AQ Monitoring Results:
Crockett: Formaldehyde at John Swett

This page last reviewed September 27, 2010


One of the important contributors to health risk, formaldehyde is a colorless gas at room temperature. The odor is irritating and pungent. Limited human studies have reported an association between formaldehyde exposure and lung and nasopharyngeal cancer. California has determined under Assembly Bill 1807 and Proposition 65 that formaldehyde is a cancer-causing compound. Formaldehyde can also induce or exacerbate asthma. Vapors are highly irritating to the eye and respiratory track. The ARB has taken regulatory actions to reduce formaldehyde emissions.

Formaldehyde is both directly emitted into the atmosphere and formed in the atmosphere as a result of photochemical reaction. The predominant sources of formaldehyde emissions are vehicle exhaust. Mobile sources contribute 85% and industry-related stationary sources contribute 15% of the statewide emissions. Naturally, formaldehyde occurs in forest fires, animal waste, microbial products of biological systems, and plant volatiles. It can also be formed in seawater by photochemical processes. Due to the adoption of the Air Resources Board's Low Emissions/Clean Fuels regulations, the formaldehyde emissions from cars and light-duty trucks are expected to decrease.

Ambient Monitoring Results

Ambient levels of formaldehyde are routinely monitored at approximately twenty sites in the California air toxics monitoring network. The statewide average concentration of formaldehyde during 1998-2000 was 2.8 ppb (parts per billion), with values ranging from 0.05 ppb to 13 ppb. The current routine monitor closest to Crockett is in Fremont. Relative to the statewide average, the Fremont region was 32% lower, with an average concentration of 1.9 ppb for the same time period.

The ambient monitoring results at John Swett are provided here:

  • A graph comparing the monthly summaries of formaldehyde at the community with historical statewide and regional levels
  • A table of summary statistics
  • Raw data in Excel format

Cancer Risk

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. Formaldehyde represents approximately 12% of the potential cancer risk of the nine measured compounds, excluding diesel particulate matter. Formaldehyde represents approximately 2% of the potential cancer risk of the nine measured compounds and the estimated diesel particulate matter.