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

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San Antonio and Its Ozone Nonattainment

TCEQ funded a field campaign in May 2017.

3-year average fourth highest MDA8 ozone

Days MDA8 exceeded 70 ppb 2005-2018

San Antonio: the second-most populous city in Texas; a warm climate; industrialized. Like other cities, it also suffers from air quality problems. San Antonio Houston

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• In 2018 San Antonio (Bexar County) was designated ozonenonattainment by EPA.

70 ppb

Field Campaign and GEOS-Chem Model Setup

GEOS-Chem Modeling Setup • GEOS-FP Assimilated Meteorology • Nested NA 0.25o x 0.3125o, Apr 2017 – May 2017 (with 2x2.5 boundary

conditions)• Anthropogenic Emissions

NEI11 scaled to 2016-2017 50% reduction NOx emission in E. US

• UH–O3, NO, NOx , NOy , CO, SO2, T, P, RH, WS, WD, Ceilometer, Canister

• Rice–HR-ToF-AMS• Baylor–PTR-MS

• UH–O3, NO, NOx, NOy , CO,SO2,T, P, RH, WS, WD, Canister, Pandora

• Baylor–PM2.5 Filter

• St. Ed.–Ozonesonde

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Two ground sitesUSTA Traveler’s World

San Antonio Field Campaign: Collaborative work of UH, Rice, Baylor and St. Edward’s. PI: James Flynn (UH).

Model Evaluation of Ozone Shows Good Performance

05/07/2017 11:00 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.

05/07/2017 20:00 UTCOzonesonde

Model

Observation

Simulation

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Hourly ozone concentration at Traveler’s WorldR=0.7

Wind Pattern Shows Marine Air Intrusion in May

Bermuda HighNorth Pacific High

May monthly mean wind and geopotential height 2005-2017

• 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.

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Model Captures Two Marine Air Intrusions

R=0.75observed chloride simulated sea

salt sulfate

observed ozone

R=-0.5

model ozone observed chloride

Daytime mean ozone and chloride at TW

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.

marine air intrusions

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• Chloride and sea salt sulfate are good indicators of marine air.

• Model correctly simulates two peaks of marine air intrusion.

Normalized model sea salt sulfate vs. observed chloride at TW

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, 2018.

• 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

GEOS-Chem Passive Tracers Run to Analyze Transport

• Advantage: very fast and good for long-time simulation.

• Disadvantage: does not include chemistry

West USA Central USA East

USA

North Mexico

Central Mexico

South Gulf

Texas North Gulf

South Mexico

Central America

• MERRA-2 Meteorology data• Nested NA, 0.5o x 0.625o

Apr – May 2005 – 2017 (with 2x2.5 global boundary conditions)

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Continental minus Marine Tracer as Regional 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 continental tracer at SA in May 2005-2017

Normalized monthly MDA8 and marine tracer at SA in May 2005-2017

Normalized monthly MDA8 and continental minus marine tracer at SA in May 2005-2017

Marine tracer Observed MDA8

Continental tracer Observed MDA8

Observed MDA8Continental minus Marine tracer

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R=0.29

R=-0.37

R=0.45

Nearly 60% of ozone interannual variability in May can be explained.

Regional and Local Tracers Are Important Predictors

[O3] = 2.05 × [Regional tracer]* - 2.50 × [In-state tracer]* +1.22 × [Mexico tracer] + 46.99 (* indicates significant p-val)

Prediction and observed monthly MDA8 at SA in May 2005-2017

Prediction and observed monthly MDA8 at SA in May 2005-2017

Regional transport alone can explain 20% variability.

[O3] = 1.46 × [Regional tracer]* + 46.99

R2=0.5995

Prediction

Observation

R2=0.2024

Prediction

Observation

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Nearly 40% of ozone variability can be explained, which indicates a more complex circulation pattern for Houston.

[O3] = 1.44 × [Regional tracer]* - 0.10 × [In-state tracer] + 1.18 × [Mexico tracer] + 41.35 (* indicates significant p-val)

Prediction and observed monthly MDA8 at Houston in May 2005-2017

[O3] = 1.31 × [Regional tracer]* + 41.35

Prediction and observed monthly MDA8 at Houston in May 2005-2017

Regional transport alone can explain 30%, higher than for San Antonio.

Apply the Same Tracers to Houston ozone

R2=0.4439Prediction Observation

R2=0.3147Prediction Observation

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Transport Passway

Profile:13-year mean West USA tracer

East USA mainly transports at the surface from south east to SA.

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Marine and Central USA are from south and north respectively at both surface(stronger) and higher level.

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.

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.

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Acknowledgement• All participants in the San Antonio field study

• TCEQ for funding (PGA Number: 582-18-82485-03; 582-19-94456-07)