There are a large number of causes of exceptional raw data values. AQS allows you to indicate some of the causes of these exceptional values. EPA Regional Administrators will then indicate their concurrence with an event.
There are several reports that will include or exclude data based on the type of event and on EPA concurrence.
See The Events Processing section of the Table of report output 0ptions.
Exceptional Data Types in Reports describes how AQS summarizes, identifies and reports the event qualifiers depending on what report output option has been specified.
Multiple event qualifiers can be attached to a specific raw data value. Multiple comments can be attached to each qualifier. While it is possible to have several event qualifiers attached to a raw data (or composite) value, Exceptional and Natural events should not be applied to the same value. EPA Administrators will only see one event qualifier when concurring with an event. Users have no control over which exceptional or natural event will be displayed for concurrence so it is wise to limit yourself to just the one most appropriate. Exceptional Events will always be displayed before natural events in the case where there are multiple qualifiers attached to a data point.
When the qualifiers are displayed in a List of Values they are sorted first by type then by description.
The qualifiers are currently broken into 4 different types listed below.
1. Quality Assurance
QA qualifiers are indicators of data validation. The "V" qualifier to indicate validated data is used on all parameters. The other QA qualifiers are normally only used for PM2.5. These qualifiers are used to indicate that while the indicated QA procedure may have cast doubts on the validity of the data, upon review it is considered valid. Raw data records for invalid data are entered with no data value. Such null data entries should be qualified with a null value code (see below).
2. Exceptional Events
"An exceptional event is defined as an event that is not expected to recur routinely at a given location, or that is possibly uncontrollable or unrealistic to control through the SIP process… What is exceptional in one area of the country may not be exceptional in another." (EPA Guideline on the Identification and Use of Air Quality Data Affected by Exceptional Events, OAQPS, EPA-450/4-86-007, July 1986)
In the AQS systems, exceptional events are considered to be "anthropogenic". All other causes are considered to be "Natural events" described below. AQS makes no finer distinction between intentional and unintentional exceptional events other than to describe the event itself.
3. Natural Events
Natural events that can influence raw data values include Metrological events such as high winds, inversions, intrusions or drought. Geological events such as volcanoes are included along with some seasonal events such as Forest fires and High pollen count.
Note that "Prescribed burning" is an Intentional Anthropogenic Event while "Forest fires" are considered Natural Events.
4. Null Data Values
Null Data Values explain the cause of null values that occur for reasons other than levels being below a device’s minimum detection limit. These include power failures, equipment damage and human error. Note that there is a difference between NULL and ZERO in the database. Zero is a reported value indicating undetectable pollutant levels for the device. Null indicates a missing, invalid or unknown value.
Comments
Comments can be attached to any Qualifier code to further describe an event, if necessary. This ability to attach comments applies to all qualifiers.
For further guidance refer to:
· · 40 CFR, part 50, Appendix K
· · Section 188(f) of the 1990 Clean Air Act Amendments which modify some of the Appendix K based guidelines of 1986.
· · MEMORANDUM: Areas Affected by PM-10 Natural Events, FROM: Mary Nichols, Assistant Administrator for Air and Radiation. This memorandum clarifies apparent conflicts between Appendix K, the Exceptional Events Guideline from 1986 and Section 188(f)