020-1 Wyo. Code R. 2 app 1 - INTERPRETATION OF THE ANNUAL STATE AMBIENT AIR QUALITY STANDARD FOR PM[10]
1.0. General.
(a) This appendix explains the computations necessary for analyzing particulate matter data to determine attainment of the annual standard. For the primary standard, particulate matter is measured in the ambient air as PM10 (particles with an aerodynamic diameter less than or equal to a nominal 10 micrometers) by a reference method based on 40 CFR part 50, Appendix J, and designated in accordance with 40 CFR part 53, or by an equivalent method designated in accordance with 40 CFR part 53. The required frequency of measurements is specified in 40 CFR part 58.
(b) The terms used in this appendix are defined as follows:
"Average" refers to an arithmetic mean. The particulate matter standard is expressed in terms of the annual arithmetic mean.
"Daily value" for PM10 refers to the 24-hour average concentration of PM10 calculated or measured from midnight to midnight (local time).
"Expected annual value" is the number approached when the annual values from an increasing number of years are averaged, in the absence of long-term trends in emissions or meteorological conditions.
"Year" refers to a calendar year.
(c) Although the discussion in this appendix focuses on monitored data, the same principles apply to modeling data, subject to EPA modeling guidelines.
2 0 Attainment Determinations.
2 1 Annual Primary Standard.
(a) The annual primary standard is attained when the expected annual arithmetic mean PM10 concentration is less than or equal to the level of the standard. In the simplest case, the expected annual arithmetic mean is determined by averaging the annual arithmetic mean PM10 concentrations for the past 3 calendar years. Because of the potential for incomplete data and the possible seasonality in PM10 concentrations, the annual mean shall be calculated by averaging the four quarterly means of PM10 concentrations within the calendar year. The equations for calculating the annual arithmetic mean are given in Section 3.0 of this appendix. Situations in which 3 years of data are not available and possible adjustments for unusual events or trends are discussed in Sections 2.2 and 2.3 of this appendix. The expected annual arithmetic mean is rounded to the nearest 1 µg/m3 before comparison with the annual standard (fractional values equal to or greater than 0.5 are to be rounded up).
2.2. Data Requirements.
(a) A minimum of 75 percent of the scheduled PM10 samples per quarter are required.
(b) To demonstrate attainment of the annual standard at a monitoring site, the monitor must provide sufficient data to perform the required calculations of Section 3.0 of this appendix. The amount of data required varies with the sampling frequency, data capture rate and the number of years of record. In all cases, 3 years of representative monitoring data that meet the 75 percent criterion of the previous paragraph should be utilized, if available, and would suffice. More than 3 years may be considered, if all additional representative years of data meeting the 75 percent criterion are utilized. Data not meeting these criteria may also suffice to show attainment; however, such exceptions will have to be approved by the Air Quality Division Administrator.
(c) There are less stringent data requirements for showing that a monitor has failed an attainment test and thus has recorded a violation of the particulate matter standard. Although it is generally necessary to meet the minimum 75 percent data capture requirement per quarter to use the computational equations described in Section 3.0 of this appendix, this criterion does not apply when less data is sufficient to unambiguously establish nonattainment. The following examples illustrate how nonattainment can be demonstrated when a site fails to meet the completeness criteria. Nonattainment of the annual standard can be demonstrated on the basis of quarterly mean concentrations developed from observed data combined with one-half the minimum detectable concentration substituted for missing values. Expected annual values must exceed the levels allowed by the standard.
2.3. Adjustment for Exceptional Events and Trends.
(a) An exceptional event is an uncontrollable event caused by natural sources of particulate matter or an event that is not expected to recur at a given location. Inclusion of such a value in the computation of exceedances or averages could result in inappropriate estimates of their respective expected annual values. To reduce the effect of unusual events, more than 3 years of representative data may be used. Alternatively, other techniques, such as the use of statistical models or the use of historical data could be considered so that the event may be discounted or weighted according to the likelihood that it will recur. The use of such techniques is subject to the approval of the Air Quality Division Administrator.
(b) In cases where long-term trends in emissions and air quality are evident, mathematical techniques should be applied to account for the trends to ensure that the expected annual values are not inappropriately biased by unrepresentative data. In the simplest case, if 3 years of data are available under stable emission conditions, this data should be used. In the event of a trend or shift in emission patterns, either the most recent representative year(s) could be used or statistical techniques or models could be used in conjunction with previous years of data to adjust for trends. The use of less than 3 years of data, and any adjustments are subject to the approval of the Air Quality Division Administrator.
3.0. Computational Equations for Annual Standard.
3.1. Calculation of the Annual Arithmetic Mean.
(a) An annual arithmetic mean value for PM10 is determined by averaging the quarterly means for the 4 calendar quarters of the year. The following equation is to be used for calculation of the mean for a calendar quarter:
Equation 1
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(b) The quarterly mean, expressed in µg/m3, must be rounded to the nearest tenth (fractional values of 0.05 should be rounded up).
(c) The annual mean is calculated by using the following equation:
Equation 2
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(d) The average of quarterly means must be rounded to the nearest tenth (fractional values of 0.05 should be rounded up).
(e) The use of quarterly averages to compute the annual average will not be necessary for monitoring or modeling data which results in a complete record, i.e., 365 days per year.
(f) The expected annual mean is estimated as the average of three or more annual means. This multi-year estimate, expressed in µg/m3, shall be rounded to the nearest integer for comparison with the annual standard (fractional values of 0.5 should be rounded up).
Example 1
Using Equation 1, the quarterly means are calculated for each calendar quarter. If the quarterly means are 52.4, 75.3, 82.1, and 63.2 µg/m3, then the annual mean is: Click here to view image
3.2. Adjustments for Non-scheduled Sampling Days.
(a) An adjustment in the calculation of the annual mean is needed if sampling is performed on days in addition to the days specified by the systematic sampling schedule. The quarterly averages would be calculated by using the following equation:
Equation 3
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(b) If one sample value is recorded in each stratum, Equation 3 reduces to a simple arithmetic average of the observed values as described by Equation 1.
Example 2
(a) During one calendar quarter, 9 observations were recorded. These samples were distributed among 7 sampling strata, with 3 observations in one stratum. The concentrations of the 3 observations in the single stratum were 202, 242, and 180 µg/m3. The remaining 6 observed concentrations were 55, 68, 73, 92, 120, and 155 µg/m3. Applying the weighting factors specified in Equation 3, the quarterly mean is:
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(b) Note that these values are rounded to the nearest 1 µg/m3 for the calculation of means.
Notes
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