Transcript Forecasting Air Quality in North Carolina

Forecasting Air Quality in
North Carolina
Bebhinn A. Do
Meteorologist
NC Division of Air Quality
April 27, 2006
Outline
• Fine Particulates (PM2.5) & Ozone (O3)
– What are they? & Where do they come from?
(Quick review)
• Nonattainment Areas
• Forecasting
– Forecast Areas
– The forecast products
– Meteorology 101
Fine Particles
• Also known as
– Fine particulates
– Fine particulate matter
– PM2.5
• And because we do not have any
PM10 nonattainment areas it is
sometimes referred to simply as particle
pollution
Size of Particles
Coarse Particles(PM10)
• Size: > 2.5 μm
• Smaller than a human
hair (70 μm)
Human hair (70 µm diameter)
Fine Particles (PM2.5)
• Forecast by the NC DAQ
• Greater health concern
• Size: < 2.5 μm
• Smaller than a human
hair
Human hair cross section (70 µm)
PM10
(10 µm)
PM2.5
(2.5 µm)
M. Lipsett, California Office of
Environmental Health Hazard Assessment
Sources of Fine Particles
• Combustion – Direct emission
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Fire places, Wood Stoves
Open burning (leaves, yard waste)
Vehicles ( mainly diesel-powered)
Industry
• Chemical transformation - Indirect emission
– Gases (e.g. SO2, Carbon, NH3, & NOX) condense &
combine in the air
Ozone
Stratospheric vs. Tropospheric Ozone
NC NOx Emissions, 2007 Base Future
Area
2%
Nonroad
23%
Point
44%
Mobile
31%
North Carolina VOC Emissions, 2007
Area
7%
Nonroad
2%
Mobile
3%
Biogenic
85%
Point
3%
Where Do We Have Problems
With Air Quality?
PM2.5 Nonattainment Areas
Ozone Nonattainment Areas
Forecast Areas
Forecast Products
• Color Coded Forecast
• AQI Numerical Forecast
( 0-50, 51-100, 101-150, 151-200, 201-300 )
• Forecast Discussion
• Technical Forecast Discussion
• Morning Edition
Forecasting Schedule
• 7 days a week
– May 1 – September 30 in Triangle, Fayetteville,
Rocky Mount, & Asheville (Ridge Tops & Valleys)
– Year round in Triad, Charlotte, & Hickory
• Daily Forecast Published at 3:05 pm EDT
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Emails sent at 3:10 pm EDT
Forecast Discussion (public) by 3:30 pm EDT
Technical Discussion (hidden) by 5:00 pm EDT
Morning Edition at 10:00 am EDT
• Weekend Outlook – Thursday through Saturday
Forecasting Technique
• Complete weather analysis and a solid
weather forecast
• Assess the current pollutant scenario in
concert with the weather conditions
• Apply knowledge of the pollutant
behavior under the expected weather
conditions
Forecasting Process
• 100 MB of met data downloaded per day !
• Over 100 CD’s with met data since May 1, 1999
• What meteorological factors help ozone
formation?
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Sunny skies
Warm or hot temperatures
Light winds
Stable atmospheric conditions aloft
Dry/low dew points
• Mitigating factors
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Clouds and precipitation
Windy or breezy conditions
Convectively unstable atmosphere
Frontal Passage
High Pressure
• What meteorological factors help PM2.5?
– Light winds
– Stable atmospheric conditions aloft
• Mitigating factors
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Source region
Windy or breezy conditions
Convectively unstable atmosphere
Frontal Passage
• Moisture
High Pressure
Meteorology 101
• High Pressure
– Circulation Patterns
– Affect on sensible weather
• Winds
– Horizontal advection
– Vertical Advection
• Temperature Inversions
• Cold Fronts
– Rain
– Clouds
Pressure Systems
N
Subsidence
Lift/convection
z
High Pressure
• Subsidence associated with high
pressure systems lead to :
– Clear, sunny skies
– Light winds
– Can last for several days, keeping pollution
in the same region
• Stacked highs
Winds
• Why are the winds important?
– Can move the pollution from state to state
(Horizontal advection)
– Can move the pollution vertically
(Convection or vertical mixing)
• “Mix out” or dilute concentrations
• Can even cause an increase in concentrations
Horizontal Dispersion
• Boundary layer winds
– Profiler observations
– BUFKIT – viewing model data
• Transport
– Trajectories
BUFKIT
Back Trajectories
24-hr Back Trajectory
Monday, June 10, 2002
Re-Circulation Of The Winds
Forward Trajectories
Vertical Mixing
• Convective mixing
• Inversions
Meteorology 101
Convective mixing
Meteorology 101
Temperature Inversions
Inversions and Mixing
Temperature soundings
Weak and high inversion
Height
Inversion Breaks
RL
CBL
NBL
Midnight
NBL
Sunrise
Sunset
Height
Inversion Holds
Strong and low inversion
RL
CBL
NBL
Midnight
NBL
Sunrise
RL = Residual Layer
CBL = Convective Boundary Layer
NBL = Nocturnal Boundary Layer
Pollutants mix
into a large
volume resulting
in low pollution
levels
Sunset
= Surface-based mixing depth
= Surface-based vertical mixing
Pollutants mix
into a smaller
volume
resulting in
high pollution
levels
Inversion Frequency
Cold Fronts
• Can cause mixed reactions in pollution:
– Phenomena known as “prefrontal build up”
can increase concentrations
– Exchange a dirty air mass for a cleaner
one
– Cloud and rain can reduce pollution
concentrations
Prefrontal Build Up
Fronts
• Fronts are borders between different air
masses, usually distinguishing different
points of origin.
• The air mass trailing a cold front is often
clean air from the Canada or the central
plains, where there is little pollution.
Fronts
• Due to the nature of fronts (focus for lift) they
are accompanied by clouds and often rain.
• Clouds reduce ozone by limiting the sun
available for the photochemical reaction.
• A steady rain can “wash out” particles
suspended in the air, reducing PM2.5 values.
What else do we consider?
• Diurnal Variation
• Emission/AQ Response
– Day of week, diurnal profiles,
special events
• Special & Unexpected Events
• Climatology
Diurnal Ozone Profile
• Ozone levels are typically lowest in the
morning before sunrise
• Rapid increase of ozone during the midmorning hours as sunshine intensifies
• Peak ozone concentrations are found in
the early afternoon during maximum
solar influx
• Ozone slowly starts to decrease in the
afternoon as sunshine decreases
• This is what we would expect…
Diurnal Ozone Profile
“Reverse” Diurnal Trend
• Exhibited at high elevation monitors
• Highest ozone levels occur at night
– Trapped above surface inversion
– No dispersion
– No deposition
Diurnal Ozone Profile
Diurnal Variation
• Ozone peaks in the middle of the day, when the sun’s
rays are strongest.
• Seasonally, ozone typically peaks from July to
August, when days are the longest and hottest.
• Because the length of the day grows shorter over the
winter, ozone precursors do not have enough
daylight hours to react and produce ozone to levels
similar to the summer. As a result, the ozone
forecasting season is limited to May 1 through
September 30. (monitoring starts in April and runs
through October)
• PM2.5 does not have such a limitation.
Day of Week Emissions
• Significant mobile
emissions factor during
Monday through Friday
commuter pattern
• Combined increase of
small to medium sized
industrial point sources
during workweek
• Overall emissions
reduction on Sunday,
especially in the AM
hours
Special & Unexpected Events
• Memorial Day, July 4th, and Labor Day
are usually semi-quiet ozone
exceedance days. (reduced vehicle
emissions)
• Coca-Cola 600 NASCAR race weekend
in Charlotte is the exception during the
Memorial Day holiday
• New Year’s Eve and the Fourth of July
will show spikes in the PM2.5 data due
to fireworks.
Special & Unexpected Events
July 4, 2005
180
160
140
Concentration (mg/m ^3)
120
100
NC1 HICKORY
NC2 GARINGER
NC2 Montclaire
80
60
40
20
0
0
1
2
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10 11 12 13 14 15 16 17 18 19 20 21 22 23
Hour
Special & Unexpected Events
• Tropical weather systems can create
subsidence on their outer fringe, driving
ozone values up.
Special & Unexpected Events
• In addition, debris
burning afterward will
affect PM2.5 values
Special & Unexpected Events
• Major power loss during ice storms can
also cause spikes in PM2.5, as people
begin to use their fireplaces to heat their
homes.
• Forest fires also offer the potential for
huge forecast busts in the PM2.5 / fine
particulate arena
Special & Unexpected Events
Forecast
• We weigh all the factors we have
discussed and then . . .
Questions/comments
• Forecast:
– http://daq.state.nc.us/airaware/forecast/
( Follow the links )
– Call 1-888-RU4NCAIR ( 784-6224 )
• Points of Contact
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[email protected]
715 - 0921
[email protected] 715 - 6287
[email protected]
715 - 9773
[email protected]
715 – 2106
[email protected]
[email protected]