have successfully detected - volcanic gas components, so,, hcl and hf, in the observed spectra. the...

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ῒΐ /* (,**/) 0 /01/1. 腍腊腋腑腃腐腀腆腋腁腂腅腈腎腌腀腄腇腉腏 膽膯 臸臚膟膵 ,**/ . ,, 臤膹自,**/ ++ +. 臤膹Remote FT-IR Measurements of Volcanic Gas Chemistry in the Plume of Asama Volcano Toshiya MORI and Kenji NOTSU Remote FT-IR measurements for volcanic gas chemistry were carried out twice before and four times after the ,**. Asama eruptions. In these measurements, solar infrared light scattered by higher clouds or plumes was used as a light source for the FT-IR absorption measurements. We have successfully detected - volcanic gas components, SO,, HCl and HF, in the observed spectra. The HCl/SO, ratios observed after the onset of the ,**. Asama eruptions were between *.+1 and *.,*, which are probably reflecting the ratios not influenced by any hydrothermal interactions. In contrast, the HCl/SO, ratios before the eruptions were slightly lower than those after the eruptions. The slight increase in the ratio from pre-eruptive to post-eruptive periods suggests that the hydrothermal or groundwater impact to the volcanic gas emitting system was small even three years before the eruptions. The observed HF/HCl ratios before the eruptions and in March ,**/ were about *.+, whereas the ratios were higher, over *.+3, during the high activity period from mid-September to October ,**.. During the continuous ash emitting eruptions on September +0, ,**., exceptionally low HF/HCl ratio of *.*- was observed. The HF column amount on this day was probably under detection limit, possibly due to HF depletion caused by adsorption on dense ash in the plume. Key words : FT-IR, volcanic gas, remote measurement, Asama volcano +ῐ῎ῑ῏ 臬臅腣膄膱腰腲臆臭腮膀至腨腪臢膴腢臎臛腖腫腒腟腮 臷臜腟腔腝腵腃腸腯臱膌膙臇膅臭膨臲膷膝 腺膧FT-IR 腟膦腥腍膾腦腝臺腊腩腬腙腣腤臋膎膄膱腞腉 腒腣腟腎腤 SO, + 臆臭腚腐腣臎臛腞腉腛腙 (Notsu et al., +33-)+33* +33/ 臥腣腽臊臫膢膉腣臮 膄膴腢臹膏腴腃腷腣膬膁臩臶腮臇膅膨膤腟腔腝腴腃 腷腌腩臲膼腓腬腫膄膱腰腲腣膀膇臎臛腮膫腊SO, HCl , 臆臭腣膒膺腲腶腱腳腹臎臛腢腤腕腦腝臆膩腔 (Mori et al., +33-) 腣腮臦臈腪腢臑腏腣膄膱腞 FT- IR 腮膲臺腔腙膄膱腰腲膂膈臌臆腣膀膇臎臛腍膫腭腬腫 腨腋腢腡腛腙SO, HCl 腚腐腞腡腏SiF. (Francis et al., +330), CO 膿臸+331腆腀 CO,, COS (Mori and Notsu, +331), HF (Love et al., +332 ; Francis et al., +332), H,O (Burton et al., ,***) 腣膮膝 2 腣膄膱腰腲臆臭 腣臎臛腍 FT-IR 腮臺腊腝膫腭腬腫腨腋腢腡腛腙腗腣 膧腣 FT-IR 腮臺腊腙膄膱腰腲膍臎腣臃臝腤臘腔腏膰腞腤FT-IR 腮臺腊腙膀膇臎臛腢腨腛腝膄膱腰腲腣膂 膈臌臆腣膜膴臱膂腮膻臭腢膑腍腞腎腫腨腋腢腡腛腝腎 Horrocks et al., +333 ; 膿臸+333 ; Du#ell et al., ,**- ; Allard et al., ,**/腆腁 FT-IR 腮臺腊腙膄膱腰腲膀膇 膍臎腣臎臛至致腢腜腊腝腤 Oppenheimer et al. (+332) 臀腔腊FT-IR 腮臺腊腙膄膱腰腲腣膀膇臎臛腞腤臎臛臷臨腟 腡腫膄膱腰腲 臮膐腧臮腾臆臭腢腨腫臇膅膨腣膒膺腮 臎臛腖腫腗腣腙腦腢腤膍臎臍臗腞腉腫 FT-IR 腌腩膡 臷臨膄膱腰腲腣膧至腢臇膅膨膤腍臧臻腢腡腫膍臎 腢膲臺腞腎腫臇膅膨膤腟腔腝腤臮膐臖臓腣膬膁臖臩 (Mori et al., +33/)臮膼臙膧腣臹膏腴腃腷臩臶 (Mori et al., +33-)臄膪臇膅膨膤 (Francis et al., +33/) 腧臒臼膨 (Francis et al., +332 ; Love et al., +332) 腍膔腑腩腬腫臺腞腎腫膨膤腤腗腬腘腬腣膄膱腣膊臡臮腾臖膚腣臁膖腡腠腢臔腎腏腻臏腖腫腣腞膍臎腢臠腙腛腝 ++-**-- 臟膕臞臯膕膘臵膗 1-+ 臟膕臔膈臔膈腼膈膛膠膓膃臖膆膂膈膶膣膳臉 Laboratory for Earthquake Chemistry, Graduate School of Science, The University of Tokyo, 1-+ Hongo, Bunkyo-ku, Tokyo ++-**--, Japan. Corresponding author : Toshiya Mori e-mail : [email protected]

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� �� ��� � /*� (,**/)

� 0� /01�/1.�

����������� ������

� � �� � � �

�,**/� .� ,,���� ,**/� ++� +.����

Remote FT-IR Measurements of Volcanic Gas Chemistry in the Plume of Asama Volcano

Toshiya MORI�and Kenji NOTSU�

Remote FT-IR measurements for volcanic gas chemistry were carried out twice before and four times after

the ,**. Asama eruptions. In these measurements, solar infrared light scattered by higher clouds or plumes was

used as a light source for the FT-IR absorption measurements. We have successfully detected - volcanic gas

components, SO,, HCl and HF, in the observed spectra. The HCl/SO, ratios observed after the onset of the ,**.Asama eruptions were between *.+1 and *.,*, which are probably reflecting the ratios not influenced by any

hydrothermal interactions. In contrast, the HCl/SO, ratios before the eruptions were slightly lower than those

after the eruptions. The slight increase in the ratio from pre-eruptive to post-eruptive periods suggests that the

hydrothermal or groundwater impact to the volcanic gas emitting system was small even three years before the

eruptions. The observed HF/HCl ratios before the eruptions and in March ,**/ were about *.+, whereas the

ratios were higher, over *.+3, during the high activity period from mid-September to October ,**.. During the

continuous ash emitting eruptions on September +0, ,**., exceptionally low HF/HCl ratio of *.*- was observed.

The HF column amount on this day was probably under detection limit, possibly due to HF depletion caused by

adsorption on dense ash in the plume.

Key words : FT-IR, volcanic gas, remote measurement, Asama volcano

+� � � ���������� !"#$%&'()*+,�-.,/0� 123456789�:;<= �>?�FT-IR,@A� BCD0EFGHI�J� KL��MN#� +�,OJ SO, � +��PQ�'(MNRI(Notsu et al., +33-)S +33*�T+33/��UVWXY�Z�%&� [\]2^�_`ab�89:c,/0� ]2^dG;efH*����� g'(�hF� SO,,HCl� ,���ij�klmn'(&JoD0�p/I (Mori et al., +33-)��qr#&� st���M FT-

IR�uE/I����vwx�� g'(BhyH*"z&{RIS SO,,HClPQM{t� SiF. (Francis et

al., +330), CO �|}� +331�� CO,, COS (Mori and

Notsu, +331), HF (Love et al., +332 ; Francis et al., +332),

H,O (Burton et al., ,***)�~= 2����������'(B FT-IR�EF0hyH*"z&{RIS ��?� FT-IR�EFI�����'���J�/t� ��MJ� FT-IR�EFI g'(&"R0�����vwx���%5v���&��BMO*"z&{R0OI �Horrocks et al., +333 ; |}� +333 ; Du#ell et al.,

,**- ; Allard et al., ,**/�S FT-IR�EFI���� g�'�'(!�&�F0J Oppenheimer et al. (+332)&�/FS

FT-IR�EFI����� g'(MJ� '(-�,{*���� �Z��Z�� ��&"*89:�ij�'()*S ��ID&J�'��MN* FT-IRdG�0� -������?!&89:cB��&{*S �'&uEMO*89:c,/0J� Z����_`�a(Mori et al., +33/)� Ze�?�[\]2^ab (Mori et

al., +33-)� ��89:c (Francis et al., +33/)���:(Francis et al., +332 ; Love et al., +332)B��GH*S uEMO*:cJ� �H�H���� ¡� Z�� �¢�£��¤¥{¦&§Ot¨©)*�M� �'&ªIR0

�«++-�**-- ¬­®¯­°±² 1�-�+¬­§w§w³�w´µ¶·�¸vw¹º»¼Laboratory for Earthquake Chemistry, Graduate

School of Science, The University of Tokyo, 1�-�+Hongo, Bunkyo-ku, Tokyo ++-�**--, Japan.

Corresponding author : Toshiya Mori

e-mail : [email protected]

����������������� �������� �������� ����� �� ��������� CO,, CO, H,O������ �������������� �� ������� !"��#����$%&'()��*������

,**.� 3+ +� ,*, *,���-�� ,+�./��0!12'�"#$%����� ��%��3/ �-��4&�%'�(5��67�8� 9:�);*< +,="�-�� >�./ ,**.?� 3+ +�(9 %�� 3+ +-�"�8<@�� +.�< +2���A0!%��0#��� 1� +0�2< +1�3�<7��45$���:�6B��%�C7�5�� D�E -F >3+ ,-� 3+ ,3� +++ +.�? ��0!%��GH +,+ 3�"�%��I�J��� (E%��K�@�8 >�./ ,**.?� �-� ,**.�%��8 �������6BJ� -,*** ton�day�L*� SO,�6B�I�J��� >9:M; ,**.?�

,**.� 3+ +���-� ,**.�%��N7� �-��%O�����PQ<��RS���TU��� =VW�� %�TUE�XY�� .F�I�Z[\%��>� ,***� +++\ ,**+� -+�I�Z[�?] ,**.�%�>E�����PQ<��^���_@���

,� ���������=VW�I��� AR`�BC��a%bcDde�6fg (FT-IR) (Fig. +)�h���� �6fg�BOMEMi�MB-+** >Fig. +��EF�BG? � Hj-* cm�kIl /mrad�mno1peAR` >Fig. +qJ�rKF? ���Ls�BGtMN��� _Bu� InSb_Bu� +,2**< .,/** cmv+�O�w�O��xP + cmv+������\�yP���� I�BG� =Q AR` zp{|%} ~� #R������GH +/* kg�8��H I���SF�Tk���U�V�W�X8��XY� ��!\�����Ls!\������ HY��h����� (Francis et al., +332)\5Z����h����� (Love et al., +332)�[\/������� >�� ��HYLs!\��h����� AR`����7��\�8�� ����� ��8� >���&'�]? �^��\����� >X����������H AR`��_$��|�<.]���`a�87��8 8? I�BGM%OM���Hb�Z�87��8 8� ��3�8 -���G;��c��X�� +��d��,-\e���f��

���4/�U�f�� ���qJ���� ���I�X��g������ �� E����Ls5Z�h���� �h� Ls5Z�yk��s�5Z�i���\�j ���� ��kl�m��%O���n����� i�$��������5Z������\����� I�J�����&'�]� HY��!\��h���X 3/���<��� _Bu� InSb_Bu�h����\� SO,�HCl�¡¢��� ,,*** cmv+(k�O�ow���8�]�5Z�^ ��� =VW�� I�X��p �i�$£85Z������¤���I��¥@�������I���Ls���&'�`��\ ������� SO,, HCl, HF�3�¡¢�¦ ��; ���qr��;�s����3�¡¢�¦ ��� I����&'�¦ �� �� ����m§¨� >I�BG�kI���������t�u? � I����&'� �\%O�©v��ª«'���&'�wb¬­A[x��3/a®�¯®po���\������ ��� °���¡¢±§$%}��HITRAN

«%}2%� (Rothman et al., +332 ; ,**-)�h�� ª«'���&'�²B�� LBLRTM (Line-by-Line Ra-

diation Transfer Model) (e.g., Clough et al., +33, ; Clough

and Iacono, +33/)\�6fy-ª«'��\�Ls���&'�²B��³´o§¨�h���� µFCT�������� >SO, HCl\HF? �xz� ()�¶�O�{·�¥@�� SO,� ,,.,*¸,,/3* cmv+�{·

Fig. +. FT-IR system used in volcanic gas mea-

surements at Asama volcano. The photo shows

the system at the parking area on Onioshi

Highway (B in Fig. ,) on October +, ,**..The slope on the right side of the photo

corresponds to the flank of Asama volcano.

Mt. Koasama is to the left of the slope.

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�� ���N,O�H,O������� �������� HCl� ,,2+*�,,23* cm�+������� H,O

� CH. ��� �������� HF� .,*,*�.,*0* cm�+������� H,O������������ ����������!" SO,� HCl�HF�#$%��&'���( )�*� �+�,�,�-.�HCl, SO,, HF��/�0��1����

-� �������234�� FT-IR5��� ,**. �6�7� ,***

++8 +0�� ,**+ -8 +0�� ,9�� �6:���,**. 38 +/� +0�� +*8 +�� ��� ,**/ -8+*�� .9;<��� 5���=��� � ,**+ >� ,**. �3�� �?�@�� �A���B� 6CD��E�F��64��GHI�JKL���6��M���� N+O�� ,**-P� )�3� Q9> FT-IR���64RS5�234�TE��� +OUV����!"� W� ��5�XYZ������ �� 5��Fig. ,�[. .�� NA>�DP ����� \���4� !�5����]���� 4"�#^$/�0�)��� %&7�'_�()`*�+a "� ()��A�bc��U,����d�'�]�� �� ��5���e��� -f0��A�gh`*� ()�i.��0ajkH����� 5�lm�/��UV�!��n����

,*** ++8�5��� 4">�E�00 4!�]�236412o�3pl NFig. , : A��P �q������ /��� �A�r4�5����� ���s:,�7:�'_�()`*�`��36�� �A�g&�()�b�7���ZYtuv���;<���,**+ -8� ,**. +*8 +�wx ,**/ -8 +*��5���� 234�0 4!8�yz{|}~|g�3pl NFig. , : B��P �5�9.�.��� ��7���:���3�� )�5���>���� ()�234�04�:�;���� %&7�()�4"ba<�.�� �A�0 >�0&f�5��l���� )�5��>����� ()��A�=��;���a��� G>()���������'_�;<��.�� ,**. 38 +/���� ����?��m�23645�m?�3pl NFig. , : C��P �5����� )���23645�m>���� 4"@bA4�:�()�;�)��B�� �A�A4�5�����)��'� ()��A�B:<�.���5�.�)���0�� ,**. 38 +0��� C4D NFig. , : D��P �q��5����� )���s:��A�C4D�]�Ar&f�5����� 64�E�.�KL

��6�FG���M�����'� �A����64������� �A�7������H�� �U,�]��� )��'� �A�7���� ����*��� ��'� 64����'_�Ia����H��J �A���7�()����>���0����7�64RS�� �������

.� � � Fig. -�5�S¡¢v£� +K���� ,**/ -8

+*��5���S¡¢v£[.� +,2** cm�+¤g�S¡¢v£�*�������� ¥����� InSb¦�§�¨*� +,2** cm�+>�©ª�)��«¬.�� SO,

(n+­n-)� HCl NP®P �HF NR®P �¯°�]� ,,.,*

�,,/3* cm�+� ,,2**�,,23* cm�+� .,*,*�.,*0* cm�+��� ����S¡¢v£�*�]�)��=>��Fig. .a�c�� Fig. -�[��S¡¢v£� SO,� HCl

�HF�¯°L±�� �[.� ²³��� �´��±� SO, (Fig. .a+)� HCl (Fig. .b+)�HF (Fig. .c+)�H�Mµ���'[��� Fig. .a,�5�S¡¢v£N�¶P ��� ,,/** cm�+���� SO,�¯°������� ,,/.*�,,/3* cm�+�����¯°��+�N,O�«¬.�� ·&� Fig. .b,� .c,��Na�¯°¸Y¢������� )���¹��º��+�H,O

�«¬����� 5�S¡¢v£>��HCl, HF�¯

Fig. ,. Map of Asama volcano showing locations of

the FT-IR measurements (circled letters). A :

parking area of Asama Volcano Museum, B:

parking area on Onioshi Highway, C : Asama

Volcano Observatory, D: Manzanbo lookout.

Contour lines have +**m spacing.

234�A�64RS�� �»¼5� 569

���������� �� ����������������������� HCl�HF!"#$�%$������&�' Fig. .()�*+,-+./� 01������ 2345�6� ' 0789�9%� �����:;� SO,� HCl�HF��<=>�?@A�����BCD�E�F�G���H � I�J�K@!"#$�LM '

Fig. /a�� ,**/N -O +*P�������QR�� ST� SO,!"#$� UT�HCl!"#$��GVW,�� ' E�� XYZHCl� SO,[K\�]%�D�^� )ZVW,�_4`A�a�6�� 7b_4c&�def�HCl�SO,\�Fg��' h)�6� i:�� SO,�HCl!"#$j�_4�a����� I�J�K@9%kl�mn� opq7b@��irXYZHCl�SO,\�s�� ' _4`A�a� t89PQR�u GEvwx� 'hy�HF�HCl!"#$�VW,�� /"*� Fig. /b�6�' HF�������� .,*-3cmz+

{|�D���4]}p�%$�H~G �t 2HCl

��� -}@����G �5� ��h�<=�H,O��4ED��� HFkl��&�A~G �' Fig. /b�� GEHF�HCl!"#$j�_4`A�a�wM���' ��i:�VW,�c&��s�� def�HCl�SO,�HF�HCl0�\� Table +�6�' ��� ,**+N -O89� +/ :

**�� +/ : /*���G +-�89������9%� �� �� -�������� GHCl�SO,\��A���� HF�HCl\������ ' ���XY[K=@����j�j���6�G �����D�' �� +*��������P��`A �m¡� HCl�SO,\�HF�HCl\�LM��

*.+-¢*.*+� *.++¢*.*+�Ar� ,***N ++O89QR�£¤�{  �6�'

Fig. -. Example of an observed spectrum collected

on Mach +*, ,**/. Three bars above the spec-

trum show the wavenumber ranges used for

spectral analyses for SO,, HCl and HF, re-

spectively.

Fig. .. Example spectra in the wavenumber ranges

for (a) SO,, (b) HCl and (c) HF spectral

analyses. Wavenumber ranges in a,, b, and c,correspond to those of the three bars shown in

Fig. -, and dotted and solid thin lines are

observed spectrum and the model spectrum

obtained by non-linear least-squares regression

method, respectively. Spectra shown in a+, b+and c+ are transmittance of SO,, HCl and HF,

respectively.

¥ ¦§¨©ª«¬570

Table +��� ������ SO,�� �������������� SO,�� ������ ������������ !"#$� %����&'�()��*+�� ,-� ./0#12�345��6�78���-9����:;<=� �>?� ,**.@ 3

A +0���BC�� D� SO, �� �# +,.** ppmm

C� E�����FG�HIJKL�M<NO4���N� !=�� ���PCQR�-�6�� 12�STU��B4V�--W� 12478���X�#Y�� SO,�� �#M<� �-"Z>[=� \��,**.@ +*A +����C�D�# +*,1** ppmmC� ]�L�^N SO,�� �4_`� !=�� ���-./0#� abCcd�e#�-124fg�6�78���--W� 12h�0�i�#j� k� %�$lSO,�� �#��� �--W"Z>[=�

FT-IRC���-&'mn�� 123C�cop�qrstou�vw4x�Nyz{#�� 123�cop#qr�-"�� �&'n$#|}L�~�s���=?� 123�&'mn#��k69[C�� D�� FT-IR�����'�B"��������4H��-��C� F�ClH��C\��-#� Cl�SH� FT-IR��#^NO4��- (Aiuppa et al., ,**.)�-l�� !�"����������� Cl�SH� Cl"�����"�HC�k� HCl/(SO,�H,S)H�K���\�� FT-IRC�H,S��(C��N N�C� Cl�SH�HCl�SO,H�K��� !������� �B�� Cl�SH��N�� HCl/(SO,�H,S)H"HCl�SO,H��N����"F��[=�N (Aiuppa

et al., ,**.)� ,-� Burton et al. (,**+)�� HCl#qr�-cop�|}L����-!"��123�HCl�SO,H�� 4¡¢��N� £[�� HCl" SO,

�c¤���¥��NC!�¦§4¨���N� © �Z>�ª«�"� HF�HClH�����k¬��"Z>[=#� !=�­��B�®�"!¯ N� \�� �°�±²³´µ¶·C� FT-IR��C�� 1(�

Table +. Results of the 0 FT-IR measurements carried out before and after the ,**. eruptions.

Fig. /. Gas column amounts plots for March +*,,**/ observation. (a) HCl vs. SO,, (b) HF vs.

HCl. The best-fit regression lines are shown,

and their gradients correspond to the gas con-

centration ratios in Table +.

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