PM 2.5 Forecasting Method Development and Operations for Salt Lake City, Utah

1. PM2.5 Forecasting Method Development and Operations for Salt Lake City, Utah Presented by Timothy S. Dye Dianne S. Miller Craig B. Anderson Clinton P. MacDonald Charley A. Knoderer Beverly S. Thompson Sonoma Technology, Inc. Petaluma, CA (707) 665-9900 www.sonomatech.com tim@sonomatech.com Presented at EPA’s National Air Quality Conference: Mapping and Forecasting San Francisco, CA February 4-6, 2002 901491-2146

2. Objective and Outline • Objective: Develop PM2.5 forecasting methods and forecast PM2.5 for Salt Lake City area during winter 2002 • Outline: • Data analysis • Forecasting method (tool) development • Operational forecasting • Initial results • Data issues • Future plans

3. Data Analysis • Description of data sources • PM2.5 and PM10 data (AIRS database) • Winter months (Oct. – Mar.) • 5 years of PM10 data (1996 – 2001) • 2 to 4 years of PM2.5 data (1998 – 2001) • 14 sites with PM10 data, 16 sites with PM2.5 data • Used only the 24-hr filter data • Continuous PM2.5 and PM10 data from three TEOM monitors (1999 – 2001) • Meteorological data (NOAA) • 5 years of hourly surface observations and upper-air soundings from Salt Lake City airport • Daily Weather Maps • Data processing • Performed quality control checks and time/units standardization • Used an MS Access database to store raw and computed data values

4. Data Analysis

5. Data Analysis • Developed a climatology: Examined the frequency and characteristics of PM episodes in Salt Lake City • Examined the following based on an AQI computed from PM2.5: • Yearly trend • Monthly frequency • Day of week frequency • Overview of results Higher PM2.5 tends to occur • on Thursday – Sunday • in December and January Average monthly distribution of AQI categories (based on PM2.5) for Salt Lake City

6. Data Analysis Day-of-week frequency for AQI categories (based on PM2.5) in the Salt Lake City region (1998-2001)

7. Forecasting Method Development • Analyzed PM2.5 episodes for general relationships in weather conditions and identified several important variables • 500-mb pattern (ridge or trough overhead) • Strength and duration of temperature inversion • Surface wind speed and direction • Developed forecast guidelines based on these variables (subjective) • Developed regression equations and Classification and Regression Tree (objective)

8. Forecast Guidelines Forecast PM2.5 ranges and associated meteorological conditions

9. Forecasting Method Development Objective Tools • Produced scatter plots of PM2.5 and meteorological data • Ran CART and linear regression to develop equations • Resulting regression equation: Next Day PM2.5 = 53.4 + 3.4*Holiday – 0.2*Precip – 0.5*WSday + 1.0*(700T12Z – Tmin) + 0.8*(700T00Z – Tmax) + 0.2*700Td00Z – 0.3*850WS00Z – 0.3*Tmax • Checked physical relationship between each variable and PM2.5 • Tested both techniques operationally during two weeks of forecasting

10. Monitoring Sites Utah DEQ AQ and Met Data Acquisition and Dissemination STI Weather Center E-mail forecast to Utah DEQ - Data collection - Formatting - Quality control - 24-hr average calcs. - Conversion factor - AQI calculations - Forecast creation STI SmogWatch web page for Salt Lake City FTP Phone

11. Daily Forecasting 0900 - 1000 MST • Verify that current data is being received 1100 MST • Review previous day’s observations and forecast • Review current day’s AQ data, weather forecast data, and NWS discussions • Run regression equation • Run CART • Create and review current- and next-day forecasts 1200 MST • E-mail forecast to UDEQ Afternoon • Monitor conditions for any dynamic changes

12. Forecast Dissemination Sample Daily E-mail Daily PM2.5 Forecast for Salt Lake City, UT Today's Date: January 25, 2002 Yesterday's regional maximum AQI: 49 (15 ug/m3) - Good Today's forecasted regional maximum AQI: 60 (20 ug/m3) - Moderate Tomorrow's forecasted regional maximum AQI: 60 (20 ug/m3) - Moderate Discussion: The upper-level low pressure system that was expected to move towards Utah today has slowed some resulting in a stronger inversion than originally anticipated. The models keep the inversion intact today despite increased winds aloft. This will result in Moderate PM2.5 values for today. The upper-level low pressure system moves towards Utah tomorrow increasing winds aloft; however, the inversion is forecasted to remain intact through Sunday resulting in Moderate PM2.5 levels. Forecaster: Charley Knoderer Sonoma Technology, Inc. (707) 665-9900

13. Forecast Dissemination Salt Lake City SmogWatch Web Page

14. Initial Results Slight tendency to overpredict the next-day forecast

15. Data Issues • Continuous PM2.5 values from the TEOMs can be significantly less than the FRM filter values. Difference varies, based on several meteorological parameters. • Continuous PM2.5 monitoring network is limited - only one site in each air basin. • How to communicate hourly AQI when “standard” is based on a 24-hour average?

16. Collocated TEOM (continuous) and FRM (filter) TEOM PM2.5 underestimates the FRM Continuous data underestimates AQI categories Data Issues: TEOM vs. FRM PM2.5 Continuous vs. Filter Intercomparison for the Lindon site (24-hr average data from December to March of 1999, 2000, and 2001) Unhealthy USG Moderate R2 = 0.63 R2 = 0.63

17. Adjusted TEOM data using a site specific regression equation that incorporated temperature and humidity Reduces underestimation by TEOM Unhealthy USG Moderate R2 = 0.84 Data Issues: TEOM vs. FRM Adjusted PM2.5 Continuous vs. Filter Intercomparison for the Lindon site (24-hr average data from December to March of 1999, 2000, and 2001) Tc = –1.98 + 1.08 TEOM – 0.67 Avg. Temp. + 0.08 Avg. RH

18. Next Steps • Implement relative humidity and temperature conversion factor to adjust continuous TEOM data to better match FRM filter data. • Continue forecasting until March 1 • Modify and adjust forecasting tools as “new truths” are learned • Continue to evaluate forecast performance • Acknowledgments • Utah Department of Environmental Quality • U.S. Environmental Protection Agency