5 Colo. Code Regs. § 1001-14-IV
To be added to the Colorado Air Quality Control Commission document "Ambient Air Standards for Metropolitan Denver Air Quality Control Region, State Air Pollution Control Areas and the State of Colorado."
Visibility Standard for the AIR Program Area
Level: The Visibility Standard for the AIR program area is an atmospheric extinction of.076/km1, equivalent to a standard visual range of 32 miles2
Averaging Time: The Averaging time is four hours. All four hours must be contiguous. No four-hour average in violation of the standard can have hours in common with any other four-hour period in violation of the standard.3
Applicability: The visibility standard is applicable in the AIR program area.4 The visibility standard applies during an eight-hour period from 8:00 a.m. (0800) to 4:00 p.m. (1600) each day Mountain Local Time. The visibility standard applies only during hours when the hourly average relative humidity is less than 70 percent.5
1Extinction is a measure of the ability of the atmosphere to attenuate light. It is traditionally expressed in light attenuation per kilometer. It is measured directly with a long-path transmissometer or by other equivalent methods as determined by the Air Pollution Control Division.
2Extinction (Bext) can be converted to standard visual range (SVR) in miles as follows:
SVR (Miles) = (3.912/(Bext +.01 km))*.06214
Where Bray is the Rayleigh scattering coefficient (.0099/km) for Denver's altitude and the visual range is standardized to a Rayleigh scattering coefficient of.01/km or an altitude of 1.55km. The formula assumes a contrast threshold of two percent.
3There are five possible contiguous four-hour periods from 0800 to 1600 each day (0800 to 1200, 0900 to 1300, 1000 to 1500, and 1200 to 1600). Only the periods from 0800 to 1200 and from 1200 to 1600 do not have overlapping hours. Therefore, a maximum of two standard violations are possible each day that have no overlapping hours or hours in common.
4The AIR program area is defined in C.R.S. 42-4-307 (8).
5Any hour with a relative humidity of 70 percent or over would not be included in the four-hour running averages.
* Visibility: Adopted: 12/21/89; Effective: 1/1/95
5 CCR 1001-14-IV