1. Influence of Regional Transport on San Antonio Ozone Interannual Variability in May
Wei Li1, Yuxuan Wang1, Elizabeth Klovenski1, James Flynn1, Robert Griffin2, Rebecca Sheesley3, Sascha Usenko3, Paul Walter4, Gary Morris4, Mark Estes5
IGC9, May 9, 2019 2 3 4 5 1

2. San Antonio and Its Ozone Nonattainment
Houston
San Antonio: the second-most populous city in Texas; a warm climate; industrialized. Like other cities, it also suffers from air quality problems.
In 2018 San Antonio (Bexar County) was designated ozone nonattainment by EPA.
3-year average fourth highest MDA8 ozone
70 ppb
Days MDA8 exceeded 70 ppb
TCEQ funded a field campaign in May 2017.

3. Field Campaign and GEOS-Chem Model Setup
San Antonio Field Campaign: Collaborative work of UH, Rice, Baylor and St. Edward’s. PI: James Flynn (UH).
Two ground sites
USTA
Traveler’s World
UH–O3, NO, NOx, NOy , CO,SO2,T, P, RH, WS, WD, Canister, Pandora
Baylor–PM2.5 Filter
St. Ed.–Ozonesonde
UH–O3, NO, NOx , NOy , CO, SO2, T, P, RH, WS, WD, Ceilometer, Canister
Rice–HR-ToF-AMS
Baylor–PTR-MS
1, collaborative work, we are involved in data analysis and model work.
2, monitoring sites and what they are measuring for model evaluation.
3, The purpose of this project is to conduct sophisticated analyses of monitoring data collected during SAFS.
GEOS-Chem Modeling Setup
GEOS-FP Assimilated Meteorology
Nested NA 0.25o x o, Apr 2017 – May 2017 (with 2x2.5 boundary conditions)
Anthropogenic Emissions
NEI11 scaled to
50% reduction NOx emission in E. US

4. Model Evaluation of Ozone Shows Good Performance
Hourly ozone concentration at Traveler’s World
R=0.7
Simulation
Observation
05/07/ :00 UTC
05/07/ :00 UTC
Model captures variability (R=0.7), but missing some peak values.
Overall overestimate (MB= 5.9 ppbv), esp. nighttime.
Model captures vertical ozone distribution.
Ozonesonde
Model

5. Wind Pattern Shows Marine Air Intrusion in May
The Bermuda High anticyclone picks up emissions from Central America, South Mexico and mixes with marine air in Gulf region and then goes into Eastern US. We call this the marine air intrusion.
The North Pacific High is near the west coast and two anticyclones converge in Northern and Central Mexico.
May monthly mean wind and geopotential height
Bermuda High
North Pacific High

6. Model Captures Two Marine Air Intrusions
Normalized model sea salt sulfate vs. observed chloride at TW
Chloride and sea salt sulfate are good indicators of marine air.
Model correctly simulates two peaks of marine air intrusion.
R=0.75
observed chloride
simulated sea salt sulfate
marine air intrusions
To what extent does regional transport impact ozone interannual variability?
Negative correlation of ozone with chloride indicates low ozone is associated with marine air intrusion.
Daytime mean ozone and chloride at TW
observed ozone
R=-0.5
observed chloride
model ozone

7. GEOS-Chem Passive Tracers Run to Analyze Transport
Marine tracer: South Gulf + North Gulf + Central America + South Mexico
Continental tracer: West USA + Central USA + East USA
Mexico tracer: North Mexico + Central Mexico
In-state tracer: Houston + San Antonio + Dallas + Rest of Texas
Advantage: very fast and good for long-time simulation.
Disadvantage: does not include chemistry
West USA
Central USA
East USA
Texas
MERRA-2 Meteorology data
Nested NA, 0.5o x 0.625o Apr – May 2005 – 2017 (with 2x2.5 global boundary conditions)
North Mexico
North Gulf
1, different tracers.
2, As marine air can decrease ozone, we want to group those tracers to continental, marine and local tracer.
South Gulf
Central Mexico
South Mexico
Central America
Reference: Wang, S.-C., Y. Wang, M. Estes, R. Lei, R. Talbot, L. Zhu, and P. Hou, Transport of Central American Fire Emissions to the U.S. Gulf Coast: Climatological pathways and impacts on ozone and PM2.5, J. Geophys. Res., 123, 8344–8361,

8. Normalized monthly MDA8 and continental tracer at SA in May 2005-2017
Continental minus Marine Tracer as Regional Tracer
Normalized monthly MDA8 and continental tracer at SA in May
R=0.29
Observed MDA8
Continental tracer
The Continental minus the Marine tracer has the highest R (0.45).
Thus we define the Continental minus the Marine tracer as the Regional tracer.
Normalized monthly MDA8 and marine tracer at SA in May
R=-0.37
Marine tracer
Observed MDA8
Normalized monthly MDA8 and continental minus marine tracer at SA in May
R=0.45
Continental minus Marine tracer
Observed MDA8

9. [O3] = 2.05 × [Regional tracer]* - 2.50 × [In-state tracer]*
Regional and Local Tracers Are Important Predictors
[O3] = 2.05 × [Regional tracer]* × [In-state tracer]*
+1.22 × [Mexico tracer] (* indicates significant p-val)
Prediction and observed monthly MDA8 at SA in May
Observation
R2=0.5995
Nearly 60% of ozone interannual variability in May can be explained.
Prediction
[O3] = 1.46 × [Regional tracer]*
Both C-M tracer and local tracer are significant( less than 0.05). Local tracer is anticorrelated with ozone. Why is this?
Prediction and observed monthly MDA8 at SA in May
R2=0.2024
Observation
Regional transport alone can explain 20% variability.
Prediction

10. Apply the Same Tracers to Houston ozone
[O3] = 1.44 × [Regional tracer]* × [In-state tracer]
× [Mexico tracer] (* indicates significant p-val)
Prediction and observed monthly MDA8 at Houston in May
Nearly 40% of ozone variability can be explained, which indicates a more complex circulation pattern for Houston.
Observation
R2=0.4439
Prediction
[O3] = 1.31 × [Regional tracer]*
Both C-M tracer and local tracer are significant( less than 0.05). Local tracer is anticorrelated with ozone. Why is this?
Prediction and observed monthly MDA8 at Houston in May
R2=0.3147
Observation
Regional transport alone can explain 30%, higher than for San Antonio.
Prediction

11. Transport Passway
Profile:13-year mean West USA tracer
Mexico and Western USA tracers can be lifted up. The Mexico tracer is strong at all levels from south to north. The Western USA tracer is stronger at higher levels travelling from west to east and subsides in the east.
Marine and Central USA are from south and north respectively at both surface(stronger) and higher level.
East USA mainly transports at the surface from south east to SA.

12. Conclusion and Acknowledgement
GEOS-Chem model can capture ozone variability in San Antonio and shows a good performance in ozone vertical distribution.
Marine air intrusions from the Gulf can reduce the ozone concentration in San Antonio, which shows the influence of regional transport on ozone in southeast Texas.
Nearly 60% of San Antonio ozone interannual variability in May can be explained by regional and local tracers. The regional tracer alone (continental minus marine air) can explain 20% of the variability.
Wind convergence in Mexico caused by two high pressure systems can influence the transport of air masses into Texas.
Acknowledgement
All participants in the San Antonio field study
TCEQ for funding (PGA Number: ; )