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Outdoor Air Quality Data

One Point Quality Control Single Point Precision and Bias Graphics For Criteria Pollutants

In order to provide decision makers with data of adequate quality, OAQPS is using the Data
Quality Objective (DQO) process to determine our data quality needs for our ambient air criteria
pollutants. There are some data quality indicators, such as precision, bias, and completeness that
directly affect the attainment of the DQOs. These variables need to be in certain acceptable
ranges (called measurement quality objectives) in order for us to make decisions (like
comparison with the NAAQS) with specified levels of confidence. 40 CFR Part 58 Appendix A
provides the minimum requirements for the collection and reporting of data to assess the data
quality indicators of precision, bias, and completeness. On an annual basis, the Ambient Air
Monitoring Group (AAMG) develop summary reports on these data quality indicators.


In 2006 OAQPS revised 40 CFR Part 58 Appendix A in order to base the precision and bias
measurement quality objectives on confidence intervals at the site level of data aggregation.
Since the criteria pollutant data are used for very important decisions (comparison to the
NAAQS) it is felt that providing precision and bias estimates at upper confidence limits provides
a higher probability of making appropriate decisions. This statistic provides a conservative
approach to measuring precision and bias. A document describing these statistics is available on
AMTIC. (http://www.epa.gov/ttn/amtic/parslist.html)


Estimates of both bias and precision for the four automated gaseous methods (CO, NO2, O3, and
SO2) are derived from the bi-weekly one-point QC checks. Since every site should perform the
QC checks at an acceptable frequency, there is enough information to assess and control data
quality at the site level.


In 2005, OAQPS developed a new report in AQS (AMP255 – P/A Quality Indicator Summary
Report) that summarized precision, bias, and completeness of the required QC data for each
criteria pollutant. The data tables may be generated at any time within the AQS application using
the standard report. Earlier reports also generated this data graphically which monitoring
organizations found very useful. Since AQS presently does not have this capability, AAMG is
providing these graphs annually as an addendum to the summary tables. The AMP255 was later
updated and replaced by the AMP256 report.


This document defines the elements displayed in the corresponding box and whisker graphics as
well as base assumptions of the data contained within the AMP256 report.

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