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Petrified Forest National Park |
Site Name
IMPROVE:
PEFO1
Region
Colorado Plateau
Terrain
Petrified Forest National Park is situated within the upper Little Colorado
River drainage in northeastern Arizona. The
PEFO1 monitoring site is in a
well-exposed location near the crest of a ridge, an extension from higher
terrain to the northeast into lower terrain towards the Little Colorado to
the southwest. It is located between two separated parcels that comprise the
Petrified Forest National Park, one about 5 km (3 mi) across a low-lying
area to the north and west, and the other about 15 km (10 mi) across a
similar low-lying area to the south. Elevation at the monitoring site is
1,767 m (5,796 ft). Elevations in the two National Park sections are similar
range from 1,650 to 1,750 m (5,400 to 5,750 ft). Terrain is shown in the
20 km and
2 km terrain maps. Terrain is generally badland hills, flat-topped mesas
and buttes, with sparse ground cover.
Representativeness
Aerosol data collected at the Petrified Forest IMPROVE site (PEFO1) should
provide good representation of conditions throughout the Petrified Forest
National Park.
Nearby Population/Industrial Centers and Local Sources
The town of Holbrook (population 6,000) is located 40 km (25 mi) southwest of
the monitoring site. Gallup, New Mexico (population 20,000) is located 100
km (60 mi) northeast. The city of Flagstaff, population 53,000 (2002), is
located 180 km (110 mi) west. The nearest major metropolitan area is
Phoenix, population ~ 1.5 million, ~ 275 km (170 mi) southwest of the
monitoring site and separated from the Little Colorado River drainage by the Mogollon Rim. There are several coal-fired power plants in the region,
including Navajo, Cholla, Coronado, and Springerville power plants in
northeastern Arizona, and Four Corners and San Juan power plants in
northwestern New Mexico.
This emissions
map shows local emission sources. There is very little vegetation in the
vicinity, so nearby vegetative burning is probably not a significant local
source. Potential local sources include dirt and paved roads. Interstate
Highway 40 is located about 1.5 km (1 mi) south of the monitoring site. The
995 MW Cholla Power Plant is located just outside of Holbrook 40 km (25 mi)
southwest.
Nearby Data Stations
This map shows the location of the nearest air quality and meteorological
monitoring sites, with respect to the PEFO1 aerosol monitoring site.
Meteorology is not presently monitored at the site, and there are no
meteorological monitoring sites within 20 km. There is an
ASOS (Automated Surface
Observing System) site at Winslow, 85 km (~50 mi) west of the monitoring
site and within the Little Colorado River drainage that may provide the best
representation of meteorology at the PEFO1 site. Other surface
meteorological data stations can be identified at the
US Climate Archive.
Surface data from the Flagstaff RAOB site should be representative of
regional wind patterns, although at the PEFO1 site there may be some
large-scale channeling of surface winds by the Little Colorado River
drainage, a major southeast to northwest drainage and the major drainage for
northeastern Arizona.
The nearest upper air site is the Flagstaff RAOB site, which conducts
atmospheric soundings twice daily. Sounding data from Flagstaff should be
representative of regional upper air structure.
Wind Patterns
Long-term wind roses from the
Flagstaff NWS site for
January,
April,
July, and
October, should be regionally representative of exposed areas, including
the PEFO1 site, although there may be some large-scale channeling of surface
winds by the Little Colorado River valley. Flagstaff wind roses show a
predominance of south to south-westerly wind directions, especially in the
summer, with a significant frequency of more northerly wind directions
during the fall and winter. Summertime southerly flow may in part result
from the North
American Monsoon, bringing with it precipitation events. Prevailing
south and southwesterly flow may have implications with respect to aerosol
transport from areas to the southwest. The Cholla power plant near Holbrook
may thus be upwind most of the time.
Inversions/Trapping
Inversion conditions in the area will likely be large-scale inversions, such
as subsidence inversions associated with buildup and stagnation of synoptic
high-pressure ridges over periods of a few days or longer. These are most
likely to occur during the extended summer (May - October), when pressure
and temperature gradients in the region are weakest, and wind circulations
therefore weaker. Long-term data have shown the southwestern United States
to be a region prone to regional stagnation episodes (Wang
and Angell, 1999). The terrain is not as confining as in narrow and deep
valleys and canyons, so that trapping inversions with diurnal patterns are
not likely. In any case, the PEFO1 monitoring site is near a ridge crest and
likely above local surface-based inversions.
Climatological Statistics
Climatological statistics for
Winslow
include long-term normal means and extremes of temperature, relative
humidity, wind and precipitation that should be representative of the PEFO1
monitoring site.
Meteorological Indicators for Local Sources
There are few local sources of aerosol emissions. Since there are relatively
few local emission sources and the air is likely generally clean, major
impacts may only result from advection from distant source regions or major
point sources. Locally, there may be an impact from emissions from the
Cholla power plant 40 km (25 mi) southwest, near Holbrook. Emissions from
this and from nearby dust sources are most likely to build up during periods
of light westerly to southwesterly flow, or during periods of regional
stagnation. Such conditions would be indicated by calm to light westerly to
southwesterly wind directions measured at Winslow, and by summertime
regional stagnation indicated by prolonged regional high-pressure buildup on
synoptic weather maps. There may also be intermittent periods when the
monitoring site is impacted by entrained surface dust during windy
conditions. Such conditions would be indicated by high (>6-8 mph) windspeeds
measured at the Winslow ASOS
station.
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Last updated 17 December 2004
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