AQ Monitoring Results:
Fresno: Polycyclic Aromatic Hydrocarbons at Fremont School

This page last reviewed September 28, 2010


Polycyclic aromatic hydrocarbons (PAHs) exist in the atmosphere mainly as particles, and are soluble in benzene, toluene, and xylene, but insoluble in water. California has determined under Proposition 65 that some of the PAHs including benzo[a]pyrene are cancer-causing compounds. Chronic exposure to benzo[a]pyrene in humans has resulted in dermatitis, photosensitization in sunlight, eye irritation, and cataracts. The ARB has take regulatory actions to reduce benzo[a]pyrene emissions.

Benzo[a]pyrene is mainly produced by the incomplete combustion of fossil fuels and vegetable matter. The primary industrial sources that have reported emissions of benzo[a]pyrene in California are petroleum refineries, industrial machinery manufacturers, and the wholesale trade in petroleum and petroleum products. Indoor sources of benzo[a]pyrene include tobacco smoking, wood-burning in fireplaces and wood stoves. Benzo[a]pyrene occurs naturally in crude oils, shale oils, and coal tars. It is also emitted with gases and fly ash from active volcanoes.

The select polycyclic aromatic hydrocarbons monitored in the California air toxics network include:

Benzo[a]pyrene; Benzo[b]fluoranthene; Benzo[g,h,i]perylene; Benzo[k]fluoranthene; Dibenz[a,h]anthracene; Indeno[1,2,3-c,d]pyrene.

Ambient Monitoring Results

Ambient levels of select polycyclic aromatic hydrocarbons are routinely monitored at approximately twenty sites in the California air toxics monitoring network. The statewide average concentration of the selected polycyclic aromatic hydrocarbons during 1998-2001 was 1.21 ng/m3. Relative to the statewide average, the Fresno region within the California air toxics network was 134% higher for the same time period, averaging 2.82 ng/m3. The method used by the air toxics monitoring network is filter based and only includes a select subset of the PAHs, where the method used at Fremont School is based on continuous hourly average measurements of all the PAHs using a different monitoring instrument. Therefore, there are no statewide or regional comparisons for the aggregate PAHs.

The ambient monitoring results at Fremont School are provided here:

  • A graph comparing the monthly summaries of polycyclic aromatic hydrocarbons (there are no comparisons available for statewide and regional aggregate PAHs)
  • A table of summary statistics
  • Raw data in Excel format

Cancer Risk

Cancer risk estimates represent the chance of excess cancer cases among a million people if the people breathe the average levels of a toxic air pollutant over 70 years. At this time, the percentage cancer risk at Fremont School attributable to the aggregate of polycyclic aromatic hydrocarbons has not been determined.