Skip to content

Juneau Floyd Dryden Site

Site Location

Open map in ArcGIS Web app

Views of Site from Four Cardinal Directions

Floyd Dryden - View From North
Floyd Dryden - View From East
Floyd Dryden - View From South
Floyd Dryden - View From West

Views from Site in Four Cardinal Directions

Floyd Dryden - Looking North
Floyd Dryden - Looking East
Floyd Dryden - Looking South
Floyd Dryden - Looking West

Monitoring Siting Criteria for the Floyd Dryden Air Quality Monitoring Site


The Code of Federal Regulation Title 40 Part 58 covers Ambient Air Quality Surveillance. Appendix E to Part 58—Probe and Monitoring Path Siting Criteria for Ambient Air Quality Monitoring contains specific location criteria applicable to State and Local air Monitoring Stations (SLAMS) ambient air quality monitoring probes and inlets. These siting criteria are necessary to ensure the uniform collection of compatible and comparable air quality data. The probe siting criteria discussed in Appendix E must be followed to the greatest extent possible, although there may be situations where some deviation from the siting criteria may be necessary. Specific siting criteria that are phrased with a “must” are defined as requirements and exceptions must be approved through the waiver provisions. However, siting criteria that are phrased with a “should” are defined as goals to meet for consistency but are not requirements.

The Floyd Dryden site, located on the roof of Floyd Dryden Middle School in Juneau’s Mendenhall Valley, consists of a continuous PM10 and PM2.5 Met One Beta Attenuation Monitor (BAM) with particle size selective inlets, and a radiation air monitor as part of the Environmental Protection Agency’s (EPA) RadNet monitoring program. Below is a list of criteria from Appendix E to 40 CFR 58 applicable to these types of particulate matter monitors. Note, only references to probes or inlets will be addressed as any reference to monitoring paths are not applicable because the instruments in use are not open path monitors.

Horizontal and Vertical Placement

“The probe or at least 80 percent of the monitoring path must be located between 2 and 15 meters above ground level for all O3 and SO2 monitoring sites, and for neighborhood or larger spatial scale Pb, PM10, PM10-2.5, PM2.5, NO2, and CO sites”

Juneau is classified as a neighborhood scale monitoring site requiring inlet heads be located 2 to 15 meters above ground level. The monitors are located on the roof approximately 6 meters above ground, with the inlet heads approximately 8 meters above ground.

“The probe or at least 90 percent of the monitoring path must be at least 1 meter vertically or horizontally away from any supporting structure, walls, parapets, penthouses, etc., and away from dusty or dirty areas.”

Monitors are located more than 15 meters from the rooftop penthouse wall, and all inlet heads are more than 1 meter from any other inlet head. The high volume RadNet monitor is located approximately 10 meters from the nearest BAM inlet head.

Spacing from Minor Sources

“If a monitoring site is to be used to determine air quality over a much larger area, such as a neighborhood or city, a monitoring agency should avoid placing a monitor probe, path, or inlet near local, minor sources. The plume from the local minor sources should not be allowed to inappropriately impact the air quality data collected at a site. Particulate matter sites should not be located in an unpaved area unless there is vegetative ground cover year round, so that the impact of windblown dusts will be kept to a minimum.”

The Floyd Dryden monitoring site is located on the roof of Floyd Dryden Middle School opposite the school’s parking lot. The rooftop site is located approximately 60 meters from the school’s furnace flue and about 10 meters from a nearby kitchen vent. The schools paved parking lot is locate approximately 80 meters from the site, and the nearest residences are approximately 80 meters from the site.

Spacing from Obstructions

“A probe, inlet, or monitoring path must have unrestricted airflow in an arc of at least 180 degrees. This arc must include the predominant wind direction for the season of greatest pollutant concentration potential.”

No obstructions restrict the airflow to the monitor inlets. The nearby obstructions are the schools roof penthouse (~15 meters) and the tree line (~20 meters).

Spacing from Trees

“Trees can also act as obstructions in cases where they are located between the air pollutant sources or source areas and the monitoring site, and where the trees are of a sufficient height and leaf canopy density to interfere with the normal airflow around the probe, inlet, or monitoring path. To reduce this possible interference/obstruction, the probe, inlet, or at least 90 percent of the monitoring path must be at least 10 meters or further from the drip line of trees.”

Running from the north of the school to the east of the school is a woods that separates the school from a nearby residential area. At its closest, the dripline for the trees is located approximately 20 meters from the Floyd Dryden site.

Spacing from Roadways

“Spacing for Particulate Matter (PM2.5, PM10, Pb) Inlets. (a) Since emissions associated with the operation of motor vehicles contribute to urban area particulate matter ambient levels, spacing from roadway criteria are necessary for ensuring national consistency in PM sampler siting.”

“For the middle scale site, a range of acceptable distances from the roadway is shown in figure E-1 of this appendix. This figure also includes separation distances between a roadway and neighborhood or larger scale sites by default. Any site, 2 to 15 meters high, and further back than the middle scale requirements will generally be neighborhood, urban or regional scale."

The only nearby roadway with documented traffic counts near the Floyd Dryden site is Mendenhall Loop Road, located 180 meters from the site at the closest point. In 2018 the Annual Average Daily Traffic (AADT) for Mendenhall Loop Rd was 13,014 cars per day. Given the traffic flow from the nearby roadway, the Floyd Dryden Site meets the roadway criteria for ensuring national consistency in PM sampler siting.

external link indicator Indicates an external site.