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Weekend Effect Research. Ozone Precursor Trends (Chapter 5.2) April 13, 2000. Ozone Precursor Trends. Objectives of trend analysis: ID response of ozone to precursor changes ID spatial & temporal changes ID changes in chemistry. Ozone Precursor Trends. Methodology:

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Weekend Effect Research

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Weekend Effect Research

Ozone Precursor Trends

(Chapter 5.2)

April 13, 2000


Ozone Precursor Trends

  • Objectives of trend analysis:

    • ID response of ozone to precursor changes

    • ID spatial & temporal changes

    • ID changes in chemistry


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


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


Ozone Trends in SoCAB


Ozone Trends


Ozone Trends


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


Ozone Precursor Trends


Ozone Precursor Trends


Ozone Trends


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


Ozone Precursor Trends


Ozone Precursor Trends


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


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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