Report on PM2.5 Weighing Lab Temperature and Humidity Control

And 

The Effect on PM2.5 Filter Weighing

Aug 2014

Report Prepared By Robert Brawner
2

Table of Contents

Background ...................................................................................................................................................3

Proposed Actions..........................................................................................................................................4

Results and Recommendations.....................................................................................................................4

Table 1. Pearson Correlation Data Comparisons.....................................................................................6

Graphic 1 Location Map for TDEC and TVA PM2.5 Sampling Sites.............................................................7

Response to Comments Provided by EPA on Review of the Draft Report ...................................................8

Filter Data Statistical Analysis Performed by TDH, Caleb Wiedeman, MPH, Epidemiologist, Tennessee 

Department of Health, Communicable and Environmental Diseases and Emergency Preparedness .......13

Knox County Filter Data Evaluation 2009 to 2013 ......................................................................................21

All Sites Filter Data Evaluation 2009 to 2012..............................................................................................22

Additional Documents Referenced in this Report (Provided as separate attachments)............................23

Environmental Condition Testing of 31 Sampled Measurement Technology Laboratories 46.2-mm 

PTFE (Teflon®) Filters by Paige Presler-Jur, RTI International, July 18, 2014..........................................23

Quality Assurance Project Plan, TDEC PM2.5 Filter Investigation Study, June 17, 2014, by Robert 

Brawner, Technical Services Program, Air Pollution Control Division, Tennessee Department of 

Environment and Conservation ..............................................................................................................23
3

Background

The Environmental Protection Agency (EPA) provides strict criteria that must be followed by a weighing 

laboratory if it is performing weighing analysis for PM2.5 filters. Specialized weighing equipment (micro 

balance), temperature and humidity controlled weighing environment and other requirements must be 

met and maintained on an ongoing basis in order to perform weighing analysis. Filters that are initially 

weighed at one laboratory must be returned to the same laboratory for final weighing and must also be 

processed within a fixed timeframe. Filters once exposed must be returned for analysis either 

immediately or kept under refrigeration and return shipped to the lab for analysis.

During the period from 2010 through August 2012, the Tennessee Department of Health (TDH)

laboratories in both Knoxville and Nashville began experiencing significant problems with the 

environmental controls used to maintain the temperature and relative humidity in the PM2.5 weighing 

rooms operated by each facility. These deviations from the acceptable ranges of temperature and 

humidity resulted in an increasing number of filters being identified by the two laboratories as not 

meeting the criteria set by EPA for valid PM2.5 data and potentially subject to being flagged or invalidated 

because of these excursions in the environmental conditions within the weighing laboratories.

The impact of the proposed invalidation of the affected data for the state and local program PM2.5 

monitoring networks could be very significant as the network monitors are required to collect and 

report at least 75% of the data and to have that data available for a contiguous 3 year period to use in 

calculation of the design values for the sites and areas the monitors represent. An initial evaluation of 

the entire dataset during the period from January 1, 2010 to December 31, 2012 indicates that both the 

state and local programs that were customers of the TDH environmental laboratories in Knoxville and 

Nashville potentially will have insufficient PM2.5 data available to calculate valid design values for a 

number of the monitoring sites operating during this period of time.
4

Proposed Actions

1). All PM2.5 data should be reviewed for possible invalidation or additional flagging including looking as 

far back as the 2008 through 2012 datasets to identify all data previously flagged as temperature or 

humidity affected data.

2). Investigate methods to identify data that may be salvaged based upon Measurement Quality 

Objectives (MQO) criteria being met at the extreme ranges of the MQO acceptance by employing the 

following techniques.

Employ rounding to the humidity or temperature measurement data found to be slightly above 

or below the acceptance criteria.

Apply the stated calibration measurement accuracy range to the temperature and humidity 

acceptance ranges.

3). Conduct an investigation into the effects of elevated or lowered temperature and humidity (outside 

of the acceptable MQO stated ranges) on the weighing of PM2.5 filters post exposure.

4). Review collocated datasets where more than one laboratory may have been employed to analyze 

PM2.5 filter data to determine if the data are similar to each other.

Results and Recommendations

1) All of thePM2.5 filter data collected from 2008 through 2012 were reviewed and a number of filters 

were identified including in some cases up to 30% of the available filters with humidity or temperature 

flags already applied.

2) (a) The results of the rounding study identified some filters that may be considered valid and should 

have the existing data flags removed. 

 (b) The results of the calibration measurement accuracy range study also identified additional filters 

that may be considered valid and should have the existing data flags removed.

3) The results of the filter reweighing study indicate that the filters selected for the study were not 

substantively affected by changes in the temperature or humidity over the ranges of temperature or 

humidity selected to investigate.

The attached RTI report detailing these findings shows that there is essentially no difference in 

filters weighed at normal temperature and humidity and those weighed at higher or lower 

temperature or relative humidity (based upon the ranges of control specified within the EPA 

required procedures).
5

The attached statistical evaluation prepared by the TDH staff indicates there is no difference in 

the RTI data when comparing the effects of weighing’s of exposed filters over the controlled 

environmental conditions employed in the testing.

The conclusions from both of these evaluations are that the differences seen in the filters 

selected for the RTI study fall well within the acceptable ranges for field blanks, lab blanks and 

duplicate filter weighing’s. These level of errors are acceptable differences in filter weights and 

are identified in the MQO’s as operational criteria that when identified are to be flagged but not 

rising to the level of invalidation.

4) Filter datasets were evaluated to identify any sampling sites where samples were collected in the 

same relative location but were analyzed by different weighing laboratories. PM2.5 filters collected in the 

Kingston and Harriman areas of Roane County by TDEC and Tennessee Valley Authority (TVA) were 

found to have been analyzed by different support laboratories.

There were several site identified that collected filters during the times the TDH weighing 

laboratory experienced environmental control issues. The filters from these sites were 

processed by an independent lab and not by the TDH lab. The filters were also found to have 

met the environmental control requirements for weighing. These filters were then evaluated 

against the filters collected on the same dates that were processed by the TDH laboratory 

during periods of time when environmental conditions in the weighing room were out of 

control. These data show high correlations between the filters processed by the TDH lab during 

periods of environmental temperature and humidity instability and filters processed by the TVA 

lab under controlled environmental weighing conditions. The following table 1 provides the 

correlation analysis data. An additional graphic “Location Map for the TDEC and TVA Sampling 

Sites” depicts the relative locations of the 7 different PM2.5 samplers that were used in this data 

correlation study. It is interesting to note that the TDEC site is approximately 2.3 miles from the 

nearest TVA site and yet has a high level of correlation with all of the TVA sites. The sites 

evaluated are listed below in the table “TDEC and TVA PM2.5 Sampling Sites”. The data 

evaluated include samples collected from Feb. 2009 through July 2011.

TDEC and TVA PM2.5 Sampling Sites

AQSSiteID POC CBSA LocalSiteName Address Latitude Longitude

Elevation

metersMS

47-145-0004 1 Harriman, TN TDEC HARRIMAN HIGH SCHOOL HARRIMAN HIGH 1002 N. ROAN ST MOVED FROM 501 CARTER ST 35.9387 -84.5437 240

47-145-1001 2 Harriman, TN TVA Fly ash spill site 199 Lake Shore Rd, Kingston TN 37763 35.9168 -84.5035 349

47-145-1001 4 Harriman, TN TVA Fly ash spill site 199 Lake Shore Rd, Kingston TN 37763 35.9168 -84.5035 349

47-145-3005 1 Harriman, TN PS05 TVA FLY ASH SPILL 1025 Swan Pond Road, Harriman, TN 37748 35.90257 -84.5241 242

47-145-3006 1 Harriman, TN PS06 TVA FLY ASH SPILL 130 Birkshire Road, Harriman, TN 37748 35.9181 -84.5112 239

47-145-3008 1 Harriman, TN PS08 TVA FLY ASH SPILL 540 Emory River Road, Harriman, TN 37748 35.90712 -84.4971 245

47-145-3009 1 Harriman, TN PS09 TVA FLY ASH SPILL 304 Windswept Lane, Kingston, TN 37763 35.88982 -84.5171 231
6

Table 1. Pearson Correlation Data Comparisons

Table 1.

Sites

471450004-1 

PM2.5 

(ug/m3

)

471451001-2 

PM2.5 

(ug/m3

)

471451001-4 

PM2.5 

(ug/m3

)

471453005-1 

PM2.5 

(ug/m3

)

471453006-1 

PM2.5 

(ug/m3

)

471453008-1 

PM2.5 

(ug/m3

)

471453009-1 

PM2.5 

(ug/m3

)

471450004-1 

PM2.5 (ug/m3

)

1.00

471451001-2 

PM2.5 (ug/m3

)

0.94 1.00

471451001-4 

PM2.5 (ug/m3

)

0.91 0.99 1.00

471453005-1 

PM2.5 (ug/m3

)

0.85 0.96 0.96 1.00

471453006-1 

PM2.5 (ug/m3

)

0.96 0.99 0.99 0.97 1.00

471453008-1 

PM2.5 (ug/m3

)

0.86 0.97 0.98 0.97 0.98 1.00

471453009-1 

PM2.5 (ug/m3

)

0.93 0.99 0.99 0.98 0.99 0.98 1.00

Value of the 

Correlation CoEfficient

Strength of the 

Correlation 6/2/2011 0.7 21.1

1 Perfect

0.8 - 0.9 Very Strong0.5 - 0.8 Strong0.3 - 0.5 Moderate

0.1 - 0.3 Modest

> 0.1 Weak

0 Zero

Pearson Correlation Data Comparisons Feb. 2009 to July 2011 TDEC Site vs TVA Sites

Excluding outlier 6/2/2011 
7

Graphic 1 Location Map for TDEC and TVA PM2.5 Sampling Sites
8

Response to Comments Provided by EPA on Review of the Draft Report

The EPA auditing team that conducted the TSA during September 2013 in which the laboratory 

environmental weighing room issues were noted, commented during the exit interview that TDEC APCD 

should consider conducting an investigation into the effect that variable temperature and humidity may 

have on PM2.5 filter processing. This was initially presented to the EPA audit team by the TDEC staff as a 

“glove box” study and was described as a possible method to help determine the overall effect the 

variable environmental conditions may have on filters being processed. Following this discussion 

planning was begun to design a PM2.5 filter re-weighing study and to determine if equipment or a 

suitable lab might be available to perform the final study.

The EPA Region 4 staff that participated in the TSA, were appraised of the progress in developing the 

final study and were given an opportunity to review a draft of the study report this final document 

represents.

EPA staff were requested to provide comments on the draft report and provided comments verbally 

during a conference call with EPA on 7/7/2014. The EPA provided a summary of the verbal comments in 

an email provided to TDEC APCD on 8/1/2014.

The following are the written comments received (in bold) and a response to each of the comments 

provided:

Overall, the study shows very little effect on the weights (of filters selected for this study) due to 

varied lab conditions (humidity and temperature). The study’s intent was to replicate the lab 

conditions that affected TN PM2.5 samples. Specifically, the study should be representative of the TN 

PM2.5 samples that were weighed outside of temperature and humidity criteria in the Nashville and 

Knoxville labs during 2008-2013 (target population). However, the filters analyzed in the study are less 

representative of the affected/target filter population for several reasons:

1. TN sent RTI filters that had passed the required 30 day timeframe from sample collection. 

In this respect, the study filters were not representative of the target population. The 

target filter population were weighed within 30 days of sample collection, but did not 

meet temperature and humidity criteria. This introduces another variable into the study 

that would not have affected the target population.

Response: The study filters were selected from filters recently processed by the TDH lab using the same 

weighing chamber and analytical equipment that were used to process the other filters that were 

outside of the required critical criteria for humidity and temperature. TDEC did not select filters that 

were generated during routine sampling to specifically avoid the possibility of having to void the filters 
9

and cause further data loss or invalidation. The 30 day time frame from sample collection to filter 

analysis is very short and may not allow for the variable conditioning and weighing to be performed.

2. It seems that none of the sample filters in the study were selected from samples collected 

by the local agencies (Memphis/Shelby County, Nashville, or Knoxville). Samples collected 

by local agencies are more likely to have been exposed to urban PM2.5 and have likely 

would have had different PM2.5 composition and possibly higher PM2.5 mass than TDEC 

collected filters. The omission of local agency collected filters creates a potential selection 

bias. The selection bias could limit the representativeness of the study to the desired 

target population.

Response: Prior to selection of the final filters used for the study, a draft list of filter that only included 

net mass gains were circulated to the three local program with affected filters. After evaluation of the 

filters to be employed, the three local programs all agreed that the filters would be suitable for use. 

Therefore the randomly selected filters were allowed to be used in the study. The filters selected 

included filters from the following sites.

Site Name AQS ID#

Athens 471071002

Clarksville 471251009

Columbia 471192007

Dyersburg 470450004

Harriman 471450004

Hendersonville 471650007

Jackson 471130006

Kingsport 471631007

Lawrence 470990002

Loudon 471050108

Maryville 470090011

These sites represent areas across the entire state including sites that are in or near the Knoxville MSA 

and Nashville MSA. The filters also were selected to include recently sampled filters and were collected 

over the timeframe of 11/03/2013 through 1/24/2014. The filters were also selected to include only 

filters that were processed during period of time when the lab weighing room environmental conditions 

were in control and not outside of the humidity or temperature limits established for the method. 

These filters were selected because they were the most recent available filters with the shortest storage 

life after the expiration of the typical 30 day time limit. Given the need to process filters relatively 

quickly to minimize the amount of time post 30 day expiration, it was decided to only look at these 

filters initially.

3. The filters sent to RTI were weighed under high and low temperatures outside of critical 

criteria and then the same filters were weighed in humidity conditions outside of critical. 

This introduces another factor into the study that would not have affected the target filter 
10

population. The response to humidity on the study filters could have been confounded by 

being previously conditioned at high and low temperatures prior to the variation in 

humidity.

Response: The filters used in the study were initially processed by the TDH lab within the proper 

humidity and temperature critical criteria. The filters were processed by the contract lab for this study, 

first under the proper humidity and temperature controls and within the critical criteria limits. The 

filters were then re-equilibrated under temperature and humidity conditions outside of the critical 

criteria limits and weighed to determine the affect the temperature and humidity had on the filters. 

Although changes in temperature and humidity during the weighing process are mentioned as 

confounding, the entire sampling and transport process is subject to uncontrolled humidity and 

temperature variations which can swing widely in the field. This variable is not accounted for in the 

sampling methodology and is not addressed as a factor that should be considered in filter processing.

4. The QAPP and study plan should have been provided to RTI and EPA for comment before 

the study was conducted.

Response: In fact the draft study plan was presented to RTI for consideration before the study was 

undertaken because RTI was initially not able to determine if their weighing lab could accommodate the 

ranges of humidity and temperature called for in the study. After undergoing stability testing and 

confirming that their chamber could control at the extreme ranges then be brought back into normal 

operating parameters for routine work, it was determined the RTI lab would be able to conduct this 

required testing. Several other labs were also contacted and provided with the details of the study and 

upon internal investigation, declined to participate based on the inability to control at the ranges 

specified. It was determined that the scope of the study should not be to investigate the extreme 

ranges of humidity or temperature actually found during the TDH filter processing, but to investigate the 

ranges where a majority of the filter weighing occurred and to determine if the actual data recovery for 

all sites could be brought up to at least 75% minimum. RTI employs their own QAPP for filter weighing 

and processing, which should by itself address any questions about the analytical or weighing related 

operations. TDEC developed and presented a draft QAPP for review to both RTI and EPA. The draft 

TDEC study QAPP was presented after EPA requested that this be provided as a part of the overall study.

5. It appears that there was no seasonal variability incorporated into the filters selected for 

the study and there is an impact on PM2.5 measurements depending on the season.

Response: As was previously discussed, the filters selected (collected over the timeframe of 11/03/2013 

through 1/24/2014), would be broadly classified as seasonally representative of the fall/winter season. 

If seasonal selection were to be included, the study would have to be extended from January through 

December and would drastically prolong reporting of any usable data. The contract lab was informed 

that additional analytical work might be required after the initial results were presented in the study to 

help address these types of questions. Provisions are already in place to utilize the lab for further study 

work and to selectively address additional areas of interest. EPA has discouraged any additional work or 

study proposals.
11

The filter subset selected for the TDEC TVA sampling site comparison did include seasonal variability and 

was representative over a period that ran from Feb. 2009 through July 2011. An analysis of all of the 

filter data collected from 2008 to 2012 by all of the state and local PM2.5 sampling sites in Tennessee 

indicated the following seasonal variation:

The TDEC TVA dataset upon seasonal analysis produced the following graph which provides the number 

of filters evaluated by quarter and also shows the relative frequency of filters representing each quarter 

(season) and therefore the distribution of filters across all seasons.

The entire states dataset indicates that the second and third quarters are more likely to have higher 

PM2.5 filter loading than the first and fourth quarters. The filters selected in the TDEC TVA study appear 

to adequately address the concern about seasonal variation in the study.

6. The sample size may be too small to be able to make any definitive statements about the 

results (i.e., may not be statistically significant).

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

1 2 3 4

ug/m3 PM2.5

Qtr'ly Avg. 2008 to 2012

All Sites Qtr'ly Avg. (Seasonal Differences)

0

10

20

30

40

1 2 3 4

# of Filters

Qtr. (Season)

2009 to 2011 Filters Evaluated by Qtr. TDEC 

TVA Study
12

Response: In the process of preparing to begin the study, the contract lab was requested to investigate 

the number of filters to select from the population of affected filters (critical criteria exceeded for 

temperature or humidity during weighing) and determine what the number of filters should be to be 

able to statistically represent the entire population of filters. The reasoning behind this is included in 

the QAPP and is believed to justify the number of filters selected. The requirement to not include any 

filters that failed to meet the critical criteria for filter weighing reduces the filter population to select 

from. The number of filters affected appears to be approximately 30 to 35% of the total filters collected, 

which would reduce the number of filters in the population from which to determine what the actual 

test sample size should be. The TDH has prepared an additional analysis of the study results and also 

prepared graphics depicting the number of affected filters in both the Knox County area and for the 

other areas outside of Knox County. This report immediately follows the comment and response section 

of the report on the next page and following. 
13

Filter Data Statistical Analysis Performed by TDH, Caleb Wiedeman, 

MPH, Epidemiologist, Tennessee Department of Health, Communicable 

and Environmental Diseases and Emergency Preparedness

Methods

Thirty-two filters were weighed and then reweighed at under the recommended conditions. The 

same filters were weighed and reweighed at different relative humidity levels (25%, 45%, and a second 

weighing under the recommended condition at 35%) and different temperature levels (18oC, 25oC, and 

a second weighing under the recommended condition at 22oC). Filter # 3654706 was excluded from the 

analysis due to debris being dislodged from the filter between weight measurements and filter # 

14334066 was excluded because it was a different type of filter from the remaining thirty filters. 

The Two One-Sided Test (TOST) procedure was chosen to determine if the mean differences 

between the filters weighed at control and experimental conditions were greater than the + 15 μg of 

imprecision allowed between duplicate measures of weight. TOST is often used in randomized 

controlled trials to determine if two treatments should be considered equal based on a predetermined 

equivalence margin. TOST combines the results of two one sided paired t-tests, one testing the 

likelihood that the mean difference is larger than the smallest allowable difference, and the other 

testing whether the mean difference is smaller than the largest allowable mean difference.

Differences in weight were calculated by subtracting the weight of each individual filter 

weighed under the recommended conditions with the measured weight of the same filter under the 

experimental conditions. The mean differences in weight were then tested using the TOST procedure, to 

determine if the estimated mean difference between the initial measurement and the experimental 

measurement of each filter fell between the equivalence margin of + 15 μg (the range considered to be 

the allowable “noise” during a typical repeat measurement). A power calculation was performed 

(assuming a mean difference as large as 8 and a standard deviation of 6) and power was assessed to be 

greater than 0.8 for the TOST procedure using the thirty, paired filter measurements and an alpha of 

0.025. All statistics were calculated using SAS version 9.3. 

Results

The mean differences in weight between the filters at control conditions (weighed at the ideal 

conditions) and the experimental conditions (weighed at non-ideal conditions) are shown in Figures 1 

and 2. The green box in each chart represents the + 15 μg allowable range. The blue diamond markers 

are the differences in weight when the filters were re-measured later under the ideal conditions.
14

-20

-15

-10

-5

0

5

10

15

20

0 5 10 15 20 25 30

Difference Between Weight Measurements in 

Micrograms (Weight at 36% RH Used as Control)

Filters Tested

Figure 1: Raw Weight Difference in Filters 

Measured at Different Relative Humidities

Difference in μg at 25% RH

Difference in μg at 45% RH

Difference in μg at 35% RH

Difference in filter weight 

calculated by using the initial 

weight at 36% RH and 

subtracting the weight of the 

filter in the test condition.

-20

-15

-10

-5

0

5

10

15

20

0 5 10 15 20 25 30

Difference Between Weight Measurements in Micrograms 

(Weight at 22o C used as Control)

Filters Tested

Figure 2: Raw Weight Differences in Filters 

Measured at Different Temperatures

Difference in μg at 18°C

Difference in μg at 25°C

Difference in μg at 22°C (repeat)

Difference in filter weight 

calculated by using the initial 

weight at 22o C and subtracting 

the weight of the filter in the 

test condition.
15

Most of the differences in the filter measurements fell within + 15 μg regardless of the conditions. There 

were some outliers in the measurements taken at different temperatures, but most of these occurred 

during the repeat weighing two days later under the ideal conditions. Table 1 shows the mean 

differences, 95% confidence intervals, standard deviations, standard errors, and ranges for all filters 

under the different conditions. 

Table 1: Mean Differences (From First Measured Weight at 36% RH or 22 °C), Standard Deviations, 

Standard Errors, and Ranges for Filters Under Different Conditions

Mean 

Difference

95% Confidence 

Interval

Std. 

Deviation

Std. Error Range

Reweighed at 36% RH 2.4 1.5 - 3.3 2.5 0.5 -4 to 6

Weighed at 35% RH 0.6 -0.7 - 2.0 3.7 0.7 -8 to 10

Weighed at 25% RI 3.3 1.9 - 4.7 3.7 0.7 -4 to 12

Weighed at 45% RH -1.6 -3 - -0.1 3.9 0.7 -9 to 5

Reweighed at 22 degrees C 3.1 1.8 - 4.3 3.4 0.6 -5 to 9

Weighed at 22 degrees C 

two days later

5 2.2 - 7.7 5 1.3 -5 to 22

Weighed at 18 degrees C 5.5 3.9 - 7.2 4.4 0.8 -4 to 15

Weighed at 25 degrees C 2.1 -0.1 - 4.3 5.9 1.1 -7 to 16

Figure 3 shows the mean differences and 95% confidence intervals plotted out for side by side 

comparison, and demonstrate that the level of variation is well within expected error of measurement.

2.4

0.6

3.3

-1.6

3.1

5

5.5

2.1

-15

-10

-5

0

5

10

15

Reweighed

at 36% RH

Weighed at

35% RH

Weighed at

25% RI

Weighed at

45% RH

Reweighed

at 22

degrees C

Weighed at

22 degrees C

two days

later

Weighed at

18 degrees C

Weighed at

25 degrees C

Figure 3: Mean Difference and 95% Confidence Intervals for Weight 

Difference between Control Conditions (First Measured Weight at 36 % 

RH or 22o C) and Other Conditions

95% CI Lower

95% CI Upper

Mean Difference
16

Figures 4, 5, 6, 7, 8, 9, 10, and 11 show box plots and TOST results for the mean differences each filter 

category. All TOST results concluded that the mean difference between the control and experimental 

condition was highly likely to be between + 15 μg. Plots were done using SAS, version 9.3.
17
18
19

The TOST procedure in all of the experimental cases gave results indicating that the estimated mean 

differences between the measurements were highly likely to be between + 15 ug. 
20

Discussion

The majority of the weight measurements taken under the experimental conditions fell within +

15 μg of the original measurements (see Figure 1 and 2). Confidence intervals for the mean differences 

were calculated using the TOST procedure. The mean differences between the filter weights measured 

under the recommended conditions and the experimental conditions were highly likely to fall within +

15 μg, based on the data collected. 

All the calculated mean differences seen between the filters weighed under the recommended 

conditions and the experimental conditions were very small. If the changes in the environment had an 

effect on the weight of the filters, there was not enough precision between the measurements to tease 

out the difference. For instance, the filters that were weighed at 22oC under ideal conditions and then

immediately reweighed (see Figure 8) showed a “significant” (the 95% confidence interval did not 

include 0) mean difference in weight between the measures. This is highly unlikely to be a true 

difference in weight, but is likely a reflection of the random “noise” that occurs between instruments. 

Per the testing recommendations, the two measurements at the ideal conditions would be considered 

the same, despite the small amount of noise seen between the measurements. 

Given these results, measures of filter weight under the experimental conditions (relative 

humidity levels of 45% and 25%, and temperatures of 18oand 25oC) have little or no measurable effect 

on the filter weight. Measures within these extended ranges should be considered statistically similar to 

measures of filter weight made under the recommended conditions with a high degree of confidence. 
21

Knox County Filter Data Evaluation 2009 to 2013
22

All Sites Filter Data Evaluation 2009 to 2012
23

Additional Documents Referenced in this Report (Provided as separate 

attachments)

Environmental Condition Testing of 31 Sampled Measurement Technology 

Laboratories 46.2-mm PTFE (Teflon®) Filters by Paige Presler-Jur, RTI 

International, July 18, 2014

Quality Assurance Project Plan, TDEC PM2.5 Filter Investigation Study, June 

17, 2014, by Robert Brawner, Technical Services Program, Air Pollution 

Control Division, Tennessee Department of Environment and Conservation