R18-2-604. Open Areas, Dry Washes, or Riverbeds 

A. No person shall cause, suffer, allow, or permit a building or its appurtenances, or a building or 

subdivision site, or a driveway, or a parking area, or a vacant lot or sales lot, or an urban or suburban 

open area to be constructed, used, altered, repaired, demolished, cleared, or leveled, or the earth to be 

moved or excavated, without taking reasonable precautions to limit excessive amounts of particulate 

matter from becoming airborne. Dust and other types of air contaminants shall be kept to a minimum 

by good modern practices such as using an approved dust suppressant or adhesive soil stabilizer, 

paving, covering, landscaping, continuous wetting, detouring, barring access, or other acceptable 

means. 

B. No person shall cause, suffer, allow, or permit a vacant lot, or an urban or suburban open area, to 

be driven over or used by motor vehicles, trucks, cars, cycles, bikes, or buggies, or by animals such 

as horses, without taking reasonable precautions to limit excessive amounts of particulates from 

becoming airborne. Dust shall be kept to a minimum by using an approved dust suppressant, or 

adhesive soil stabilizer, or by paving, or by barring access to the property, or by other acceptable 

means. 

C. No person shall operate a motor vehicle for recreational purposes in a dry wash, riverbed or open 

area in such a way as to cause or contribute to visible dust emissions which then cross property lines 

into a residential, recreational, institutional, educational, retail sales, hotel or business premises. For 

purposes of this subsection “motor vehicles” shall include, but not be limited to trucks, cars, cycles, 

bikes, buggies and 3-wheelers. Any person who violates the provisions of this subsection shall be 

subject to prosecution under A.R.S. § 49-463. 

Historical Note

Adopted effective May 14, 1979 (Supp. 79-1). Former Section R9-3-604 renumbered without change 

as Section R18-2-604 (Supp. 87-3). Amended effective September 26, 1990 (Supp. 90-3). Former 

Section R18-2-604 renumbered to R18-2-804, new Section R18-2-604 renumbered from R18-2-404 

and amended effective November 15, 1993 (Supp. 93-4).

R18-2-404. Offset Standards 

A. Increased emissions by a major source or major modification subject to R18-2-403 shall be offset 

by real reductions in the actual emissions of each pollutant for which the area has been designated as 

nonattainment and for which the source or modification is classified as major. Except as provided in 

R18-2-405, emissions increases shall be offset by decreases at a ratio of at least 1 to 1. 

B. Except as provided in subsection (B)(1) or (2), for sources and modifications subject to this 

Section, the baseline for determining credit for emissions reductions is the emissions limit for the 

source generating the offset credit under the applicable implementation plan in effect at the time the 

application for a permit or permit revision is filed. 

1. The offset baseline shall be the actual emissions of the source from which offset credit is obtained 

where either of the following conditions is satisfied: 

a. The demonstration of reasonable further progress and attainment of ambient air quality standards is 

based upon the actual emissions of sources located within a designated nonattainment area for which 

the preconstruction review program was adopted. 

b. The applicable implementation plan does not contain an emissions limitation for that source or 

source category. 

2. Where the emissions limit under the applicable implementation plan allows greater emissions than 

the potential to emit of the source, emissions offset credit will be allowed only for control below this 

potential. 
C. For an existing fuel combustion source, emissions offset credit shall be based on the allowable 

emissions under the applicable implementation plan for the type of fuel being burned at the time the 

application to construct is filed. If the existing source commits to switch to a cleaner fuel at some 

future date, emissions offset credit based on the allowable or actual emissions for the fuels involved 

is not acceptable, unless the permit for the existing source is conditioned to require the use of a 

specified alternative control measure which would achieve the same degree of emissions reduction 

should the source switch back to a fuel generating higher emissions. The owner or operator of the 

existing source must demonstrate that adequate long-term supplies of the new fuel are available 

before granting emissions offset credit for fuel switches. 

D. Offset Credit for Shutdowns. 

1. Emissions reductions achieved by shutting down an existing emission unit or curtailing production 

or operating hours may be credited for offsets if they meet both of the following conditions. 

a. The reductions are surplus, permanent, quantifiable, and federally enforceable. 

b. The shutdown or curtailment occurred after the last day of the base year for the SIP planning 

process. For purposes of this subsection, the Director may choose to consider a prior shutdown or 

curtailment to have occurred after the last day of the base year if the projected emissions inventory 

used to develop the attainment demonstration explicitly includes the emissions from such previously 

shutdown or curtailed emission units. However, in no event may credit be given for shutdowns that 

occurred before August 7, 1977. 

2. Emissions reductions achieved by shutting down an existing emissions unit or curtailing 

production or operating hours and that do not meet the requirements in subsection (D)(1)(b) may be 

credited only if one of the following conditions is satisfied: 

a. The shutdown or curtailment occurred on or after the date the construction permit application is 

filed.

b. The applicant can establish that the proposed new emissions unit is a replacement for the shutdown 

or curtailed emissions unit, and the emissions reductions achieved by the shutdown or curtailment 

met the requirements of subsection (D)(1)(a). 

E. No emissions credit may be allowed for replacing one hydrocarbon compound with another of 

lesser reactivity, except for those compounds listed in Table 1 of EPA’s “Recommended Policy on 

Control of Volatile Organic Compounds,” 42 FR 35314 (July 8, 1977). 

F. All emission reductions claimed as offset credits shall be federally enforceable by the time a 

permit is issued to the owner or operator of the major source subject to this Section and shall be in 

effect by the time the new or modified source subject to the permit commences operation. 

G. The owner or operator of a major source or major modification subject to this Section must obtain 

offset credits from the same source or from other sources in the same nonattainment area, except that 

the Director may allow the owner or operator to obtain offset credits from another nonattainment area 

if both of the following conditions are satisfied: 

1. The other area has an equal or higher nonattainment classification than the area in which the 

source is located. 

2. Emissions from such other area contribute to a violation of the national ambient air quality 

standard in the nonattainment area in which the source is located. 

H. Credit for an emissions reduction can be claimed to the extent that the Director has not relied on it 

in issuing any permit under this Article or the state has not relied on it in a demonstration of 

attainment or reasonable further progress. 

I. The total tonnage of increased emissions, in tons per year, resulting from a major modification that 

must be offset under this Section shall be determined by summing the difference between the 

allowable emissions after the modification and the actual emissions before the modification for each 

emissions unit. 
J. In ozone nonattainment areas classified as marginal, total emissions of VOC and oxides of nitrogen 

from other sources shall offset those proposed or permitted from the major source or major 

modification by a ratio of at least 1.10 to 1. In ozone nonattainment areas classified as moderate, total 

emissions of VOC and oxides of nitrogen from other sources shall offset those proposed or permitted 

from the major source or major modification by a ratio of at least 1.15 to 1. New major sources and 

major modifications in serious and severe ozone nonattainment areas shall comply with this Section 

and R18-2-405. 

Historical Note 

Former Section R9-3-404 repealed, new Section R9-3-404 adopted effective May 14, 1979 (Supp. 

79-1). Amended by adding subsection (C) effective September 22, 1983 (Supp. 83-5). Former 

Section R9-3-404 renumbered without change as Section R18-2-404 (Supp. 87-3). Amended 

subsection (C) effective December 1, 1988 (Supp. 88-4). Section R18-2-404 renumbered to R18-2-

604, new Section R18-2-404 adopted effective November 15, 1993 (Supp. 93-4). Amended effective 

February 28, 1995 (Supp. 95-1). Amended by final rulemaking at 5 A.A.R. 4074, effective September 

22, 1999 (Supp. 99-3). Amended by final rulemaking at 8 A.A.R. 1815, effective March 18, 2002 

(Supp. 02-1). Amended by final rulemaking at 18 A.A.R. 1542, effective August 7, 2012 (Supp. 12-2).