Wyoming Administrative Code › Agency 020 - Environmental Quality, Dept. of › Sub-Agency 0002 - Air Quality › Chapter 2 - Ambient Standards › Appendix 1 - INTERPRETATION OF THE ANNUAL STATE AMBIENT AIR QUALITY STANDARD FOR PM[10]

Current through July 13, 2024
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/3, 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/3, 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:
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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
(c) 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/
m
3. 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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(d) Note that these values are rounded to the nearest 1
				  µg/m3 for the calculation of means.