have successfully detected - volcanic gas components, so,, hcl and hf, in the observed spectra. the...
TRANSCRIPT
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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]
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,� ���������=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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�,,/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.
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���������� �� ����������������������� HCl�HF!"#$�%$������&�' Fig. .()�*+,-+./� 01������ 2345�6� ' 0789�9%� �����:;� SO,� HCl�HF��<=>�?@A�����BCD�E�F�G���H � I�J�K@!"#$�LM '
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**�� +/ : /*���G +-�89������9%� �� �� -�������� GHCl�SO,\��A���� HF�HCl\������ ' ���XY[K=@����j�j���6�G �����D�' �� +*��������P��`A �m¡� HCl�SO,\�HF�HCl\�LM��
*.+-¢*.*+� *.++¢*.*+�Ar� ,***N ++O89QR�£¤�{ �6�'
Fig. -. Example of an observed spectrum collected
on Mach +*, ,**/. Three bars above the spec-
trum show the wavenumber ranges used for
spectral analyses for SO,, HCl and HF, re-
spectively.
Fig. .. Example spectra in the wavenumber ranges
for (a) SO,, (b) HCl and (c) HF spectral
analyses. Wavenumber ranges in a,, b, and c,correspond to those of the three bars shown in
Fig. -, and dotted and solid thin lines are
observed spectrum and the model spectrum
obtained by non-linear least-squares regression
method, respectively. Spectra shown in a+, b+and c+ are transmittance of SO,, HCl and HF,
respectively.
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Table +��� ������ SO,�� �������������� SO,�� ������ ������������ !"#$� %����&'�()��*+�� ,-� ./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,
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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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