AQ Monitoring Results: Crockett: Benzo[a]pyrene at John Swett
This page last reviewed September 21, 2010
Benzo[a]pyrene is a polycyclic aromatic hydrocarbon (PAH). It exists in the atmosphere mainly in particle phase, and it is soluble in benzene, toluene, and xylene, but insoluble in water. California has determined under Proposition 65 that benzo[a]pyrene as a cancer-causing compound. 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.
Ambient Monitoring Results
Ambient levels of benzo[a]pyrene are routinely monitored at approximately twenty sites in the California air toxics monitoring network. The statewide average concentration of benzo[a]pyrene during 1998-2000 was 0.19 ng/m3, based
on values ranging from 0.025 ng/m3 to 4.6 ng/m3. The current routine monitor closest to Crockett is in Fremont.
Relative to the statewide average, the Fremont region was 32% lower for the same time period, averaging 0.13 ng/m3.
The ambient monitoring results at John Swett are provided here:
- A graph comparing the monthly summaries of benzo[a]pyrene at the community with historical statewide and regional levels
- A table of summary statistics
- Raw data in Excel format
Cancer risk is the number of excess cancer cases among a million people if the people are exposed to levels of a toxic air pollutant over 70 years. Benzo[a]pyrene is equivalent to less than 1% of the potential cancer risk of the nine measured compounds and the estimated diesel particulate matter.