operational use of air quality numerical forecast model guidance
DESCRIPTION
Operational Use of Air Quality Numerical Forecast Model Guidance. William Ryan Michelle Palmer Department of Meteorology The Pennsylvania State University. International Workshop on Air Quality Forecasting Research Boulder, CO December, 2009. What Do We Forecast?. - PowerPoint PPT PresentationTRANSCRIPT
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Operational Use of Air Quality Numerical Forecast Model Guidance
William RyanMichelle Palmer
Department of MeteorologyThe Pennsylvania State University
International Workshop on Air Quality Forecasting ResearchBoulder, CO December, 2009
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What Do We Forecast?
Forecasts are verified by peak 8-hour averaged O3 at location of
state and local monitors
While model forecast location of peak O3
is of interest, air quality alert applies toentire metropolitan area in order to
reduce emissions as well as protect health
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Complex Land-Sea Boundary Effects
Numerical O3 models (NAQC shown at right) often forecast high
O3 along land-sea boundaries.
These areas of high concentrationscan “bleed” inland.
First Order Post-Processing: Restrict domain peak O3
guidance to location of monitors.
Can retrieve “point” data quicklyfrom www/weather.gov/aq
using Firefox
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Philadelphia O3 Monitor Network (2007-2009)
NAQC “Forecast” is peak8-h O3 at location of
monitors.
Addition of “proxy” monitorsin locations with less dense
coverage does not affectresults.
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Numerical Forecast Model Guidance: NAQC Model Changes During Period of Interest
2007 2008 2009
Emissions Updated Yearly (May)
NAQC Upgrade : Sept, 2007 (Experimental Operational)BC, ACM PBL, NAM photolysis
NAM Upgrade: Mar, 2008 (horizontal advection, AIRS radiance, soil moisture)
NAM Upgrade: Dec, 2008 (GDAS, absorption coefficient water, ice)
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NAQC Forecast Skill in PHL 2007-2008
PHL NAQC Forecastsr r2
2007 0.76 0.582008 0.76 0.58
Bias Median AE Mean AE0
2
4
6
8
10
12
20072008
NAQC Forecast Error for PHL Area(2007-2008)
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Ladder of Simple Post Processing in the Operational Environment
Temperature/O3 Correction
“Poor Man’s” Ensemble
Trend Adjustment
Running Bias Correction
Bias CorrectionDetails? In-DepthSlides: Topic 1
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Results of Bias, Trend and Ensemble Methods
• All methods showed slight improvement in overall skill. Bias removed, mean absolute error improvement from 0-9%.
• 2-Day Running Bias Correction reduced False Alarms with only slight reduction of the Hit Rate.
• NB: 2009 may be ananomolous O3 season (In Depth Slides: Topic 2)
NAQC Season BC 2d BC Trend Ensemble0
0.2
0.4
0.6
0.8
Hit False Alarm Threat
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Temperature and NAQC Forecast Guidance
Peak O3 concentrations, eitherforecast or observed, are
correlated to Tmax.
NAQC forecasts (2009shown left) appear to besensitive at Tmax > 82⁰F
Evidence of decoupling ofTmax-O3 association in recent
years? In-Depth Slides: Topic 3
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Transported O3 and NAQC Forecast Guidance
IR Channel 41515 UTCAugust 4
Back Trajectories Initialized 1200 UTC August 4,24-h Duration, Terminate at 1500 (red), 1000 (blue)
and 500 (green) m AGL.
Hourly O3 inPHL on August 5
Peak 8-h Ave: 69 ppbv
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Temperature and Persistence Adjustment
• Fit regression model with observed O3 (2007-2008) as predicand, Tmax, persistence O3 and NAQC forecast O3 as predictors.
• Modest improvement overall but large reduction in false alarms with only minor reduction in hit rate.
Details? In-Depth Slides: Topic 4
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2009 Results
NAQC TempC 2d BC Forecast-1
0
1
2
3
4
5
6
7
8
Bias Mean AE Median AE
NAQC TempC 2d BC Forecast0
0.2
0.4
0.6
0.8
Hit False Alarm Threat
“NAQC” is uncorrected model forecast, “TempC” is temperature and persistent adjusted forecast, “2dBC” is running two-day bias correction, “Forecast” is
expert forecast issued to public.
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Summary
• Metric of interest to forecasters is peak domain wide O3 and particularly at the threshold of 76 ppbv (Code Orange).
• Numerical model forecasts in PHL are skillful but suffer from over-prediction at the Code Orange threshold.
• Overall forecast skill is improved by running bias corrections.• Skill at Code Orange threshold improved by excluding coastal
regions and correcting for temperature and persistence O3.• Another year of data is necessary to fully test these
conclusions due to unusual circumstances in 2009.
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Acknowledgements
• Air quality forecasting and research in the Philadelphia Metropolitan area is supported by the Delaware Valley Regional Planning Commission (www.dvrpc.org) and the States of PA, NJ and DE.
• Additional research support was provided by the Air and Radiation Management Administration of the Maryland Department of the Environment (http://www.mde.state.md.us).
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In Depth Slides
• Topic 1: Post Processing of Numerical Guidance
• Topic 2: Comments on the 2009 Ozone Season in the mid-Atlantic
• Topic 3: Temperature-Ozone Relationship Following the NOx SIP Rule Implementation
• Topic 4: Using Temperature and Persistence O3 to Adjust NAQC Forecasts
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In Depth Slides: Topic 1Post-Processing of Numerical Guidance
• Simple bias correction (BC)– Bin forecasts by concentration and correct for historical bias in
those ranges.• Running bias correction (RBC)
– 2 day running bias correction.• Trend correction
– Add recent trend in forecast O3 to current day observed O3
• Blend with statistical models– “Poor Man’s Ensemble”
• Statistical post-processing– Predictors: Forecast, temperature and persistence O3
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Simple Bias Correction Applied to 2009
< 40 40-49 50-59 60-69 70-79 80-89 >= 90
-6
-4
-2
0
2
4
6
8
10
NAQC Forecast Bias (2007-2008)
Forecast Peak Domain 8-Hour Ozone (ppbv)
Fore
cast
Bia
s (pp
bv)
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2009 Bias Corrected Forecasts
N = 143
r = 0.82r2 = 0.67
[O3] = 3.52 + 0.89*[O3]BC
Overall absolute error similar to uncorrected
forecast. No improvement in higher end of observed
O3 distribution.
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Running Bias Correction (Two Day)
• RB O3 = fd+1 - [((fd0 – obsd0) + (fd-1 - obsd-1))/2]
• Current day (do) O3 must be estimated from early afternoon observations.
• Running bias correction is the average forecast bias over two days preceding the forecast day.
• “f” is peak 8-hour O3 forecast at monitor locations by the NAQC model. “obs” is observed peak 8-hour O3 from same locations.
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Two-Day Running Bias Correction
2007-2009
N = 406
r = 0.80r2 = 0.64
[O3] = 14.4 + 0.76*[O3]2dBias
Overall, little change in absoluteerror from NAQC. Some
improvementin bias.
In 75th%ile (> 65 ppbv), slightdegradation in absolute error.
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Trend Correction
• Trend Corrected O3 = (obsd0 + [fcd+1 – fcd0
])
– Today’s Peak O3 + [Tomorrow’s Forecast O3 – Yesterday’s Forecast O3 for Today]
• Shortcoming: Forecast is issued before today’s peak observed O3 is known.
• Current day forecast from either 0600 or 1200 UTC NAQC runs have not proven reliable so current day peak is typically extrapolated from early afternoon O3 observations.
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Trend Correction Results (2007-2009)
2007-2009
N = 409
r = 0.79r2 = 0.62
[O3] = 17.2 + 0.72*[O3]Trend
Overall, little improvement toNAQC forecast.
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Blend of Statistical and Numerical Models
• Statistical models typically use meteorological, seasonal and persistence predictors to forecast peak domain-wide O3.
• These models are simple and cost-effective and have historically provided reasonably accurate forecast guidance.
• Statistical models require relatively long training data sets. Usually 5 or more summer seasons of data.
• Significant changes in regional scale NOx emissions beginning in 2002 due to the “NOx SIP Rule” have had an impact on the skill of statistical models that are “tuned” to earlier years.
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Statistical Model Bias (2003-2009)
2003 2004 2005 2006 2007 2008 20090
2
4
6
8
10
12
R0302
Fore
cast
Bia
s (pp
bv)
Bias in forecasts of peak domain-wide 8-hour O3 by two models used in PHLand trained on pre-NOx SIP Rule historical data.
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Newest Statistical Model (Trained on Post-NOx SIP Rule data) Improves Performance
Bias Mean AE Median AE0
2
4
6
8
10
12
14
R2009R0302Ln2001
Erro
r Mea
ure
(ppb
v)
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Weighted Blend of Statistical and Numerical Models
2009N = 143
NAQC Blendr 0.83 0.85r2 0.68 0.73
NAQFS:[O3] = 8.5 + 0.78 * [O3]FC
Blend:[O3] = 2.0 + 0.87 * [O3]FC
Blend 3: 30% R2009 (post-NOx SIP), 20% R0302 (pre-NOx SIP), 50% NAQFS
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Bias and Absolute Error Statistics for 2009
NAQC Season BC 2d BC Trend Ensemble-1
0
1
2
3
4
5
6
7
8
9
BiasMean AEMedian AE
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Skill Score for Code Orange Threshold (2009)
NAQC Season BC 2d BC Trend Ensemble0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
Hit False AlarmThreat
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In Depth Slides: Topic 2Comments on the 2009 O3 Season
• 2009 was a very unusual summer. Low frequency of O3 conducive weather locally and regionally.
• “Standard” high O3 weather – westward extension of the Bermuda High, sustained westerly transport from the Ohio River Valley – was infrequent.
• This weather pattern contributed to historically low frequency of high O3 cases but there may have been lower emissions due to economic recession.
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Mean Summer Upper Air Pattern Featured a Strong and Persistent Area of Low Pressure in Eastern Canada
Climate figures courtesy of NOAA-CDC, http://www.cdc.noaa.gov/data/composites/day/
Mean 500 mbGeopotential
HeightJune-August
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Boundary Layer (925 mb) Mean Winds
For June-August, mean winds(left panel) are NW for PHL andnortheastern US. Change from
normal (right panel) show strongerwinds with northerly component
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This Resulted in Very Cool Boundary Layer Temperatures Across the Northeast
Mean 925 mb TemperatureFor JJA (left panel).
Departure from normal (bottompanel).
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The northern US was quite cool in June and July with slightly higher than normal precipitation
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Philadelphia Summer Weather
• Average temperature for MJJA was near normal. However, June and July were 1.5°F below normal.
• August had an average number of hot days (≥ 90°F) but MJJ had only 5 hot days compared to ≈ 11 on average.
• All months had more than average number of days with measureable precipitation (17 days in June alone). For the season, 14 additional days of measureable rain (≥ 0.01”).
• August was excessively wet with 10.3” of rain, primarily due to 5 days with > 1” of rain (average is 1.2 days).
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Weather and Air Quality
• The combination of cooler and wetter than normal weather, and the absence of persistent Bermuda High circulation, led to lower than normal O3 regionally and locally– Shenandoah National Park has historically low
frequency of high O3 days.
– PM2.5 concentrations in PHL very low - pointing to few “dirty” air mass episodes.
– Almost no high O3 episodes in Philadelphia.
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Philadelphia: Frequency of High O3 Days(Peak 8-Hour O3 in the Metropolitan Area)
2000 2001 2002 2003 2004 2005 2006 2007 2008 20090
10
20
30
40
50
60
70
> 76 ppbv> 96 ppbv>= 105 ppbv
Year
Days
Abo
ve T
hres
hold
(8-H
our O
zone
)
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Shenandoah National ParkNumber of Days with 8-Hour O3 Above Thresholds
2003 2004 2005 2006 2007 2008 20090
10
20
30
40
50
60
>= 60 ppbv>= 70 ppbv
Year
Peak
8-H
our O
zone
(ppb
v)
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Shenandoah National Park – Big MeadowsRegional Effect of NOx Reductions
1994 1996 1998 2000 2002 2004 2006 20080
10
20
30
40
50
60
70
80
20
43
2925
71
57
26
3438
11 10 1115
8 7
0Num
ber o
f Day
s with
8-h
Ozo
ne >
= 70
pp
bv
No days in excess of 70 ppbv in 2009
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PHL PM2.5 Concentrations Remarkably Low in 2009
2004 2005 2006 2007 2008 20090
5
10
15
20
25
6
1213
78
0
15
18
23
1718
0
> 35.5> 30.0
Num
ber o
f Day
s Abo
ve P
M2.
5 Co
ncen
-tr
ation
Thr
esho
ld (m
icro
g/m
3)
Note: Data for 2004-2008 uses gravimetric filter monitors (FRM) while 2009uses 24-average from continuous monitors.
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Philadelphia: Number of Days with PM2.5 (Daily Average in μgm-3) Above Given Threshold
2004 2005 2006 2007 2008 20090
10
20
30
40
50
60
70
>= 20>= 30
Year
Days
Abo
ve T
hres
hold
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Shenandoah NP PM2.5 Daily Average Concentrations (May-August, 2004-2009)
N Median(µg/m3)
Mean ± 1 σ(µg/m3)
Ratio (Days > 20 µg/m3)
Ratio (Days > 30µg/m3)
2004-2008 487 14.2 15.1 ±7.8 0.23 0.04
2009 116 9.5 9.8 ± 4.3 0.02 0.00
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In Depth Slides: Topic 3Changes in the Temperature-Ozone Relationship
• O3 concentrations are strongly associated with surface temperature (Tmax)
• Hot weather is necessary, but not sufficient for high O3
• Since the implementation of the NOx SIP Rule emissions controls, the likelihood of “bad” air given hot temperature has decreased.
• This has impacted the skill of both numerical and statistical forecast models.
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Philadelphia Ozone- Temperature Relationship
Peak 8-Hour O3 in metropolitan PHL and Tmax (PHL Int’l Airport) for May-Sept, 1993-2009
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Hot Weather is Necessary but not Sufficient for High O3
1998 2000 2002 2004 2006 20080.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
Ratio > 76 ppbvRatio > 96 ppbv
Ratio
of D
ays >
90
F to
Giv
en O
zone
Th
resh
olds
Post-NOx SIP Rule
If Tmax is ≥ 90⁰F, what is the chance of Code Orange (≥ 76 ppbv)or Code Red (≥ 96 ppbv) O3 occurring?
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O3 – Temperature Relationship in PHL: NOx SIP Rule
80-84 85-89 90-94 >= 9540
50
60
70
80
90
100
110
1993-20022003-2009
Maximum Surface Temperature (degrees F)
Mea
n Pe
ak 8
-Hou
r Ozo
ne (p
pbv)
Post-NOx Rule
Pre-NOx Rule
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In Depth Slides: Topic 4Using Temperature and Persistence O3 to Post-Process
NAQC Guidance
• Using 2007-2008 data, fit observed O3 and NAQC forecast with two models:– NREG01: NAQC and Tmax as predictors
– NREG02: NAQC, Tmax and LagO3 as predictors
• As applied to 2009 data, both models gave an increase in skill– Reduced “false alarms” of high O3 by two thirds.– With no reduction in probability of detection.
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Simple Post-Processing Method[O3]obs = f([O3]forecast, [O3]persistence, Tmax)
2007-2008
N = 268r = 0.79r2 = 0.62
[O3]obs = 0.56 * [O3]NAQC + 0.44 * Tmax + 0.17 * [O3]lag -20.1
Modest improvement in explainedvariance and correlation
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Fit to Observations in 2009
Error Statistics – 2009(all values in ppbv)
Bias MedAE MnAE
NAQC 3.9 7.0 7.4
NREG01 3.1 6.0 6.7
NREG02 2.7 5.9 6.4
Hit Rate unchanged but number ofFalse Alarms reduced from 14 to 5.
3 of 5 False Alarms are “near misses”with observed O3 ≥ 71 ppbv.