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Air Quality

Exceptional Events

South Carolina Department of Health and Environmental Control (Department) operates an ambient monitoring network that measures concentrations of various air pollutants. Other environmental agencies operate similar networks throughout the United States. When an event outside human control causes an exceedance of an ambient standard, the event may be excluded from compliance calculations. There is a specific process for excluding an event, which includes public notice of each request. This notice provides an opportunity for public review and comment on the supporting documentation.

Following the opportunity for public comment, the Department submits this information to the United States Environmental Protection Agency (EPA) for their review and approval. If the EPA concurs that the appropriate flagged data were affected by an Exceptional Event, data generated by the state's monitors affected by the Exceptional Event are not used to determine compliance with the National Ambient Air Quality Standards (NAAQS).

Contact information is provided below for questions about this process or about a specific Exceptional Event proposal. Public comments on this web page are also welcome.

What is an Exceptional Event?

According to federal regulations:

"An exceptional event is defined as an event that affects air quality, an event that is not reasonably controllable or preventable, is an event caused by human activity that is unlikely to recur at a particular location or a is a natural event, and is determined by the EPA to be an exceptional event."

Exceptional Events may include, but are not limited to, prescribed burnings, wildfires, and large firework displays.

Exceptional Events do not include stagnation of air masses or meteorological inversions, meteorological events involving high temperature or a lack of precipitation, or air pollution relating to source noncompliance.

To summarize, an Exceptional Event is one that:

  • Affects air quality.
  • Is not reasonably controllable or preventable.
  • Is an event that is caused by human activity that is unlikely to recur at a particular location, or is a natural event; and
  • Is determined by the Administrator of the EPA through the process established in the rule to be an exceptional event.

What Event Documents are available for Public Review and Comment?

This area contains information on events that the Department proposes to submit to EPA for approval. Public comments are welcome on the information in this section.

There are no Event Documents available for Public Review and Comment at this time.

Prior Event Documentation and EPA Responses

This area contains information on past events that DHEC has submitted to the EPA and EPA's responses to this information.



Additional Resources

Qualifier Codes

Qualifier Codes (also referred to as "Flags") are used to indicate data which are valid, but are affected by some unusual local or distant event which makes the data not representative of “normal” conditions (conditions without the event).

  • Any data identified as impacted by events or operational deviations requiring qualifiers will be flagged by the Department. Requests for EPA concurrence may be submitted for data values that are, or contribute to, exceedances of the National Ambient Air Quality Standards.
  • All qualifiers indicate events or operational deviations, which are not sufficient to require voiding the measurement. The Qualifier indicates to data users that the data should be reviewed for appropriate application in the intended use or analysis.
  • Not all defined Qualifiers listed below are available for use with all pollutants.
Qualifier Code Definition
1 Deviation from a Code of Federal Regulations /critical criteria requirement
2 Operational Deviation
3 Field Issue
4 Lab Issue
5 Outlier
6 Quality Assurance Program Plan Issue
7 Below Lowest Calibration Level
9 Negative value detected - zero reported
A High winds
B Stratospheric ozone intrusions
C Volcanic eruptions
D Sandblasting
E Forest fire
F Structural fire
G High pollen count
H Chemical spills & Industrial accidents
I Unusual traffic congestion
J Construction/Demolition
K Agricultural tilling
L Highway construction
M Rerouting of traffic
MD Value between Minimum Detectable Limit and Instrument Detectable Limit
N Sanding/Salting of streets
ND No Value Detected
O Infrequent large gatherings
P Roofing operations
Q Prescribed burning
R Cleanup after a major disaster
S Seismic activity
SQ Values Between Sample Quantitation Limit and Minimum Detectable Limit
U Sahara dust
V Validated value
W Flow rate average out of spec.
X Filter temperature difference out of spec.
Y Elapsed sample time out of spec.

Glossary and Links to Acronyms

Acronym Definition
AA Atomic Absorption Spectroscopy
AIRS Aerometric Information Retrieval System (obsolete)
ANSI American National Standards Institute
APTI Air Pollution Training Institute
AQS Air Quality System national ambient air database
ARM Approved Regional Methods.
ASTM American Society for Testing and Materials
AWMA Air and Waste Management Association
BACM Best Available Control Measures.
BAQ Bureau of Air Quality
BES Bureau of Environmental Services
CAA Clean Air Act
CAAA Clean Air Act Amendments.
CFR Code of Federal Regulations
CO Carbon Monoxide
CO2 Carbon Dioxide
COC Chain of Custody
DAQA Division of Air Quality Analysis
DAS Data Acquisition System
DHEC South Carolina Department of Health and Environmental Control
DQA Data Quality Assessment
DQOs Data Quality Objectives
EDO Environmental Data Operation
EPA United States Environmental Protection Agency
EQC Environmental Quality Control (DHEC)
EQCSOP EQC Environmental Investigations Standard Operating Procedures and Quality Assurance Manual
FEM Federal Equivalent Method
FIP Federal Implementation Plan.
FIPS Federal Information Processing Standards
FR Federal Register.
FRM Federal Reference Method
GC Gas Chromatography
GC/MS Gas Chromatography / Mass Spectrometry
GIS Geographical Information Systems
GLP Good Laboratory Practice
HPLC High Pressure Liquid Chromatography
IC Ion Chromatography
ICP Inductively Coupled Plasma Spectroscopy
LAN Local Area Network
µg/M3 Micrograms per Cubic Meter
MPA Monitoring Planning Area (obsolete)
MQOs Measurement Quality Objectives
MSA Metropolitan Statistical Area
MSR Management System Review
NAAQS National Ambient Air Quality Standards
NAMS National Air Monitoring Station (obsolete)
NCore National Core Multipollutant Site (used after 2007)
NEAP Natural Events Action Plan.
NEPA National Environmental Policy Act.
ng/M3 Nanograms per Cubic Meter
NIST National Institute of Standards and Technology (formerly National Bureau of Standards)
NOx, NO, NO2 Nitrogen Oxides, Nitrogen Oxide, Nitrogen Dioxide
NTTA National Technology Transfer Advancement Act of 1995.
O3 Ozone
OAQPS Office of Air Quality Planning and Standards
OMB Office of Management and Budget.
ORD Office of Research and Development
PAMS Photochemical Assessment Monitoring Stations
Part 50 section of CFR containing NAAQS, FRMs and interpretation of Standards
Part 58 section of CFR containing monitoring Network requirements
PC Personal Computer
PD Percent Difference
PE Performance Evaluation
pH 0 (acidic) 7 (neutral) 14 (basic)
PM Particulate Matter
PM10 or PM10 Particles with a nominal mean aerodynamic diameter less than or equal to 10 micrometers.
PM10 - 2.5 Particles with a nominal mean aerodynamic diameter greater than 2.5 micrometers and less than or equal to 10 micrometers.
PM2.5 or PM2.5 Particles with a nominal mean aerodynamic diameter less than or equal to 2.5 micrometers.
POC Pollutant (parameter) Occurrence Code
PPB Parts per Billion
PPM Parts per Million
PQAO Primary Quality Assurance Organization
PSD Prevention of Significant Deterioration
QA Quality Assurance
Qa sampler flow rate at ambient (actual) conditions of temperature and pressure.
QA/QC Quality Assurance/Quality Control
QAPP Quality Assurance Project Plan
QMP Quality Management Plan
RACM Reasonably Available Control Measures.
SAFE-TEA-LU Safe Accountable Flexible Efficient-Transportation Equity Act-A Legacy for Users.
SIGIS Shared and Integrated Geographic Information System (DHEC)
SIP State Implementation Plan
SLAMS State and Local Air Monitoring Station primarily designed for NAAQS comparisons
SMP Smoke Management Program (or Plan)
SO2 or SO2 Sulfur Dioxide
SOP Standard Operating Procedure
SPM or SPMS Special Purpose Monitor Station not counted as part of minimum requirements
SQAMO State Quality Assurance Management Officer
Ta temperature, ambient or actual
TAR Tribal Authority Rule.
TIP Tribal Implementation Plan.
TSA Technical System Audit
TSP Total Suspended Particulate
USDA U.S. Department of Agriculture.
Va air volume, at ambient or actual conditions
VOC Volatile Organic Compound

For additional information on Exceptional Events, please contact:
Clay Lawson - (803)898-7410
S.C. DHEC
2600 Bull Street
Columbia, SC 29201


For more information please contact the Bureau of Air Quality at (803) 898-4123 or by email.