Site Name

IMPROVE: SYCA1

Region

Colorado Plateau

Terrain

Sycamore Canyon is a deep branched canyon system comprising the Sycamore Creek and tributaries drainage. The canyon is generally oriented north to south, draining to the south. Terrain is shown in the 20 km and 2 km terrain maps. The SYCA1 monitoring site is located on the large open plateau terrain near the rim of the canyon, ~ 3 km northeast of the canyon’s most northerly extent. Elevation at the monitoring site is 2,040 m (6,691 ft), while elevations at the canyon bottom range from about 1,800 m at the north end to 1,080 m where it joins with the Verde River, about 40 km (25 mi) south of the monitoring site. Terrain near the monitoring site is forested rolling land, part of the Kaibab National Forest. Within the canyon, terrain is steep and populated with shrubs and cacti.

Representativeness

Aerosol data collected at the Sycamore Canyon IMPROVE site (SYCA1) should be representative of visibility conditions at the Sycamore Canyon rim. It should represent conditions at lower elevations of the Sycamore Canyon when the atmosphere is uniformly mixed. Aerosol measurements at SYCA1 may not represent conditions at lower elevations within the canyon when lower canyon elevations are within a stable (inversion) layer with height below the canyon rim, although light extinction measurements should be indicative of visibility for vistas above the canyon rim.

Nearby Population/Industrial Centers

The city of Flagstaff, population 53,000 (2002), is located 30 km (20 mi) east-northeast of the monitoring site. The town of Williams (population ~3,000) is located ~20 km (14 mi) northwest of the monitoring site. The Camp Navajo military reservation is located 5 to 10 km northeast of the site and may be a source of road related particulates (road dust). The nearest major metropolitan area is Phoenix, population ~ 1.5 million, ~ 180 km (110 mi) south of the monitoring site.

Local sources of particulate matter that could affect aerosol measurements at the SYCA1 monitoring site are primarily wildland fire emissions and road dust. Road dust emissions may be of major significance if there is considerable unpaved road travel in and near the Camp Navajo military reservation. There are also several minor dirt roads that approach the canyon rim, although there are no roads into the canyon.

Major point sources in the region include the Navajo and Mojave coal-fired generating stations. The Mojave Generating Station is located near the lower Colorado River near Laughlin Nevada, some 230 km (140 mi) to the west. The Navajo generating station is located near the Colorado River near Page, Arizona, ~ 180 km (110 mi). Both of these point sources are at lower elevation river locations on the Colorado River, and emissions would have to be transported aloft to impact the SYCA1 site. Other major point sources in the region include the Four Corners and San Juan power plants in northwestern New Mexico. Under some conditions, urban emissions from the Phoenix area may be significant.

Nearby Data Stations

This map shows the location of the nearest air quality and meteorological monitoring sites, with respect to the SYCA1 aerosol monitoring site. Meteorology is not presently monitored at the site. Surface data from the Flagstaff RAOB site should be reasonably representative of the SYCA1 site, although not of meteorological conditions within the canyon. There are also a few RAWS network sites in the vicinity, and a SNOTEL network site, although there is no meteorological data to directly represent conditions at lower elevations within the canyon. Information on these sites, including period of record, is available from the U.S. Climate Archive.

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

Canyon rim:

Long-term wind roses from the Flagstaff NWS site for January, April, July, and October, should be regionally representative of exposed areas, including the SYCA1 site. The 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 frequent precipitation events.

Canyon Interior:

Wind directions and resulting transport flow at lower elevations within the Sycamore Canyon should be significantly different from those for rim locations. Directions will be steered more in line with canyon orientation. Wind patterns in the main canyon and side canyons should have a well-defined diurnal drainage/upslope pattern. Nighttime drainage flow in the canyon during periods of regional high pressure and stagnation should be generally from north to south. During this condition, drainage from the canyon rim should bring regionally representative air, represented by measurements at SYCA1, into the canyon.

Inversions/Trapping

Within the canyon there is a potential for trapping inversions. In such cases aerosol measurements from the SYCA1 may not represent interior canyon conditions where aerosols are trapped within the stable layer, and where particulate concentrations may be much higher than above the rim. These situations are most likely to occur in the fall and winter, when surface cooling at the canyon bottom is greatest

At canyon rim locations including the SYCA1 site, inversions will not be trapping inversions of the sort that occur in deep valleys and canyons, but subsidence inversions associated with buildup and stagnation of synoptic high pressure ridges. 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).

Climatological Statistics

The following table shows long-term climatological statistics for Flagstaff. Data in this table should represent canyon rim locations. Climatological patterns at canyon interior locations may not be well represented by data from Flagstaff and could be significantly different, with generally much higher temperatures and lower relative humidity, especially in the summer.



Meteorological Indicators

At canyon rim locations, highest aerosol concentrations from local sources are likely to occur during synoptic stagnation periods in spring and summer, especially in conjunction with significant wildland burning. The strongest meteorological indicator of this condition would be prolonged (>4-5 days) regional high pressure from synoptic weather maps, and/or light to calm wind speeds and high temperatures measured at rim locations (SYCA1, Flagstaff), especially during periods of wild fires or prescribed burns. At canyon interior locations, highest aerosol concentrations from local sources may occur during fall and winter, when particulate concentrations build up during prolonged canyon inversions. This would also be indicated by persistent regional high pressure during fall and winter.

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