Title: Advancing Assessment of NOx Emissions and Temporal Variability using TEMPO NO2 and CAMx
Institution(s) Represented: Ramboll Americas Engineering Solutions, Inc. (Shah, Johnson)
Lead PI: Tejas Shah
AQRP Project Manager: Elena McDonald-Buller
TCEQ Project Liaison: Benjamin Yusuf
Awarded Budget: $230,849
Abstract
Nitrogen oxide (NOx) emissions are key precursors to ozone formation. Accurate characterization of these emissions is critical for understanding ozone formation in both urban and regional environments, and for supporting attainment and maintenance of the ozone (O3) National Ambient Air Quality Standards (NAAQS). Our previous work using Tropospheric Emissions: Monitoring of Pollution (TEMPO) satellite NO2 observations demonstrated the potential to constrain NOx emissions by source sector across Texas, including Houston, Dallas-Fort Worth, and rural areas. That effort developed methods to integrate TEMPO observations with Comprehensive Air quality Model with extensions (CAMx) chemical transport model results, including flux divergence and multiple linear regression approaches, and revealed persistent discrepancies between modeled and observed NO₂ columns during September 2023. Those results indicated that on-road and off-road vehicle emissions are often underestimated especially in the morning; soil and lightning NOx contributions carry substantial uncertainties; and current inventories need better spatiotemporal allocation of emissions. Building on these findings, the proposed work will further quantify and assess uncertainties in NOx emission inventories, including in the temporalization of emissions, using refined emission inputs for selected source sectors.
To address observed model biases, this project will examine key sources of uncertainty in the regional NOx emission inventory. Specifically, the analysis will evaluate whether medium- and heavy-duty diesel vehicle tampering and mal-maintenance (T&M) prevalence is higher than currently represented in MOVES5 and update natural soil and lightning NOx emissions using state of the science approaches. EPA's technical documentation for MOVES5 recommends that T&M rates be re-evaluated and updated, suggesting that current rates may underestimate real world T&M prevalence and on-road NOx emissions in urban corridors such as Houston and Dallas-Fort Worth. Separately, outdated soil NOx and lightning NOx parameterizations may contribute to discrepancies in background NOx across agricultural regions and transitional rural-urban zones. The original and updated inventories will be evaluated using tropospheric NO2 column retrievals from the TEMPO satellite instrument in conjunction with CAMx simulations.
This work aligns with multiple Texas Air Quality Research Program (AQRP) Research Priority Areas, as summarized in Table 1.
Table 1. How this project will respond to the AQRP Research Priority Areas.
|
Research Priority Area |
How this project addresses the Research Priority |
|
Improve emissions inventories |
This project will improve NOx emission inventories by updating soil, on-road, and lightning sources. It will apply the updated MEGAN soil NOx module, which incorporates revised temperature and soil moisture responses, updated nitrogen inputs, and soil HONO emissions. On-road emissions will be adjusted to account for diesel vehicle T&M and lightning NOx will be updated based on recent literature. The updated inventory will be evaluated using TEMPO NO₂ measurements. |
|
Use of satellite and other remote sensing data |
TEMPO satellite measurements will be used to better understand diurnal patterns of NO2 and their relationship to NOx emissions. TEMPO data will serve as the primary satellite dataset, and comparisons will also be made with TROPOMI data during periods of afternoon overlapping observations. |
Technical Reports:
