An Insight into the Vertical Structure of the Atmosphere during TEXAQS-II:

Understanding the Effect of the Upper-level Meteorology on Houston’s Surface

Ozone Levels

Ryan PernaRyan PernaPrincipal Findings Data Analysis WorkshopPrincipal Findings Data Analysis Workshop

May 29, 2007May 29, 2007

IntroductionIntroduction

1)1) Composite 850 hPa mapsComposite 850 hPa maps2)2) Background ozoneBackground ozone3)3) The role of frontal passagesThe role of frontal passages4)4) Vertical ozone profilesVertical ozone profiles5)5) The role of elevated temperature inversionsThe role of elevated temperature inversions6)6) ConclusionsConclusions

Composite Maps / Synoptic AnalysisComposite Maps / Synoptic Analysis

Composite maps were created to understand the upper-level meteorological patterns associated with ozone episodes (8 hour average > 85 ppb)Source for composite maps: http://www.cdc.noaa.gov/Composites/Day/(National Climatic Data Center)

850 hPa Analysis (August)850 hPa Analysis (August)

850 hPa composite map for 850 hPa composite map for nonnon--episode days episode days

August 2006. August 2006.

850 hPa composite map for August ozone episodes 2006

(4 episodes).

850 hPa Analysis (September)850 hPa Analysis (September)

850 hPa composite map 850 hPa composite map for nonfor non--episode days episode days

September 2006September 2006

850 hPa composite map for September ozone episodes

2006 (10 episodes)

Effect of Wind Direction on Effect of Wind Direction on Background OzoneBackground Ozone

“Background Ozone” was defined using criteria set forth by John Nielsen-Gammon (2005)Defined as minimum 8 hour average peak for stations upwind of the Houston area

Houston Croquet

Houston Westhollow

Conroe (off map)

Galveston (off map)

Effect of Wind Direction on Effect of Wind Direction on Background OzoneBackground Ozone

CategoryCategory C1(E)C1(E) C2(Hc)C2(Hc) C3(SE)C3(SE) C4(SW)C4(SW) C5(N)C5(N) C6(S)C6(S)

AverageAverageBackground Background Ozone(ppb)Ozone(ppb)

42.242.2 -------------- 3131 2828 52.752.7 20.620.6

The Role of Frontal Passages on The Role of Frontal Passages on HoustonHouston’’s 8 Hour Ozone Peakss 8 Hour Ozone Peaks

Frontal PassageFrontal Passage EpisodeEpisode

8/298/29 8/31, 9/1, 9/38/31, 9/1, 9/3

9/59/5 9/79/7

9/129/12 9/13, 9/149/13, 9/14

9/189/18 9/209/20

9/249/24 9/26, 9/279/26, 9/27

9/289/28 nonenone

Ozonesonde EvidenceOzonesonde Evidence

Ozonesondes were launched by a collaboration Ozonesondes were launched by a collaboration with Dr. Gary Morris of Valparaiso Universitywith Dr. Gary Morris of Valparaiso UniversityAugust 31 episode launches reveal an increase in August 31 episode launches reveal an increase in background ozone within and above the background ozone within and above the boundary layerboundary layer

August 28 (preAugust 28 (pre--frontal)frontal)August 28, 2006 1:00 PM LDT

Ozone(ppb) Potential Temperature(K)

0 20 40 60 80 100 290 300 310 320

Altit

ude(

m)

0

1000

2000

3000

4000

5000

August 29 (preAugust 29 (pre--frontal)frontal)August 29, 2006 1:00 PM LDT

Ozone(ppb) Potential Temperature(K)

0 20 40 60 80 100 290 300 310 320

Alti

tude

(m)

0

1000

2000

3000

4000

5000

August 30, 2006 1:15 PM LDT

Ozone(ppb) Potential Temperature(K)

0 20 40 60 80 100 290 300 310 320

Altit

ude(

m)

0

1000

2000

3000

4000

5000

August 30 (postAugust 30 (post--frontal)frontal)

August 31 (postAugust 31 (post--frontal, episode day)frontal, episode day)August 31, 2006 7:00 AM

Ozone (ppb) Potential Temperature(K)

0 20 40 60 80 100 290 300 310 320

Alti

tude

(m)

0

1000

2000

3000

4000

5000

August 31, 2006 1:30 PM LDT

Ozone(ppb) Potential Temperature(K)

0 20 40 60 80 100 290 300 310 320

Altit

ude(

m)

0

1000

2000

3000

4000

5000

Backward TrajectoriesBackward Trajectories

Pre-frontal Post-frontal

Ozonesonde ConclusionsOzonesonde Conclusions

Backward trajectories reveal continental transport likely cause for increase in background ozone aloftVertical mixing may play a role by increasing surface ozone concentration, as described in Zhang & Rao (1999)

Local Meteorology: The Rawinsonde Local Meteorology: The Rawinsonde CampaignCampaign

Rawinsondes launched twice daily (7AM and 7 PM) in August and SeptemberDuring “Intensive Operations” days (IOP’s), launches took place at 5 AM, 10 AM, 1 PM, 4 PM, and 10 PMMost IOP days had elevated ozone levels

PBL development August 9, 2006

Water Vapor Mixing Ratio (g/kg) Potential Temperature(K)

0 10 20 300 310 320

Alti

tude

(m)

0

1000

2000

3000

4000

5000

Decrease in Water Mixing Ratio

Increase in Potential Temperature

PBL Height (1000 m)

Effect of the PBL Height on Afternoon Effect of the PBL Height on Afternoon 8 Hour Ozone Peak8 Hour Ozone Peak

Time

07:00:00 10:00:00 13:00:00 16:00:00 19:00:00

Ave

rage

PB

L H

eigh

t (m

)

0

500

1000

1500

2000

2500

Ozone Episode DaysNon-Episode Days

Time Episode Days

Non-Episode Days

7:00 10 46

10:00 8 4

13:00 11 6

16:00 8 3

19:00 10 45

The Effect of the Morning Inversion The Effect of the Morning Inversion Height / Strength on HoustonHeight / Strength on Houston’’s 8 Hour s 8 Hour

Peak Ozone ConcentrationPeak Ozone ConcentrationMorning inversion height and strength has an Morning inversion height and strength has an effect of concentrating ozone precursors and effect of concentrating ozone precursors and may lead to higher hourly ozone peaks during may lead to higher hourly ozone peaks during the day (Berman et al., 1999) the day (Berman et al., 1999)

y = 1108.7x + 55.735R2 = 0.0325

0

20

40

60

80

100

120

140

0 0.005 0.01 0.015 0.02 0.025Peak

8 H

our A

vera

ge O

zone

Con

cent

ratio

n (p

pb)

Strength of morning inversion (Strength of morning inversion (°°C) C) compared to 8 Hour Peak Ozonecompared to 8 Hour Peak Ozone

ΔT / ΔZ (°C/m)

Are Elevated Inversions Related to Are Elevated Inversions Related to HoustonHouston’’s 8 Hour Ozone Peak?s 8 Hour Ozone Peak?

Zhang and Rao (1999) showed that downward vertical mixing may increase observed ozone concentrationsSubsidence may enhance this effectOzone can also become trapped above and underneath this elevated inversion, and can mix downward into the boundary layer circulation (Alonso et al., 2000).

Are Elevated Inversions Related to Are Elevated Inversions Related to HoustonHouston’’s 8 Hour Ozone Peak?s 8 Hour Ozone Peak?

Also, could be coincidental since ozone episodes are associated with High pressure, and a clear sky.

““ClassicClassic”” Ozone Episode Sounding (7 Ozone Episode Sounding (7 AM August 31, 2006)AM August 31, 2006)

Elevated Inversion AnalysisElevated Inversion Analysis

Inversions were classified by height, strength, Inversions were classified by height, strength, and moisture contentand moisture contentMorning inversions were ignoredMorning inversions were ignored

8 Hour Average Ozone Peak Compared with Elevated 8 Hour Average Ozone Peak Compared with Elevated Inversion Strength (Inversion Strength (°°C) and Relative Humidity at the Top C) and Relative Humidity at the Top

of the Inversionof the Inversion

Composite SoundingsComposite Soundings

August 2006August 2006

Non-Episode DaysEpisode Days

September 2006September 2006

Non-Episode DaysEpisode Days

ConclusionsConclusions

Composite Maps revealed upper-level ridges associated with ozone episodesMost of Houston’s late summer ozone episodes occurred in a post-frontal environment.Northerly flow helps to increase background ozone, increasing the probability of an ozone episode

ConclusionsConclusions

Little relation was found between morning inversion strength and peak 8 hour ozone averages.There may be a delay in the PBL morning development on episode days, otherwise PBL height seemed to have little direct relation to ozone episodes in August and September 2006.

ConclusionsConclusions

Elevated inversion analysis reveals dry elevated inversions associated with episode days, however the strongest and driest inversions are not.Composite soundings reveal light winds in boundary layer, elevated inversions common in September episodes.

Future PossibilitiesFuture Possibilities

Composite synoptic maps should be completed for other years in order to draw more general conclusions.Is there a relation between Houston’s ozone episodes and the amount of tropical activity? (2006 was a “different” year).Rawinsonde launches should be completed more often in the morning, the NWS protocol should be departed from.Remote sensing should be added!