Air Guidance Values

The Minnesota Department of Health (MDH) develops health-based guidance values to evaluate potential human health risks from exposures to chemicals in ambient air.

An air guidance value is a concentration of a chemical that is likely to pose little or no risk to human health. All air values are expressed as micrograms of chemical per cubic meter of air (μg/m3). Air values are developed to protect human health for a specific length of exposure; generally acute (24 hours or less), short-term (>24 hours - 30 days), sub-chronic (>30 days - ~ 8 years), and chronic (>8 years - lifetime) durations.

Air guidance values may be used by the public, industry, state and local risk managers, and other stakeholders to assist in evaluating potential health risks to people from exposures to a chemical in air. These values can be used for assessing risks in the environmental review process, developing air pollution permits, health risk assessments and other site-specific assessments. MDH does not enforce air guidance values.

Air guidance values are developed using public health protective practices that protect susceptible portions of the population (including but not limited to children, pregnant women and their fetuses, individuals compromised by pre-existing diseases, and elderly persons). However, these values may not be protective of hypersensitive individuals who may respond to low level chemical exposures. Additionally, the values do not determine health risk from exposure to several toxic chemicals at once.

There are three categories of air guidance values: Health Based Values (HBVs), Risk Assessment Advice (RAA), and Health Risk Values (HRVs). These values are divided into two tables below: Health-Based Values and Risk Assessment Advice (more current air guidance values) and 2002 Health Risk Values (that were developed over 18 years ago and appear in rule). MDH should be consulted before using the 2002 Health Risk Values.

Health Based Values and Risk Assessment Advice

MDH currently develops Health Based Values (HBVs) and Risk Assessment Advice (RAA) when there is a need for guidance to evaluate health risks to chemicals in air, often by request of the Minnesota Pollution Control Agency or other state agencies. HBVs are developed after undergoing a comprehensive chemical review of available toxicity studies. RAA may contain greater uncertainty than HBVs as a result of a less rigorous chemical review or because toxicity information is more limited. MDH also develops RAA on a case-by-case basis for specific conditions or specific sites. It is not appropriate to apply a site-specific RAA to other sites without consulting MDH.

HBVs and RAA have not been promulgated using a public rulemaking process. Instead, an HBV/RAA is technical guidance made available by MDH.

In 2020, MDH standardized and updated its definitions of durations for air guidance.  The updated duration key is found in the below table, and a more detailed description of the durations can be found in the document Air Exposure Durations (PDF).

Note that because the standardization of duration definitions occurred in 2020, all chemicals reviewed before 2020 may not have the exact same definition for durations.  Please contact MDH if you have questions about a specific duration for a specific chemical. MDH will be updating the list of HBVs and RAAs to make them consistent with the 2020 definitions as time allows.  The date that a chemical review is completed is noted as a subscript under the Value Type in the table.  For example, Acrolein is HBV₁₂, meaning that it is a Health Based Value completed in 2012.

HBVs and RAA have not been promulgated using a public process. Instead, an HBV/RAA is technical guidance made available by MDH.

NA = Not Applicable
ND = Not Derived.

^*The Minnesota Pollution Control Agency has calculated an inhalation unit risk of 400 (μg/m3)-1 using the MDH recommended oral slope factor for 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD).

^† This value may not provide protection for individuals who have been previously sensitized to this chemical.

^‡Set at short-term value

2002 Health Risk Values

Health Risk Values (HRV) were adopted into Rule in 2002 using the best peer-reviewed science and public health policies available at the time of their development. For more information, see Health Risk Values Rules for Ambient Air. The application of HRVs is not specified in Minnesota rule. Some HRVs have been superseded by more recent MDH advice, as indicated on the HRV table below. There may be critical new scientific chemical information available since the HRVs were developed. Please contact MDH for further guidance regarding the use of HRVs.

^§This HRV is for a chemical where there is little magnitude difference between the level where mild irritancy occurs and levels where more severe adverse health effects occur.

^¶This HRV may not provide protection for individuals who have been previously sensitized to this chemical.

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