Herculaneum Mott Street Air Monitoring Site

Since 2008, the primary and secondary ambient air standards for lead have remained at 0.15 micrograms per cubic meter (μg/m³). The primary standard reflects EPA's concern for public health, while the second standard demonstrates concern for public welfare. EPA bases the standard on the highest rolling three-month average over a period of three years and two months. A monitoring site meets the standard when the lead concentration is less than or equal to 0.15 μg/m³ averaged over three months. The standard is not met if the concentration exceeds that level once or more within a three-year period. 

In 2010, EPA not only established a new one-hour standard, but also introduced a new form for determining compliance. The primary National Ambient Air Quality Standard (NAAQS), based on health effects, for SO₂ is 75 parts per billion (ppb) averaged over one hour. The new form requires three years of data — the average SO₂ concentration from each hour of the year. The department and EPA calculate the design value, using the 99th percentile of one-hour daily maximum concentrations, averaged over three years.