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 RayNational Park Service, Air Resources Division, Denver, Colorado 1

Structure What do we know from previous studies of Rocky Mountain National Park Ozone ? Design and Performance of Remote Ozone instrument Field Study of Summertime O 3 Conclusions

RMNP O 3 Monitoring Locations

Are O 3 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).

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

Conclusions from previous studies Past studies point to the need for O 3 measurement within the Rocky Mountain National Park to: determine spatial distribution identify conditions under which exceedances occur improve forecasting

Remote O 3 Instrument Requirements Solar powered Small, easy to transport and install Inbuilt datalogging Low maintenance during Summer season Low sensor drift

Ozone instrument based on WO 3 sensor Heated WO 3 semiconductor sensor is a good candidate for low power ozone instrument. –WO 3 shows resistance increase at elevated temperature in response to traces of ozone in air –high sensitivity and selectivity to O 3 Advantages –low power (800 mW) –robust, reliable to manufacture –gas response principles well understood Challenges –cross-interferences, –temperature/humidity response.

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 O 3 Air-flow modulation for continual zero drift correction –Diagnostic: heater power for air flow check; baseline resistance for sensor drift check

Typical WO 3 Sensor Response to O 3

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

Performance of measurement method

Ozone Sensor Fabrication Screen printed platinum heater track Screen printed gold electrode structure WO 3 deposited onto electrode structure 2mm x 2mm alumina substrate

Ozone Sensor Fabrication 16 mm 12 mm

Ozone Module Design electronicspump sensor

Typical O 3 instrument calibration co-located with reference photometer for 1 week

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.

June-Oct 2010 O 3 Monitoring Locations

East Side Instrument

East side data Reference instrument at Longs Peak AQM at Beaver Meadows scatter plot y = x R2 =

West Side Dual O 3 Instruments AQM1 & AQM2 Dual O3 modules, O3A O3B Datalogger Zero scrubber (not used) 12 VDC power Sample inlet T/RH sensor PTFE filter

West Side O3 AQM 1 AQ M2 O3A = red, O3B = blue June July August Sep Oct

West side O3A vs O3B Scatter plots y = x R2 = y = x R2 = O3A O3B O3A AQM1 AQM2

West side AQM 1 O3A and O3B vs 2B y = x R2 = y = x R2 = AQM1 O3B under- read 2B O3A O3B

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.

East vs West max 8 hr O 3 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).

Front Range O3 Longs Peak

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.

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.