Measurement and spatial distribution of ozone in the Rocky Mountain National Park, Colorado .

1. Measurement and spatial distribution of ozone in the Rocky Mountain National Park, Colorado. Geoff Henshaw, Aeroqual Ltd, Auckland, New Zealand. John Faust and Jessica Ward, Air Resource Specialists, Fort Collins, Colorado. John D Ray National Park Service, Air Resources Division, Denver, Colorado 1

2. Structure • What do we know from previous studies of Rocky Mountain National Park Ozone ? • Design and Performance of Remote Ozone instrument. • 2010 Field Study of Summertime O3 • Conclusions

3. RMNP O3 Monitoring Locations

4. Are O3 exceedances to be expected ?...yes! • Earliest expected month for an 8-hr exceedance is April. • Highest frequency month for ozone exceedances is July. • Sept. is borderline for exceedances; only once in ten years (2002).

5. Do the Front Range monitors predict for RMNP ? .....not very well

6. Conclusions from previous studies Past studies point to the need for O3 measurement within the Rocky Mountain National Park to: • determine spatial distribution • identify conditions under which exceedances occur • improve forecasting

7. Remote O3 Instrument Requirements • Solar powered • Small, easy to transport and install • Inbuilt datalogging • Low maintenance during Summer season • Low sensor drift

8. Ozone instrument based on WO3 sensor • Heated WO3 semiconductor sensor is a good candidate for low power ozone instrument. • WO3 shows resistance increase at elevated temperature in response to traces of ozone in air • high sensitivity and selectivity to O3 • Advantages • low power (800 mW) • robust, reliable to manufacture • gas response principles well understood • Challenges • cross-interferences, • temperature/humidity response.

9. Challenges solved - how ? • Precise sensor temperature control • Diagnostic: heater resistance • Two - temperature cycling to define initial state and then use a rate measurement to determine O3 • Air-flow modulation for continual zero drift correction • Diagnostic: heater power for air flow check; baseline resistance for sensor drift check

10. Typical WO3 Sensor Response to O3

11. Two-Temperature Operation Slow Response Constant T 2 -Temperature measure sample measure baseline Resistance Gas on Low T High T Time

12. Performance of measurement method

13. Ozone Sensor Fabrication Screen printed gold electrode structure Screen printed platinum heater track 2mm x 2mm alumina substrate WO3 deposited onto electrode structure

14. Ozone Sensor Fabrication 16 mm 12 mm

15. Ozone Module Design sensor pump electronics

16. Typical O3 instrument calibration co-located with reference photometer for 1 week

17. Summer 2010 RMNP Study Two Rocky Mountain National Park sites were chosen: • East side (Beaver Meadows) • AQM with single O3 module • installed 18 July 2010 until 12 October 2010 • West side (West Entrance) • AQM1 with dual O3 module installed 7 July 2010 until 27 August 2010 • AQM2 with dual O3 modules installed 27 August to 12 October 2010 • 2B Technologies UV photometer also co-located • No field calibrations or adjustments were made to the instruments over the length of the study.

18. June-Oct 2010 O3 Monitoring Locations

19. East Side Instrument

20. East side data Reference instrument at Longs Peak scatter plot y = 1.0517x - 9.9816 R2 = 0.6296 AQM at Beaver Meadows

21. West Side Dual O3 Instruments AQM1 & AQM2 Dual O3 modules, O3A O3B Datalogger Zero scrubber (not used) 12 VDC power PTFE filter Sample inlet T/RH sensor

22. West Side O3 O3A = red, O3B = blue AQM 1 AQM2 June July August Sep Oct

23. West side O3A vs O3B Scatter plots AQM1 O3B AQM2 O3B O3A O3A y = 0.9939x + 0.6441 R2 = 0.9984 y = 0.7984x + 2.6389 R2 = 0.9949

24. West side AQM 1 O3A and O3B vs 2B O3B O3A 2B 2B y = 1.0408x - 3.6776 R2 = 0.9508 y = 0.8355x - 0.4489 R2 = 0.9568 AQM1 O3B under- read

25. RMNP O3 East side vs West side • Both sites have daily ozone cycles of about 30 ppb (west) and 20+ ppb (east). • The east side ozone is 5‐10 ppb higher during the day and doesn’t go so low overnight.

26. East vs West max 8 hr O3 Neither site had an exceedance of the 75 ppb 8‐hr standard. The East site (red) had some peak days that were not high O3 days on the west side (blue).

27. Front Range O3 Longs Peak

28. RMNP O3 Spatial Relationships • Three 8 hr max O3 peaks seen on East Side at Beaver Meadows were also found at Longs Peaks station. But not identified at Boulder & Fort Collins stations. This suggests the events were associated with transport from west. • However, on West side the first two peaks arent seen although the third peak was. • It is unclear what the origin of the first two peaks at Beaver Meadows was and further work is underway.

29. Conclusions • Simple solar powered monitoring stations based on WO3 ozone sensors are a useful method to collect data in remote locations. • The instruments performed well in the field over the 5 month summertime period with no calibration or adjustment. • Differences in 8 hr max ozone concentrations between lower elevation Front Range and 2 sites in Rocky Mtn NP has been demonstrated. Reasons for the differences are unclear at this time. • Since summertime ozone at RMNP is not always associated with Front Range ozone, an O3 forecast for visitors needs to based on monitors within the Park.