Linking Isotopes, Satellite Observations, and Aerosol Optical Properties to Constrain NOx Sources and Nitrate Formation in Coastal Urban PM2.5
J. David Felix1,2, Conner Guidry3, Abril Garcia Lunar1,2, and Allyson Girard1,2
1 Department of Chemistry and Biochemistry, University of North Carolina - Wilmington, Wilmington, NC
2 Center for Marine Science, University of North Carolina - Wilmington, Wilmington, NC
3 Department of Physical and Environmental Science, Texas A&M University - Corpus Christi, Corpus Christi, TX
Particulate matter (PM2.5) pollution is a major concern for human and environmental health in coastal urban airsheds shaped by both anthropogenic and natural emissions, and recent tightening of the U.S. PM2.5 National Ambient Air Quality Standard (9.0 μg/m3 annual mean, averaged over 3 years) has increased the need to better constrain emission sources and atmospheric formation pathways. Particulate nitrate (pNO3-), a key component of PM2.5 formed from NOx, represents an important target for mitigation efforts. This study integrates ground-based sampling, stable isotope analysis, satellite remote sensing techniques, and aerosol optical measurements to improve PM and NOx source apportionment and understanding of nitrate formation in a coastal urban environment approaching PM2.5 nonattainment (Corpus Christi, Texas, USA). PM2.5 samples were collected over two-week periods for one year using a medium volume particulate sampler and analyzed for the isotopic composition of nitrate (δ15N and δ18O). Isotope data was incorporated into a Bayesian mixing framework to differentiate among NOx emission sources, including industrial activities, vehicles, biomass burning, soils, and lightning. To better constrain intermittent sources (i.e., lightning, biomass burning), a complementary approach integrating lightning detection, fire and smoke mapping products, and air mass back trajectories was used to evaluate their influence on individual collection periods prior to application in the isotope-based mixing model. The oxygen isotopic composition of nitrate, atmospheric composition, fractionation scenarios, and mixing models were used to assess dominant atmospheric oxidation pathways contributing to pNO3- formation. In parallel, aerosol optical properties measured using a Cimel Sun Photometer within NASA's AERONET network were used to classify aerosol types and evaluate source influences through cluster-based analysis and compared with nitrate source apportionment. The integration of these datasets enables cross-validation between chemical tracers, optical signatures, and atmospheric transport patterns, capturing both local emissions and regional transport dynamics to improve confidence in source attribution while resolving temporal variability in underlying processes. Results are being shared with state agencies and regional stakeholders to inform targeted mitigation strategies in coastal urban environments.