Southeast PM2.5 Data Analysis 

Analysis of PM2.5 FRM data and data for monitors in southeast Pennsylvania. 

Monitor Information 

Site Name County FRM 

Start Date

FRM 

Sample 

Frequency 

Speciated 

Start Date 

Speciated 

Frequency

Lancaster Lancaster 1/1999 1/3 4/2002 1/6 

Freemansburg Northampton 1/1999 1/1 NA NA 

Bristol Bucks 2/1999 1/3 NA NA 

New Garden Chester 1/2002 1/3 4/2002 1/6 

Chester Delaware 1/1999 1/3 4/2002 1/6 

Norristown Montgomery 2/1999 1/3 NA. NA 

AMS Lab Philadelphia 2/1999 1/1 5/2006 1/6 

500 Broad St Philadelphia 2/1999 1/3 to 1/1 NA. NA 

Items in BOLD are within the Philadelphia-Wilmington nonattainment area. 

Data Analysis: 

Design Value Contribution Analysis: 

Only one monitor in southeast Pennsylvania currently exceeds the annual PM2.5 NAAQS 

(15.0 μg/m3

). PM2.5 annual design values for 2006 are listed in Table 1 for six FRM 

monitoring sites in southeast Pennsylvania. Design values across southeast Pennsylvania 

have remained relatively stable for most monitors over the last five years. 

Table 1. 

Annual PM2.5 Design Values 

Site 2002-04 2003-05 04-06 

Lancaster 16.8 17.5 16.3 

Freemansburg 14.0 14.1 13.6 

Bristol 13.9 13.9 13.2 

New Garden 14.8 15.2 14.2 

Chester 15.0 15.6 15.2 

Norristown 13.2 12.8 12.2 

AMS Lab 14.5 14.3 13.9 

500 Broad St 15.4 15.0 15.0 

Items in BOLD are within the Philadelphia-Wilmington nonattainment area.

The nature of the annual standard makes it difficult to determine what causes a monitor to 

exceed the annual PM2.5 standard. For a well-run monitor, between 365 to 1096 FRM 
measurements make up its annual design value. The shear number of samples makes it 

very difficult to determine what days (samples) are contributing to monitor’s annual 

design value. 

A monitor’s annual PM2.5 design value is determined by first calculating its quarterly 

average. Quarterly averages are then averaged to calculate the monitor’s average annual 

PM2.5 concentration. Three consecutive years of average annual PM2.5 concentrations are 

then averaged to determine a monitor’s annual PM2.5 design value. Thus any one 

particular sample will make only a minor contribution to a monitor’s annual PM2.5 design 

value. 

The Pennsylvania DEP has come up with a methodology to quickly analyze a monitor’s 

design value and determine which measurements (or types of measurements) are 

contributing to a site’s design value. Each twenty-four hour PM2.5 FRM measurement’s 

contribution to the monitor’s annual design value is calculated. FRM 24-hour 

concentrations are then grouped into different sample ranges to gauge each sample 

range’s contribution to the monitor’s annual design value. Monitors then can be 

compared to determine which monitor sample ranges are important. 

For the purposes of this analysis, contributions are determined such that contributions 

from samples less than 15.0 μg/m3

 are negative and those samples that are greater than 

15.0 μg/m3 are positive. The break point of 15.0 μg/m3 represents the break-off point for 

the annual PM2.5 standard. Mathematically the contributions for each sample range can 

be represented by this equation: 

For values less than or equal to 15.0 μg/m3: 

0 < x ≤ 15 

For values greater 15.0 μg/m3: 

15 < x < Max 
Contributions from several ranges of sample concentrations then can be summed to 

determine a monitor’s annual design-value concentration. Table 2 shows the results of 

the design-value contribution analysis for six monitors in southeast Pennsylvania. The 

list includes all of the PA DEP maintained monitors in the Philadelphia-Wilmington 

PM2.5 nonattainment area plus the Lancaster monitor which lies west of Philadelphia and 

the Freemansburg monitor which lies to the north. 

Table 2. 

Design Value Contribution Analysis 

Site 0-15.0 15.0-40.5 40.5-65.5 >65.5 Sum 

Lancaster -3.0663 3.7532 0.6286 0.0000 1.3155 

Freemansburg -4.2393 2.5064 0.2885 0.0000 -1.4444 

Bristol -4.3432 2.5612 0.0000 0.0000 -1.7820 

New Garden -3.7375 2.8114 0.2304 0.0000 -0.6956 

Chester -3.2745 3.3408 0.0719 0.0000 0.1000 

Norristown -4.7638 1.9427 0.0000 0.0000 -2.8211 

AMS Lab -3.9434 2.6133 0.2299 0.0000 -1.1000 

500 Broad St -3.2481 3.0771 0.1973 0.0000 0.0000 

Items in BOLD are within the Philadelphia-Wilmington nonattainment area.

 

The break lines in Table 2 are roughly based on the twenty-four hour AQI scale for PM2.5

with the lower scale being cut off at 15.0 μg/m3. Most of the PA DEP monitors within 

the Philadelphia PM2.5 nonattainment area meet the annual standard (except Chester). 

Surprisingly, there appear to be fewer days with high PM2.5 concentrations (> 40.5 μg/m3) 

in the Philadelphia nonattainment area than in areas to the west (Lancaster) and north 

(Freemansburg). The Chester and to a lesser extent the 500 Broad Street monitors also 

appear to have fewer days with concentrations less than 15 μg/m3 than the other four (4) 

Philadelphia monitors in this analysis. 

Design Value Contribution Analysis Summary: 

• Only one monitor in the Philadelphia-Wilmington PM2.5 nonattainment area 

exceeds the annual standard though there are data capture issues for the 

Philadelphia County monitors. 

• There appear to be fewer days with high PM2.5 concentrations (> 40.5 μg/m3

) 

in the Philadelphia-Wilmington nonattainment area than there are in areas 

to the west (Lancaster) and north (Freemansburg). 

• The Chester and 500 Broad Street monitors appear to have fewer days with 

PM2.5 concentrations less than 15 μg/m3

 than other monitors in the region. 
Correlation Coefficient Analysis: 

Correlation coefficients are a statistical measure to determine how well two different 

samples track one another. There are three possibilities; the two samples react similarly, 

they appear to be random or they react oppositely. Daily FRM PM2.5 measurements from 

six monitors in southeast Pennsylvania (2000-06) were correlated with one another to 

determine how well the monitors tracked each other over time. PA DEP monitors were 

also compared with monitors to the west and north to determine how well the 

Philadelphia area monitors tracked concentrations in nearby regions. 

The largest distance between monitors is approximately 80 miles (between Lancaster and 

Bristol). The bulk of the monitors are within 30 miles of one another. There are no large 

terrain features in the region so airflow is generally unrestricted. 

Table 3 lists the correlation coefficients for several FRM monitoring sites in southeast 

Pennsylvania. Coefficients range from 1.0 to –1.0. Correlation ranges and their meaning 

are broken down as follows: 

1.0 to 0.667 Positive correlation (samples move in a similar direction) 

0.667 to -0.667 Samples not well correlated (0.334 to – 0.334, random) 

-0.667 to –1.0 Negative correlation (samples move in opposite direction) 

Table 3. 

Southeast Pennsylvania PM2.5 Correlation Coefficients 

Lancaster Freemansburg Bristol New Garden Chester Norristown

Lancaster 0.8528 0.8594 0.9211 0.8346 0.8639 

Freemansburg 0.8528 0.8855 0.8751 0.8113 0.8838 

Bristol 0.8594 0.8855 0.8915 0.8602 0.9059 

New Garden 0.9211 0.8751 0.8915 0.8928 0.9030 

Chester 0.8346 0.8113 0.8602 0.8928 0.8580 

Norristown 0.8639 0.8838 0.9059 0.9030 0.8580 

AMS 500 Broad Bristol New Garden Chester Norristown

AMS 0.9480 0.9346 0.9346 0.9076 0.9159 

500 Broad 0.9480 0.8985 0.9111 0.9024 0.8792 

Bristol 0.9346 0.8985 0.8915 0.8602 0.9059 

New Garden 0.9346 0.9111 0.8915 0.8928 0.9030 

Chester 0.9076 0.9024 0.8602 0.8928 0.8580 

Norristown 0.9159 0.8792 0.9059 0.9030 0.8580 

Correlation coefficients indicate that the six monitors within the PhiladelphiaWilmington nonattainment area respond similarly. There are greater similarities in the 

FRM data between monitors that are relatively close together than for monitors that are 

far apart. Correlations also tend to be slightly lower between monitors exceeding the 

annual PM2.5 standard (Lancaster and Chester) and those that do meet the standard. 
Correlation coefficients for the Chester and Broad Street monitors appear to be lower 

than any of the other monitors. This may indicate these monitors are behaving differently 

than the surrounding monitors within the nonattainment area. There also does not seem 

to be as much seasonal variability in correlations as was found in other areas of 

Pennsylvania. 

Correlation Coefficient Analysis Summary: 

• Correlation coefficients constructed from 2000-06 FRM data indicate all of 

the monitors in the Philadelphia generally respond in a similar fashion. 

• Correlations are better between the monitors that are close to one another. 

• Correlations between Chester and the 500 Broad Street monitor are a bit 

lower than correlations between the other monitors indicating these monitors 

may be behaving differently than other monitors in the nonattainment area. 

• There appears to be little change in correlations based on time of year. This 

is different than other areas of Pennsylvania where correlations were 

analyzed. 

Coefficients of Divergence Analysis: 

Correlation of divergence is a statistical measure to quantify the magnitude of difference 

between two groups of samples. FRM samples between 2000 and 2006 were analyzed to 

determine the coefficients of divergence for six monitors in southeast Pennsylvania and 

the Lancaster and Fremansburg monitors to the west and north respectively. Table 4 

summarizes the results of this analysis. In general numbers close to zero indicate small 

differences in daily concentrations between monitors. Numbers close to one or above 

indicate significant differences in the daily PM2.5 concentrations between the two 

monitors. 

Table 4. 

Southwest Pennsylvania PM2.5 Coefficient of Divergence 

Lancaster Freemansburg Bristol New Garden Chester Norristown 

Lancaster 0.9632 0.7667 0.2749 0.6090 0.6597 

Freemansburg 0.9632 0.5653 0.5752 0.9398 0.5024 

Bristol 0.7667 0.5653 0.4270 0.7206 0.3910 

New Garden 0.2749 0.5752 0.4270 0.4603 0.4160 

Chester 0.6090 0.9398 0.7206 0.4603 0.7349 

Norristown 0.6597 0.5024 0.3910 0.4160 0.7349 

AMS 500 Broad Bristol New Garden Chester Norristown 

AMS 0.3274 0.2023 0.2703 0.4149 0.2343 

500 Broad 0.3274 0.4952 0.3351 0.3389 0.6003 

Bristol 0.2023 0.4952 0.4270 0.7206 0.3910 

New Garden 0.2703 0.3351 0.4270 0.4603 0.4160 

Chester 0.4149 0.3389 0.7206 0.4603 0.7349 

Norristown 0.2343 0.6003 0.3910 0.4160 0.7349 
The results of this analysis indicate there are some significant differences in daily fineparticulate concentrations across southeast Pennsylvania. In particular there are 

significant differences in daily monitor values between the Philadelphia nonattainment 

area and the Lancaster and Freemansburg monitors, with the exception of the Lancaster 

and New Garden monitors, which surprisingly showed little difference in daily 

concentrations. Again there are significant differences in values between the Chester and 

500 Broad Street monitors and the other monitors in the Philadelphia-Wilmington 

nonattainment area. This is similar to patterns observed in the correlation coefficient 

analysis and supports the contention that these monitors are behaving differently than 

other monitors in the nonattainment area. Coefficients of divergence values do not 

appear to vary much by time of year. This differs for from other areas of Pennsylvania 

that appear to show some seasonal variability 

Coefficients of Divergence Analysis Summary: 

• Coefficients of Divergence constructed from 2000-06 FRM data indicate 

there are some significant differences in daily PM2.5 concentrations between 

the Chester and 500 Broad Street and other monitors in the PhiladelphiaWilmington nonattainment area. 

• Coefficients of Divergence do not appear to vary much by season. This 

differs from other areas of Pennsylvania that have been analyzed.