Over the last year, air pollution predictive modeling was performed by the Division to determine the air quality impacts of numerous direct and indirect sources. Also, modeling was used to support Division enforcement and engineering functions to verify modeling performed by others. The modeling capability of the Division has expanded over the last year.

Regional Assessment of Air Quality

Assessment of the air pollution problem in Colorado will be broken down into discussions of the eight national Air Quality Control Regions (AQCRS) in Colorado, using State numerical identifiers.

These AQCRS are groups of counties which, for reasons of topography, meteorology, and other considerations, are treated as units for air pollution control purposes. The eight AQCRS in Colorado are shown in Figure 1.

The Federal ambient air quality standards, which appear in Appendix A, are the same in all of these AQCRs.

As can

There are also State Designated and Non-Designated areas which are also shown on Figure 1. A detailed delineation of these areas is available from the office of the Air Pollution Control Commission. be seen from the standards list in Appendix A, the State Ambient air quality standards differ for these two types of areas.

The Colorado Air Pollution Control Division and the U.S. Environmental Protection Agency have assigned priorities for controlling each major pollutant found in each of these AQCRS. Priorities are assigned based on several considerations:

a. existing air quality data

b. demographic (population) factors and their trends

c. degree and type of industrialization (emission inventory)
d. amount of vehicular traffic

e. topographic and meteorological factors

Pollutant priorities for the regions determine the amount and type of air pollution control program emphasis to be applied in each region. These include the amount of monitoring for each pollutant, the development of regional abatement plans, the frequency of enforcement inspections, etc.

These priorities are shown in Table I. (A Priority I pollutant is of more concern in a given region than a Priority II or Priority III pollutant.)

* A suffix of "A" on a priority indicates that most of the pollutants in question can be attributed to a single source. In the case of AQCR 6, the point source is the Four Corners Power Plant, located 23 miles outside the Colorado State boundary.

The monitoring network consists of a Statewide system of particulate samplers and a number of gaseous sampling stations. During the 1975 calendar year six continuous gaseous stations were operational in the Denver AQCR. In addition, carbon monoxide sites were established in Colorado Springs, Pueblo, and Fort Collins. The Colorado Springs station is equipped with analyzers for ozone and oxides of nitrogen in addition to the equipment for carbon monoxide.

Through the continuing efforts of the air pollution staff of local health departments in Colorado Springs, Pueblo and Fort Collins, these stations are now fully operational and are providing valuable data for the State and local agencies.

The data obtained from a monitoring network can be used as a measure of the effectiveness of the Colorado State Implementation Plan (SIP). The SIP is an air resource plan having as its goal the achievement and maintenance of clean air in the State and the prevention of any unnecessary degradation of air quality.

The air monitoring network further assists the control agency in observing pollution trends by providing baseline data against which new programs of air pollution control can be measured. Such programs can also lead to more effective zoning and transportation planning.

The data handling team statistically analyzes the air pollution data as well as maintains computer files consisting of varied types of air pollution related data. In 1975 two new computer based systems which handle compliance and emissions data from stationary sources were installed. In late 1975 a similar system was installed on the State computer to handle air quality data.

The Denver air monitoring network supplies the data base for the Emergency Episode Plan. The staff meteorologist uses pollutant data as it is acquired in conjunction with various national and local meteorological information to assess and predict the local air

pollution problems. The prediction of high levels of pollutants triggers the institution of emergency control measures which are designed to prevent the further buildup of harmful pollutant concentrations.

As a general rule, it could be said that the air quality in the Denver area was better in 1975. It would be a hasty assumption to assume that this indicates a new trend. A close look at the weather parameters may provide the answer. Throughout the entire year, the surface wind speed averaged higher than normal. As a possible result of this phenomenon, there were no air pollution episodes announced during 1975. That is, no alert, waming, or emergency levels were reached and sustained for the required minimum twelve hours.

There were many days during which levels of one or more pollutants were much above normal, and/or visibility was much lower than usual. On 22 days a total of 28 air quality messages were relayed over the weather wire of the National Weather Service. These messages advised the public of the presence of temperature inversions and light winds and discussed the resultant conditions of generally low visibilities and high contaminant levels.

The "smog season" is generally during the months of September through April, and this is reflected in the fact that all the advisories, except one in July, were issued in this period.

The weather wire is received by most of the radio stations, television stations, and newspapers throughout the Denver area, and most of the media announce the advisory to the public within minutes. This reflects the general high level of interest and concern that people have on the subject.

The advisory that follows was issued on November 28, 1975 and is typical of those sent:

"SMOG HANGS HEAVY OVER METRO DENVER.......

A COMBINATION OF HIGH HUMIDITY, LIGHT WINDS, AND A PERSISTENT TEMPERATURE INVERSION HAS RESULTED IN LOW VISIBILITY OVER THE METRO DENVER AREA.

THE HIGHEST POLLUTION LEVELS ARE IN THE DOWNTOWN DENVER AREA, WITH PARTICULATES RUNNING ABOUT TWO THIRDS OF THE ALERT LEVEL, AND CARBON MONOXIDE ABOUT ONE FOURTH OF THE ALERT LEVEL.

NO ALERT IS EXPECTED TO BE ANNOUNCED AS WINDS ARE PREDICTED TO INCREASE TONIGHT WITH THE APPROACH OF A MAJOR STORM SYSTEM FROM THE WEST.

THE OUTLOOK FOR TOMORROW LOOKS MUCH BETTER. COOLER AIR ALOFT WILL BE MOVING IN, WIPING OUT THE PERSISTENT TEMPERATURE INVERSION, AND SNOW IS POSSIBLE, CLEANSING THE AIR AS IT FALLS.

FURTHER ADVISORIES WILL BE ISSUED AS CONDITIONS WARRANT."

In the future, as additional gaseous monitoring stations are added in areas outside of the greater Denver area, the episode actions taken will include these areas. It must be noted that the criteria for episode actions is that certain pollution levels must be reached, or expected to be reached, and this requires real time air quality monitoring.

Since the episode system was initiated in early 1971, there have been eight alerts. (See Table II)

The provisions of Regulation No. 3, pertaining to new source permits, provide that significant sources curtail activities during declared emergency episodes. The new source permitting process is a major method of addressing the practical means by which air pollution can be reduced quickly when necessary. Operational curtailment proceedings have been agreed upon by the Division and all major stationary sources of air pollution. Implementation of these procedures would be directed by enforcement personnel.

Sources and Distribution of Pollutants

Suspended particulate matter data for 1975 are presented in Appendix B, where the samplers are shown by name and number and the data summarized for arithmetic and geometric means.

Included in the description of the air quality in each AQCR is a tabulation showing the types of major point sources in the region, and the tonnages of pollutants emitted by these sources. The tables can give an indication of the air pollution potential in a given region; however, it should be noted that area sources can be very significant, particularly automobiles and fugitive dust sources. (Fugitive dust is particulate matter that cannot be attributed to a precisely located emission point. Examples are construction sites, unpaved roads, and wind blown soil.)

When area source inventories are completed, a more accurate picture of the pollution problem in each AQCR will emerge. Also, the point source emission totals for a given pollutant may vary considerably from region to region because different types of point sources are noted for different types of pollutants, and each region has its own particular set of point sources. For instance, a large total for SO2 can indicate the presence of one or two large sources.

Pawnee

Air Quality Control Region 1
Logan, Morgan, Phillips, Sedgwick, Washington, Weld, and Yuma Counties

The Pawnee AQCR is primarily an agricultural area with major population centers in Larimer and Weld counties. Due to concern over automotive related pollutants, a carbon monoxide analyzer was installed in the city of Fort Collins in mid-1975.