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

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 2005-2018 TCEQ funded a field campaign in May 2017.

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 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

Model Evaluation of Ozone Shows Good Performance Hourly ozone concentration at Traveler’s World R=0.7 Simulation Observation 05/07/2017 20:00 UTC 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. Ozonesonde Model

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 2005-2017 Bermuda High North Pacific High

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

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, 2018.

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 2005-2017 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 2005-2017 R=-0.37 Marine tracer Observed MDA8 Normalized monthly MDA8 and continental minus marine tracer at SA in May 2005-2017 R=0.45 Continental minus Marine tracer Observed MDA8

[O3] = 2.05 × [Regional tracer]* - 2.50 × [In-state tracer]* 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 Observation R2=0.5995 Nearly 60% of ozone interannual variability in May can be explained. Prediction [O3] = 1.46 × [Regional tracer]* + 46.99 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 2005-2017 R2=0.2024 Observation Regional transport alone can explain 20% variability. Prediction

Apply the Same Tracers to Houston ozone [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 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]* + 41.35 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 2005-2017 R2=0.3147 Observation Regional transport alone can explain 30%, higher than for San Antonio. Prediction

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.

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: 582-18-82485-03; 582-19-94456-07)