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Analyzing Ozone Precursor Trends and Their Impact on Ozone Levels: Weekend Effect Insights

This chapter investigates the trends in ozone precursor concentrations and their response to changes in emission levels from 1980 to 1997, focusing on the Southern California Air Basin (SoCAB). The analysis identifies spatial and temporal variations, responses of ozone concentrations to precursor changes, and highlights significant trends such as the decline in peak ozone levels and the weekend effect (WE). Findings indicate that mid-day ozone concentrations show different behaviors, with an emphasis on the need to understand changes around 1989 that significantly impacted air quality.

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Analyzing Ozone Precursor Trends and Their Impact on Ozone Levels: Weekend Effect Insights

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  1. Weekend Effect Research Ozone Precursor Trends (Chapter 5.2) April 13, 2000

  2. Ozone Precursor Trends • Objectives of trend analysis: • ID response of ozone to precursor changes • ID spatial & temporal changes • ID changes in chemistry

  3. Ozone Precursor Trends • Methodology: • hrly mean CO, NOX, NO, NO2, & O3, 1980-97 • Day of Week (DOW) -- Tue-Thur = mid-week • averaged into 6 equal Periods of Day (POD) • running 3-year means

  4. Ozone Precursor Trends • ID response of ozone to precursor change • SoCAB peak ozone has declined steadily • PM ozone declined in most areas of SoCAB • ozone decline for WDs appears WEs

  5. Ozone Trends in SoCAB

  6. Ozone Trends

  7. Ozone Trends

  8. Ozone Precursor Trends • ID spatial & temporal changes • mid-day NOX trends generally similar by DOW • 4-8 a.m. NOX trend often nearly flat in 1990s • O3 DOW “crossover” in late 1980s in eastern SoCAB

  9. Ozone Precursor Trends

  10. Ozone Precursor Trends

  11. Ozone Trends

  12. Ozone Precursor Trends • ID changes in chemistry: • mid-AM NOX trend often flat but late-AM & early-PM NOX & NO2 down in 1990s • NO2 trends by DOW match NOX trends by DOW at most sites - NO2/NOX constant by DOW during late-AM & early-PM

  13. Ozone Precursor Trends

  14. Ozone Precursor Trends

  15. Ozone Precursor Trends • Initial Findings: • peak ozone down irrespective of NOX trend • ozone WE Effect much greater in 1990s than earlier but no commensurately greater NOX WE Effect • DOW “crossover” (WE > WD) has now occurred at all sites in SoCAB

  16. Ozone Precursor Trends • Recommendation: • Investigate cause of step-wise change in mid-day ozone concentrations around 1989 as it accounts for much of ozone improvement and seems stronger for WDs than WEs.

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