OTAG Air Quality Analysis Workgroup

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OTAG Air Quality Analysis Workgroup
Telling the OTAG Ozone Story with Data

Dave Guinnup and Bob Collom, Workgroup co-chair
Volume I EXECUTIVE SUMMARY
Draft, June 2, 1997
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Workgroup Objective
The Workgroup is to provide assessments of air
quality and meteorological data relevant to the
mission of OTAG.
OTAG mission To understand the role of
transported ozone and precursors in the current
ozone nonattainment problem
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Description of the Air Quality Analysis WG

• AQA WG members were affiliated with EPA, state
  agencies, industry (power,transportation),
  consultants, academia
• Members were analysts or research managers
  generally representing their organizations (??)
• Interaction occurred through meetings, conference
  calls (monthly), and e-mail
• Sharing of reports, data and comments was
  conducted through the AQA-WG interactive web
  site. (http\\capita.wustl.edu\OTAG\)

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Types of Analyses

• Spatial pattern percentile analyses
• Trajectory residence time analyses
• Spatial, temporal correlation analyses
• Statistical cluster analyses
• Model/data comparisons
• Tracer analyses
• Temporal pattern and trends analyses
• Meta analysis analysis of analysis
• Results integration

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Problem Statement
From the OTAG Background Document

• Some nonattainment areas (e.g. NE corridor, Lake
  Michigan) experience considerable influx of ozone
  across their boundaries
• They cannot demonstrate nonattainment by local
  measures only
• Significant ozone reductions at their boundaries
  will also be necessary

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Counties not meeting the 80 ppb standard are more
numerous. Therefore, impacts of one area on
another are more likely.
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Area source NOx emissions are highest near
cities.Point sources dominate the center of
OTAG.
Area Source Density of NOx
Point Source Density of NOx
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The OTAG domain corners are at tropospheric O3
levels. The highest avg. O3 is over the
megalopolis and Ohio Valley.There is an
increasing trend from west to east.
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Highest (90 -ile) O3 occurs near urban
areas.Lowest (10 -ile) ozone is high in the
central domain.
10th percentile of daily max.ozone
90th percentile of daily max.ozone
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Northeast O3 exceedances have been
declining.OTAG domain exceedances show less
decline.
Ten year station-day exceedances for the
Northeast.
Ten year station-day exceedances for the OTAG
domain.
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At slow wind speeds, O3 accumulates near source
areas.At high wind speeds, O3 is dispersed from
sources.The dispersion leads to long range
transport and regional O3.
Average ozone during high (gt6 m/s) wind speeds.
Average ozone during low ( lt 3 m/s) wind speeds.
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In the Northeast, regional O3 is transported
mainly through synoptic and channeled flows while
local O3 is moved by near surface flows.
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On high O3 days, the transport winds are slow
with clockwise circulation around the
south-center of the domain.On low O3 days, the
swift transport winds are from outside the domain.
Transport winds during high (90-ile) local ozone
days.
Transport winds during low (10-ile) local ozone
days.
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During regional episodes, air masses meander over
the high emission regions and accumulate O3.The
88,91,95 modeling episodes lasted 6-9 days.
Ozone pattern and air mass histories during the
1995 episode.
Daily maximum ozone averaged over all monitors in
the domain.
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OTAG-wide episodes tend to be associated with
stagnation followed by transport.
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The 4 episode avg. model concentration shows high
O3 over the central section of the domain. The
measured O3 pattern roughly corresponds to the
model.
Model-average daily maximum O3 during the four
episodes.
Measured average daily maximum O3 during the four
episodes.
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The model underpredicts O3 in the North and
overpredicts in the South by 10-20 ppb.The
modeling periods over-represent O3 in the North
and under-represent O3 in the South.
Difference between the OTAG domain episodes and
the 90th percentile O3.
Difference between UAM-V model prediction and
measured O3.
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Transport winds during the 91,93,95 episodes
are representative of region scale episodes.OTAG
episode transport winds differ from winds at high
local O3 levels.
Comparison of transport winds during the 91,
93, 95 episodes with winds during regional
episodes in general.
Comparison of transport winds during the 91,
93, 95 episodes with winds during locally high
O3.
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OTAG is a well defined control region. Low O3 air
comes from outside, high O3 air from inside OTAG.
Back trajectory frequencies for low ozone days.
Back trajectory frequencies for high ozone days.
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The transport winds on high O3 days are slow in
the center of the domain.At many sites, the avg.
O3 is higher when the wind blows from the center
of the domain.
Ozone roses for selected 100 mile size
sub-regions.
Superposition of O3 contours and transport winds
during high (90th percentile) O3 conditions.
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Emission changes do change O3 levels. 120 ppb
exceedances are 3Xs higher on Fridays than on
Sundays.
Map of exceedances on Fridays.
Map of exceedances on Sundays.
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Conclusions

• Transport is real, characterized by time and
  space scales as noted
• Spatially, transport from central portion of OTAG
  domain more closely associated with high ozone
  levels
• Model may understate transport impacts --
  interpret results accordingly