Title: Advanced Analysis of Ozone Formation Potential, VOC Sensitivity, and Source Apportionment in the El Paso-Juarez Airshed
Institution(s) Represented: University of Texas at Austin (Misztal, Hildebrandt Ruiz, Sullivan, McDonald-Buller)
Lead PI: Pawel Misztal
AQRP Project Manager: Erin Tullos
TCEQ Project Liaison: Erik Gribbin
Awarded Budget: $247,132
Abstract
El Paso County is designated as marginal nonattainment for the 2015 ozone National Ambient Air Quality Standards (NAAQS), and the 2024 tightening of the annual PM2.5 standard from 12 to 9 µg/m3 has placed the region closer to PM2.5 nonattainment. The El Paso-Juárez metropolitan area is one of the largest binational communities in North America, with air quality challenges arising from complex terrain, transboundary transport from Mexico, and diverse emission sources. AQRP Project 24-024, completed in August 2025, produced the most comprehensive air quality dataset collected in El Paso since the 1996 Paso del Norte Ozone Study, using an electric mobile laboratory equipped with a Vocus PTR-ToF-MS, an HR-TOF-AMS, and an aethalometer, complemented by a Comprehensive Air Quality Model with Extensions (CAMx) photochemical modeling platform for the 2022 base year. Initial extended analyses of these datasets, including ozone reactivity potential mapping and aerosol source apportionment, were presented to the Texas Commission on Environmental Quality (TCEQ) at the May 2026 State Implementation Plan Informational Meeting.
Project 26-030 will conduct advanced analyses of these existing datasets across five tasks. Ozone formation potential will be calculated under three independent frameworks (mass-based, molecular weight-based, and OH reactivity-weighted maximum incremental reactivity) using the El Paso-specific SAPRC-11 ELPTX scenario. Ozone sensitivity regimes will be mapped across the airshed using complementary indicator ratios and cross-validated against the existing CAMx simulations. Source apportionment will integrate Project 24-024 mobile Vocus and HR-TOF-AMS data with long-term TCEQ auto-GC records (2011 through 2025) and offline PM2.5 filter samples, applying combined Vocus-AMS Positive Matrix Factorization (PMF), reactivity-weighted PMF, and roadway-influence stratification. Existing CAMx Reactive Tracer outputs will be reanalyzed to characterize domestic and international emission source contributions to toluene at five El Paso monitoring sites.
The project will deliver spatially resolved priority VOC rankings for ozone reduction, ozone sensitivity regime classifications with TCEQ-validated indicator ratios, an integrated VOC and PM source apportionment that elucidates sources of ozone and aerosol precursors, and refined toluene source attribution to support binational air quality coordination. Although El Paso is not currently in serious ozone nonattainment, the methodological framework developed under this project is directly transferable to serious and severe nonattainment areas in Texas and will support Houston-Galveston-Brazoria, Dallas-Fort Worth, and Bexar County regulatory analyses.
Technical Reports:
