OEHHA health-based exposure levels and typical background levels of air pollution

OEHHA is the department within the California Environmental Protection Agency responsible for evaluating health risks related to chemical contaminants. The OEHHA health-based exposure levels (known as Reference Exposure Levels) are based on available studies for a wide variety of health conditions other than cancer. Pollution levels below the health-based standards are not expected to cause non-cancer health effects. OEHHA establishes three types of Reference Exposure Levels based on different time intervals:

• Short-term (Acute) exposure: Exposure for 1 hour or less.

• Long-term (Chronic) exposure: Exposure anywhere from 1 year to a lifetime

• Offsite Worker Exposure: Exposure for 8 hours/day, repeated over a year.

The specific values for pollutants can be found on this webpage: 
https://oehha.ca.gov/air/general-info/oehha-acute-8-hour-and-chronic-reference-exposure-level-rel-summary. 

Please Note: These OEHHA long-term exposure levels are meant to be compared to data averaged over the course of one year. However, South Coast AQMD is taking a conservative, health-protective approach, by comparing each individual laboratory result against long-term exposure levels. Based on this, should any single result be above the long-term exposure level, it does not mean that negative health effects would be experienced.

There are no equivalent “thresholds” for cancer risk.  Instead, the higher the concentration of pollution, the higher the risk. Given that there is no “threshold” for comparison, each sample is compared to typical “background” levels of the same pollutant. These typical “background” levels are established through the Multiple Air Toxics Exposure Study. This comparison helps answer the question about whether the levels in the sample are similar to levels found in typical residential or commercial locations in the region.