Goals

1. Trends in Ambient Ozone Concentrationsin the South Coast Air Basin, 1980-1998 Hien Tran & Lawrence C. LarsenPlanning and Technical Support DivisionCalifornia Air Resources BoardApril 13, 2000

2. Goals • To examine trends in ambient ozone over the years • To identify any pattern differences between days of the week • To identify any shift over time away from weekdays having highest ozone towards weekends having highest ozone

3. Data & Methods • use daily 1-hour maximum ozone for each site, 1980-1998 • average the 2nd to 11th highest ozone values for each DOW in each year • good indicator of ozone potential by DOW over the years • average similar weekdays (Mon - Thurs) to plot with Fri, Sat, Sun. • to explore patterns between DOW

4. Data & Methods, cont’d • average all weekdays (Mon-Fri) to plot versus all weekend days (Sat, Sun) • to assess rate of ozone improvement between weekdays and weekends

5. Results • maximum ozone values have decreased over the years regardless of DOW • rate of decrease for weekdays and weekends in 1980’s and in 1990’s is the same for some sites • Los Angeles, Lynwood, Anaheim • weekend ozone higher throughout 1980-98

6. Ex. of same rate of decrease

7. Results, cont’d • rate of decrease for weekends is lesser than for weekdays in 1990’s (compared to 1980’s) for some sites • Azusa, Burbank, Riverside, Pico Rivera, L. Gregory, Upland • weekday ozone decreased at a faster rate, leaving weekends as the higher

8. Ex. of different rate of decrease

9. Conclusions • ozone continues to decline on all days • rate of ozone decrease is faster for weekdays than for weekend days at certain sites and the same for others • some sites shifted highest ozone from weekdays to weekends in later years while others always showed highest ozone on weekends during 1980-98

10. Possible Further Work • our approach is basic and descriptive only • uncertainty estimates would help determine whether the differences are real (or statistically significant)