The Pattern and Transport of Ozone in the Missouri Region

1
The Pattern and Transport of Ozone in the
Missouri Region
Prepared for a briefing of the Missouri Director
of Natural Resources
Rudolf Husar and Bret Schichtel CAPITA Washington
University April 9, 1997
The content of the report is based largely on the
analysis conducted by the OTAG Air Quality
Analysis Workgroup, including CAPITA. The
comments were adapted to emphasize the
conditions relevant to the state of Missouri.
Limited additional analysis was conducted to
document the Missouri region in more detail.
2
Missouri Ozone Concentrations and Background
Ozone Entering the OTAG Domain
Average ozone concentrations in Missouri are
elevated (50-65 ppb) compared to tropospheric
background (30-40 ppb) found at all four corners
of the OTAG domain. However, they are lower than
the Ohio River Valley and the Eastern Megalopolis
concentrations.
3
Pattern of Ozone Precursor Emissions
The high area source emission densities of NOx
are located in the vicinity of urban-metropolitan
areas such as St. Louis and Kansas City.
The high point source emission densities are
located mostly in the industrial Midwestern
states.
4
Changing Average O3 Concentrations from West to
East
West-east cross-section through
Kansas-Ohio-Maryland. Note the accumulation of
ozone from west to east.
Ozone concentration maps with west-east and
north-south cross-sections.
5
Areas of Violations (AOV) for 1hr-120 ppb and
8-hr-80 ppb Exceedances
Areas of violation for 1 hr - 120 ppb standard.
Areas of violation for 8 hr - 80 ppb standard.
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Average Daily Max and Exceedance Rose for Ozone
in St. Louis
The highest average ozone concentrations are to
the north and east of the city.
The exceedances tend to occur when the wind
direction is from the city.
7
Average Daily Max and Exceedance Rose for Ozone
in Kansas City
The highest average ozone concentrations are to
the east of the city.
The exceedances tend to occur when the wind
direction is from the city.
8
Origin of High Ozone Concentrations
The highest ozone concentrations occur in major
metropolitan areas, Washington- New York,
Atlanta, St. Louis and a large region near Ohio
River Valley.
9
Origin of High Ozone Concentrations, Cont.
Back trajectories for receptor sites for low
ozone days point to outside the OTAG region as
the source of low ozone.
Back trajectories for receptor sites for high
ozone days point to the central OTAG region as
the source of high ozone.
10
Role of Horizontal and Vertical Transport
Transport wind vector during low ozone days
indicate transport of clean air from outside the
OTAG region.
Transport wind vector during high ozone days
occurs when the winds are slow and variable,
except in the Northeast where they occur during
westerly winds.
11
St. Louis Transport Speed and Directions
Low ozone concentrations in St. Louis are
associated with ventilating flow from the
southwest.
High ozone concentrations in St. Louis are
associated with slower transport from the
east-southeast.
12
Kansas City Transport Speed and Directions
Low ozone concentrations are associated with
transport from the southwest as well as from the
northwest.
High ozone concentrations are associated with
slower transport predominantly from the
southwest.
13
Ozone Transport Visualization
Measured ozone concentration isopleths overlaid
with tracer particles tracking the atmospheric
flow.
14
Ozone in Urban and Power Plant Plumes
The St. Louis ozone plume measured on July 18,
1975. The excess ozone within the plume is 20-30
ppb.
Ozone production in a power plant plume on August
23, 1978. Ozone production begins after about 100
km.
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Spatial Pattern of High and Low Ozone
Concentrations
Spatial pattern of the 10th percentile of daily
max. ozone. Elevated ozone concentrations are
evident only in the Industrial Midwest.
Spatial pattern of the 90th percentile of daily
max. ozone. Highest ozone occurs in metropolitan
regions.
St. Louis and Kansas City impact their
surrounding only on high ozone days.
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Evidence that Precursor Emission Changes Cause
Ozone Changes
Map of exceedances on Fridays.
Map of exceedances on Sundays.
Any control strategy that mimics the
Weekday-Weekend Emission change would be
effective in reducing exceedances over 120 ppb.