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(continued) * [bcheck] 1HH:mm, 2HH:mm, etc Hrs. min
start time of first 10. ....
User-entered information, such as 7.4.16............. [bcheck] [bcheck] [bcheck] [bcheck][msh As entered......... ...................
sampler and site identification. box]
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[bcheck] Provision of this information is required.
*Provision of this information is optional. If information related to the entire sample period is optionally provided prior to the end of the sample
period, the value provided should be the value calculated for the portion of the sampler period completed up to the time the information is provided.
[mshbox] Indicates that this information is also required to be provided to the AIRS data bank; see § § 58.26 and 58.35 of this chapter.
\1\ Information is required to be available to the operator at any time the sampler is operating, whether sampling or not.
\2\ Information relates to the entire sampler period and must be provided following the end of the sample period until reset manually by the operator or
automatically by the sampler upon the start of a new sample period.
\3\ Information shall be available to the operator visually.
\4\ Information is to be available as digital data at the sampler's data output port specified in section 7.4.16 of this appendix following the end of
the sample period until reset manually by the operator or automatically by the sampler upon the start of a new sample period.
\5\ Digital readings, both visual and data output, shall have not less than the number of significant digits and resolution specified.
\6\ Flag warnings may be displayed to the operator by a single-flag indicator or each flag may be displayed individually. Only a set (on) flag warning
must be indicated; an off (unset) flag may be indicated by the absence of a flag warning. Sampler users should refer to section 10.12 of this appendix
regarding the validity of samples for which the sampler provided an associated flag warning.
8.0 Filter Weighing. See reference 2 in section 13.0 of this appendix, for additional, more detailed guidance.
8.1 Analytical balance. The analytical balance used to weigh filters must be suitable for weighing the type and size of filters specified, under section 6.0 of this appendix, and have a readability of ±1 µg. The balance shall be calibrated as specified by the manufacturer at installation and recalibrated immediately prior to each weighing session. See reference 2 in section 13.0 of this appendix for additional guidance.
8.2 Filter conditioning. All sample filters used shall be conditioned immediately before both the pre- and post-sampling weighings as specified below. See reference 2 in section 13.0 of this appendix for additional guidance.
8.2.1 Mean temperature. 20 - 23 °C.
8.2.2 Temperature control. ±2 °C over 24 hours.
8.2.3 Mean humidity. Generally, 30–40 percent relative humidity; however, where it can be shown that the mean ambient relative humidity during sampling is less than 30 percent, conditioning is permissible at a mean relative humidity within ±5 relative humidity percent of the mean ambient relative humidity during sampling, but not less than 20 percent.
8.2.4 Humidity control. ±5 relative humidity percent over 24 hours.
8.2.5 Conditioning time. Not less than 24 hours.
8.3 Weighing procedure.
8.3.1 New filters should be placed in the conditioning environment immediately upon arrival and stored there until the pre-sampling weighing. See reference 2 in section 13.0 of this appendix for additional guidance.
8.3.2 The analytical balance shall be located in the same controlled environment in which the filters are conditioned. The filters shall be weighed immediately following the conditioning period without intermediate or transient exposure to other conditions or environments.
8.3.3 Filters must be conditioned at the same conditions (humidity within ±5 relative humidity percent) before both the pre- and post-sampling weighings.
8.3.4 Both the pre- and post-sampling weighings should be carried out on the same analytical balance, using an effective technique to neutralize static charges on the filter, under reference 2 in section 13.0 of this appendix. If possible, both weighings should be carried out by the same analyst.
8.3.5 The pre-sampling (tare) weighing shall be within 30 days of the sampling period.
8.3.6 The post-sampling conditioning and weighing shall be completed within 240 hours (10 days) after the end of the sample period, unless the filter sample is maintained at 4 °C or less during the entire time between retrieval from the sampler and the start of the conditioning, in which case the period shall not exceed 30 days. Reference 2 in section 13.0 of this appendix has additional guidance on transport of cooled filters.
8.3.7 Filter blanks.
8.3.7.1 New field blank filters shall be weighed along with the pre-sampling (tare) weighing of each lot of PM2.5 filters. These blank filters shall be transported to the sampling site, installed in the sampler, retrieved from the sampler without sampling, and reweighed as a quality control check.
8.3.7.2 New laboratory blank filters shall be weighed along with the pre-sampling (tare) weighing of each set of PM2.5 filters. These laboratory blank filters should remain in the laboratory in protective containers during the field sampling and should be reweighed as a quality control check.
8.3.8 Additional guidance for proper filter weighing and related quality assurance activities is provided in reference 2 in section 13.0 of this appendix.
9.0 Calibration. Reference 2 in section 13.0 of this appendix contains additional guidance.
9.1 General requirements.
9.1.1 Multipoint calibration and single-point verification of the sampler's flow rate measurement device must be performed periodically to establish and maintain traceability of subsequent flow measurements to a flow rate standard.
9.1.2 An authoritative flow rate standard shall be used for calibrating or verifying the sampler's flow rate measurement device with an accuracy of ±2 percent. The flow rate standard shall be a separate, stand-alone device designed to connect to the flow rate measurement adapter, Figure L–30 of this appendix. This flow rate standard must have its own certification and be traceable to a National Institute of Standards and Technology (NIST) primary standard for volume or flow rate. If adjustments to the sampler's flow rate measurement system calibration are to be made in conjunction with an audit of the sampler's flow measurement system, such adjustments shall be made following the audit. Reference 2 in section 13.0 of this appendix contains additional guidance.
9.1.3 The sampler's flow rate measurement device shall be re-calibrated after electromechanical maintenance or transport of the sampler.
9.2 Flow rate calibration/verification procedure.
9.2.1 PM2.5 samplers may employ various types of flow control and flow measurement devices. The specific procedure used for calibration or verification of the flow rate measurement device will vary depending on the type of flow rate controller and flow rate measurement employed. Calibration shall be in terms of actual ambient volumetric flow rates (Qa), measured at the sampler's inlet downtube. The generic procedure given here serves to illustrate the general steps involved in the calibration of a PM2.5 sampler. The sampler operation/instruction manual required under section 7.4.18 of this appendix and the Quality Assurance Handbook in reference 2 in section 13.0 of this appendix provide more specific and detailed guidance for calibration.
9.2.2 The flow rate standard used for flow rate calibration shall have its own certification and be traceable to a NIST primary standard for volume or flow rate. A calibration relationship for the flow rate standard, e.g., an equation, curve, or family of curves relating actual flow rate (Qa) to the flow rate indicator reading, shall be established that is accurate to within 2 percent over the expected range of ambient temperatures and pressures at which the flow rate standard may be used. The flow rate standard must be re-calibrated or re-verified at least annually.
9.2.3 The sampler flow rate measurement device shall be calibrated or verified by removing the sampler inlet and connecting the flow rate standard to the sampler's downtube in accordance with the operation/instruction manual, such that the flow rate standard accurately measures the sampler's flow rate. The sampler operator shall first carry out a sampler leak check and confirm that the sampler passes the leak test and then verify that no leaks exist between the flow rate standard and the sampler.
9.2.4 The calibration relationship between the flow rate (in actual L/min) indicated by the flow rate standard and by the sampler's flow rate measurement device shall be established or verified in accordance with the sampler operation/instruction manual. Temperature and pressure corrections to the flow rate indicated by the flow rate standard may be required for certain types of flow rate standards. Calibration of the sampler's flow rate measurement device shall consist of at least three separate flow rate measurements (multipoint calibration) evenly spaced within the range of -10 percent to =10 percent of the sampler's operational flow rate, section 7.4.1 of this appendix. Verification of the sampler's flow rate shall consist of one flow rate measurement at the sampler's operational flow rate. The sampler operation/instruction manual and reference 2 in section 13.0 of this appendix provide additional guidance.
9.2.5 If during a flow rate verification the reading of the sampler's flow rate indicator or measurement device differs by ±4 percent or more from the flow rate measured by the flow rate standard, a new multipoint calibration shall be performed and the flow rate verification must then be repeated.
9.2.6 Following the calibration or verification, the flow rate standard shall be removed from the sampler and the sampler inlet shall be reinstalled. Then the sampler's normal operating flow rate (in L/min) shall be determined with a clean filter in place. If the flow rate indicated by the sampler differs by ±2 percent or more from the required sampler flow rate, the sampler flow rate must be adjusted to the required flow rate, under section 7.4.1 of this appendix.
9.3 Periodic calibration or verification of the calibration of the sampler's ambient temperature, filter temperature, and barometric pressure measurement systems is also required. Reference 3 of section 13.0 of this appendix contains additional guidance.
10.0 PM2.5 Measurement Procedure. The detailed procedure for obtaining valid PM2.5 measurements with each specific sampler designated as part of a reference method for PM2.5 under part 53 of this chapter shall be provided in the sampler-specific operation or instruction manual required by section 7.4.18 of this appendix. Supplemental guidance is provided in section 2.12 of the Quality Assurance Handbook listed in reference 2 in section 13.0 of this appendix. The generic procedure given here serves to illustrate the general steps involved in the PM2.5 sample collection and measurement, using a PM2.5 reference method sampler.
10.1 The sampler shall be set up, calibrated, and operated in accordance with the specific, detailed guidance provided in the specific sampler's operation or instruction manual and in accordance with a specific quality assurance program developed and established by the user, based on applicable supplementary guidance provided in reference 2 in section 13.0 of this appendix.
10.2 Each new sample filter shall be inspected for correct type and size and for pinholes, particles, and other imperfections. Unacceptable filters should be discarded. A unique identification number shall be assigned to each filter, and an information record shall be established for each filter. If the filter identification number is not or cannot be marked directly on the filter, alternative means, such as a number-identified storage container, must be established to maintain positive filter identification.
10.3 Each filter shall be conditioned in the conditioning environment in accordance with the requirements specified in section 8.2 of this appendix.
10.4 Following conditioning, each filter shall be weighed in accordance with the requirements specified in section 8.0 of this appendix and the presampling weight recorded with the filter identification number.
10.5 A numbered and preweighed filter shall be installed in the sampler following the instructions provided in the sampler operation or instruction manual.
10.6 The sampler shall be checked and prepared for sample collection in accordance with instructions provided in the sampler operation or instruction manual and with the specific quality assurance program established for the sampler by the user.
10.7 The sampler's timer shall be set to start the sample collection at the beginning of the desired sample period and stop the sample collection 24 hours later.
10.8 Information related to the sample collection (site location or identification number, sample date, filter identification number, and sampler model and serial number) shall be recorded and, if appropriate, entered into the sampler.
10.9 The sampler shall be allowed to collect the PM2.5 sample during the set 24-hour time period.
10.10 Within 96 hours of the end of the sample collection period, the filter, while still contained in the filter cassette, shall be carefully removed from the sampler, following the procedure provided in the sampler operation or instruction manual and the quality assurance program, and placed in a protective container. The protective container shall contain no loose material that could be transferred to the filter. The protective container shall hold the filter cassette securely such that the cover shall not come in contact with the filter's surfaces. Reference 2 in section 13.0 of this appendix contains additional information.
10.11 The total sample volume in actual m 3 for the sampling period and the elapsed sample time shall be obtained from the sampler and recorded in accordance with the instructions provided in the sampler operation or instruction manual. All sampler warning flag indications and other information required by the local quality assurance program shall also be recorded.
10.12 All factors related to the validity or representativeness of the sample, such as sampler tampering or malfunctions, unusual meteorological conditions, construction activity, fires or dust storms, etc. shall be recorded as required by the local quality assurance program. The occurrence of a flag warning during a sample period shall not necessarily indicate an invalid sample but rather shall indicate the need for specific review of the QC data by a quality assurance officer to determine sample validity.
10.13 After retrieval from the sampler, the exposed filter containing the PM2.5 sample should be transported to the filter conditioning environment as soon as possible ideally to arrive at the conditioning environment within 24 hours for conditioning and subsequent weighing. During the period between filter retrieval from the sampler and the start of the conditioning, the filter shall be maintained as cool as practical and continuously protected from exposure to temperatures over 25 °C. See section 8.3.6 of this appendix regarding time limits for completing the post-sampling weighing. See reference 2 in section 13.0 of this appendix for additional guidance on transporting filter samplers to the conditioning and weighing laboratory.
10.14. The exposed filter containing the PM2.5 sample shall be re-conditioned in the conditioning environment in accordance with the requirements specified in section 8.2 of this appendix.
10.15. The filter shall be reweighed immediately after conditioning in accordance with the requirements specified in section 8.0 of this appendix, and the postsampling weight shall be recorded with the filter identification number.
10.16 The PM2.5 concentration shall be calculated as specified in section 12.0 of this appendix.
11.0 Sampler Maintenance. The sampler shall be maintained as described by the sampler's manufacturer in the sampler-specific operation or instruction manual required under section 7.4.18 of this appendix and in accordance with the specific quality assurance program developed and established by the user based on applicable supplementary guidance provided in reference 2 in section 13.0 of this appendix.
12.0 Calculations
12.1 (a) The PM2.5 concentration is calculated as:
PM2.5 = (Wf - Wi)/Va
where:
PM2.5 = mass concentration of PM2.5, µg/m 3 ;
Wf, Wi = final and initial weights, respectively, of the filter used to collect the PM2.5 particle sample, µg;
Va = total air volume sampled in actual volume units, as provided by the sampler, m 3 .
Note: Total sample time must be between 1,380 and 1,500 minutes (23 and 25 hrs) for a fully valid PM2.5 sample; however, see also section 3.3 of this appendix.
13.0 References.
1. Quality Assurance Handbook for Air Pollution Measurement Systems, Volume I, Principles. EPA/600/R–94/038a, April 1994. Available from CERI, ORD Publications, U.S. Environmental Protection Agency, 26 West Martin Luther King Drive, Cincinnati, Ohio 45268.
2. Copies of section 2.12 of the Quality Assurance Handbook for Air Pollution Measurement Systems, Volume II, Ambient Air Specific Methods, EPA/600/R–94/038b, are available from Department E (MD-77B), U.S. EPA, Research Triangle Park, NC 27711.
3. Quality Assurance Handbook for Air Pollution Measurement Systems, Volume IV: Meteorological Measurements, (Revised Edition) EPA/600/R–94/038d, March, 1995. Available from CERI, ORD Publications, U.S. Environmental Protection Agency, 26 West Martin Luther King Drive, Cincinnati, Ohio 45268.
4. Military standard specification (mil. spec.) 8625F, Type II, Class 1 as listed in Department of Defense Index of Specifications and Standards (DODISS), available from DODSSP-Customer Service, Standardization Documents Order Desk, 700 Robbins Avenue, Building 4D, Philadelphia, PA 1911–5094.
14.0 Figures L–1 through L–30 to Appendix L.
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[62 FR 38714, July 18, 1997, as amended at 64 FR 19719, Apr. 22, 1999]
Appendix M to Part 50 [Reserved]
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Appendix N to Part 50—Interpretation of the National Ambient Air Quality Standards for PM2.5
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1.0 General.
(a) This appendix explains the data handling conventions and computations necessary for determining when the annual and 24-hour primary and secondary national ambient air quality standards for PM specified in §50.7 of this part are met. Particulate matter is measured in the ambient air as PM2.5 (particles with an aerodynamic diameter less than or equal to a nominal 2.5 micrometers) by a reference method based on appendix L of this part, as applicable, and designated in accordance with part 53 of this chapter, or by an equivalent method designated in accordance with part 53 of this chapter. Data handling and computation procedures to be used in making comparisons between reported PM2.5 concentrations and the levels of the PM standards are specified in the following sections.
(b) Data resulting from uncontrollable or natural events, for example structural fires or high winds, may require special consideration. In some cases, it may be appropriate to exclude these data because they could result in inappropriate values to compare with the levels of the PM standards. In other cases, it may be more appropriate to retain the data for comparison with the level of the PM standards and then allow the EPA to formulate the appropriate regulatory response. Whether to exclude, retain, or make adjustments to the data affected by uncontrollable or natural events is subject to the approval of the appropriate Regional Administrator.
(c) The terms used in this appendix are defined as follows:
Average and mean refer to an arithmetic mean.
Daily value for PM refers to the 24-hour average concentration of PM2.5 calculated or measured from midnight to midnight (local time).
Designated monitors are those monitoring sites designated in a State PM Monitoring Network Description for spatial averaging in areas opting for spatial averaging in accordance with part 58 of this chapter.
98th percentile means the daily value out of a year of PM2.5 monitoring data below which 98 percent of all values in the group fall.
Year refers to a calendar year.
(d) Sections 2.1 and 2.5 of this appendix contain data handling instructions for the option of using a spatially averaged network of monitors for the annual standard. If spatial averaging is not considered for an area, then the spatial average is equivalent to the annual average of a single site and is treated accordingly in subsequent calculations. For example, paragraph (a)(3) of section 2.1 of this appendix could be eliminated since the spatial average would be equivalent to the annual average.
2.0 Comparisons with the PM2.5 Standards.
2.1 Annual PM2.5 Standard.
(a) The annual PM2.5 standard is met when the 3-year average of the spatially averaged annual means is less than or equal to 15.0 µg/m 3 . The 3-year average of the spatially averaged annual means is determined by averaging quarterly means at each monitor to obtain the annual mean PM2.5 concentrations at each monitor, then averaging across all designated monitors, and finally averaging for 3 consecutive years. The steps can be summarized as follows:
(1) Average 24-hour measurements to obtain quarterly means at each monitor.
(2) Average quarterly means to obtain annual means at each monitor.
(3) Average across designated monitoring sites to obtain an annual spatial mean for an area (this can be one site in which case the spatial mean is equal to the annual mean).
(4) Average 3 years of annual spatial means to obtain a 3-year average of spatially averaged annual means.
(b) In the case of spatial averaging, 3 years of spatial averages are required to demonstrate that the standard has been met. Designated sites with less than 3 years of data shall be included in spatial averages for those years that data completeness requirements are met. For the annual PM2.5 standard, a year meets data completeness requirements when at least 75 percent of the scheduled sampling days for each quarter have valid data. However, years with high concentrations and more than a minimal amount of data (at least 11 samples in each quarter) shall not be ignored just because they are comprised of quarters with less than complete data. Thus, in computing annual spatially averaged means, years containing quarters with at least 11 samples but less than 75 percent data completeness shall be included in the computation if the resulting spatially averaged annual mean concentration (rounded according to the conventions of section 2.3 of this appendix) is greater than the level of the standard.
(c) Situations may arise in which there are compelling reasons to retain years containing quarters which do not meet the data completeness requirement of 75 percent or the minimum number of 11 samples. The use of less than complete data is subject to the approval of the appropriate Regional Administrator.
(d) The equations for calculating the 3-year average annual mean of the PM2.5 standard are given in section 2.5 of this appendix.
2.2 24-Hour PM2.5 Standard.
(a) The 24-hour PM2.5 standard is met when the 3-year average of the 98th percentile values at each monitoring site is less than or equal to 65 µg/m 3 . This comparison shall be based on 3 consecutive, complete years of air quality data. A year meets data completeness requirements when at least 75 percent of the scheduled sampling days for each quarter have valid data. However, years with high concentrations shall not be ignored just because they are comprised of quarters with less than complete data. Thus, in computing the 3-year average 98th percentile value, years containing quarters with less than 75 percent data completeness shall be included in the computation if the annual 98th percentile value (rounded according to the conventions of section 2.3 of this appendix) is greater than the level of the standard.
(b) Situations may arise in which there are compelling reasons to retain years containing quarters which do not meet the data completeness requirement. The use of less than complete data is subject to the approval of the appropriate Regional Administrator.
(c) The equations for calculating the 3-year average of the annual 98th percentile values is given in section 2.6 of this appendix.
2.3 Rounding Conventions. For the purposes of comparing calculated values to the applicable level of the standard, it is necessary to round the final results of the calculations described in sections 2.5 and 2.6 of this appendix. For the annual PM2.5 standard, the 3-year average of the spatially averaged annual means shall be rounded to the nearest 0.1 µg/m 3 (decimals 0.05 and greater are rounded up to the next 0.1, and any decimal lower than 0.05 is rounded down to the nearest 0.1). For the 24-hour PM2.5 standard, the 3-year average of the annual 98th percentile values shall be rounded to the nearest 1 µg/m 3 (decimals 0.5 and greater are rounded up to nearest whole number, and any decimal lower than 0.5 is rounded down to the nearest whole number).
2.4 Monitoring Considerations.
(a) Section 58.13 of this chapter specifies the required minimum frequency of sampling for PM2.5. Exceptions to the specified sampling frequencies, such as a reduced frequency during a season of expected low concentrations, are subject to the approval of the appropriate Regional Administrator. Section 58.14 of 40 CFR part 58 and section 2.8 of appendix D of 40 CFR part 58, specify which monitors are eligible for making comparisons with the PM standards. In determining a spatial mean using two or more monitoring sites operating in a given year, the annual mean for an individual site may be included in the spatial mean if and only if the mean for that site meets the criterion specified in §2.8 of appendix D of 40 CFR part 58. In the event data from an otherwise eligible site is excluded from being averaged with data from other sites on the basis of this criterion, then the 3-year mean from that site shall be compared directly to the annual standard.
(b) For the annual PM2.5 standard, when designated monitors are located at the same site and are reporting PM2.5 values for the same time periods, and when spatial averaging has been chosen, their concentrations shall be averaged before an area-wide spatial average is calculated. Such monitors will then be considered as one monitor.
2.5 Equations for the Annual PM2.5 Standard.
(a) An annual mean value for PM2.5 is determined by first averaging the daily values of a calendar quarter:
Equation 1
where:
x q,y,s = the mean for quarter q of year y for site s;
nq = the number of monitored values in the quarter; and
xi,q,y,s = the ith value in quarter q for year y for site s.
(b) The following equation is then to be used for calculation of the annual mean:
Equation 2
where:
x y,s = the annual mean concentration for year y (y = 1, 2, or 3) and for site s; and
x q,y,s = the mean for quarter q of year y for site s.
(c)(1) The spatially averaged annual mean for year y is computed by first calculating the annual mean for each site designated to be included in a spatial average, x y,s, and then computing the average of these values across sites:
Equation 3
where:
x y = the spatially averaged mean for year y;
x y,s = the annual mean for year y and site s; and
ns = the number of sites designated to be averaged.
(2) In the event that an area designated for spatial averaging has two or more sites at the same location producing data for the same time periods, the sites are averaged together before using Equation 3 by:
Equation 4
where:
x y,s* = the annual mean for year y for the sites at the same location (which will now be considered one site);
nc = the number of sites at the same location designated to be included in the spatial average; and
x y,s = the annual mean for year y and site s.
(d) The 3-year average of the spatially averaged annual means is calculated by using the following equation:
Equation 5
where:
x = the 3-year average of the spatially averaged annual means; and
x y = the spatially averaged annual mean for year y.
Example 1—Area Designated for Spatial Averaging That Meets the Primary Annual PM2.5 Standard.
a. In an area designated for spatial averaging, four designated monitors recorded data in at least 1 year of a particular 3-year period. Using Equations 1 and 2, the annual means for PM2.5 at each site are calculated for each year. The following table can be created from the results. Data completeness percentages for the quarter with the fewest number of samples are also shown.
Table 1_Results from Equations 1 and 2
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Site Site Site Site
[bottom]1 [bottom]2 [bottom]3 [bottom]4 Spatial mean
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Year 1......................................... Annual mean (µg/m\3\)...... 12.7 ............ ............ ............ 12.7
% data completeness.............. 80 0 0 0 ............
Year 2......................................... Annual mean (µg/m\3\)...... 12.6 17.5 15.2 ............ 15.05
% data completeness.............. 90 63 38 0 ............
Year 3......................................... Annual mean (µg/m\3\)...... 12.5 18.5 14.1 16.9 15.50
% data completeness.............. 90 80 85 50 ............
3-year mean.................................... ................................. ............ ............ ............ ............ 14.42
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b. The data from these sites are averaged in the order described in section 2.1 of this appendix. Note that the annual mean from site #3 in year 2 and the annual mean from site #4 in year 3 do not meet the 75 percent data completeness criteria. Assuming the 38 percent data completeness represents a quarter with fewer than 11 samples, site #3 in year 2 does not meet the minimum data completeness requirement of 11 samples in each quarter. The site is therefore excluded from the calculation of the spatial mean for year 2. However, since the spatial mean for year 3 is above the level of the standard and the minimum data requirement of 11 samples in each quarter has been met, the annual mean from site #4 in year 3 is included in the calculation of the spatial mean for year 3 and in the calculation of the 3-year average. The 3-year average is rounded to 14.4 µg/m 3 , indicating that this area meets the annual PM2.5 standard.
Example 2—Area With Two Monitors at the Same Location That Meets the Primary Annual PM2.5 Standard.
a. In an area designated for spatial averaging, six designated monitors, with two monitors at the same location (#5 and #6), recorded data in a particular 3-year period. Using Equations 1 and 2, the annual means for PM2.5 are calculated for each year. The following table can be created from the results.
Table 2_Results From Equations 1 and 2
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Average of
Site Site Site Site Site Site [bottom]5 Spatial
Annual mean (µg/m\3\) [bottom]1 [bottom]2 [bottom]3 [bottom]4 [bottom]5 [bottom]6 and mean
[bottom]6
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Year 1............................................ 12.9 9.9 12.6 11.1 14.5 14.6 14.55 12.21
Year 2............................................ 14.5 13.3 12.2 10.9 16.1 16.0 16.05 13.39
Year 3............................................ 14.4 12.4 11.5 9.7 12.3 12.1 12.20 12.04
3-Year mean....................................... ........... ........... ........... ........... ........... ........... .......... 12.55
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b. The annual means for sites #5 and #6 are averaged together using Equation 4 before the spatial average is calculated using Equation 3 since they are in the same location. The 3-year mean is rounded to 12.6 µg/m 3 , indicating that this area meets the annual PM2.5 standard.
Example 3—Area With a Single Monitor That Meets the Primary Annual PM2.5 Standard.
a. Given data from a single monitor in an area, the calculations are as follows. Using Equations 1 and 2, the annual means for PM2.5 are calculated for each year. If the annual means are 10.28, 17.38, and 12.25 µg/m 3 , then the 3-year mean is:
b. This value is rounded to 13.3, indicating that this area meets the annual PM2.5 standard.
2.6 Equations for the 24-Hour PM2.5 Standard.
(a) When the data for a particular site and year meet the data completeness requirements in section 2.2 of this appendix, calculation of the 98th percentile is accomplished by the following steps. All the daily values from a particular site and year comprise a series of values (x1, x2, x3, ..., xn), that can be sorted into a series where each number is equal to or larger than the preceding number (x[1], x[2], x[3], ..., x[n]). In this case, x[1] is the smallest number and x[n] is the largest value. The 98th percentile is found from the sorted series of daily values which is ordered from the lowest to the highest number. Compute (0.98) × (n) as the number “i.d”, where “i” is the integer part of the result and “d” is the decimal part of the result. The 98th percentile value for year y, P0.98, y, is given by Equation 6:
Equation 6
where:
P0.98,y = 98th percentile for year y;
x[i=1] = the (i=1)th number in the ordered series of numbers; and
i = the integer part of the product of 0.98 and n.
(b) The 3-year average 98th percentile is then calculated by averaging the annual 98th percentiles:
Equation 7
(c) The 3-year average 98th percentile is rounded according to the conventions in section 2.3 of this appendix before a comparison with the standard is made.
Example 4—Ambient Monitoring Site With Every-Day Sampling That Meets the Primary 24-Hour PM2.5 Standard.
a. In each year of a particular 3 year period, varying numbers of daily PM2.5 values (e.g., 281, 304, and 296) out of a possible 365 values were recorded at a particular site with the following ranked values (in µg/m 3 ):
Table 3_Ordered Monitoring Data For 3 Years
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Year 1 Year 2 Year 3
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j rank Xj value j rank Xj value j rank Xj value
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275 57.9 296 54.3 290 66.0
276 59.0 297 57.1 291 68.4
277 62.2 298 63.0 292 69.8
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b. Using Equation 6, the 98th percentile values for each year are calculated as follows:
c.1. Using Equation 7, the 3-year average 98th percentile is calculated as follows:
2. Therefore, this site meets the 24-hour PM2.5 standard.
[62 FR 38755, July 18, 1997, as amended at 69 FR 45595, July 30, 2004]