Cal. Code Regs. Tit. 17, div. 3, ch. 1, subch. 1.5, art. 3, app 2

Current through Register 2024 Notice Reg. No. 45, November 8, 2024

Appendix 2 - Air Resources Board Procedure for Reviewing Air Quality Data Possibly Affected by a Highly Irregular or Infrequent Event

This Appendix describes the procedures that the Air Resources Board will use for reviewing air quality data possibly affected by a highly irregular or infrequent event with regard to the state ambient air quality standards. All decisions regarding the identification of data as being affected by a highly irregular or infrequent event will be made by the Executive Officer or his or her delegate.

The Executive Officer or his or her delegate will review air quality data for possible identification as affected by a highly irregular or infrequent event if the data are the only exceedances of a state ambient air quality standard in the area or if such identification would otherwise affect the designation of the area.

Three types of highly irregular or infrequent events may be identified:

1. Extreme Concentration Event

2. Exceptional Event

3. Unusual Concentration Event.

Extreme Concentration Events

An extreme concentration event is an event beyond reasonable regulatory control which causes an exceedance of a state standard. An extreme concentration event is based on a statistical procedure and may not always be linked to a specific identifiable cause. The causes of an extreme concentration event include but are not limited to unusual meteorology.

The steps for identifying an extreme concentration event are:

1. A district (or the Executive Officer or his or her delegate) identifies questionable data.

2. In evaluating a possible extreme concentration event, the Executive Officer or his or her delegate will use the data for the site at which the event is suspected to determine a limit for concentrations expected to recur no more frequently than once in one year. The limit will be determined using the "exponential tail method" described in Procedure for Computing the Values Used in Identifying Extreme Concentration Events (August 1998), which is incorporated by reference herein.

Using conventional rounding procedures, the limit will be consistent with the level of precision in which the state standard is expressed. If the possible extreme concentration exceeds the concentration expected to recur no more frequently than once in one year, the Executive Officer or his or her delegate will consult with the district in identifying the data as affected by an extreme concentration event.

3. When an extreme concentration event is identified, the Executive Officer or his or her delegate will review other information, including but not limited to meteorological data, to determine whether air quality data for other sites in the area were affected by the extreme concentration event.

Exceptional Events

An exceptional event is an event beyond reasonable regulatory control which causes an exceedance of a state standard. An exceptional event must be linked to a specific cause such as an act of nature or unusual human activity. As guidance to the states for determining exceptional events, the federal Environmental Protection Agency (EPA) has published Guideline on the Identification and Use of Air Quality Data Affected by Exceptional Events, (EPA-450/4-86-007), July 1986 (the EPA Guideline). The EPA Guideline provides overall criteria for determining whether an event is exceptional with regard to the national standards. The Executive Officer or his or her delegate will use the EPA Guideline as a general basis for reviewing ambient data, but will not be bound by the specific definitions in the EPA Guideline for the various types of exceptional events because those definitions are made on a national basis. In addition, since what may be exceptional in one part of the state may be common in another, each possible event will be evaluated on a case-by-case basis.

The steps for identifying an exceptional event are:

1. A district (or the Executive Officer or his or her delegate) identifies questionable data.

2. If a known exceptional event has occurred, the district gathers relevant data to document the occurrence.

3. If an exceptional event is only suspected, the district investigates available data for the possible event.

4. The district submits to the Executive Officer or his or her delegate a request for identifying the data as affected by an exceptional event and also provides supporting documentation.

5. If the Executive Officer or his or her delegate concurs with the district, he or she will identify the data as affected by an exceptional event.

6. If the district's request for identifying data as affected by an exceptional event cannot be supported, the district will be notified of the reasons. The Executive Officer or his or her delegate will consider any additional data to support the request, but in the absence of any new evidence, will disapprove the request.

Unusual Concentration Events

An unusual concentration event is an event which causes an anomalous exceedance of a state standard and which does not qualify as an extreme concentration event or an exceptional event. An exceedance affected by an unusual concentration event may be identified only for an area designated as attainment or unclassified at the time of the exceedance.

The steps for identifying an unusual concentration event are:

1. A district (or the Executive Officer or his or her delegate) identifies a questionable exceedance(s).

2. If the exceedance(s) has not been identified as having been affected by an extreme concentration event or an exceptional event, and if the area was designated as attainment or unclassified at the time of the exceedance(s), the Executive Officer or his or her delegate will review the exceedance(s) to determine whether it was affected by an unusual concentration event.

3. In evaluating a possible unusual concentration event, the Executive Officer or his or her delegate will consider all relevant information, including but not limited to the amount and characteristics of air quality data, emission data, meteorological data, potential public health and welfare impacts, and any applicable state, district, and federal rules and regulations. To identify the exceedance(s) as affected by an unusual concentration event, the Executive Officer or his or her delegate must find, based on the relevant information, that the impact of the exceedance(s) is limited to the local area, the exceedance(s) is not expected to recur, and that the data do not support a nonattainment designation.

4. If the exceedance(s) qualifies as possibly affected by an unusual concentration event, the Executive Officer or his or her delegate will consult with the district in identifying the exceedance(s) as affected by an unusual concentration event.

5. An area may retain its attainment or unclassified designation based on the identification and exclusion of an exceedance(s) affected by an unusual concentration event for no more than three consecutive years. If the Executive Officer or his or her delegate identifies an exceedance(s) affected by an unusual concentration event in the area in the fourth consecutive year, the area will be redesignated as nonattainment.

Cal. Code Regs. Tit. 17, div. 3, ch. 1, subch. 1.5, art. 3, app 2

1. Amendment of Appendix 2 to sections 70300-70306 filed 1-2-91; operative 1-2-91 pursuant to Government Code section 11346.2(d) (Register 91, No. 10).
2. Amendment filed 4-16-93; operative 5-17-93 (Register 93, No. 16).
3. Amendment filed 8-20-96; operative 9-19-96 (Register 96, No. 34).
4. Amendment filed 8-26-99; operative 9-25-99 (Register 99, No. 35).
5. Amendment filed 6-7-2004; operative 7-7-2004 (Register 2004, No. 24).
6. Amendment filed 8-26-2010; operative 9-25-2010 (Register 2010, No. 35).

Note: Authority cited: Sections 39600, 39601, 39607 and 39608, Health and Safety Code. Reference: Sections 39607 and 39608, Health and Safety Code.