RAPID: Water Concentrations and Emissions of Sewage-Related Compounds for the Tijuana River--Air Quality Effects for San Diego County, California

This RAPID project will investigate high ambient air levels of hydrogen sulfide in south San Diego County associated with the ongoing discharge of untreated municipal and industrial sewage to the Tijuana River. There are health concerns caused by breathing in fumes of hydrogen sulfide, as well as concerns about adverse health effects from the particulate sulfate that can be formed from the oxidation of hydrogen sulfide.

It is important to measure the concentration of these toxic compounds in the river water and determine the related amounts in the air during wintertime periods of low precipitation before the spring rains dilute their concentrations. This work will address important issues regarding the emissions of acutely and chronically harmful substances being discharged into the river and subsequently released into the atmosphere.

This project focuses on time and location dependent water-phase concentration data and modeling of the air-to-water emissions of important volatilizable compounds from the Tijuana River system. This data will be used with other information needed for estimating overall air-liquid mass transfer coefficients based on (a) the liquid-side resistance values (as determined primarily by flow velocity and depth regimes); and (b) the air-side resistance (as determined primarily by wind velocity regimes).

The relative magnitudes of the two resistances are affected by the compound itself and temperature-dependent Henry’s Gas Law Constant. Researchers from the University of California at San Diego and the University of California at Riverside will collaborate on efforts that use river water concentration data with temperature-dependent Henry’s Gas Law Constant values, flow rate and depth data/estimates, and meteorological wind data to estimate temporally dependent emissions from the Tijuana River system to the San Diego/Tijuana air shed for use in air quality modeling.

The knowledge gained from this work will inform the understanding of the air quality affecting populations at widely different scales, ranging from those who live and work in the local area, to the region surrounding and including the city of San Diego, and ultimately to the entire area affected by the transport of these emissions into other regions of the country.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.