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Hawaii Volcanic National Park |
Representative IMPROVE Site
IMPROVE: HAV01
CASTNET: HTV424
Region
Hawaii
Terrain
The Hawaii Volcanoes National Park IMPROVE Site is located on the east to
southeastern slopes of Mauna Loa on the island of Hawaii. More specifically, it
is situated on the northeastern rim of the Kilauea crater. The site elevation is
1204 m (3949 ft), some 124 m above the crater floor at 1080 m (3542 ft).
Volcanic emissions (SO2) from the Kilauea crater (caldera) presently amount to
100 to 200 metric tons per day. This area is all part of the active Kilauea
Volcano. There are other sources, including lava flows and other craters along
the East Rift Zone extending out to ~ 20 km to the east-southeast from the
monitoring site. The most recent and continuing activity, which has been in
progress since 1983, is centered on the Pu’u O’o crater some 20 km (12 miles)
east-southeast from the monitoring site. SO2 Emissions from Pu’u O’o amount to
1000 to 2000 metric tons per day, mostly from the main vent at an elevation of ~
600 m (2000 ft) (Okamura, 2003).
Besides the Kilauea Volcano system, the major terrain feature affecting
meteorology and air quality at the monitoring site is the 4170 m (13,681 ft)
high Mauna Loa cone, about 35 km (22 mi) to the west of the monitoring site.
Wind
Located on the Southeast slope of Mauna Loa, the monitoring site is well exposed
to the east-to-west trade-wind flow. During trade-wind conditions, which
predominate 80 to 95% of the time from May through September, and 50 to 80%
during the rest of the year, prevailing wind directions should thus be generally
east to west, typically with speed of 5 mps or greater. During northeast
trade-wind conditions, a clock-wise eddy is produced to the west of the island
which has significant effects on transport of local (volcanic) emissions to the
islands lee-side (west side). Mountain-valley slope flow should be evidenced at
the site by nighttime westerly to northerly drainage flow and daytime easterly
to southerly upslope flow. Exceptions to these conditions would occur during
frontal passages associated with synoptic weather systems, and, at the site
elevation, during upper atmosphere low pressure system passages.
Inversions
The predominant inversion phenomenon is the Trade-layer inversion, or Marine
Boundary Layer. The marine layer will have much less diurnal variability than
continental inversions because of the oceanic influence. Typical trade-layer
inversion heights in the vicinity of Volcanoes NP are probably near 2000m above
sea level, with some variability due to seasonal effects. At the site elevation
of 1204 m the monitoring site would thus probably be within this layer most of
the time, when trade-wind conditions predominate. During this condition,
relative humidity will be typically be high, 70% or greater. When the trade-wind
layer height is below the monitoring site, relative humidity will be much lower.
If more continental types of inversions occur, say within the Kilauea crater
during periods when the trade winds are absent or light and variable, they would
occur over a much smaller scale, with significant diurnal variability. Over a
period of time aerosol concentrations could presumably build up due to SO2
emissions within the crater, although it is not clear that such conditions can
occur with any frequency.
Meteorological Indicators
A unique atmospheric phenomenon of this region is the so-called vog (volcanic
smog) that occurs when SO2 and other volcanic pollutants react with oxygen and
atmospheric moisture. Information on this phenomenon is available at:
http://wrgis.wr.usgs.gov/fact-sheet/fs169-97/
Thus, volcanic emissions are a likely candidate for the source of aerosols
monitored at the IMPROVE site, which are typically high in particulate sulfate
composition (43.3 % of the light extinction overall, 69.7% during the 20% worst
days). There are nevertheless other potential sources, particularly sea salt
sulfate or transported Asian dust, that also typically have high sulfate
composition. Asian dust emissions have been detected at the NOAA Mauna Loa
Observatory. A good indicator of Asian dust as a significant aerosol source at
the monitoring site would be high correlation with Asian dust events, or
occurrence during low relative humidity conditions, when the site is above the
trade-wind layer. Local volcanic emissions might be indicated by a strong
correlation of high mass concentrations with wind direction from sources to the
east southeast clockwise to southwest and low or negligible concentrations
during light downslope (northerly) winds, or by buildup during calm or light
wind periods. At low concentrations, a significant sea sulfate contribution
might be indicated by high correlation with Haleakala NP measurements when both
sites are within the trade-wind layer and have similar relative humidity
measurements. (Note however that significant volcanic plume impaction has been
observed at Haleakala NP when transported from the vicinity of Volcanoes NP). (Hollingshead
et al., 2003)
Nearby Data Stations
Meteorology is monitored at the site, in addition to aerosol composition, and
this is probably the best source for representative surface meteorological data
(wind direction, wind speed, temperature, relative humidity, etc.)
Meteorological data are available at
http://www.epa.gov/castnet//metdata.html
For information on regional vertical structure, especially the height of the
marine layer at the monitoring site, twice daily upper air sounding data are
collected at the NWS upper air site at Hilo. Vertical temperature profile data
from Hilo are probably the best routinely collected and long term data
representative of conditions at Volcanoes NP.
Keywords
Trade Winds
Marine Layer
Marine sulfate
VOG
References
Hollingshead, Anette T., S. Businger, R. Draxler, J. Porter, and D. Stevens.
Dispersion Modeling of the Kilauea Plume. Boundary Layer Meteorology 108:
124-144. 2003.
Okamura, Arnold, Hawaii Volcanoes Observatory, personal conversation with Dan
Freeman.
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