Decrease in Ambient Polycyclic Aromatic Hydrocarbon Concentrations in California's San Joaquin Valley 2000-2019

Area of Science:

• Environmental Science
• Air Quality Monitoring
• Public Health

Background:

• Polycyclic aromatic hydrocarbons (PAHs) are significant air pollutants linked to adverse health outcomes.
• Understanding long-term trends in PAH concentrations is crucial for assessing public health risks in urban and industrial areas.
• The San Joaquin Valley faces unique air quality challenges due to its geography and diverse emission sources.

Purpose of the Study:

• To evaluate the trends of airborne polycyclic aromatic hydrocarbon (PAH) concentrations in Fresno, California, over a 19-year period (2000-2019).
• To identify potential sources responsible for observed changes in PAH levels.
• To inform public health strategies related to air pollution exposure in the San Joaquin Valley.

Main Methods:

• Analysis of 19 years of continuous and filter-based PAH concentration data from a central air monitoring site in Fresno.
• Statistical evaluation of temporal trends in both particle-bound and individual PAHs.
• Correlation analysis with potential emission sources including industrial, on-road vehicle, residential wood burning, and agricultural/biomass waste burning.

Main Results:

• A dramatic decline in outdoor airborne PAH concentrations was observed between 2000 and 2004, with levels maintained through 2019.
• This decline was evident in both continuous particle-bound PAHs (62% reduction by 2017-2018) and filter-based individual PAHs (82% reduction by 2001-2018).
• The most significant reduction in PAHs coincided with a decrease in agricultural and biomass waste burning in Fresno and Madera Counties.

Conclusions:

• Significant reductions in airborne PAH concentrations have been achieved in Fresno, California.
• The primary driver for the observed PAH decline appears to be reduced agricultural and biomass waste burning.
• Continued monitoring and source attribution are essential for managing air quality and protecting public health.