Validity of Colorado Springs Municipal Airport Meteorological Data for 

SO2 NAAQS Compliance Modeling

Background

In their October 15, 2015 briefing to the Air Quality Control Commission (Commission) of the 

Colorado Department of Public Health and Environment (CDPHE), the Colorado Air Pollution Control

Division (APCD) claimed that SO2 dispersion modeling in AERMOD, for the Martin Drake Power 

Plant, must be dismissed if using meteorological (met) data from the Colorado Springs Municipal 

Airport (KCOS).

Although modeling is the EPA preferred technique for analyzing compliance with the 2010 National 

Ambient Air Quality Standards (NAAQS) for one-hour concentrations of SO2, neither Colorado 

Springs Utilities (CSU), nor CDPHE made any attempt prior to 2015 to monitor a more accurate met 

data source than the KCOS, Class 1 National Weather Service data. This dismissal of airport weather 

data that at least two other professional air quality services firms found to be entirely representative and

suitable for use with AERMOD is irresponsible to the residents and visitors of the City of Colorado 

Springs, who must breathe the air containing significant amounts of criteria pollutants emitted from the 

Martin Drake Plant, including sulfur dioxide.

The Martin Drake Plant is less than seven miles from the airport with no significant terrain between the

two sites.

Illustration 1: Martin Drake Plant to Airport is Less Than 7 Miles (Source: Google Maps)
Met Data Near Martin Drake Shows Close Correlation to KCOS Data

The Weather Underground (wunderground.com) has 

established a large number of micro met stations in 

Colorado Springs. The closest of these is the Crown 

Hill Mesa Person Weather Station (PWS) which lies 

5800 feet west of Martin Drake. The specific source 

for the Crown Hill Mesa historical data can be found 

at: tinyurl.com/hvzeck5

Coordinates for this site are: 38.825N 104.854W.

This PWS collects temperature, dew point, wind 

direction and speed, atmospheric pressure and 

precipitation data at approximately five minute 

intervals.

The Weather Underground also provides historical met data from the National Weather Service met 

station at KCOS. Five continuous months (1 Aug through 31 Dec 2015) of data from these two stations

were used for the following graphs. The specific source for the KCOS historical data can be found at: 

tinyurl.com/hqmpkbs

Illustration 3: Crown Hill Mesa PWS (Source: 

wunderground.com)

Illustration 2: View from Martin Drake to Airport (Source: Google Earth)
Temperature and Dew Point Correlation

In the graphs below, the upper chart is from the Crown Hill Mesa site and the lower chart from KCOS. 

Both charts depict temperature and dew point information for Aug through December 2015. The charts

indicate a strong correlation between the two sites for temperature and dew point.

Wind Velocity Correlation

Below, the upper chart shows the five-month wind velocity data for the Crown Hill site and the lower 

chart for the KCOS airport. The steady state (non-gust) winds are depicted by the continuous lines. 

Again, the data indicates a strong correlation in wind velocity between the two sites, with only slightly 

higher winds at the airport. 

Illustration 4: Temperature and Dew Point Correlation

Illustration 5: Wind Velocity Correlation
Wind Direction Correlation

Below, the upper chart shows the five-month wind direction data for the Crown Hill site and the lower 

chart for the KCOS airport. The data indicates the Crown Hill Mesa site has predominant winds more 

from the east and east-southeast, while the airport winds tend to be more from the east and eastnortheast. The shift being a relatively minor fifteen to twenty degrees.

Conclusion

The close proximity, lack of significant terrain, and closely correlated met data between the Martin 

Drake Power Plant and the Colorado Springs Municipal Airport, indicate that the airport data is 

sufficiently representative of the Martin Drake weather for the purpose of NAAQS compliance 

modeling in AERMOD.

It is reasonable to presume that a meteorological station directly located at the Martin Drake Plant with 

a minimum of one-hour sampling will be most representative, however would likely be only marginally

more accurate than the Colorado Springs Airport met data and therefore not necessary for purposes of 

the current designation.

 However, CSU and CDPHE took no steps to procure such a station until 2015, five years after the 

Revised NAAQS 2010 Standard for Sulfur Dioxide was released, and only after a federal court Consent

Decree mandated such action. Therefore, the airport met data, as the most accurate and representative 

information available, should be used for initial NAAQS compliance modeling and, thus, the analyses 

by Wingra Engineering should be given deference in the EPA review of this matter of significant 

importance to public health and safety. 

Illustration 6: Wind Direction Correlation