Ambient Monitoring Background Data for Use In Air Quality Impact Evaluation

The Monitoring Section conducts air quality studies and is responsible for the continuous ambient air monitoring program that measures and records ambient ozone, nitrogen oxides, carbon monoxide, particulate matter, sulfur dioxide and toxic element concentrations. There are monitoring stations in Underhill, Burlington, Rutland and Bennington, VT. This information is collected as part of a federal Environmental Protection Agency program and published annually by the EPA. This data is also used to establish ambient air quality background concentrations, which must be considered when determining allowable permit limits during an Air Quality Impact Evaluation. More information on ambient air quality monitoring can be found on the Air Quality & Climate Division's Monitoring page.

Carbon Monoxide (CO)

Sulfur Dioxide (SO2)

* The 1-hour SO2 primary standard became effective June 22, 2010. The reported 1-hour value for each respective year is the 99th percentile value of the daily maximums, not the overall maximum 1-hour value. See 40 CFR Part 50 Appendix T for details. For an area to attain the 1-hour SO2 primary standard, the 99th percentile of 1-hour daily maximum concentrations for each year, averaged over 3 years, must not exceed the standard. For an area to attain the 3-hour SO2 secondary standard, the respective standard may not be exceeded more than once per year.
** To convert ppb values to units of ug/m3 multiply ppb value by 2.618.
*** This value is an average of the three years.

Nitrogen Dioxide (NO2)

* The 1-hour primary NO2 standard became effective April 12, 2010. The reported 1-hour value for each respective year is the 98th percentile value of the daily maximums, not the overall maximum 1-hour value. See 40 CFR Part 50 Appendix N for details. For an area to attain the 1-hour NO2 primary standard, the 98th percentile 1-hour value for each year, averaged over 3 years, must not exceed the standard. For an area to attain the annual NO2 primary and secondary standard, the annual mean of the 1-hour values must not exceed the standard.
** To convert ppb values to units of μg/m3 multiply ppb value by 1.881.
*** This value is an average of the three years.

Particulate Matter (PM2.5)

* The 24-hour PM2.5 standard was revised from 65 μg/m3 downward to 35 μg/m3 effective December 18, 2006. The annual primary PM2.5 standard was revised from 15 μg/m3 to 12 μg/m3 effective March 18, 2013 and further strengthened to 9.0 μg/m3 on February 7, 2024. The reported 24-hour value for each respective year is the 98th percentile value, not the maximum 24-hour value. For an area to attain the 24-hour PM2.5 primary and secondary standard, the 98th percentile 24-hour value for each year, averaged over 3 years, must not exceed the standard. For an area to attain the annual PM2.5 primary and secondary standard, the annual mean of the 24-hour values, averaged over 3 years, shall not exceed the standard.
** This value is an average of the three years

Particulate Matter (PM10)

* The annual PM10 National Ambient Air Quality Standard (NAAQS) was eliminated effective December 18, 2006. The 24-hour PM10 NAAQS was retained as the new primary and secondary standard for coarse particulates. For an area to attain the 24-hour PM10 primary and secondary standard, the standard must not be exceeded more than once per year on average over 3 years.
** This value is an average of the three years.

All monitored values reported above are the maximum measured values from the respective monitoring stations, except where noted for SO2 (1-hour), NO2 (1-hour), and PM2.5. These values are based on 99th or 98th percentile value as established by the standard. The background value to use in modeling analyses is an average of the reported monitored values over the three years. The appropriate background value to use for modeling analyses for locations in the state not having its own monitoring station will be determined by the Agency. The selected background value should be used with the appropriate source impact predicted by the air pollutant dispersion model. The above monitored values need to be added to the modeled source impact from the dispersion model for comparison to the ambient air quality standard. Only the modeled source impact alone is used for comparison to Prevention of Significant Deterioration (PSD) increments. The appropriate source impact from the dispersion model to use for determining compliance with the standards or increments depends on the type of standard, the averaging time of the standard being analyzed and the number of years of meteorological data being modeled. Please consult 40 CFR Part 51 Appendix W.