Sheriff’s Office

NAAQS Pollutants & Air Toxics

The Clean Air Act, which was last amended in 1990, requires EPA to set National Ambient Air Quality Standards (40 CFR part 50) for pollutants considered harmful to public health and the environment. The Clean Air Act identifies two types of national ambient air quality standards. Primary standards provide public health protection, including protecting the health of "sensitive" populations such as asthmatics, children, and the elderly. Secondary standards provide public welfare protection, including protection against decreased visibility and damage to animals, crops, vegetation, and buildings.

The EPA has set National Ambient Air Quality Standards for six principal pollutants, which are called "criteria" air pollutants. Periodically, the standards are reviewed and may be revised. The current standards are listed below. Units of measure for the standards are parts per million (ppm) by volume, parts per billion (ppb) by volume, and micrograms per cubic meter of air (µg/m3). 

Pollutant

Primary/
Secondary

Averaging Time

Level

Form

Carbon Monoxide (CO)

primary

8 hours

9 ppm

Not to be exceeded more than once per year

1 hour

35 ppm

Lead (Pb)

primary and
secondary

Rolling 3 month average

0.15 μg/m3 (1)

Not to be exceeded

Nitrogen Dioxide (NO2)

primary

1 hour

100 ppb

98th percentile of 1-hour daily maximum concentrations, averaged over 3 years

primary and
secondary

1 year

53 ppb (2)

Annual Mean

Ozone (O3)

primary and
secondary

8 hours

0.070 ppm (3)

Annual fourth-highest daily maximum 8-hour concentration, averaged over 3 years

Particle Pollution (PM)

PM2.5

primary

1 year

12.0 μg/m3

annual mean, averaged over 3 years

secondary

1 year

15.0 μg/m3

annual mean, averaged over 3 years

primary and
secondary

24 hours

35 μg/m3

98th percentile, averaged over 3 years

PM10

primary and
secondary

24 hours

150 μg/m3

Not to be exceeded more than once per year on average over 3 years

Sulfur Dioxide (SO2)

primary

1 hour

75 ppb (4)

99th percentile of 1-hour daily maximum concentrations, averaged over 3 years

secondary

3 hours

0.5 ppm

Not to be exceeded more than once per year

(1) In areas designated nonattainment for the Pb standards prior to the promulgation of the current (2008) standards, and for which implementation plans to attain or maintain the current (2008) standards have not been submitted and approved, the previous standards (1.5 µg/m3 as a calendar quarter average) also remain in effect.

(2) The level of the annual NO2 standard is 0.053 ppm. It is shown here in terms of ppb for the purposes of clearer comparison to the 1-hour standard level.

(3) Final rule signed October 1, 2015, and effective December 28, 2015. The previous (2008) O3 standards additionally remain in effect in some areas. Revocation of the previous (2008) O3 standards and transitioning to the current (2015) standards will be addressed in the implementation rule for the current standards.

(4) The previous SO2 standards (0.14 ppm 24-hour and 0.03 ppm annual) will additionally remain in effect in certain areas: (1) any area for which it is not yet 1 year since the effective date of designation under the current (2010) standards, and (2)any area for which an implementation plan providing for attainment of the current (2010) standard has not been submitted and approved and which is designated nonattainment under the previous SO2 standards or is not meeting the requirements of a SIP call under the previous SO2 standards (40 CFR 50.4(3)).  A SIP call is an EPA action requiring a state to resubmit all or part of its State Implementation Plan to demonstrate attainment of the required NAAQS.

 

Contact Us

Phone: (515)-286-3705
Fax: (515)-286-3437
Email: airquality@polkcountyiowa.gov
Operating Hours: 7am - 4:30pm / M-F
Address:
5885 NE 14 Street
Des Moines, IA 50313