ARTICLE 2. AMBIENT AIR QUALITY STANDARDS; AREA DESIGNATIONS; 

CLASSIFICATIONS 

R18-2-201. Particulate Matter: PM10 and PM2.5 

A. PM10 Standards 

1. The level of the primary and secondary ambient air quality standards for PM10 is 150 

micrograms per cubic meter of PM10 - 24-hour average concentration. 

2. To determine attainment of the primary and secondary standards, a person shall measure 

PM10 in the ambient air by: 

a. A reference method based on 40 CFR 50, Appendix J, and designated according to 40 

CFR 53; or 

b. An equivalent method designated according to 40 CFR 53. 

3. The primary and secondary 24-hour ambient air quality standards for PM10 are attained 

when the expected number of days per calendar year with a 24-hour average concentration 

above 150 micrograms per cubic meter, determined according to 40 CFR 50, Appendix K, 

is less than or equal to one. 

B. PM2.5 Standards 

1. The primary ambient air quality standards for PM2.5 are: 

a. 15 micrograms per cubic meter of PM2.5 - annual arithmetic mean concentration. 

b. 35 micrograms per cubic meter of PM2.5 - 24-hour average concentration. 

2. The secondary ambient air quality standards for PM2.5 are: 

a. 15 micrograms per cubic meter of PM2.5 - annual arithmetic mean concentration. 

b. 35 micrograms per cubic meter of PM2.5 - 24-hour average concentration. 

3. To determine attainment of the primary and secondary standards, a person shall measure 

PM2.5 in the ambient air by: 

a. A reference method based on 40 CFR 50, Appendix L, and designated according to 40 

CFR 53; or 

b. An equivalent method designated according to 40 CFR 53. 

4. The primary and secondary annual ambient air quality standards for PM2.5 are met when 

the annual arithmetic mean concentration, determined according to 40 CFR 50, Appendix 

N, is less than or equal to 15 micrograms per cubic meter. 

5. The primary and secondary 24-hour ambient air quality standards for PM2.5 are met when 

the 98th percentile 24-hour concentration, determined according to 40 CFR 50, Appendix 

N, is less than or equal to 35 micrograms per cubic meter. 

Historical Note 

Amended effective December 22, 1976 (Supp. 76-5). Former Section R9-3-201 repealed, 

new Section R9-3-201 adopted effective May 14, 1979 (Supp. 79-1). Amended effective 

October 2, 1979 (Supp. 79-5). Editorial correction, subsection (E) (Supp. 80-2). 

Amended effective August 29, 1980 (Supp. 80-4). Amended subsection(B)(1) and 

deleted subsections (C) through (E) effective September 22, 1983 (Supp. 83-5). Former 

Section R9-3-201 renumbered without change as Section R18-2-201 (Supp. 87-3). 

Amended effective September 26, 1990 (Supp. 90-3). Amended by final rulemaking at 11 

A.A.R. 3305, effective October 3, 2005 (Supp. 05-3). Section corrected to include 

subsection (B), which was inadvertently omitted in Supp. 05-3 (Supp. 07-4). Amended by 

final rulemaking at 18 A.A.R. 1542, effective August 7, 2012 (Supp. 12-2). 
R18-2-202. Sulfur Oxides (Sulfur Dioxide) 

A. The primary ambient air quality standards for sulfur oxides, measured as sulfur dioxide, are: 

1. 0.03 parts per million (ppm) (80 μg/m3) -- annual arithmetic mean. 

2. 0.14 parts per million (ppm) (365 μg/m3) - maximum 24-hour concentration not to be 

exceeded more than once per calendar year. 

3. 75 parts per billion (ppb) - maximum one-hour concentration. 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 parts per billion, as determined according to 40 CFR 50, Appendix T. 

B. The secondary ambient air quality standard for sulfur oxides, measured as sulfur dioxide, is 0.5 

parts per million (ppm) (1300 μg/m3) -- maximum three-hour concentration not to be exceeded 

more than once per year. 

C. The level of the standards shall be measured by a reference method based on 40 CFR 50, 

Appendix A or A-1, or by a Federal Equivalent Method designated according to 40 CFR 53. 

D. The standards in subsections (A)(1) and (2) shall apply: 

1. In an area designated nonattainment for a standard in subsection (A)(1) or (2) as of August 

23, 2011, and areas not meeting a state implementation plan call for a standard in 

subsection (A)(1) or (2), until the state submits pursuant to section 191 of the Act, and the 

Administrator approves, a state implementation plan providing for attainment the standard 

in subsection (A)(3) in that area. 

2. In areas other than those identified in subsection (D)(1), until the effective date of the 

designation of that area, pursuant to section 107 of the act, for the standard in subsection 

(A)(3). 

Historical Note 

Amended effective December 22, 1976 (Supp. 76-5). Former Section R9-3-202 repealed, 

new Section R9-3-202 adopted effective May 14, 1979 (Supp. 79-1). Amended effective 

October 2, 1979 (Supp. 79-5). Amended effective August 29, 1980 (Supp. 80-4). 

Amended subsection (B) effective May 28, 1982 (Supp. 82-3). Amended by deleting 

subsections (C) through (E) effective September 22, 1983 (Supp. 83-5). Former Section 

R9-3-202 renumbered without change as Section R18-2-202 (Supp. 87-3). Amended 

effective September 26, 1990 (Supp. 90-3). Amended by final rulemaking at 11 A.A.R. 

3305, effective October 3, 2005 (Supp. 05-3). Amended by final rulemaking at 18 A.A.R. 

1542, effective August 7, 2012 (Supp. 12-2). 
R18-2-203. Ozone: One-hour Standard and Eight-hour Average Standard 

A. One-hour standard. Until June 15, 2005: 

1. The one-hour ambient air quality standard for ozone is 0.12 ppm (235 micrograms per cubic 

meter). 

2. The one-hour secondary ambient air quality standard for ozone is 0.12 ppm (235 micrograms 

per cubic meter). 

3. The one-hour standards are attained when the expected number of days per calendar year 

with maximum hourly average concentrations above 0.12 ppm (235 micrograms per cubic 

meter) is less than or equal to 1, determined by 40 CFR 50, Appendix H. 

B. Eight-hour averaged standard. 

1. The eight-hour average primary ambient air quality standard for ozone is 0.075 ppm. 

2. The eight-hour average secondary ambient air quality standard for ozone is 0.075 ppm. 

3. To determine attainment of the primary and secondary standards, a person shall measure 

ozone in the ambient air by: 

a. A reference method based on 40 CFR 50, Appendix D, and designated according to 40 

CFR 53; or 

b. An equivalent method designated according to 40 CFR 53. 

4. Eight-hour average primary and secondary ambient air quality standards for ozone are met 

at an ambient air quality monitoring site when the three-year average of the annual fourth 

highest daily maximum eight-hour average ozone concentration is less than or equal to 

0.075 ppm, determined according to 40 CFR 50, Appendix P. 

Historical Note 

Amended effective December 22, 1976 (Supp. 76-5). Former Section R9-3-204 repealed, 

new Section R9-3-204 adopted effective May 14, 1979 (Supp. 79-1). Amended effective 

October 2, 1979 (Supp. 79-5). Amended effective August 29, 1980 (Supp. 80-4). 

Amended by deleting subsections (B) through (D) effective September 22, 1983 (Supp. 

83-5). Former Section R9-3-204 renumbered without change as Section R18-2-204 

(Supp. 87-3). Section R18-2-103 renumbered from R18-2-204 and amended effective 

September 26, 1990 (Supp. 90-3). Amended by final rulemaking at 11 A.A.R. 3305, 

effective October 3, 2005 (Supp. 05-3). Amended by final rulemaking at 18 A.A.R. 1542, 

effective August 7, 2012 (Supp. 12-2). 
R18-2-204. Carbon monoxide 

A. The primary ambient air quality standards for carbon monoxide are: 

1. 9 parts per million (10 milligrams per cubic meter) -- maximum eight-hour concentration 

not to be exceeded more than once per year. 

2. 35 parts per million (40 milligrams per cubic meter) -- maximum one-hour concentration 

not to be exceeded more than once per year. 

B. An eight-hour average shall be considered valid if at least 75% of the hourly averages for the 

eight-hour period are available. In the event that only six or seven hourly averages are 

available, the eight-hour average shall be computed on the basis of the hours available using 6 

or 7 as the divisor. 

C. When summarizing data for comparison with the standards, averages shall be stated to one 

decimal place. Comparison of the data with the levels of the standards in parts per million shall 

be made in terms of integers with fractional parts of 0.5 or greater rounding up. 

Historical Note 

Amended effective December 22, 1976 (Supp. 76-5). Former Section R9-3-205 repealed, 

new Section R9-3-205 adopted effective May 14, 1979 (Supp. 79-1). Amended effective 

October 2, 1979 (Supp. 79-5). Amended effective August 29, 1980 (Supp. 80-4). 

Amended by deleting subsections (B) through (D) effective September 22, 1983 (Supp. 

83-5). Former Section R9-3-205 renumbered without change as Section R18-2-205 

(Supp. 87-3). Former Section R18-2-204 renumbered to R18-2-203, new Section R18-2-

204 renumbered from R18-2-205 and amended effective September 26, 1990 (Supp. 90-

3). 
R18-2-205. Nitrogen Oxides (Nitrogen Dioxide) 

A. The primary ambient air quality standards for oxides of nitrogen, measured in the ambient air as nitrogen dioxide, are: 

1. 53 parts per billion - annual average concentration. 

2. 100 parts per billion - one-hour average concentration. 

B. The secondary ambient air quality standard for nitrogen dioxide is 0.053 (parts per million (100 micrograms per cubic meter) -

- annual arithmetic mean. 

C. The levels of the standards shall be measured by a reference method based on 40 CFR 50, Appendix F or a federal equivalent 

method designated in accordance with 40 CFR 53. 

D. The annual primary standard is met when the annual average concentration in a calendar year is less than or equal to 53 ppb, as 

determined in accordance with 40 CFR, Appendix S for the annual standard. 

E. The one-hour primary standard is met when the three-year average of the annual 98th percentile of the daily maximum one-hour 

average concentration is less than or equal to 100 parts per billion, as determined in accordance with 40 CFR 50, Appendix S. 

F. The secondary standard is attained when the annual arithmetic mean concentration in a calendar year is less than or equal to 

0.053 ppm, rounded to three decimal places, with fractional parts equal to or greater than 0.0005 ppm rounded up. To 

demonstrate attainment, an annual mean shall be based upon hourly data that is at least 75% complete or upon data derived 

from the manual methods, that is at least 75% complete for the scheduled sampling days in each calendar quarter. 

Historical Note 

Amended effective December 22, 1976 (Supp. 76-5). Former Section R9-3-206 repealed, new Section R9-3-206 adopted 

effective May 14, 1979 (Supp. 79-1). Amended effective October 2, 1979 (Supp. 79-5). Amended effective August 29, 

1980 (Supp. 80-4). Amended by deleting subsections (B) through (D) effective September 22, 1983 (Supp. 83-5). 

Former Section R9-3-206 renumbered without change as Section R18-2-206 (Supp. 87-3). Former Section R18-2-205 

renumbered to R18-2-204, new Section R18-2-205 renumbered from R18-2-206 and amended effective September 26, 

1990 (Supp. 90-3). Amended by final rulemaking at 18 A.A.R. 1542, effective August 7, 2012 (Supp. 12-2). 
R18-2-206. Lead 

A. The primary ambient air quality standard for lead and its compounds, measured as elemental 

lead, is 0.15 micrograms per cubic meter - maximum arithmetic mean averaged over a threemonth period. 

B. The secondary ambient air quality standard for lead and its compounds, measured as elemental 

lead, is 0.15 micrograms per cubic meter - maximum arithmetic mean averaged over a threemonth period. 

C. The level of the standards shall be measured by a reference method based on 40 CFR 50, 

Appendix G and designated in accordance with 40 CFR 53, or by an equivalent designated in 

accordance with part 53 of this chapter. 

D. The national primary and secondary ambient air quality standards for lead are met when the 

maximum arithmetic three-month mean concentration for a three-year period, as determined 

in accordance with 40 CFR 50, Appendix R, is less than or equal to 0.15 micrograms per cubic 

meter. 

E. The former primary and secondary ambient air quality standards for lead of 1.5 micrograms per 

cubic meter averaged over a calendar quarter shall apply to an area until one year after the 

effective date of the designation of that area, pursuant to section 107 of the Act, for the 

standards in subsections (A) and (B). 

Historical Note 

Former Section R9-3-207 repealed effective May 14, 1979 (Supp. 79-1). New Section R9-3-

207 adopted effective October 2, 1979 (Supp. 79-5). Amended effective August 29, 1980 

(Supp. 80-4). Amended by deleting subsections (B) through (D) effective September 22, 

1983 (Supp. 83-5). Former Section R9-3-207 renumbered without change as Section 

R18-2-207 (Supp. 87-3). Former Section R18-2-206 renumbered to R18-2-205, new 

Section R18-2-206 renumbered from R18-2-207 and amended effective September 26, 

1990 (Supp. 90-3). Amended by final rulemaking at 18 A.A.R. 1542, effective August 7, 

2012 (Supp. 12-2).