The Influence of Tijuana River Pollution on Coastal and Inland Aerosol Populations

JUSTIN HAMLIN, Jena Herbst, Benjamin Rico, Leila El Masri, Kimberly Prather, University of California, San Diego

     Abstract Number: 481
     Working Group: Urban Aerosols

Abstract
Mass-based measurements of particulate matter (PM) within the National Ambient Air Quality Standards (NAAQS) often overlook the significance of fine and ultrafine aerosols—particles with diameters less than 1 µm and 100 nm, respectively. New particle formation (NPF), which can considerably influence air quality and human health, may be underrepresented if aerosols do not grow to an appreciable mass. Number-based measurements fill this void and are essential in capturing the influence of fine and ultrafine aerosols. In southern San Diego County, residents have endured noxious odors linked to discharge of raw sewage and industrial waste into the Tijuana River (TJR). A potential yet underrecognized risk is the contribution of TJR emissions to NPF and elevated ultrafine aerosol concentrations.

To investigate this, two monitoring sites were established in Summer 2024: one near a turbulent TJR branch (~4 km inland) and another at the Pacific coast (~1 km north of the TJR mouth). Each site was equipped to measure the particle number size distribution (PNSD) from 12 nm to 20 µm, select criteria gas pollutants, and meteorological conditions. Preliminary results have shown that during high wastewater flow rates, elevated concentrations of ultrafine aerosol were present. A subsequent shift in meteorological conditions and decrease in wastewater flow coincided with a decrease in aerosol concentrations.

This study evaluates the influence of TJR pollution on the PNSD and frequency of NPF events, providing crucial insight into overlooked sources of ultrafine aerosols in coastal environments.