Code of Massachusetts Regulations
310 CMR - DEPARTMENT OF ENVIRONMENTAL PROTECTION
Title 310 CMR 6.00 - Ambient Air Quality Standards For The Commonwealth Of Massachusetts
Section 6.04 - Standards

1. The level of the primary one hour ambient air quality standard for oxides of sulfur is 75 parts per billion (ppb, which is 1 part in 1,000,000,000), measured in the ambient air as sulfur dioxide (SO2).

2. The one hour primary standard is met at an ambient air quality monitoring site when the three-year average of the annual (99th percentile) of the daily maximum one hour average concentrations is less than or equal to 75 ppb, as determined in accordance with 40 CFR Part 50, Appendix T.

3. The level of the standard shall be measured by a reference method based on 40 CFR Part 50, Appendix A or A-1 or by a federal equivalent method (FEM) designated in accordance with 40 CFR Part 53.

1. The level of the secondary three-hour ambient air quality standard for oxides of sulfur is 0.5 parts per million (ppm), not to be exceeded more than once per calendar year. The three-hour averages shall be determined from successive non-overlapping three-hour blocks starting at midnight each calendar day and shall be rounded to one decimal place (fractional parts equal to or greater than 0.05 ppm shall be rounded up).

2. Oxides of sulfur shall be measured in the ambient air as sulfur dioxide by the reference method described in 40 CFR Part 50, Appendix A or by a federal equivalent method designated in accordance with 40 CFR Part 53.

3. To demonstrate attainment, the second-highest three-hour average must be based upon hourly data that are at least 75% complete in each calendar quarter. A three hour block average shall be considered valid only if all three hourly averages for the three hour period are available. If only one or two hourly averages are available, but the three hour average would exceed the level of the standard when zeros are substituted for the missing values, subject to the rounding rule of 310 CMR 6.04(1), then this shall be considered a valid three-hour average. In all cases, the three-hour block average shall be computed as the sum of the hourly averages divided by three.

1. The level of the primary and secondary 24-hour ambient air quality standards for particulate matter is 150 micrograms per cubic meter (µg/m3), 24-hour average concentration. The standards are attained when the expected number of days per calendar year with a 24-hour average concentration above 150 µg/m3, as determined in accordance with 40 CFR Part 50, Appendix K is equal to or less than one.

2. For the purpose of determining attainment of the primary and secondary standards, particulate matter shall be measured in the ambient air as PM10 (particles with an aerodynamic diameter less than or equal to a nominal 10 micrometers) by:

1. The primary ambient air quality standards for PM2.5 are 12.0 micrograms per cubic meter (µg/m3) annual arithmetic mean concentration and 35 µg/m3 24-hour average concentration measured in the ambient air as PM2.5 (particles with an aerodynamic diameter less than or equal to a nominal 2.5 micrometers) by either:

2. The primary annual PM2.5 standard is met when the annual arithmetic mean concentration, as determined in accordance with 40 CFR Part 50, Appendix N is less than or equal to 12.0 µg/m3.

3. The primary 24-hour PM2.5 standard is met when the 98th percentile 24-hour concentration, as determined in accordance with 40 CFR Part 50, Appendix N is less than or equal to 35 µg/m3.

1. The secondary ambient air quality standards for PM2.5 are 15.0 micrograms per cubic meter (µg/m3) annual arithmetic mean concentration, and 35 µg/m3 24-hour average concentration measured in the ambient air as PM2.5 (particles with an aerodynamic diameter less than or equal to a nominal 2.5 micrometers) by either:

2. The annual secondary PM2.5 standard is met when the annual arithmetic mean concentration, as determined in accordance with 40 CFR Part 50, Appendix N is less than or equal to 15.0 µg/m3.

3. The 24-hour secondary PM2.5 standard is met when the 98th percentile 24-hour concentration, as determined in accordance with 40 CFR Part 50, Appendix N is less than or equal to 35 µg/m3.

1. 9 parts per million (10 milligrams per cubic meter) for an eight-hour average concentration not to be exceeded more than once per year; and

2. 35 parts per million (40 milligrams per cubic meter) for a one hour average concentration not to be exceeded more than once per year.

1. A reference method based on 40 CFR Part 50, Appendix C and designated in accordance with 40 CFR Part 53; or

2. An equivalent method designated in accordance with 40 CFR Part 53.

1. A reference method based on 40 CFR Part 50, Appendix F; or

2. By a Federal equivalent method (FEM) designated in accordance with 40 CFR Part 53.

1. A reference method based on 40 CFR Part 50, Appendix G and designated in accordance with 40 CFR Part 53 or;

2. An equivalent method designated in accordance with 40 CFR Part 53.