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Changes in diurnal patterns related to changes in ozone levels
A S Lefohn1, J K Foley, D S Shadwick
1A.S.L. & Associates, Helena, Montana.
Air & Waste : Journal of the Air & Waste Management Association
|November 1, 1993
Summary
Ozone (O3) pollution impacts health and vegetation. Analysis shows improved air quality can alter O3 diurnal patterns, potentially increasing exposure hours in some areas, highlighting the need to evaluate these shifts.
Area of Science:
- Environmental Science
- Atmospheric Chemistry
- Public Health
Background:
- Ozone (O3) is a widespread air pollutant with known adverse effects on human health and vegetation.
- Concerns exist regarding prolonged human exposure to O3 levels exceeding established health effect thresholds, particularly in US nonattainment areas.
- Air quality improvements may inadvertently alter O3 diurnal profiles, potentially leading to increased multi-hour exposures at harmful levels.
Purpose of the Study:
- To investigate changes in the seasonally averaged diurnal pattern of ozone concentrations.
- To assess how these diurnal patterns shift in response to varying ozone levels and attainment status.
- To determine if altered diurnal profiles influence exposure durations at critical O3 concentration levels.
Main Methods:
- Analysis of aerometric data to examine the evolution of seasonally averaged diurnal ozone profiles.
- Statistical evaluation of changes in the shape of diurnal ozone patterns across different years and compliance statuses.
- Focus on sites in southern California and Dallas-Fort Worth, Texas, with documented O3 level improvements but continued nonattainment.
Main Results:
- Out of 36 sites that changed compliance status, 25 showed no significant alteration in their average diurnal ozone profile shape.
- A statistically significant change in the diurnal profile shape was observed in 71% (10 out of 14) of sites in southern California and Dallas-Fort Worth.
- These sites experienced O3 level improvements but remained in nonattainment, indicating a shift in the timing of peak concentrations.
Conclusions:
- Evaluating diurnal ozone patterns is crucial for understanding the interplay between emission changes and meteorological factors affecting air quality attainment.
- Improvements in O3 levels, particularly in nonattainment areas, can lead to significant modifications in the daily ozone concentration profile.
- Observed changes in seasonally averaged diurnal profiles in southern California and Dallas-Fort Worth underscore the complexity of O3 control strategy impacts.
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