Appendix S to Part 50 - Interpretation of the Primary National Ambient Air Quality Standards for Oxides of Nitrogen (Nitrogen Dioxide)
40:2.0.1.1.1.0.1.20.20 : Appendix S
Appendix S to Part 50 - Interpretation of the Primary National
Ambient Air Quality Standards for Oxides of Nitrogen (Nitrogen
Dioxide) 1. General
(a) This appendix explains the data handling conventions and
computations necessary for determining when the primary national
ambient air quality standards for oxides of nitrogen as measured by
nitrogen dioxide (“NO2 NAAQS”) specified in 50.11 are met. Nitrogen
dioxide (NO2) is measured in the ambient air by a Federal reference
method (FRM) based on appendix F to this part or by a Federal
equivalent method (FEM) designated in accordance with part 53 of
this chapter. Data handling and computation procedures to be used
in making comparisons between reported NO2 concentrations and the
levels of the NO2 NAAQS are specified in the following
sections.
(b) Whether to exclude, retain, or make adjustments to the data
affected by exceptional events, including natural events, is
determined by the requirements and process deadlines specified in
50.1, 50.14 and 51.930 of this chapter.
(c) The terms used in this appendix are defined as follows:
Annual mean refers to the annual average of all of the
1-hour concentration values as defined in section 5.1 of this
appendix.
Daily maximum 1-hour values for NO2 refers to the maximum
1-hour NO2 concentration values measured from midnight to midnight
(local standard time) that are used in NAAQS computations.
Design values are the metrics (i.e., statistics)
that are compared to the NAAQS levels to determine compliance,
calculated as specified in section 5 of this appendix. The design
values for the primary NAAQS are:
(1) The annual mean value for a monitoring site for one year
(referred to as the “annual primary standard design value”).
(2) The 3-year average of annual 98th percentile daily maximum
1-hour values for a monitoring site (referred to as the “1-hour
primary standard design value”).
98th percentile daily maximum 1-hour value is the value
below which nominally 98 percent of all daily maximum 1-hour
concentration values fall, using the ranking and selection method
specified in section 5.2 of this appendix.
Quarter refers to a calendar quarter.
Year refers to a calendar year.
2. Requirements for Data Used for Comparisons With the NO2 NAAQS
and Data Reporting Considerations
(a) All valid FRM/FEM NO2 hourly data required to be submitted
to EPA's Air Quality System (AQS), or otherwise available to EPA,
meeting the requirements of part 58 of this chapter including
appendices A, C, and E shall be used in design value calculations.
Multi-hour average concentration values collected by wet chemistry
methods shall not be used.
(b) When two or more NO2 monitors are operated at a site, the
State may in advance designate one of them as the primary monitor.
If the State has not made this designation, the Administrator will
make the designation, either in advance or retrospectively. Design
values will be developed using only the data from the primary
monitor, if this results in a valid design value. If data from the
primary monitor do not allow the development of a valid design
value, data solely from the other monitor(s) will be used in turn
to develop a valid design value, if this results in a valid design
value. If there are three or more monitors, the order for such
comparison of the other monitors will be determined by the
Administrator. The Administrator may combine data from different
monitors in different years for the purpose of developing a valid
1-hour primary standard design value, if a valid design value
cannot be developed solely with the data from a single monitor.
However, data from two or more monitors in the same year at the
same site will not be combined in an attempt to meet data
completeness requirements, except if one monitor has physically
replaced another instrument permanently, in which case the two
instruments will be considered to be the same monitor, or if the
State has switched the designation of the primary monitor from one
instrument to another during the year.
(c) Hourly NO2 measurement data shall be reported to AQS in
units of parts per billion (ppb), to at most one place after the
decimal, with additional digits to the right being truncated with
no further rounding.
3. Comparisons With the NO2 NAAQS 3.1 The Annual Primary NO2 NAAQS
(a) The annual primary NO2 NAAQS is met at a site when the valid
annual primary standard design value is less than or equal to 53
parts per billion (ppb).
(b) An annual primary standard design value is valid when at
least 75 percent of the hours in the year are reported.
(c) An annual primary standard design value based on data that
do not meet the completeness criteria stated in section 3.1(b) may
also be considered valid with the approval of, or at the initiative
of, the Administrator, who may consider factors such as monitoring
site closures/moves, monitoring diligence, the consistency and
levels of the valid concentration measurements that are available,
and nearby concentrations in determining whether to use such
data.
(d) The procedures for calculating the annual primary standard
design values are given in section 5.1 of this appendix.
3.2 The 1-hour Primary NO2 NAAQS
(a) The 1-hour primary NO2 NAAQS is met at a site when the valid
1-hour primary standard design value is less than or equal to 100
parts per billion (ppb).
(b) An NO2 1-hour primary standard design value is valid if it
encompasses three consecutive calendar years of complete data. A
year meets data completeness requirements when all 4 quarters are
complete. A quarter is complete when at least 75 percent of the
sampling days for each quarter have complete data. A sampling day
has complete data if 75 percent of the hourly concentration values,
including State-flagged data affected by exceptional events which
have been approved for exclusion by the Administrator, are
reported.
(c) In the case of one, two, or three years that do not meet the
completeness requirements of section 3.2(b) of this appendix and
thus would normally not be useable for the calculation of a valid
3-year 1-hour primary standard design value, the 3-year 1-hour
primary standard design value shall nevertheless be considered
valid if one of the following conditions is true.
(i) At least 75 percent of the days in each quarter of each of
three consecutive years have at least one reported hourly value,
and the design value calculated according to the procedures
specified in section 5.2 is above the level of the primary 1-hour
standard.
(ii)(A) A 1-hour primary standard design value that is below the
level of the NAAQS can be validated if the substitution test in
section 3.2(c)(ii)(B) results in a “test design value” that is
below the level of the NAAQS. The test substitutes actual “high”
reported daily maximum 1-hour values from the same site at about
the same time of the year (specifically, in the same calendar
quarter) for unknown values that were not successfully measured.
Note that the test is merely diagnostic in nature, intended to
confirm that there is a very high likelihood that the original
design value (the one with less than 75 percent data capture of
hours by day and of days by quarter) reflects the true
under-NAAQS-level status for that 3-year period; the result of this
data substitution test (the “test design value”, as defined in
section 3.2(c)(ii)(B)) is not considered the actual design value.
For this test, substitution is permitted only if there are at least
200 days across the three matching quarters of the three years
under consideration (which is about 75 percent of all possible
daily values in those three quarters) for which 75 percent of the
hours in the day, including State-flagged data affected by
exceptional events which have been approved for exclusion by the
Administrator, have reported concentrations. However, maximum
1-hour values from days with less than 75 percent of the hours
reported shall also be considered in identifying the high value to
be used for substitution.
(B) The substitution test is as follows: Data
substitution will be performed in all quarter periods that have
less than 75 percent data capture but at least 50 percent data
capture, including State-flagged data affected by exceptional
events which have been approved for exclusion by the Administrator;
if any quarter has less than 50 percent data capture then this
substitution test cannot be used. Identify for each quarter (e.g.,
January-March) the highest reported daily maximum 1-hour value for
that quarter, excluding State-flagged data affected by exceptional
events which have been approved for exclusion by the Administrator,
looking across those three months of all three years under
consideration. All daily maximum 1-hour values from all days in the
quarter period shall be considered when identifying this highest
value, including days with less than 75 percent data capture. If
after substituting the highest non-excluded reported daily maximum
1-hour value for a quarter for as much of the missing daily data in
the matching deficient quarter(s) as is needed to make them 100
percent complete, the procedure in section 5.2 yields a
recalculated 3-year 1-hour standard “test design value” below the
level of the standard, then the 1-hour primary standard design
value is deemed to have passed the diagnostic test and is valid,
and the level of the standard is deemed to have been met in that
3-year period. As noted in section 3.2(c)(i), in such a case, the
3-year design value based on the data actually reported, not the
“test design value”, shall be used as the valid design value.
(iii)(A) A 1-hour primary standard design value that is above
the level of the NAAQS can be validated if the substitution test in
section 3.2(c)(iii)(B) results in a “test design value” that is
above the level of the NAAQS. The test substitutes actual “low”
reported daily maximum 1-hour values from the same site at about
the same time of the year (specifically, in the same three months
of the calendar) for unknown values that were not successfully
measured. Note that the test is merely diagnostic in nature,
intended to confirm that there is a very high likelihood that the
original design value (the one with less than 75 percent data
capture of hours by day and of days by quarter) reflects the true
above-NAAQS-level status for that 3-year period; the result of this
data substitution test (the “test design value”, as defined in
section 3.2(c)(iii)(B)) is not considered the actual design value.
For this test, substitution is permitted only if there are a
minimum number of available daily data points from which to
identify the low quarter-specific daily maximum 1-hour values,
specifically if there are at least 200 days across the three
matching quarters of the three years under consideration (which is
about 75 percent of all possible daily values in those three
quarters) for which 75 percent of the hours in the day have
reported concentrations. Only days with at least 75 percent of the
hours reported shall be considered in identifying the low value to
be used for substitution.
(B) The substitution test is as follows: Data substitution will
be performed in all quarter periods that have less than 75 percent
data capture. Identify for each quarter (e.g., January-March) the
lowest reported daily maximum 1-hour value for that quarter,
looking across those three months of all three years under
consideration. All daily maximum 1-hour values from all days with
at least 75 percent capture in the quarter period shall be
considered when identifying this lowest value. If after
substituting the lowest reported daily maximum 1-hour value for a
quarter for as much of the missing daily data in the matching
deficient quarter(s) as is needed to make them 75 percent complete,
the procedure in section 5.2 yields a recalculated 3-year 1-hour
standard “test design value” above the level of the standard, then
the 1-hour primary standard design value is deemed to have passed
the diagnostic test and is valid, and the level of the standard is
deemed to have been exceeded in that 3-year period. As noted in
section 3.2(c)(i), in such a case, the 3-year design value based on
the data actually reported, not the “test design value”, shall be
used as the valid design value.
(d) A 1-hour primary standard design value based on data that do
not meet the completeness criteria stated in 3.2(b) and also do not
satisfy section 3.2(c), may also be considered valid with the
approval of, or at the initiative of, the Administrator, who may
consider factors such as monitoring site closures/moves, monitoring
diligence, the consistency and levels of the valid concentration
measurements that are available, and nearby concentrations in
determining whether to use such data.
(e) The procedures for calculating the 1-hour primary standard
design values are given in section 5.2 of this appendix.
4. Rounding Conventions 4.1 Rounding Conventions for the Annual
Primary NO2 NAAQS
(a) Hourly NO2 measurement data shall be reported to AQS in
units of parts per billion (ppb), to at most one place after the
decimal, with additional digits to the right being truncated with
no further rounding.
(b) The annual primary standard design value is calculated
pursuant to section 5.1 and then rounded to the nearest whole
number or 1 ppb (decimals 0.5 and greater are rounded up to the
nearest whole number, and any decimal lower than 0.5 is rounded
down to the nearest whole number).
4.2 Rounding Conventions for the 1-hour Primary NO2 NAAQS
(a) Hourly NO2 measurement data shall be reported to AQS in
units of parts per billion (ppb), to at most one place after the
decimal, with additional digits to the right being truncated with
no further rounding.
(b) Daily maximum 1-hour values are not rounded.
(c) The 1-hour primary standard design value is calculated
pursuant to section 5.2 and then rounded to the nearest whole
number or 1 ppb (decimals 0.5 and greater are rounded up to the
nearest whole number, and any decimal lower than 0.5 is rounded
down to the nearest whole number).
5. Calculation Procedures for the Primary NO2 NAAQS 5.1 Procedures
for the Annual Primary NO2 NAAQS
(a) When the data for a site and year meet the data completeness
requirements in section 3.1(b) of this appendix, or if the
Administrator exercises the discretionary authority in section
3.1(c), the annual mean is simply the arithmetic average of all of
the reported 1-hour values.
(b) The annual primary standard design value for a site is the
valid annual mean rounded according to the conventions in section
4.1.
5.2 Calculation Procedures for the 1-hour Primary NO2 NAAQS
(a) Procedure for identifying annual 98th percentile
values. When the data for a particular site and year meet the
data completeness requirements in section 3.2(b), or if one of the
conditions of section 3.2(c) is met, or if the Administrator
exercises the discretionary authority in section 3.2(d),
identification of annual 98th percentile value is accomplished as
follows.
(i) The annual 98th percentile value for a year is the higher of
the two values resulting from the following two procedures.
(1) Procedure 1.
(A) For the year, determine the number of days with at least 75
percent of the hourly values reported including State-flagged data
affected by exceptional events which have been approved for
exclusion by the Administrator.
(B) For the year, from only the days with at least 75 percent of
the hourly values reported, select from each day the maximum hourly
value excluding State-flagged data affected by exceptional events
which have been approved for exclusion by the Administrator.
(C) Sort all these daily maximum hourly values from a particular
site and year by descending value. (For example: (x[1], x[2], x[3],
* * *, x[n]). In this case, x[1] is the largest number and x[n] is
the smallest value.) The 98th percentile is determined from this
sorted series of daily values which is ordered from the highest to
the lowest number. Using the left column of Table 1, determine the
appropriate range (i.e., row) for the annual number of days
with valid data for year y (cny) as determined from step (A). The
corresponding “n” value in the right column identifies the rank of
the annual 98th percentile value in the descending sorted list of
daily site values for year y. Thus, P0.98, y = the nth largest
value.
(2) Procedure 2.
(A) For the year, determine the number of days with at least one
hourly value reported including State-flagged data affected by
exceptional events which have been approved for exclusion by the
Administrator.
(B) For the year, from all the days with at least one hourly
value reported, select from each day the maximum hourly value
excluding State-flagged data affected by exceptional events which
have been approved for exclusion by the Administrator.
(C) Sort all these daily maximum values from a particular site
and year by descending value. (For example: (x[1], x[2], x[3], * *
*, x[n]). In this case, x[1] is the largest number and x[n] is the
smallest value.) The 98th percentile is determined from this sorted
series of daily values which is ordered from the highest to the
lowest number. Using the left column of Table 1, determine the
appropriate range (i.e., row) for the annual number of days
with valid data for year y (cny) as determined from step (A). The
corresponding “n” value in the right column identifies the rank of
the annual 98th percentile value in the descending sorted list of
daily site values for year y. Thus, P0.98, y = the nth largest
value.
(b) The 1-hour primary standard design value for a site is mean
of the three annual 98th percentile values, rounded according to
the conventions in section 4.
Annual number
of days with
valid data for
year “y” (cny) |
P0.98, y is the
nth maximum
value of the
year, where n
is the listed
number |
1-50 |
1 |
51-100 |
2 |
101-150 |
3 |
151-200 |
4 |
201-250 |
5 |
251-300 |
6 |
301-350 |
7 |
351-366 |
8 |
[75 FR 6532, Feb. 9, 2010]