1. Fong (Fantine) Ngan and DaeWon Byun IMAQS, Department of Earth Sciences, University of Houston 7 th Annual CMAS Conference, October 6th, 2008

2.  Introduction  Methodology  Cluster Characteristics  Clusters.vs. Ozone Episodes  Clusters.vs. CMAQ Forecasting  Summary and Future Work

3. Synoptic flow patterns have been classified during 2005/2006 TexAQS-II. Understanding the dependence of O3 on meteorology How high O3 events are associated with certain weather scenarios Evaluating AQF results according to the weather clusters Houston/Galveston area is a unique environment for O3 development. (Various emissions + complex geophysical characteristics) Banta et al. (2005), Darby (2005) – Met. factors are a key on determining the production, dilution and transport of O3. Muller & Jackson (1985), Eder et al. (1995), Davis et al. (1998) – The development of O3 levels depends greatly on meteorological conditions which affect photochemical reaction and transport of O3 precursors. Appel et al. (2007) – model biases in O3 prediction vary based on the meteorological conditions.

4. Methodology The study period encompassed 5-month ozone season (May-September) recorded in 2005 and 2006; 5 days were excluded since they were influenced strongly by Hurricanes. (total 301 days) The meteorological grid data (100*100 in 12-km resolution) from UH-RDAS (NAM + objective analysis) was used for the cluster analysis. The weather conditions were categorized using a two-stage (average linkage then convergent k-means) clustering approach based on the 850 mb wind fields (U & V components of wind) at 12 UTC. PCA (fortran programs) SAS (commercial software) Average linkage Convergent K-means 8 PCs (80%) Principle Component Analysis: reduce size of dataset 850mb U/V from UH-RDAS 12-km domain

5. C1: SE/S, 93 days (30%) C2: E, 56 days (19%)C3: clam, 69 days (23%) C4: N, 41 days (14%) C5: SW, 40 days (13%)C6: strong SW, 2 days (1%)

6. Mean hourly dew point depression associated with clusters Mean hourly temperature associated with clusters CAMS sites & cluster average of T and T-TD C4 (northerly): Lowest min T and driest C1 & C5 (southerly): Relative lower T and more humid C6 (warm section): highest T and most humid C4 C2, C3 C1, C5, C6 C6 C4

7. Mean hourly wind SPD associated with clusters Mean hourly ozone associated with clusters CAMS sites & cluster average of wind speed & O3 conc. Good correlation of cluster wind speed & O3 conc.  Lower wind, higher O3 Higher O3 level group: C2 (easterly) – 65 ppb C3 (clam condition) – 61 ppb C4 (northerly) – 56 ppb Peak happens at 14 CST Lower O3 level group: C1 (southerly) – 35 ppb C5 (southwesterly) – 40 ppb Lowest O3 level: C6 (strong SW) – 20 ppb C6 C2, C3, C4 C1 C5 C2, C3, C4 C6 C1 C5

8. Both met. and chemical data are from CAMS sites (TCEQ). Around 45 sites are available in HGA (region 12) during the study period. Criteria for defining O3 Episodes: 8 hr average O3 >= 85 ppb 92 ozone events Criteria for defining rainy days: precip. recorded during 10 – 16 CST 98 rainy days CAMS sites map

9. 11.86% 47.22% 58.33% 58.82% 17.39% 0% Black bars: number days White bars: number of O3 days C1 & C5: not good for O3 development. Why C1 & C5 get O3 events on certain days? System passes through quickly, light wind C2, C3 & C4: good for O3 development. Why C2, C3 & C4 don’t get O3 events on some days? Rainy day, clouds & relatively strong wind Percentages: ratio of O3 days and total days in clusters

10. Cluster Characteristics during TexAQS-II intensive period O3 events occurred in C2, C3 & C4 Precip. Prevents O3 events O3 events occurred in C2, C3 & C4 Precip. Prevents O3 events Sub-tropical high was dominant No C4 was identified Sub-tropical high was dominant No C4 was identified Active frontal passage Before front – C5 Cool air reached – C4 After front – C3 Before front – C5 Cool air reached – C4 After front – C3

11. C4 C2 Observed O3 (CAMS sites, 8-hr average) on event days have been sorted. The three sites with the highest values were marked on the maps. The circle color indicates how many times were marked at that CAMS site. O3 peak is subjected to the flow pattern. C2: SW of downtown C3: wide spread over the city C4: S of Harris County C3 Harris Brazoria

12. Mean max 8hr O3 for clusters: UH-AQF (F1, shaded) CAMS OBS (circle) C2 C3 Figures are generated by Dr. HyunCheol Kim

13. Clusters.vs. CMAQ Forecasting (O3) C4 Mean max 8hr O3 for clusters: UH-AQF (F1, shaded), CAMS OBS (circle) Mean max O3 for cluster 4 in AQF further south than CAMS observations by Dr. HyunCheol Kim

14. Weather condition: Mostly clear to partly cloudy Light northerly winds all day Weak sea breeze in late afternoon Max T 93F at IAH Front passed through HGA It is classified as cluster 4. SFC weather map at 06z 9/13 SFC weather map at 12z 9/13SFC weather map at 18z 9/13

15. O3 level started to build up at noon. Too strong northerly (northeasterly) wind in the morning pushed pollutants southward (or southwestward). O3 peak ended up in Brazoria. 06 CST 12 CST18 CST Figures are from UH-AQF web display

16. Over-prediction of wind speed in the morning 08 CST Figures are from UH-AQF web display

17. Time Series of O3 on 9/13 forecasting at CAMS site C1 & C619 Red: AQF O3 Blue: observed O3 Figures are from UH-AQF web display Located in Houston downtown Under-prediction of O3 Located south of Houston Good estimation of O3

18.  Synoptic weather patterns in HGA during summer 2005/2006 were classified into 6 clusters.  C1, C5 & C6 (southerly): lower mean hourly O3, higher average wind speed. C2 (easterly), C3 (stagnant condition) and C4 (northerly) have larger contributions on high O3 events. Precip., clouds and strong wind prevent O3 development in these clusters.  August 2006: dominated by southerly flow (C1 & C5), less O3 events September 2006: frequent frontal passage (C4), more O3 events (C2 & C3)  In cluster 4 (northerly), CMAQ forecasting of O3 peak was placed south of the city due to over-prediction of wind speed in the morning.  Include more years for weather pattern classification (2007 & 2008)  Develop secondary factor base on weather pattern for O3 forecasting