Appendix R to Part 50 - Interpretation of the National Ambient Air Quality Standards for Lead
40:2.0.1.1.1.0.1.20.19 : Appendix R
Appendix R to Part 50 - Interpretation of the National Ambient Air
Quality Standards for Lead 1.
General.
(a) This appendix explains the data handling conventions and
computations necessary for determining when the primary and
secondary national ambient air quality standards (NAAQS) for lead
(Pb) specified in § 50.16 are met. The NAAQS indicator for Pb is
defined as: lead and its compounds, measured as elemental lead in
total suspended particulate (Pb-TSP), sampled and analyzed by a
Federal reference method (FRM) based on appendix G to this part or
by a Federal equivalent method (FEM) designated in accordance with
part 53 of this chapter. Although Pb-TSP is the lead NAAQS
indicator, surrogate Pb-TSP concentrations shall also be used for
NAAQS comparisons; specifically, valid surrogate Pb-TSP data are
concentration data for lead and its compounds, measured as
elemental lead, in particles with an aerodynamic size of 10 microns
or less (Pb-PM10), sampled and analyzed by an FRM based on appendix
Q to this part or by an FEM designated in accordance with part 53
of this chapter. Surrogate Pb-TSP data (i.e., Pb-PM10 data),
however, can only be used to show that the Pb NAAQS were violated
(i.e., not met); they can not be used to demonstrate that
the Pb NAAQS were met. Pb-PM10 data used as surrogate Pb-TSP data
shall be processed at face value; that is, without any
transformation or scaling. Data handling and computation procedures
to be used in making comparisons between reported and/or surrogate
Pb-TSP concentrations and the level of the Pb 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 monitoring network plan refers to the plan
required by section 58.10 of this chapter.
Creditable samples are samples that are given credit for
data completeness. They include valid samples collected on required
sampling days and valid “make-up” samples taken for missed or
invalidated samples on required sampling days.
Daily values for Pb refer to the 24-hour mean
concentrations of Pb (Pb-TSP or Pb-PM10), measured from midnight to
midnight (local standard time), that are used in NAAQS
computations.
Design value is the site-level metric (i.e.,
statistic) that is compared to the NAAQS level to determine
compliance; the design value for the Pb NAAQS is selected according
to the procedures in this appendix from among the valid three-month
Pb-TSP and surrogate Pb-TSP (Pb-PM10) arithmetic mean concentration
for the 38-month period consisting of the most recent 3-year
calendar period plus two previous months (i.e., 36 3-month
periods) using the last month of each 3-month period as the period
of report.
Extra samples are non-creditable samples. They are daily
values that do not occur on scheduled sampling days and that can
not be used as “make-up samples” for missed or invalidated
scheduled samples. Extra samples are used in mean calculations. For
purposes of determining whether a sample must be treated as a
make-up sample or an extra sample, Pb-TSP and Pb-PM10 data
collected before January 1, 2009 will be treated with an assumed
scheduled sampling frequency of every sixth day.
Make-up samples are samples taken to replace missed or
invalidated required scheduled samples. Make-ups can be made by
either the primary or collocated (same size fraction) instruments;
to be considered a valid make-up, the sampling must be conducted
with equipment and procedures that meet the requirements for
scheduled sampling. Make-up samples are either taken before the
next required sampling day or exactly one week after the missed (or
voided) sampling day. Make-up samples can not span years; that is,
if a scheduled sample for December is missed (or voided), it can
not be made up in January. Make-up samples, however, may span
months, for example a missed sample on January 31 may be made up on
February 1, 2, 3, 4, 5, or 7 (with an assumed sampling frequency of
every sixth day). Section 3(e) explains how such month-spanning
make-up samples are to be treated for purposes of data completeness
and mean calculations. Only two make-up samples are permitted each
calendar month; these are counted according to the month in which
the miss and not the makeup occurred. For purposes of determining
whether a sample must be treated as a make-up sample or an extra
sample, Pb-TSP and Pb-PM10 data collected before January 1, 2009
will be treated with an assumed scheduled sampling frequency of
every sixth day.
Monthly mean refers to an arithmetic mean, calculated as
specified in section 6(a) of this appendix. Monthly means are
computed at each monitoring site separately for Pb-TSP and Pb-PM10
(i.e., by site-parameter-year-month).
Parameter refers either to Pb-TSP or to Pb-PM10.
Pollutant Occurrence Code (POC) refers to a numerical
code (1, 2, 3, etc.) used to distinguish the data from two or more
monitors for the same parameter at a single monitoring site.
Scheduled sampling day means a day on which sampling is
scheduled based on the required sampling frequency for the
monitoring site, as provided in section 58.12 of this chapter.
Three-month means are arithmetic averages of three
consecutive monthly means. Three-month means are computed on a
rolling, overlapping basis. Each distinct monthly mean will be
included in three different 3-month means; for example, in a given
year, a November mean would be included in: (1) The
September-October-November 3-month mean, (2) the
October-November-December 3-month mean, and (3) the
November-December-January(of the following year) 3-month mean.
Three-month means are computed separately for each parameter per
section 6(a) (and are referred to as 3-month parameter means) and
are validated according to the criteria specified in section 4(c).
The parameter-specific 3-month means are then prioritized according
to section 2(a) to determine a single 3-month site mean.
Year refers to a calendar year.
2. Use of Pb-PM10 Data as Surrogate Pb-TSP
Data.
(a) As stipulated in section 2.10 of Appendix C to 40 CFR part
58, at some mandatory Pb monitoring locations, monitoring agencies
are required to sample for Pb as Pb-TSP, and at other mandatory Pb
monitoring sites, monitoring agencies are permitted to monitor for
Pb-PM10 in lieu of Pb-TSP. In either situation, valid collocated Pb
data for the other parameter may be produced. Additionally, there
may be non-required monitoring locations that also produce valid
Pb-TSP and/or valid Pb-PM10 data. Pb-TSP data and Pb-PM10 data are
always processed separately when computing monthly and 3-month
parameter means; monthly and 3-month parameter means are validated
according to the criteria stated in section 4 of this appendix.
Three-month “site” means, which are the final valid 3-month mean
from which a design value is identified, are determined from the
one or two available valid 3-month parameter means according to the
following prioritization which applies to all Pb monitoring
locations.
(i) Whenever a valid 3-month Pb-PM10 mean shows a violation and
either is greater than a corresponding (collocated) 3-month Pb-TSP
mean or there is no corresponding valid 3-month Pb-TSP mean
present, then that 3-month Pb-PM10 mean will be the site-level mean
for that (site's) 3-month period.
(ii) Otherwise (i.e., there is no valid violating 3-month
Pb-PM10 that exceeds a corresponding 3-month Pb-TSP mean),
(A) If a valid 3-month Pb-TSP mean exists, then it will be the
site-level mean for that (site's) 3-month period, or
(B) If a valid 3-month Pb-TSP mean does not exist, then there is
no valid 3-month site mean for that period (even if a valid
non-violating 3-month Pb-PM10 mean exists).
(b) As noted in section 1(a) of this appendix, FRM/FEM Pb-PM10
data will be processed at face value (i.e., at reported
concentrations) without adjustment when computing means and making
NAAQS comparisons.
3. Requirements for Data Used for Comparisons With the Pb
NAAQS and Data Reporting Considerations.
(a) All valid FRM/FEM Pb-TSP data and all valid FRM/FEM Pb-PM10
data 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. Pb-TSP and Pb-PM10 data representing sample
collection periods prior to January 1, 2009 (i.e.,
“pre-rule” data) will also be considered valid for NAAQS
comparisons and related attainment/nonattainment determinations if
the sampling and analysis methods that were utilized to collect
that data were consistent with previous or newly designated FRMs or
FEMs and with either the provisions of part 58 of this chapter
including appendices A, C, and E that were in effect at the time of
original sampling or that are in effect at the time of the
attainment/nonattainment determination, and if such data are
submitted to AQS prior to September 1, 2009.
(b) Pb-TSP and Pb-PM10 measurement data are reported to AQS in
units of micrograms per cubic meter (µg/m 3) at local conditions
(local temperature and pressure, LC) to three decimal places; any
additional digits to the right of the third decimal place are
truncated. Pre-rule Pb-TSP and Pb-PM10 concentration data that were
reported in standard conditions (standard temperature and standard
pressure, STP) will not require a conversion to local conditions
but rather, after truncating to three decimal places and processing
as stated in this appendix, shall be compared “as is” to the NAAQS
(i.e., the LC to STP conversion factor will be assumed to be
one). However, if the monitoring agency has retroactively
resubmitted Pb-TSP or Pb-PM10 pre-rule data converted from STP to
LC based on suitable meteorological data, only the LC data will be
used.
(c) At each monitoring location (site), Pb-TSP and Pb-PM10 data
are to be processed separately when selecting daily data by day (as
specified in section 3(d) of this appendix), when aggregating daily
data by month (per section 6(a)), and when forming 3-month means
(per section 6(b)). However, when deriving (i.e.,
identifying) the design value for the 38-month period, 3-month
means for the two data types may be considered together; see
sections 2(a) and 4(e) of this appendix for details.
(d) Daily values for sites will be selected for a site on a size
cut (Pb-TSP or Pb-PM10, i.e., “parameter”) basis; Pb-TSP
concentrations and Pb-PM10 concentrations shall not be commingled
in these determinations. Site level, parameter-specific daily
values will be selected as follows:
(i) The starting dataset for a site-parameter shall consist of
the measured daily concentrations recorded from the designated
primary FRM/FEM monitor for that parameter. The primary monitor for
each parameter shall be designated in the appropriate state or
local agency annual Monitoring Network Plan. If no primary monitor
is designated, the Administrator will select which monitor to treat
as primary. All daily values produced by the primary sampler are
considered part of the site-parameter data record (i.e.,
that site-parameter's set of daily values); this includes all
creditable samples and all extra samples. For pre-rule Pb-TSP and
Pb-PM10 data, valid data records present in AQS for the monitor
with the lowest occurring Pollutant Occurrence Code (POC), as
selected on a site-parameter-daily basis, will constitute the
site-parameter data record. Where pre-rule Pb-TSP data (or
subsequent non-required Pb-TSP or Pb-PM10 data) are reported in
“composite” form (i.e., multiple filters for a month of
sampling that are analyzed together), the composite concentration
will be used as the site-parameter monthly mean concentration if
there are no valid daily Pb-TSP data reported for that month with a
lower POC.
(ii) Data for the primary monitor for each parameter shall be
augmented as much as possible with data from collocated (same
parameter) FRM/FEM monitors. If a valid 24-hour measurement is not
produced from the primary monitor for a particular day (scheduled
or otherwise), but a valid sample is generated by a collocated
(same parameter) FRM/FEM instrument, then that collocated value
shall be considered part of the site-parameter data record
(i.e., that site-parameter's monthly set of daily values).
If more than one valid collocated FRM/FEM value is available, the
mean of those valid collocated values shall be used as the daily
value. Note that this step will not be necessary for pre-rule data
given the daily identification presumption for the primary
monitor.
(e) All daily values in the composite site-parameter record are
used in monthly mean calculations. However, not all daily values
are given credit towards data completeness requirements. Only
“creditable” samples are given credit for data completeness.
Creditable samples include valid samples on scheduled sampling days
and valid make-up samples. All other types of daily values are
referred to as “extra” samples. Make-up samples taken in the (first
week of the) month after the one in which the miss/void occurred
will be credited for data capture in the month of the miss/void but
will be included in the month actually taken when computing monthly
means. For example, if a make-up sample was taken in February to
replace a missed sample scheduled for January, the make-up
concentration would be included in the February monthly mean but
the sample credited in the January data capture rate.
4. Comparisons With the Pb NAAQS.
(a) The Pb NAAQS is met at a monitoring site when the identified
design value is valid and less than or equal to 0.15 micrograms per
cubic meter (µg/m 3). A Pb design value that meets the NAAQS
(i.e., 0.15 µg/m 3 or less), is considered valid if it
encompasses 36 consecutive valid 3-month site means (specifically
for a 3-year calendar period and the two previous months). For
sites that begin monitoring Pb after this rule is effective but
before January 15, 2010 (or January 15, 2011), a 2010-2012 (or
2011-2013) Pb design value that meets the NAAQS will be considered
valid if it encompasses at least 34 consecutive valid 3-month means
(specifically encompassing only the 3-year calendar period). See
4(c) of this appendix for the description of a valid 3-month mean
and section 6(d) for the definition of the design value.
(b) The Pb NAAQS is violated at a monitoring site when the
identified design value is valid and is greater than 0.15 µg/m 3,
no matter whether determined from Pb-TSP or Pb-PM10 data. A Pb
design value greater than 0.15 µg/m 3 is valid no matter how many
valid 3-month means in the 3-year period it encompasses; that is, a
violating design value is valid even if it (i.e., the
highest 3-month mean) is the only valid 3-month mean in the 3-year
timeframe. Further, a site does not have to monitor for three full
calendar years in order to have a valid violating design value; a
site could monitor just three months and still produce a valid
(violating) design value.
(c)(i) A 3-month parameter mean is considered valid
(i.e., meets data completeness requirements) if the average
of the data capture rate of the three constituent monthly means
(i.e., the 3-month data capture rate) is greater than or
equal to 75 percent. Monthly data capture rates (expressed as a
percentage) are specifically calculated as the number of creditable
samples for the month (including any make-up samples taken the
subsequent month for missed samples in the month in question, and
excluding any make-up samples taken in the month in question for
missed samples in the previous month) divided by the number of
scheduled samples for the month, the result then multiplied by 100
but not rounded. The 3-month data capture rate is the sum of the
three corresponding unrounded monthly data capture rates divided by
three and the result rounded to the nearest integer (zero decimal
places). As noted in section 3(c), Pb-TSP and Pb-PM10 daily values
are processed separately when calculating monthly means and data
capture rates; a Pb-TSP value cannot be used as a make-up for a
missing Pb-PM10 value or vice versa. For purposes of assessing data
capture, Pb-TSP and Pb-PM10 data collected before January 1, 2009
will be treated with an assumed scheduled sampling frequency of
every sixth day.
(ii) A 3-month parameter mean that does not have at least 75
percent data capture and thus is not considered valid under 4(c)(i)
shall be considered valid (and complete) if it passes either of the
two following “data substitution” tests, one such test for
validating an above NAAQS-level (i.e., violating) 3-month
Pb-TSP or Pb-PM10 mean (using actual “low” reported values from the
same site at about the same time of the year (i.e., in the
same month) looking across three or four years), and the second
test for validating a below-NAAQS level 3-month Pb-TSP mean (using
actual “high” values reported for the same site at about the same
time of the year (i.e., in the same month) looking across
three or four years). Note that both tests are merely diagnostic in
nature intending to confirm that there is a very high likelihood if
not certainty that the original mean (the one with less than 75%
data capture) reflects the true over/under NAAQS-level status for
that 3-month period; the result of one of these data substitution
tests (i.e., a “test mean”, as defined in section
4(c)(ii)(A) or 4(c)(ii)(B)) is not considered the actual 3-month
parameter mean and shall not be used in the determination of design
values. For both types of data substitution, substitution is
permitted only if there are available data points from which to
identify the high or low 3-year month-specific values, specifically
if there are at least 10 data points total from at least two of the
three (or four for November and December) possible year-months.
Data substitution may only use data of the same parameter type.
(A) The “above NAAQS level” test is as follows: Data
substitution will be done in each month of the 3-month period that
has less than 75 percent data capture; monthly capture rates are
temporarily rounded to integers (zero decimals) for this
evaluation. If by substituting the lowest reported daily value for
that month (year non-specific; e.g., for January) over the 38-month
design value period in question for missing scheduled data in the
deficient months (substituting only enough to meet the 75 percent
data capture minimum), the computation yields a recalculated test
3-month parameter mean concentration above the level of the
standard, then the 3-month period is deemed to have passed the
diagnostic test and the level of the standard is deemed to have
been exceeded in that 3-month period. As noted in section 4(c)(ii),
in such a case, the 3-month parameter mean of the data actually
reported, not the recalculated (“test”) result including the low
values, shall be used to determine the design value.
(B) The “below NAAQS level” test is as follows: Data
substitution will be performed for each month of the 3-month period
that has less than 75 percent but at least 50 percent data capture;
if any month has less than 50% data capture then the 3-month mean
can not utilize this substitution test. Also, incomplete 3-month
Pb-PM10 means can not utilize this test. A 3-month Pb-TSP mean with
less than 75% data capture shall still be considered valid (and
complete) if, by substituting the highest reported daily value,
month-specific, over the 3-year design value period in question,
for all missing scheduled data in the deficient months
(i.e., bringing the data capture rate up to 100%), the
computation yields a recalculated 3-month parameter mean
concentration equal or less than the level of the standard (0.15
µg/m 3), then the 3-month mean is deemed to have passed the
diagnostic test and the level of the standard is deemed not to have
been exceeded in that 3-month period (for that parameter). As noted
in section 4(c)(ii), in such a case, the 3-month parameter mean of
the data actually reported, not the recalculated (“test”) result
including the high values, shall be used to determine the design
value.
(d) Months that do not meet the completeness criteria stated in
4(c)(i) or 4(c)(ii), and design values that do not meet the
completeness criteria stated in 4(a) or 4(b), may also be
considered valid (and complete) 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 site-level design value for a 38-month period (three
calendar years plus two previous months) is identified from the
available (between one and 36) valid 3-month site means. In a
situation where there are valid 3-month means for both parameters
(Pb-TSP and Pb-PM10), the mean originating from the reported Pb-TSP
data will be the one deemed the site-level monthly mean and used in
design value identifications unless the Pb-PM10 mean shows a
violation of the NAAQS and exceeds the Pb-TSP mean; see section
2(a) for details. A monitoring site will have only one site-level
3-month mean per 3-month period; however, the set of site-level
3-month means considered for design value identification
(i.e., one to 36 site-level 3-month means) can be a
combination of Pb-TSP and Pb-PM10 data.
(f) The procedures for calculating monthly means and 3-month
means, and identifying Pb design values are given in section 6 of
this appendix.
5. Rounding Conventions.
(a) Monthly means and monthly data capture rates are not
rounded.
(b) Three-month means shall be rounded to the nearest hundredth
µg/m 3 (0.xx). Decimals 0.xx5 and greater are rounded up, and any
decimal lower than 0.xx5 is rounded down. E.g., a 3-month mean of
0.104925 rounds to 0.10 and a 3-month mean of .10500 rounds to
0.11. Three-month data capture rates, expressed as a percent, are
round to zero decimal places.
(c) Because a Pb design value is simply a (highest) 3-month mean
and because the NAAQS level is stated to two decimal places, no
additional rounding beyond what is specified for 3-month means is
required before a design value is compared to the NAAQS.
6. Procedures and Equations for the Pb NAAQS.
(a)(i) A monthly mean value for Pb-TSP (or Pb-PM10) is
determined by averaging the daily values of a calendar month using
equation 1 of this appendix, unless the Administrator chooses to
exercise his discretion to use the alternate approach described in
6(a)(ii).
Where: Xm,y,s = the mean for month m of the
year y for sites; and nm = the number of daily values in the month
(creditable plus extra samples); and Xi,m,y,s = the i th value in
month m for year y for site s.
(a)(ii) The Administrator may at his discretion use the
following alternate approach to calculating the monthly mean
concentration if the number of extra sampling days during a month
is greater than the number of successfully completed scheduled and
make-up sample days in that month. In exercising his discretion,
the Administrator will consider whether the approach specified in
6(a)(i) might in the Administrator's judgment result in an
unrepresentative value for the monthly mean concentration. This
provision is to protect the integrity of the monthly and 3-month
mean concentration values in situations in which, by intention or
otherwise, extra sampling days are concentrated in a period during
which ambient concentrations are particularly high or low. The
alternate approach is to average all extra and make-up samples (in
the given month) taken after each scheduled sampling day (“Day X”)
and before the next scheduled sampling day (e.g., “Day X + 6”, in
the case of one-in-six sampling) with the sample taken on Day X
(assuming valid data was obtained on the scheduled sampling day),
and then averaging these averages to calculate the monthly mean.
This approach has the effect of giving approximately equal weight
to periods during a month that have equal number of days,
regardless of how many samples were actually obtained during the
periods, thus mitigating the potential for the monthly mean to be
distorted. The first day of scheduled sampling typically will not
fall on the first day of the calendar month, and there may be
make-up and/or extra samples (in that same calendar month)
preceding the first scheduled day of the month. These samples will
not be shifted into the previous month's mean concentration, but
rather will stay associated with their actual calendar month as
follows. Any extra and make-up samples taken in a month before the
first scheduled sampling day of the month will be associated with
and averaged with the last scheduled sampling day of that same
month.
(b) Three-month parameter means are determined by averaging
three consecutive monthly means of the same parameter using
Equation 2 of this appendix.
Where: X m1, m2, m3; s = the 3-month parameter
mean for months m1, m2, and m3 for site s; and nm = the number of
monthly means available to be averaged (typically 3, sometimes 1 or
2 if one or two months have no valid daily values); and Xm, y: z, s
= The mean for month m of the year y (or z) for site s.
(c) Three-month site means are determined from available 3-month
parameter means according to the hierarchy established in 2(a) of
this appendix.
(d) The site-level Pb design value is the highest valid 3-month
site-level mean over the most recent 38-month period (i.e.,
the most recent 3-year calendar period plus two previous months).
Section 4(a) of this appendix explains when the identified design
value is itself considered valid for purposes of determining that
the NAAQS is met or violated at a site.
[73 FR 67054, Nov. 12, 2008]