

100.7

5.3

ND

20.7

ND

3.36

70.2

0.031

5

0.07

ND

7.48

ND

173.3

8.7

ND

7.5

ND

1.68

89.2

0.062

6

0.04

ND

12.6

ND

66.2

3.8

ND

12.6

ND

3.42

80.5

0.029

7

0.02

ND

36.4

ND

173.3

5.0

ND

36.4

ND

2.0

52.2

0.010

8

0.02

ND

40.5

ND

66.2

5.8

ND

40.5

ND

2.12

50.1

0.011

9

0.10

ND

5.86

ND

59.4

2.7

ND

5.8

ND

1.46

90.3

0.089

10

0.04

ND

13.2

ND

60.2

7.4

ND

13.2

ND

2.36

81.1

0.035

11

0.14

1.3

12.1

ND

42.4

1.5

93.9

12.1

ND

7.4

-

-

12

0.06

ND

22.0

ND

71.8

2.1

ND

22

ND

21

51.9

0.030

13

0.05

ND

8.68

ND

41.2

29.4

ND

8.7

ND

4.3

85.4

0.043

14

0.07

ND

13.2

ND

43.3

7.5

ND

13.2

ND

5.4

79.3

0.052

15

0.05

ND

15.3

ND

112.9

8.2

ND

15.3

ND

6.21

75.4

0.041

16

0.06

ND

12.4

ND

81.4

7.1

ND

12.4

ND

5.5

79.3

0.048

Mean

0.06

1.4

18.6

0.88

76

7.05

-

18.6

12

5.05

71

0.03

SD

0.03

0.14

9.85

0.5

43

6.7

-

9.8

2.3

4.7

14.8

0.05

Notes: *R OH : nmol h-1 m-3 **QSU: Quinine Sulfate Unitafi = [ki[Ci]/R OHtotal ] x 100 (%)

cf

unknown = 100-(f NO3- + f NO2- + f H2O2 )(%)***

mg C m-3

f Photo-Fenton b f Unknown c- : not available ND: not detectedbGeneration potential of ●OH from photo-Fenton reaction
dR

OHunknown = (R OH X f unknown )/100-68-

R OH unknown dTable 3-7. Wind direction (WD), Direction (D), ship speed (SS) in nautical miles and (SS’)
in m/min.
Sample
#1
#2
#3
#4
#5
#6
#7
#8
#9
#10
#11
#12
#13
#14
#15
#16

WD
213.1
192.3
237.1
265.9
256.2
294.09
292.3
258.8
322.5
252.1
176.8
317.8
261.2
294.3
248.6
193.4

D
SWW
SWW
SSW
SSW
SSW
SSE
SSE
SSW
SEE
SSW
NWW
SEE
SSW
SSE
SSW
SWW

-69-

SS
9.2
10
11.1
9.9
10.8
9.44
8.22
6.3
8.33
9.9
10.9
10.6
10.3
9.7
10.2
10.1

SS'
4.9
5.4
6
5.3
5.8
5.1
4.4
3.4
4.5
5.3
5.9
5.7
5.6
5.2
5.5
5.5

Figure 3-7. ●OH photoformation rate variation in Seto Inland Sea region-70-Figure 3-8. Variations in the photoformation rates of ●OH and concentrations of NO 3 - and
DOC in the WEA samples of marine aerosol collected in the Seto Inland Sea

-71-

(a)

R = 0.13

(b)

(c)

(d)
Figure 3-9. Correlation coefficient between: (a) R OHtotal and [NO 3 -] (b) R OHunknown andFI, (c) [DOC] and FI and (d) R OHunknown and [DOC]-72-

Table 3-8. Multi-correlation coefficients (R) involving major sources of ●OH determinedin marine aerosols (p<0.01)
R OH (nmol h-1m-3)
NO 3 -(nmol m-3)
DOC(mg C m-3)

FI (QSU)R OHunk (nmol h-1m-3)
a

FI A (QSU)
FI B (QSU)
FI C (QSU)
NO 2 -(nmol m-3)

H 2 O 2 (nmol m-3)
Notes:aR

R OH NO 3 - DOC
10.63 0.27
0.63
1
0.37
0.27 0.37
1
0.26 0.56 0.47

FI
0.26
0.56
0.47
1

R OHunk
0.10
0.02
0.07

FI A
0.20
0.50
0.45
-

FI B
0.12
0.48
0.53
-

FI C
0.06
0.52
0.33
-

NO 2 - H 2 O 2
-

-

0.10

0.02

0.07

1

0.20

0.21

0.50

-

-

0.20
0.12
0.06
-

0.50
0.48
0.52
-

0.45
0.53
0.33
-

-

0.21
0.21
0.50
-

1
-

1
-

1
-

1
-

1

OHunknown = (R OH X f unknown )/100- : not available

Table 3-9. The contribution of major sources of ●OH to the marine aerosols and sea watercollected in the Seto Inland Sea, Japan.
Contributiona, %Site

Notes:nf NO3 - f NO2 - f H2O2 f photo-Fenton b

WEA

16

18.6

<1

<1

Sea Water

-

<1

32

<1

af

i = [ki[Ci]/R OHtotal ] x 100 (%)

f Unknown c

References

5.1%

74.3

This study

-

66.2

Takeda et al.,2004

- : not available

bGeneration potential of ●OH from photo-Fenton reaction

-73-

cf

unknown = 100-(f NO3- +f NO2- +f H2O2 )(%)

Table 3-10. R OH rate in water-extracts of aerosols
R OH (nmol.h-1.m-3)
Lightb

n

Mean

Range

References

Seto Inland Sea,
Hiroshima-Japana

Solar

16

0.06 a0.019-0.14

This study

Higashi-Hiroshima,
Japana

Solar

41

0.33a

0.02-1.91

Kondo et al., 2009

Bodega Bay,
California, USA

Solar

1

0.092

-c

Anastasio andNewberg, 2007

Alert, Canada

313

2

0.010

0.008-0.013

Anastasio andJordan, 2004

Okinawa, Japan

313

14

0.11

ND-0.21

Arakaki et al., 2006

Site

Notes :a Normalized to J 2-NB = 0.0093 s-1 b Light used to irradiate sample (simulated light) c no data

-74-

B

A
C

Figure 3-10. Contour plots of 3D-EEMs of marine aerosol (sample 5). The spectra were
not corrected for Raman and second order light peaks.

Table 3-11. Fluorescence intensity (FI) of peaks A, B and C (QSU)
Sample
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
Mean
SD

A
33.21
19.85
35.48
30.67
107.59
42.2
38.9
37.99
30.62
45.53
27.37
29.4
62.86
45.81
42.46
38.51
43.65
19.72

Note: QSU: Quinine Sulfate Unit-: not detectable

B
14.87
19.98
40.03
65.76
24.04
20.54
22.26
11.79
26.26
13.8
13.88
50.07
35.58
27.08
21.71
27.18
16.01

FI=A+B+C

*

-75-

C

FI*

17.9
26.3
49.3
22.3
24.3
22.7
16.3
14.4
28.2
19.4
20.1
22.1
23.61
8.63

48.08
19.85
73.36
97
222.65
88.54
83.74
82.95
42.41
71.79
57.47
57.68
141.13100.79
89.64
82.32
84.96
46.02

(a)

(b)

(c)

Figure 3-11. Correlation between R OHunknown and fluorescence of peaks A (a), B (b) and C
(c).
-76-

Chapter 4-77-

Chapter 44- General Discussion
Photochemical reactions involving the oxidation capacity of●

OH taking place innatural water (river and sea waters) and in the atmospheric condensed phase (cloud, fog,
and rain drops, aqueous aerosols and dew) were reported in the past (Mopper and Zhou,
1990; Faust and Hoigné, 1990; Arakaki et al., 1998; Arakaki et al., 2006) (Figure 4-1).

1993

2004

2008

River water

Cloud andfogwaters

Snowpacks

MarineAerosol

1998

2001

2007

1990

1992

Rain

Sea
water

2004

2004
Aerosol
Particles

2011
2010

This work

2007
2006
Aqueous solutionof water-soluble
gases

2009

This work
Figure 4-1. Previous and recent studies involving •OH generation in aqueous phase
Studies on other natural water such as river and sea water (Nakatani et al., 2007;
Takeda et al., 2004) help characterize the potential and possible significant sources of ●OH-78-

existing in the atmospheric aqueous-phase (Nakajima et al., 2009). The results point out
the photo-Fenton reaction as an important and significant source of ●OH generation. Thesestudies were essential for initiating our present research.
In our study case, we showed the similarities of mechanisms of ●OH photoformation
occurring in atmospheric water-extracts of aerosols, aqueous solution of water-soluble gas
fraction and natural waters. The results also contributed in clarifying the oxidation capacity
of ●OH and identified the main sources from samples collected at different locations.
Although the photochemistry of ●OH in the WEA and WSG showed to be the same, thecontribution from identified sources of ●OH was observed different and might be relatedwith sampling location.
Our study focused on the ●OH formation from ambient aerosol of Higashi-Hiroshimadescribed in Chapter 2, the first findings revealed ●OH generation in atmospheric aqueous
solution of water-soluble gas, suggesting the same photochemistry of ●OH production as
occurring in atmospheric water-extracts of aerosols. Therefore, the capacity of ●OHformation in the aqueous gas phase may contribute significantly on changing the chemicalcomposition of aerosols.
In addition, the presence of HULIS was suggested as a possible and important sourceof ●OH generation in aqueous solution of water-soluble gas fraction.

-79-

Recent studies detected the presence of HULIS in the atmosphere (Graber and Rudich,
2006; Kondo et al., 2009; Stone et al., 2009; Lin et al., 2010; Ziese et al., 2008) whichmight causes night-time reaction of Fe (III) converting to Fe (II) and subsequent ●OHformation. The results suggested that although HULIS had a relatively small impact on Fe(II) photoformation during the daytime, the night-time formation of Fe(II) in atmosphericcondensed phases (e.g., cloud, fog, and rain) by HULIS could be important, and therefore,
the “dark” Fenton reaction should also be incorporated into fate models for atmosphericpollutants (Arakaki et al, 2010).
More research is required for the aqueous solution of atmospheric water-soluble gas
fraction in order to understand the significance of this fraction on the oxidizing capacity of●OH generation involved in the photochemical reactions occurring in the aerosol aqueous

phase and its impacts and effect on the environment and human health.
The ●OH photochemically generated from the water-extract of marine aerosol of the
Seto Inland Sea showed lower photoformation rates than land aerosols. Our results are inagreement with results obtained for the water-extracts of aerosols collected in the coastal
and remote locations (Arakaki et al., 2006; Nakajima et al., 2009; Anastasio and Jordan,
2004).

-80-

The capacity of ●OH generation determined in the water-extract of marine aerosol
particles is useful to estimate the anthropogenic effect through the transport of pollutantsfrom the land to coastal areas.
The results also revealed that among the major sources of ●OH, the unknown source
was the most important source in the marine aerosol samples as so seawater samples
collected in Seto Inland Sea reported by Takeda et al, 2004. No clear correlation between
the dissolved organic carbon and the fluorescence intensity was found however thepresence of 2 major peaks, characteristic of HULIS, leads to discussion about HULIS as thepossible and major source of ●OH in marine aerosol.
4-1- Conclusion
This study revealed that sources and sinks of ●OH in the WEA fractions from land andmarine aerosols are almost same to those of the WSG fractions. In addition, mechanism of●

OH generations occurring in atmospheric aqueous phase, in which HULIS is involved, areprobably same/identical to those in natural waters. Therefore, in the analogue ofphotoformed ●OH in natural waters, ●OH in the WEA and WSG fractions in the atmosphere
may significantly control the aqueous phase chemistry, especially degradation rates ofseveral organic matters.

-81-4-2- Suggestions for further research
The results presented in this thesis showed the significant percentage of contribution
from unknown sources on ●OH photoproduction. Further investigations is needed for abetter comprehension of the oxidation capacity of the ●OH generation in the atmosphericaqueous solution of water-soluble gases and the relationship with dissolved organic
compounds found in the unknown sources. In addition, research focused on identificationof the organic water-soluble fraction, characterization of the organic compounds present
and ●OH photogeneration mechanisms are important. Optical properties and absorbance
may be related with seasons, e.g., summer and winter, would be an important factor to
elucidate the origin of the HULIS in the aqueous aerosol environment.

-82-

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Acknowledgements

It would not have been possible to write this doctoral thesis without the help andsupport of the kind people around me, to only some of whom it is possible to give particularmention here. Thank you to the examiners committee members: Dr. Kaneyuki Nakane, Dr.
Yoshikuni Masaoka and Dr. Kazuhiko Takeda for the constructive comments contributing
for the improvement of my thesis. A particular thanks to Dr. Kazuhiko Takeda for his
suggestions, advices, criticism, motivation and guidance. I cannot forget to thank our lab
mates for the support gave during the chemical analysis handling and explanations.
I am thankful to my supervisor, Dr. Hiroshi Sakugawa, whose encouragement,
supervision and support from the preliminary to the concluding level enabled me to develop
an understanding of the subject.
Thank you my special friends: Luciano de Freitas (Brazil), Marcos Slomp (Brazil),Mia Soejoso (Indonesia), Rocio Sanchez (Mexico) and Scott Cronin (U.S.A) for thefriendship and English corrections.
I would not forget to thanks my parents Masami and Sumie who have being so far
away, however, supporting me spiritually.
I wish to extend my gratitude to the Japanese Ministry of Education, Culture, Sports,
Science and technology (MEXT) and Hiroshima University for the financial support
through three years as overseas doctor student.
Lastly, I offer my regards and blessings to all of those who supported me in any respectduring the completion of the project.

“I was taught that the way of progress is neither swift nor easy.”
Marie Curie