Troost Air Monitoring Site

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.

In 2010, EPA revised the one-hour NO₂ standard. The primary National Ambient Air Quality Standard (NAAQS), based on health effects, for NO₂ is 100 parts per billion (ppb) averaged over one hour. The one-hour standard is based on a three-year design value, which is calculated by taking the 98th percentile of the one-hour daily maximum concentrations recorded each year, and averaging three years together. The annual standard of 0.053 parts per million (ppm) – or 53 ppb – is based on the annual arithmetic mean and is not to be exceeded. An area is in compliance if the design value is at or below the standard.

The primary National Ambient Air Quality Standards (NAAQS), based on health effects, for fine particulate matter smaller than 2.5 micrometers in diameter, PM_2.5, is 35 micrograms per cubic meter of air (μg/m³) averaged over 24 hours (98th percentile, averaged over three years) and 12 μg/m³ annual average (averaged over three years). 

The primary National Ambient Air Quality Standard (NAAQS), based on health effects, for particulate matter smaller than 10 micrometers, PM₁₀, is 150 micrograms per cubic meter of air (μg/m³) averaged over 24 hours — not to be exceeded more than once per year on average over three years.