EPA's 1997 Decision on Ozone and Particulate Matter Standards
Explanation of Data Handling Requirements and Forms of the National Ambient Air Quality Standards for Particulate Matter
Note: EPA no longer updates this information, but it may be useful as a reference or resource.Note: EPA no longer updates this information, but it may be useful as a reference or resource.
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FACT SHEET EXPLANATION OF DATA HANDLING REQUIREMENTS AND FORMS OF THE NATIONAL AMBIENT AIR QUALITY STANDARDS FOR PARTICULATE MATTER
BACKGROUND On July 18, 1997, EPA issued revised National Ambient Air Quality Standards (NAAQS) for Particulate Matter and Ozone. EPA revised the form of the daily standard for particulate matter of 10 microns in diameter or less (PM10). EPA also issued daily and annual standards for particulate matter of 2.5 microns in diameter or less (PM2.5). Particulate matter is the general term for solid or liquid particles found in the atmosphere. Coarse particles (between 2.5 and 10 microns in diameter) come from a variety of sources including windblown dust and grinding operations. Fine particles (less than 2.5 microns in diameter) often come from fuel combustion, power plants, and diesel buses and trucks. Exposure to particulate matter can result in the aggravation of respiratory conditions such as asthma, increased hospital admissions and emergency room visits, increased respiratory symptoms and disease, decreased lung function, and in some cases, premature death. WHAT TYPE OF INFORMATION IS CONTAINED IN THIS FACT SHEET? This fact sheet summarizes the basic information on data handling requirements and the forms of the air quality standards for particulate matter. It is designed to demonstrate through plain language and a few simple calculations how to determine whether data meet the national air quality standards for particulate matter. This document supplements Part 50, Appendices K and N of the Clean Air Act. It is not meant to replace Appendix K or Appendix N, which contain additional requirements, details, and examples (including examples for spatial averaging and for data which do not meet data completeness requirements). WHO IS THE TARGET AUDIENCE FOR THIS TYPE OF INFORMATION? This fact sheet is designed to assist Regional, State, and local air pollution officials and others in comparing measured particulate matter data to EPA's recently revised National Ambient Air Quality Standards for Particulate Matter (40 CFR Part 50). THE PM10 STANDARDS The revised standards became effective September 16, 1997. For a time, areas will be subject to both the pre-existing standards (which use Appendix K) and the revised standards (which use Appendix N). The pre-existing PM10 standards remain in effect in a given area until they are revoked for that area.
Annual PM10 Standard (as stated in Appendix N)
Level: 50 µg/m3
Form: At each site, calculate the annual mean from 4
quarterly means. Average the annual means for
3 years.
Rounding: 50.4 rounds to 50
50.5 rounds to 51 (first value above the standard)
Data Completeness Requirement: Need 75% of scheduled
sampling days per quarter. However, if the mean for the
year is above the level of the standard and each quarter
has at least 11 samples, then the annual mean for that
year is considered valid.
24-Hour PM10 Standard (as stated in Appendix N)
Level: 150 µg/m3
Form: At each site, calculate the 99th percentile for
the year. Average the 99th percentiles for 3
years.
Rounding: 154 rounds to 150
155 rounds to 160 (first value above the standard)
Data Completeness Requirement: Need 75% of scheduled
sampling days per quarter. However, if a quarter has
less than 75% of scheduled samples and the 99th
percentile value for the year is above the level of the
standard, the annual 99th percentile for that year is
considered valid.
Assume data completeness requirements have been met for this example. At each site, average all the 24-hour measurements in a quarter to find the quarterly mean. Then average the 4 quarterly means to find the annual mean. In this example, the 4 quarterly means for the first year are 43.23, 54.72, 50.96, and 60.77 µg/m3 . Find the annual mean for the first year.
43.23 + 54.72 + 50.96 + 60.77 = 52.42 µg/m3
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Similarly, the annual means for the second and third year are calculated to be 82.17 and 63.23 µg/m3 .
Find the 3-year average annual mean.
52.42 + 82.17 + 63.23 = 65.94 µg/m3
3
Round 65.94 to 66 µg/m3 before comparing to the standard. This example does not meet the PM10 annual standard.
Assume for this example that the data completeness requirements have been met. At each site, sort all values collected in a year from lowest to highest. Number their rankings as in the following table:
In this example, the site collected 110 samples out of possible 121 samples in year 1; 98 out of 121 in year 2; and 100 out of 121 in year 3. Calculate the 99th percentile for each year.
0.99 x 110 = 108.9
0.99 x 98 = 97.02
0.99 x 100 = 99
Take the integer part of the product and add 1 to find which ranking corresponds to the 99th percentile.
108 + 1 = 109
97 + 1 = 98
99 + 1 = 100
Find the value which corresponds to the ranking using the table above.
109 corresponds to 128 µg/m3
98 corresponds to 150 µg/m3
100 corresponds to 147 µg/m3
Find the 3-year average of the 99th percentiles.
128 + 150 + 147 = 141.7 µg/m3
3
Round 141.7 to 140 µg/m3 before comparing to the standard. This example meets the PM10 24-hour
standard.
THE PM2.5 STANDARDS Use Appendix N for PM2.5 data handling and comparisons to the standards effective September 16, 1997.
Annual PM2.5 Standard (as stated in Appendix N)
Level: 15.0 µg/m3
Form: At each site, calculate the annual mean from 4
quarterly means. If spatial averaging is used,
average the annual means of the designated
monitors in the area to get an annual spatial
mean. Then average the annual spatial means
for 3 years.
Rounding: 15.04 rounds to 15.0
15.05 rounds to 15.1(first value above the standard)
Data Completeness Requirement: Need 75% of scheduled
sampling days per quarter. However, if the spatially
averaged mean for the year is above the level of the
standard and each quarter has at least 11 samples, then
the spatially averaged annual mean for that year is
considered valid.
24-Hour PM2.5 Standard (as stated in Appendix N)
Level: 65 µg/m3
Form: At each site, calculate the 98th percentile for
the year. Average the 98th percentiles for 3
years.
Rounding: 65.4 rounds to 65
65.5 rounds to 66 (first value above the standard)
Data Completeness Requirement: Need 75% of scheduled
sampling days per quarter. However, if a quarter has
less than 75% of scheduled samples and the 98th
percentile value for the year is above the level of the
standard, the annual 98th percentile for that year is
considered valid.
Assume data completeness requirements and the requirements for spatial averaging (see 40 CFR Part 58, Appendix D, Section 2.8) have been met for this example. Given an area designated for spatial averaging and 3 monitors designated for spatial averaging within the area, first average all the 24-hour measurements in each quarter at each site to find the 4 quarterly means. Then calculate the annual mean from the 4 quarterly means. If, for this example, the 4 quarterly means for first site for the first year are 11.6, 12.4, 15.1, and 12.1 µg/m3 , find the annual mean for this site and year.
11.6 + 12.4 + 15.1 + 12.1 = 12.8 µg/m3
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Similarly, the annual means for the other sites and the other years can be calculated. The results appear
in the following table.
For year 1, find the annual spatial mean of the designated monitors in the area.
12.8 + 14.2 + 13.6 = 13.53 µg/m3
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Similarly, the annual spatial means for year 2 and year 3 are calculated to be 13.13 and 15.7 µg/m3 .
Find the 3-year average annual spatial mean.
13.53 + 13.13 + 15.7 = 14.12 µg/m3
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Round 14.12 to 14.1 µg/m3 before comparing to the standard. This example meets the PM-2.5 annual
standard.
Assume for this example that the data completeness requirements have been met. At each site, sort all values collected in a year from lowest to highest. Number their rankings as in the following table:
In this example, the site collected 281 samples out of possible 365 samples in year 1; 304 out of 365 in year 2; and 296 out of 365 in year 3. Calculate the 98th percentile for each year.
0.98 x 281 = 275.38
0.98 x 304 = 297.92
0.98 x 296 = 290.07
Take the integer part of the product and add 1 to find which ranking corresponds to the 98th percentile.
275 + 1 = 276
297 + 1 = 298
290 + 1 = 291
Find the value which corresponds to the ranking using the table above.
276 corresponds to 59.0 µg/m3
298 corresponds to 63.0 µg/m3
291 corresponds to 68.4 µg/m3
Find the 3-year average of the 98th percentiles.
59.0 + 63.0 + 68.4 = 63.46 µg/m3
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Round 63.46 to 63 µg/m3 before comparing to the standard. This example meets the PM2.5 24-hour
standard.
WHAT IS THE RELATIONSHIP BETWEEN SAMPLE SIZE AND THE Nth MAX FOR THE 98th AND 99th PERCENTILES? The following table may be helpful in understanding how many monitored daily PM samples collected in a year correspond to the maximum, second maximum, etc. value for the 98th or 99th percentile forms. For example, if 50 samples are collected in the course of a year, the value for the 98th percentile would be the highest value recorded (the first max). It would also be the first max for the 99th percentile. If, on the other hand, 60 samples were collected in a year, the value for the 98th percentile will be the second max, while the value for the 99th percentile will still be the first max. Footnotes 4, 5, and 6 in the table show how the number of samples correspond to sampling frequency and the requirement for data completeness.
1 Samples are the number of monitored daily PM values in a year.
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