California Code of Regulations › Title 17 - Public Health › Division 3 - Air Resources › Chapter 1 - Air Resources Board › Subchapter 1.5 - Air Basins and Air Quality Standards › Article 3 - Criteria for Determining Area Designations › Appendix 2 - Air Resources Board Procedure for Reviewing Air Quality Data Possibly Affected by a Highly Irregular or Infrequent Event

Current through Register 2024 Notice Reg. No. 28, July 12, 2024
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.
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.