Forecasting Air Quality in Forecasting Air Quality in North CarolinaNorth Carolina

Bebhinn A. Do Bebhinn A. Do MeteorologistMeteorologist

NC Division of Air QualityNC Division of Air Quality

April 27, 2006April 27, 2006

OutlineOutline

• Fine Particulates (PMFine Particulates (PM2.52.5) & Ozone (O) & Ozone (O33))– What are they? & Where do they come What are they? & Where do they come

from?from?

(Quick review)(Quick review)

• Nonattainment AreasNonattainment Areas• Forecasting Forecasting

– Forecast AreasForecast Areas– The forecast productsThe forecast products– Meteorology 101 Meteorology 101

Fine ParticlesFine Particles

• Also known asAlso known as– Fine particulatesFine particulates– Fine particulate matter Fine particulate matter – PM2.5PM2.5

• And because we do not have any And because we do not have any PM10 nonattainment areas it is PM10 nonattainment areas it is sometimes referred to simply as sometimes referred to simply as particle pollution particle pollution

Size of ParticlesSize of ParticlesCoarse Coarse

Particles(PM10)Particles(PM10)• Size: > 2.5 Size: > 2.5 μmμm• Smaller than a Smaller than a

human hair (70 human hair (70 μμm) m)

Fine Particles (PM2.5)Fine Particles (PM2.5)• Forecast by the NC DAQForecast by the NC DAQ• Greater health concernGreater health concern• Size: < 2.5 Size: < 2.5 μμmm• Smaller than a human hairSmaller than a human hair

Human hair (70 µm diameter) Human hair cross section (70 µm)

PM2.5

(2.5 µm)

PM10

(10 µm)

M. Lipsett, California Office of Environmental Health Hazard Assessment

Sources of Fine ParticlesSources of Fine Particles

• Combustion – Direct emissionCombustion – Direct emission– Fire places, Wood StovesFire places, Wood Stoves– Open burning (leaves, yard waste)Open burning (leaves, yard waste)– Vehicles ( mainly diesel-powered)Vehicles ( mainly diesel-powered)– IndustryIndustry

• Chemical transformation - Indirect emissionChemical transformation - Indirect emission– Gases (e.g. SO2, Carbon, NH3, & NOX) condense & Gases (e.g. SO2, Carbon, NH3, & NOX) condense &

combine in the aircombine in the air

OzoneOzone

Stratospheric vs. Tropospheric Stratospheric vs. Tropospheric OzoneOzone

NC NOx Emissions, 2007 Base Future

Area2%

Nonroad23%

Mobile31%

Point44%

North Carolina VOC Emissions, 2007

Area7%

Nonroad2%

Mobile3%

Point3%

Biogenic85%

Where Do We Have Where Do We Have Problems With Air Quality? Problems With Air Quality?

PM2.5 Nonattainment PM2.5 Nonattainment AreasAreas

Ozone Nonattainment Ozone Nonattainment AreasAreas

Forecast AreasForecast Areas

Forecast ProductsForecast Products• Color Coded Forecast

• AQI Numerical Forecast ( 0-50, 51-10051-100, 101-150, 151-200, 201-300 )

• Forecast Discussion• Technical Forecast Discussion• Morning Edition

Forecasting ScheduleForecasting 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

– 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 TechniqueForecasting 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 ProcessForecasting 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 What meteorological factors help ozone formation?formation?– Sunny skiesSunny skies– Warm or hot temperaturesWarm or hot temperatures– Light windsLight winds– Stable atmospheric conditions aloftStable atmospheric conditions aloft– Dry/low dew pointsDry/low dew points

• Mitigating factorsMitigating factors– Clouds and precipitationClouds and precipitation– Windy or breezy conditionsWindy or breezy conditions– Convectively unstable atmosphereConvectively unstable atmosphere– Frontal PassageFrontal Passage

High Pressure

• What meteorological factors help What meteorological factors help PM2.5?PM2.5?– Light windsLight winds– Stable atmospheric conditions aloftStable atmospheric conditions aloft

• Mitigating factorsMitigating factors– Source region Source region – Windy or breezy conditionsWindy or breezy conditions– Convectively unstable atmosphereConvectively unstable atmosphere– Frontal PassageFrontal Passage

• MoistureMoisture

High Pressure

Meteorology 101Meteorology 101• High Pressure High Pressure

– Circulation PatternsCirculation Patterns– Affect on sensible weatherAffect on sensible weather

• WindsWinds– Horizontal advection Horizontal advection – Vertical AdvectionVertical Advection

• Temperature InversionsTemperature Inversions

• Cold FrontsCold Fronts– RainRain– CloudsClouds

Pressure SystemsPressure Systems

N

Subsidence Lift/convection

z

High PressureHigh Pressure

• Subsidence associated with high Subsidence associated with high pressure systems lead to : pressure systems lead to : – Clear, sunny skies Clear, sunny skies

– Light windsLight winds

– Can last for several days, keeping Can last for several days, keeping pollution in the same regionpollution in the same region

• Stacked highsStacked highs

WindsWinds

• Why are the winds important? Why are the winds important? – Can move the pollution from state to Can move the pollution from state to

state (Horizontal advection)state (Horizontal advection)– Can move the pollution vertically Can move the pollution vertically

(Convection or vertical mixing)(Convection or vertical mixing)• ““Mix out” or dilute concentrationsMix out” or dilute concentrations• Can even cause an increase in Can even cause an increase in

concentrationsconcentrations

Horizontal DispersionHorizontal Dispersion

• Boundary layer winds– Profiler observations– BUFKIT – viewing model data

• Transport– Trajectories

BUFKITBUFKIT

Back TrajectoriesBack Trajectories

24-hr Back Trajectory24-hr Back TrajectoryMonday, June 10, 2002Monday, June 10, 2002

Re-Circulation Of The WindsRe-Circulation Of The Winds

Forward TrajectoriesForward Trajectories

Vertical MixingVertical Mixing

• Convective mixing

• Inversions

Meteorology 101Meteorology 101

Convective mixingConvective mixing

Meteorology 101Meteorology 101

Temperature InversionsTemperature Inversions

Inversions and MixingInversions and Mixing

Pollutants mix into a large volume resulting in low pollution levels

RL = Residual LayerCBL = Convective Boundary LayerNBL = Nocturnal Boundary Layer = Surface-based vertical mixing

= Surface-based mixing depth

Hei

gh

t

Temperature soundings

Midnight

Weak and high inversion

Sunrise Sunset

CBL

Inversion Breaks

NBLNBL

RL

Sunrise SunsetMidnight

Hei

gh

t

Pollutants mix into a smaller volume resulting in high pollution levels

Strong and low inversion

CBL RL

Inversion Holds

NBL NBL

Inversion FrequencyInversion Frequency

Cold FrontsCold Fronts

• Can cause mixed reactions in Can cause mixed reactions in pollution:pollution:– Phenomena known as “prefrontal Phenomena known as “prefrontal

build up” can increase concentrationsbuild up” can increase concentrations– Exchange a dirty air mass for a Exchange a dirty air mass for a

cleaner onecleaner one– Cloud and rain can reduce pollution Cloud and rain can reduce pollution

concentrationsconcentrations

Prefrontal Build UpPrefrontal Build Up

FrontsFronts

• Fronts are borders between Fronts are borders between different air masses, usually different air masses, usually distinguishing different points of distinguishing different points of origin.origin.

• The air mass trailing a cold front is The air mass trailing a cold front is often clean air from the Canada or often clean air from the Canada or the central plains, where there is the central plains, where there is little pollution.little pollution.

FrontsFronts

• Due to the nature of fronts (focus for Due to the nature of fronts (focus for lift) they are accompanied by clouds lift) they are accompanied by clouds and often rain.and often rain.

• Clouds reduce ozone by limiting the sun Clouds reduce ozone by limiting the sun available for the photochemical available for the photochemical reaction.reaction.

• A steady rain can “wash out” particles A steady rain can “wash out” particles suspended in the air, reducing PM2.5 suspended in the air, reducing PM2.5 values. values.

What else do we What else do we consider?consider?

• Diurnal VariationDiurnal Variation• Emission/AQ ResponseEmission/AQ Response

– Day of week, diurnal profiles, Day of week, diurnal profiles, special eventsspecial events

• Special & Unexpected EventsSpecial & Unexpected Events• ClimatologyClimatology

• Ozone levels are typically lowest in Ozone levels are typically lowest in the morning before sunrisethe morning before sunrise

• Rapid increase of ozone during the Rapid increase of ozone during the mid-morning hours as sunshine mid-morning hours as sunshine intensifiesintensifies

• Peak ozone concentrations are Peak ozone concentrations are found in the early afternoon during found in the early afternoon during maximum solar influxmaximum solar influx

• Ozone slowly starts to decrease in Ozone slowly starts to decrease in the afternoon as sunshine decreasesthe afternoon as sunshine decreases

• This is what we would expect…This is what we would expect…

Diurnal Ozone ProfileDiurnal Ozone Profile

Diurnal Ozone ProfileDiurnal Ozone Profile

““Reverse” Diurnal TrendReverse” Diurnal Trend

• Exhibited at high elevation Exhibited at high elevation monitorsmonitors

• Highest ozone levels occur at nightHighest ozone levels occur at night– Trapped above surface inversionTrapped above surface inversion– No dispersionNo dispersion– No depositionNo deposition

Diurnal Ozone ProfileDiurnal Ozone Profile

Diurnal VariationDiurnal Variation• Ozone peaks in the middle of the day, when Ozone peaks in the middle of the day, when

the sun’s rays are strongest. the sun’s rays are strongest. • Seasonally, ozone typically peaks from July to Seasonally, ozone typically peaks from July to

August, when days are the longest and August, when days are the longest and hottest. hottest.

• Because the length of the day grows shorter Because the length of the day grows shorter over the winter, ozone precursors do not have over the winter, ozone precursors do not have enough daylight hours to react and produce enough daylight hours to react and produce ozone to levels similar to the summer. As a ozone to levels similar to the summer. As a result, the ozone forecasting season is limited result, the ozone forecasting season is limited to May 1 through September 30. (monitoring to May 1 through September 30. (monitoring starts in April and runs through October)starts in April and runs through October)

• PM2.5 does not have such a limitation.PM2.5 does not have such a limitation.

Day of Week EmissionsDay of Week Emissions

• Significant mobile Significant mobile emissions factor emissions factor during Monday during Monday through Friday through Friday commuter patterncommuter pattern

• Combined increase Combined increase of small to medium of small to medium sized industrial point sized industrial point sources during sources during workweekworkweek

• Overall emissions Overall emissions reduction on reduction on Sunday, especially Sunday, especially in the AM hoursin the AM hours

• Memorial Day, July 4Memorial Day, July 4thth, and Labor Day , and Labor Day are usually semi-quiet ozone are usually semi-quiet ozone exceedance days. (reduced vehicle exceedance days. (reduced vehicle emissions)emissions)

• Coca-Cola 600 NASCAR race Coca-Cola 600 NASCAR race weekend in Charlotte is the weekend in Charlotte is the exception during the Memorial Day exception during the Memorial Day holidayholiday

• New Year’s Eve and the Fourth of July New Year’s Eve and the Fourth of July will show spikes in the PM2.5 data will show spikes in the PM2.5 data due to fireworks.due to fireworks.

Special & Unexpected EventsSpecial & Unexpected Events

Special & Unexpected EventsSpecial & Unexpected EventsJuly 4, 2005

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0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23

Hour

Con

cent

ratio

n (m

g/m

^3)

NC1 HICKORY

NC2 GARINGER

NC2 Montclaire

Special & Unexpected EventsSpecial & Unexpected Events

• Tropical weather systems can Tropical weather systems can create subsidence on their outer create subsidence on their outer fringe, driving ozone values up. fringe, driving ozone values up.

Special & Unexpected EventsSpecial & Unexpected Events

• In addition, debris In addition, debris burning afterward will burning afterward will affect PM2.5 valuesaffect PM2.5 values

Special & Unexpected EventsSpecial & Unexpected Events

• Major power loss during ice storms Major power loss during ice storms can also cause spikes in PM2.5, as can also cause spikes in PM2.5, as people begin to use their fireplaces people begin to use their fireplaces to heat their homes. to heat their homes.

• Forest fires also offer the potential Forest fires also offer the potential for huge forecast busts in the for huge forecast busts in the PM2.5 / fine particulate arena PM2.5 / fine particulate arena

Special & Unexpected EventsSpecial & Unexpected Events

ForecastForecast• We weigh all the factors we have We weigh all the factors we have

discussed and then . . .discussed and then . . .

Questions/commentsQuestions/comments• Forecast: Forecast:

– http://daq.state.nc.us/airaware/forecast/http://daq.state.nc.us/airaware/forecast/( Follow the links )( Follow the links )

– Call 1-888-RU4NCAIR Call 1-888-RU4NCAIR ( 784-6224 )( 784-6224 )

• Points of ContactPoints of Contact– Bebhinn.Do@ncmail.net 715 - 0921Bebhinn.Do@ncmail.net 715 - 0921– George.Bridgers@ncmail.net 715 - 6287George.Bridgers@ncmail.net 715 - 6287– Patrick.Oreilly@ncmail.net 715 - 9773Patrick.Oreilly@ncmail.net 715 - 9773– Nick.Witcraft@ncmail.net 715 – 2106Nick.Witcraft@ncmail.net 715 – 2106– Ozone.Forecaster@ncmail.netOzone.Forecaster@ncmail.net– air.awareness@ncmail.netair.awareness@ncmail.net