FAQ about air toxics data interactive tool

What are air toxics?

The term air toxics refer to a group of more than 100 air pollutants that may cause cancer or other serious health effects. Unlike criteria pollutants, which include PM2.5, ozone, sulfur dioxide, carbon monoxide, nitrogen dioxide, and lead, air toxic pollutants do not have air quality standards. Minnesota manages air toxics by requiring pollution control methods which reduce air toxics emissions. The MPCA works to ensure concentrations of all air toxics are below established guidelines called health benchmarks.

What are health benchmarks?

A health benchmark defines a value below which a pollutant is unlikely to cause adverse health effects. The MPCA uses health benchmarks to assess the health risks from both short and long-term exposures to air pollutants. More information about health benchmarks is available on the Air Toxics in Minnesota webpage.

What measures or statistics are included in the Minnesota Air Toxics Monitoring web application?

The Minnesota Air Toxics Monitoring web app summarizes annual air toxics monitoring results. Summary results include:

  • Count of Valid Samples: The number of 24-hour samples collected in a calendar year. Because air toxics are sampled once every six days, a complete year of sampling will result in 60 or 61 samples. 
  • Percent of samples detected: The number of 24-hour samples collected with results greater than or equal to the detection limit divided by the number of valid samples collected in a year.
  • Annual average:  The average of all valid 24-hour samples collected in a calendar year. To account for values below the detection limit, the annual average was calculated using maximum likelihood estimation.
  • 95% Upper Confidence Limit (95% UCL): The 95% UCL  for a mean is defined as a value that, when repeatedly calculated for randomly drawn subsets of size n, equals or exceeds the true population mean 95% of the time. We calculate the 95% UCL using bootstrap methods. In risk assessment, the 95% UCL is used when comparing measured air toxics concentrations to health benchmarks.
  • Percent of most-protective long-term health benchmark: The annual 95% UCL divided by the most protective long-term health benchmark. Results greater than 100% indicate measured pollutant concentrations are above the long-term health benchmark and may exceed risk guidelines.
  • 24-hour maximum: The highest measured 24-hour concentration in a calendar year.
  • Estimated hourly maximum: Because air toxics are collected in a single 24-hour sample once every six days we must estimate the maximum hourly air toxics concentration. To estimate the annual hourly maximum concentration we multiply the 2nd highest 24-hour maximum concentration by 10.

What is a detection limit and what does it mean if a pollutant is below the detection limit?

  • Even though modern chemical analysis can detect very low levels of pollutants, sometimes concentrations are so low that they cannot be detected. A detection limit is the lowest amount of a substance that can be distinguished from the absence of that substance, or a blank value. The detection limit is determined in the lab by running many low level standards of a pollutant, and is completed each year for each pollutant.
  • In the Minnesota Air Toxics Monitoring web app, a pollutant’s annual average concentration is considered below the detection limit if more than 80% of all samples collected in a year were measured below the detection limit.

What is the difference between the circles and the triangles on the Annual Pollutant Summary Map?

The circles represent the annual average pollutant concentration for pollutants with at least 20% of samples above the detection limit. The triangles represent pollutants that are considered below the detection limit. Pollutants are considered below the detection limit if more than 80% of samples collected in a year were measured below the detection limit.

What do the colors green, yellow, orange and blue in the Annual Pollutant Summary Map and the Annual Pollutant Results Compared to Health Benchmarks chart mean?

  • Green means that a pollutant’s 95% UCL concentration  is less than half of the most-protective long-term health benchmark.
  • Yellow means that a pollutant’s 95% UCL concentration is between half or equal to its most-protective long-term health benchmark.
  • Orange means that a pollutant’s 95% UCL concentration is over its most-protective long-term health benchmark. The health benchmarks are developed to be protective of sensitive populations. When an air toxic air concentration is over a health benchmark, it means that measured pollutant concentrations are above the long-term health benchmark and may exceed risk guidelines.
  • Blue means that a pollutant was measured but it does not have a chronic health benchmark to compare against.

Why should I care about air toxics concentrations?

Because of the following:

  • They are harmful to human and plant health at elevated exposures
  • Learning about them teaches us about sources of other air pollutants
  • Learning about them helps us learn about how air pollutants form and are transported.

How can I get the daily data?

Email the MPCA’s Data Desk, datadesk.mpca@state.mn.us.

What is the grey area and dashed line connected to the top of the solid bars in the bar chart?

The grey area of the bar chart represents the 95% Upper Confidence Limit. When looking at air toxics concentrations we create an annual summary of based on samples taken once during every six days. Because these measurements don’t include information for every day of the year, there is uncertainty surrounding our estimate for a pollutant’s true average concentration over the course of the whole year. Due to this missing information, it is possible that the average found based on the 1 in 6 day sampling could be somewhat lower or somewhat higher than if we had sampled every day of the year.

To err on the side of safety and reduce the likelihood of underestimating the pollutant’s concentration, we calculate a protective buffer around the average called the 95% upper confidence limit (the grey area above the solid bars). The far end of this buffer, which is shown by the dashed line, marks where the true average of the pollutant will fall below 95% of the time. The 95% Upper Confidence Limit is what we compare to health benchmarks to help ensure that our calculations are health protective.

I see that the air pollutants are higher in my area, what can I do about that?

There are three ways people can become more involved in lowering air pollution.

  • Becoming a public participant in MPCA work-comment on the MPCA ambient air network plan, come to a public meeting on an air permit, visit the Eco Experience at the State Fair.
  • Lowering individual air pollutants by driving less or a more fuel efficient vehicle, keeping living space a moderate temperature, and other lower impact behaviors.
  • Talking to people around you about lowering their impacts or working with your school to lower impacts such as reducing idling at pick up and drop off.

What kinds of instruments measure these air pollutants?

There are three groups of measurements that are made, and they are divided into groups of air pollutants that are collected in the same way: carbonyls (e.g. formaldehyde), volatile organic compounds (e.g. benzene), and metals (e.g. lead). Each of these pollutants are collected by pulling air with an air pump. Carbonyls are collected onto a trap, volatile organic compounds are collected in a metal canister, and metals are collected on a filter. Learn more about these methods on the U.S. Environmental Protection Agency's Air Monitoring Methods webpage

To learn more about air monitoring efforts and to see a picture of an air monitor, visit the air pollution monitoring webpage.

For more information

For more information, please call 651-296-6300 or 1-800-657-3864 and ask for air data analysis staff.  More information about the MPCA’s air monitoring program is available on the Air Monitoring webpage.