1

MEMORANDUM

SUBJECT: Near

- road NO 2 Network and Data Analysis

FROM: Nealson Watkins, AQAD/AAMG (C 339

- 02)

Adam Reff
, AQAD/AQAG (C304

- 04)

TO: Docket No. EPA

- HQ

- OAR

- 2015

- 0486

This document present s information on the characteristics of the existing near

- road NO 2 monitoring network and the relationships between NO 2 emissions, population, and traffic with a n analysis of near

- road NO 2 concentration data in support of the Revision to the Near

- road NO 2 Minimum Monit oring Requirements proposed rulemaking. The proposed

r evision would remove the existing network design requirements to install near

- road NO 2 monitor s in Core Based Statistical Areas (CBSAs) having populations between 500,000 and 1,000,000 persons, due by J anuary 1, 2017. Current near

- road NO 2 monitoring data indicate air quality in the near

- road environment to be well below the National Ambient Air Quality Standards (N AAQS) for the oxides of nitrogen. In light of this information
, and due to the corresponde nce between population, traffic, and expected NO 2 concentrations in the near

- road environment, it is anticipated that measured near

- road NO 2 concentrations in relatively smaller CBSAs (e.g., CBSAs with populations less than 1,000,000 persons) would exhibit similar, and more likely lower concentrations than what is being measured in larger urban areas. As a result, the EPA is seeking to reduce additional burden on state and local air monitoring agencies by removing monitoring requirements in smaller CBSAs wh ere measured NO 2 air quality is expected to be well below the NAAQS. Th is document is intended to provide a review and analysis of emissions data, available monitoring site meta

- data, population and traffic data, and NO 2 monitoring data in order to provide the underlying rationale for the p roposed rule.

Background
On February 9, 2010, the EPA promulgated revisions to the NO 2 NAAQS (75 FR 6474), which included a 1

- hour standard with a 98th percentile form averaged over 3 years and a lev el of 100 parts per billion (ppb), reflecting the maximum allowable NO 2 concentration anywhere in an area, while retaining the annual standard of 53 ppb. As part of the 2010 NO 2 NAAQS rulemaking, the EPA promulgated revisions to requirements for minimum

nu mbers of ambient NO 2 monitors that included new monitoring near major roads in larger urban areas, requirements to characterize NO 2 concentrations representative of2

wider spatial scales in larger urban areas (area

- wide monitors), and monitors intended to

c haracterize NO 2 exposures of susceptible and vulnerable populations. A key objective to be met by requiring near

- road monitoring was to measure maximum NO 2 concentrations that may occur anywhere in an area , as the NO 2 NAAQS review estimated that roadway

as sociated exposures account for the majority of exposures to peak NO 2 concentrations.

Per 40 CFR p art 58, Appendix D, near

- road NO 2 monitoring is currently required in each CBSA with a population of 500,000 or more persons to monitor a location of expected maximum hourly concentrations sited near a major road. An additional near

- road NO 2 monitoring station is required at a second location in any CBSA with a population of 2,500,00 0 or more persons, or in any CBSA with a population of 500,000 or more persons that has one or more roadway segments with 250,000 or greater Annual Average Daily Traffic (AADT) counts . Based upon 201 4 census estimates and data maintained by the U.S. Depart ment of Transportation Federal Highway Administration on the most heavily trafficked roads in the U.S. ( http://www.fhwa.dot.gov/policyinformation/tables/02.cfm ), approximately 1 31 near

- road NO 2 sites are required within 10 8 CBSAs nationwide. Th e near

- road NO 2 monitoring network was originally required to be operational by January 1, 2013 . H owever , in 2012
, the EPA proposed (77 FR 64244 ; October 19, 2012 ) and finalized, through a public notice and comment rulemaking, that the near

- road NO 2 monitoring station s would be installed in three phases spanning a 4

- year period . The installation schedule for the near

road NO 2 monitoring network was then modified to reflect the following:

Phase 1: In CBSAs with a population of 1,000,000 or more persons, one near

road N O 2 monitor shall be reflected in the state Annual Monitoring Network Plan submitted July 1, 2013, and that monitor shall be operational by January 1, 2014.

Phase 2: In CBSAs where two near

- road NO 2 monitors are required (either because the CBSA has a population of 2,500,000 or more persons, or has a population of 500,000 or more persons plus one or more roadway segments having annual average daily traffic (AADT) counts of 250,000 or more), the

secon d near

- road NO 2 monitor shall be reflected in the state Annual Monitoring Network Plan submitted July 1, 2014, and that monitor shall be operational by January 1, 2015.

Phase 3: In CBSAs with a population of at least 500,000 persons, but less than 1,000, 000 persons, one near

- road NO 2 monitor shall be reflected in the state Annual Monitoring Network Plan submitted July 1, 2016, and the monitor shall be operational by January 1, 2017.3

The shift to this phased installation approach was finalized and published on March 14, 2013 (78 FR 16184), to allow more time for states to establish the required monitoring sites and in order to synchronize installation with a schedule that would be cons istent with available resources.

Near

- road NO 2 Monitor ing Site Characteristics
In the preamble to the proposed 2010 NO 2 NAAQS revision, it is stated that one of the largest factors affecting ambient exposures to NO 2 above health benchmark concentrations a re mobile source emissions (74 FR 34441 )

. Further, in both the proposed (74 FR 34404) and final NO 2 NAAQS revision rulemaking (75 FR 6474), it is stated that the near

- road environment is believed to be where the greater population exposure risk to peak NO 2 levels exists . As a result, n ear

- road NO 2 monitors were required to support the NAAQS

. Near

- road NO 2 monitors were intended to be adjacent to the most highly
tra fficked roads within our nation’s urban areas , as these locations are where maximum mobile source

- derived NO 2 concentrations were typically expected to occur . Required

n ear

- road NO 2 monitors were to be installed with consideration of a number of factors known to influenc e NO 2 concentrations in the near

- road environment and using s pecific siting criter ia to ensure the monitors would be near roads where measured concentrations might represent the highest near

- road NO 2 concentrations for a given CBSA. These siting criteria are listed in 40 CFR p art 58, Appendic es D and E. Notably, near

- road NO 2 monitoring sites were required to be selected by accounting for AADT, fleet mix, roadway design, congestion patterns, terrain, and meteorology. Further, the sites were to be situated so that the monitor probe was as near as practicable to the outside n earest edge of the traffic lanes of the target road
, but not located greater than 50 meters away from the edge of the traffic lanes.

In support of the state and local air monitoring agencies responsible for install ing these

near

- road NO 2 monitoring sites, the EPA coordinate d a near

- road monitor si ting study and subsequently produced the “ Near

- road NO 2 Monitoring Technical Assistance Document, ” for which the results and finished document, respectively, can be found on the EPA’s Ambient Mon itoring Technology Information Center (AMTIC) website’s

near

- road NO 2 page located at http://www3.epa.gov/ttn/amtic/nearroad.html . The “ Near

road NO 2 Monitoring Technical Assistance Document ” goes into detail on the importance and impact each of the indivi dual factors (e.g., AADT, fleet mix, congestion patterns, terrain, and meteorology) have on the concentrations that might be measured at

a near

- road site. T he EPA has been tracking many of these important factors
, along with other physical information repr esented as site characteristics, pertaining to near

- road NO 2 monitoring sites as those sites have been installed and become operational. The se meta

data have been and will continue to be collected and updated as the near

- road network becomes fully installe d and operational . These meta

- data are available at4

( http://www3.epa.gov/ttn/amtic/nearroad.html )

. The meta

- data presented and used in this document r eflect data collected through December 2015 , and include both partial and complete meta

- data on a total of 7 1 near

- road sites

. Upon review of the available near

- road site meta

- data (as of December 2015)
, it is evident that state and local air monitoring agencies have had success in identifying and securing access to property adjacent to highly trafficked road segments within CBSAs
, pursuant to requirements in 40 CFR p art 58. It is worth noting that there are thousands of road segments in a typical CBSA. The near

- road network is appr opriately focused on the most highly trafficked road segments, as shown by the distribution of near

- road NO 2 site placements relative to the highest trafficked roads in each respective CBSA in Figure 1

. Notably, ~ 5 5 percent of the near

- road sites are adjac ent to one of the top 5 highest trafficked road s egments in their respective CBSA ; ~ 7 1 percent are adjacent to one of the top 10 roads ; and ~91 percent are adjacent to one of the top 25 roads

.

Figure 1. Relative Annual Average Daily Traffic (AADT) rankings of the target roads of near

- road monitoring sites within their individual Core Based Statistical Areas (CBSA).

In the “ Near

- road NO 2 Monitoring Technical Assistance Document, ” a metric was introduced that used both AADT and fleet mix, called Flee t Equivalent AADT (FE

AADT) for use in comparing road segments for potential NO 2 emissions with varying amounts of light

- duty and heavy

- duty vehicle make

- ups

. This comparison is important

s ince heavy

- duty diesel vehicles emit more NO X (which includes more directly emitted NO 2 and more NO, which can be oxidized into NO 2 ) than light

- duty gasoline vehicles on5

a per vehicle basis

. 1 As a result, u nderstanding the number of heavy

- duty vehicles that make up total traffic volume was an important factor in determini ng where near

- road NO 2 monitors might be placed. T he FE

- AADT metric can be viewed as a stronger metric than AADT alone for use in comparing road segments that have varied amounts of total traffic (AADT) and heavy

- duty vehicle counts when determining which road segments might be expected to have higher potential for a near

- road site to measur e peak NO 2 concentrations. Figure 2 shows the distribution of near

- road NO 2 site placements relative to the road segments with higher FE

- AADT values in each respective C BSA. Notably, ~63 percent of the near

- road sites are adjacent to one of the top 5 highest FE

- AADT trafficked road segments in their respective CBSA ; ~76 percent are adjacent to a top 10 segment ; and ~93 percent are adjacent to one of the top 25 segments

. Another key piece of information to understand about near

- road NO 2 monitoring stations is the relative distance to their target road. The relative placement of near

- road NO 2 monitors to target road segments, in the horizontal, is governed in 40 CFR p art 5 8, Appendix E, section 6.4(a)
, where it is stated that “...the monitor probe shall be as near as practicable the outside nearest edge of the traffic lanes of the target road segment, but

Figure 2. Relative Fleet Equivalent Annual Average Daily Traffic (FE

- AADT) rankings of the target roads of near

- road monitoring sites within their individual Core Based Statistical Areas (CBSA).

shall not be located at a distance greater than 50 meters, in the horizontal, from the outside nearest edge of the traffic lanes of the target road segment.” As discussed in the

1 Discussed in the Near

- road NO 2 Monitoring Technical Assistance Document at http://www3.epa.gov/ttn/amtic/files/nearroad/NearRoadTAD.pdf

.6

2010 NO 2 NAAQS review’s Integrated Science Assessment ( sections 2.5.4 and 4.3.6), the Risk and Exposure Assessment (section 7.3.2), and in the preamble to the final rule of the 2010 NO 2 NAAQS revision (75 FR 6514), on

- road, mobile source

- derived NO 2 exhibits a peak concentration on or very near the source road, and those concentrations dec line over a variable but relatively short distance back to near area

- wide or relative background concentrations. It was for this fact that near

- road NO 2 sites are required to be as near as practicable to their target roads. Upon review of the 71 near

- road NO 2 sites for which partial or complete meta

- data are available (as of December 2015), it is evident that state and local air monitoring agencies were successful in placing their near

- road monitoring stations as near as practicable to their target roads, pursuant to requirements in 40 CFR p art 58. Figure 3 shows the distribution of th e distances of near

- road NO 2 monitor probes relative to their respective target roads. Notably, ~59 percent of the sites are within 20 meters from their target road (which was a recommended target distance in the “ Near

- road NO 2 Monitoring Technical Assista nce Document ” ) ; ~87 percent are within 30 meters ; and ~96 percent are within 40 meters. All sites are within 50 meters, as prescribed.

Figure 3. Distribution of distances of near

- road NO 2 monitor s to their respective target road.7

Emissions, Population , and Traffic
In the preamble to the 2010 NO 2 NAAQS proposal , it is stated that one of the largest factors affecting ambient exposures to NO 2 above health benchmarks concentrations are mobile source emissions (74 FR 34441). A look at the NO X emis sions inventory , and more specifically, the on

- road mobile source contributi ons to the inventory that exist in individual CBSAs , can aid in understand ing how mobile sources play a role in the potential exposure to NO 2 for populations nationally
, and in an individual CBSA. The 201 1 National Emissions Inventory (NEI) indicates that mobile sources account for about 72.3 percent of the total NO X emissions inventory
, approximately 8.7 million tons out of 12 million tons , nationally . Figure 4 shows the breakdown between on

- road, non

- road, and all other NO X sources in the NEI, where on

- road mobile sources account for ~49.6 percent of the national NO X inventory ; non

- road mobile account for ~22.7 percent ; and all other NO X emission sectors account for
~ 27.7 percent

.

Figure 4. 201 1 NOx national emissions inventory, segregated into non

- road mobile, on

- road mobile, and all

non

- mobile source sectors.
Further inspection of the NEI shows that at the CBSA level, on

- road mobile source emission contributions increase with incr easing CBSA population. Figure 5 shows the breakdown of NO X emissions by on

- road, non

- road, and all other emissions categories,8

binned by CBSA population size. The CBSA population bins are sorted in correspondence to the th ree phases by which the near

- road NO 2 network is being installed : greater than 2 .5 million persons ; greater than 1 million but less than 2

. 5 million persons ; greater than 500,000 but less than 1 million persons ; and finally, a bin for all areas with populations below 500,000 persons.

Figure 5. 201 1 NOx national emissions inventory, split by non

- road mobile, on

- road mobile, and all non

mobile source sectors, binned by CBSA population corresponding to the three phases by wh ich the near

road network is being installed, plus all CBSAs having less than 500,000 persons

. In Figure 5
, on

- road mobile source emission contribution s to the binned CBSA

- level inventor ies increase with increased CBSA populations. Notably, on

- road mobile source NO X emissions of CBSA

- level inventories rise from ~28 percent in areas with populations less than 500,000 persons, to ~48.1 percent in CBSAs with populations between 500,000 and 1 million persons, to ~51.3 percent in CBSAs with populations between 1 million and 2 .5 million persons, and finally up to ~55.3 percent in CBSAs having 2

. 5 million persons or more. These data confirm the major role that on

- road mobile sources play in the potential ambient exposures of NO 2 to the public, particularly in increasingly populated areas.9

A key reason behind requiring the near

- road NO 2 network was the recognition of the role of on

- road mobile source emissions to potential public exposures, with particular emphasis on the fact th at health research indicates that certain populations may experience relatively higher NO 2 exposures with increased proximity to roads (74 FR 34419). Because there is a correspondence between population and traffic, the EPA required near

- road monitoring in relatively larger urban areas. One approach to understanding mobile source emissions impacts on potential measured NO 2 concentrations and population exposure at the CBSA level is to look at the relationship between population and Vehicle Miles Traveled (V MT). VMT is a measurement of the total number of miles traveled by all vehicles in a specific area over a specific period of time. VMT data are typically collected or determined by state or local transportation agencies. These data are eventually passed on to the U.S. Department of Transportation, Federal Highway Administration (FHWA). The VMT data used in this analysis were obtained as part of mobile model inputs submitted to the EPA through the Emissions Inventory System (EIS).

Table 1 presents the VMT d ata that is plotted in Figure 6 , with VMT data binned by CBSA populations that correspond to the three phases by which the near

- road NO 2 monitoring network is being installed, plus those areas having populations of 500,000 or fewer persons. In Table 1 and Figure 6 below, we see a positive correspondence between VMT and CBSA population, where VMT values increase with increasing CBSA populations.

Table 1. Mean and median VMT values, binned by CBSA populations corresponding to the three phases by which the ne ar - road network is being installed, and all CBSAs having less than 500,000 persons. CBSA Population Mean VMT Median VMT Less than 500,000 1,607,649,834 1,318,583,764 500,000 to 1,000,000 4,398,168,987 4,102,617,866 1,000,000 to 2,500,000 7,881,014,062 8,523,556,781 2,500,000 and greater 20,924,181,690 16,565,022,56510

Figure 6 . Plot of Vehicles Miles Traveled (VMT) of all CBSAs, nationwide, binned by CBSA populat i on ranges corresponding to the three phases by which the near

- road network is being installed plus all CBSAs having less than 500,000 persons. In each plot, the open circle is the mean, the central horizontal solid line is the median, and the box edges are the 25th and 75th percentiles. The whiskers extend to the highest value that is in between the box edge and 1.5*IQR (inter

- quartile range

– the distance between the box edges). The notches extend 1.58*IQR/sqrt(n) (where n = sample count) and give an indication of significant difference between the medians of the boxes.

Since there is an understanding that near

- road monitoring sites have been successful ly placed adjacent to the most highly trafficked roads in their respective CBSAs ( as shown and discussed in the previous section) , we can also use the AADT and FE

- AADT counts of the target roads of the near

- road NO 2 network to visualize th e relationship between CBSA population and the busiest roads in larger urban areas . Figure s 7 and 8 plot volumes of traffic, using both AADT and FE

- AADT, respectively, binned by CBSA populations corr esponding to the three phases by which the near

- road NO 2 monitoring network is being installed. In these figures, the positive correspondence between traffic volumes and CBSA pop ulation are clearly discernable, where relative target road AADT and FE

- AADT v alues increase with increasing CBSA populations.

The collective population and traffic data shown support the concept that increasingly higher populated CBSAs have increasingly more traffic throughout their urban areas. Further, higher populated CBSAs typ ically have more individual roads with relatively high traffic volumes than their lesser populated CBSA counterparts

. As a result, it is evident that higher populated areas correspondingly have more vehicles, which in turn11

increase the mobile source

- derive d emissions that lead to increased opportunity for higher NO 2 concentrations particularly in the near

- road environment

.

F igure 7

. AADT counts of the target roads of near

- road NO 2 monitoring sites, binned by CBSA populat i on ranges corresponding to the three phases by which the near

- road network is being installed.12

Figure 8

. FE

- AADT counts of the target roads of near

- road NO 2 monitoring sites, binned by CBSA poupulaton ranges corresponding to the three phases by which the near

- road network is being installed.
Measured NO 2 Concentration Data Analysis

Th e intent of this analysis of collected near

- road NO 2 concentration data from the current

near

- road network is to determine whether NO 2 concentrations in the near

- road environment are relatively lower in CBSAs with lower populations compared to larger urban areas. The EPA currently estimates that there are 6 3 operational near

- road NO 2 sites , with variable data availability dependent upon start date and completeness starting in 2011 (a Gantt chart illustrating individual site length of operation and a discussion of site installation and operations is located in the appendix of this document). To date, no

near

- road NO 2 monitor has recorded a n annual mean value that exceeds the 53 ppb NAAQS level, nor has any monitor provided a single year 98 th percentile 1

- hour daily maximum concentration value above the 100ppb NAAQS level. 2

Figure 9 depicts the annual average and 98 th percentile 1

- hour daily maximum value of the four near

- road sites that had complete data for 2013, while Table 2 provides the same statistics plus additional site specific CBSA and traffic meta

- data for these four sites

. The data presented in Figure 9 and Table 2 include near

- road NO 2 concentration data and CBSA and traffic related meta

- data for the Boise, Des Moines, Detroit, and St. Louis CBSAs. The Detroit and St. Louis CBSA s have populations in excess of 2,500,000

2 The design value for the 1

- hour NAAQS s tandard is calculated using the 3

- year average of the 98 th percentile 1

- hour daily maximum concentrations for a site.13

persons, while both Boise and Des Moin es have populations between 500,000 and 1,000,000 persons. Viewing data in Table 2, we observ e that the larger CBSAs have near

road sites situated near roads with relatively higher traffic volumes. These 2013 data, although a small sample in terms of the n umber of sites, show that the near

- road sites in the larger CBSAs measured higher concentrations of NO 2 for both the annual mean and the 98 th percentile 1

- hour daily maximum value for 2013 than in the lesser populated CBSAs. This observation fits the conce pt that higher near

- road NO 2 concentrations are expected in relatively higher populated CBSAs.

Figure 9 . 2013 Near

- road NO 2 concentration summary statistics (in ppb) from the four sites that had a complete years’ worth of data , binned by CBSA populat i o n ranges corresponding to the three phases by which the near

- road network is being installed.14

Table 2. Population, traffic, and NO 2 concentration data (in ppb) for the four CBSAs that had a full year’s worth of data collected for 2013.

CBSA Population AADT FE

- AADT Annual Mean (ppb) 98 th % 1hr

Daily Max (ppb) Detroit 4,296,611 140,500 188,200 18 48.0 St. Louis 2,806,207 159,326 360,077 14 50.4 Boise 664,422 103,000 162,000 11 39.3 Des Moines 611,549 110,000 150,140 9 34.1
Figure 1 0 presents the annual mean and 98 th percentile 1

- hour daily maximum value of the 20 near

- road sites that met data completeness requirements with their 2014 data
, and Figure 11 presents the same statistics for the 42 near

- road NO 2 sites with complete data for 2015

. T he se data are binned by CBSA population size corresponding to the three phases by which the near

- road NO 2 network is installed. Within each CBSA size bin, the data are ordered by annual averages, decreasing from left to right. In Figure 1 0 , for the annual mean data and largely for the 98 th percentile 1

- hour daily maximum data
, the highest concentrations tend to occur in the largest CBSAs . Most notable is that the NO 2 data from the 500 ,000 to 1 million person size bin are among the lowest of all reported data.

In Figures 10 and 11, we observ e that there is overlap in the highest concentrations in one CBSA size bin to the lowest concentrations in a neighboring CBSA size bin, but the data p resented generally support the concept that higher near

- road NO 2 concentrations are expected in higher populated CBSAs as compared to relatively lesser populated CBSAs. More specifically, there is some correspondence between CBSA population and NO 2 concent rations, where NO 2 concentrations increase with increasing CBSA population. It is also notable that none of the concentration data are threatening to e xceed the annual or 1

- hour daily maximum standard levels of 53 ppb and 100 ppb, respectively.15

Figure 1 0 . 2014 Near

- road NO 2 concentration summary statistics (in ppb) from the sites that had at least 7200 hourly observations in AQS , binned by CBSA poupulat i on ranges corresponding to the three phases by which the near

- road network is being installed.16

Figure 1 1 . 2015 Near

- road NO 2 concentration summary statistics (in ppb) from the sites that had at least 75 percent completeness of their h ourly observations in the 1 st
, 2 nd , and 3 rd calendar quarters of 2015 in AQS, binned by CBSA poupulaton ranges corresponding to the three phases by which the near

- road network is being installed17

Conclusions

The evidence provided for consideration in the preceding sections le a d s to multiple key findings . First, the near

- road NO 2 monitoring sites are good representatives of the peak NO 2 concentrations that can exist in the near

- road environment , due to their proxi mity to top trafficked roads within their respective CBSAs

. This is an important assertion, as having the whole of the near

- road NO 2 network be representative of expected peak, near

road NO 2 concentration s in a given CBSA allows for a fairer comparison of near

- road data across CBSAs.

Second, the analysis show s that higher populated CBSA s correspondingly have more vehicles, which in turn increase s the availability of mobile source derived emissions that lead to increased opportunity for higher NO 2 concentrations , particularly in the near

- road environment

. In short, higher populated CBSAs might expect to see relatively higher

near

- road NO 2 concentrations than their lesser populated CBSA counterparts. Although this particular relationship between CBS A population size and measured or expected

near

- road NO 2 concentrations is not absolute, the deviations are most likely due to a number of known factors including differences in near

- road NO 2 monitor target road traffic volume, fleet mixes, congestion patt erns, roadway design, terrain, and meteorology, along with some influence based upon the distance between the monitor and the road and background NO 2 concentration differences , as were presented and discussed in the 2010 rulemaking and the “ NO 2 Near

- road M onitoring Technical Assistance Document

. ” The influence of these factors is inherently part of the near

- road NO 2 network and were required to be considered in the near

- road monitor siting process. It should be noted that the measured concentrations at eve ry near

- road NO 2 site will always be influenced by any number of these factors to varying degrees in time.

Third, the available data meeting 75 percent completeness criterion indicate that
, to date,

no near

- road NO 2 site has collected data show that NO 2 concentrations are above or approaching the annual NO 2 NAAQS of 53 ppb, nor the 100 ppb level of the 98 th percentile 1

- hour daily maximum value. Notably, t he highest annual mean value of any

near

- road NO 2 monitor in 2014 was 27 ppb, found in the Los Angel es CBSA , while the highest annual value of the quarterly 2015 data is 26 ppb
, in the Denver CBSA. T he highest 98 th percentile 1

- hour daily maximum value of any near

- road NO 2 monitor in 2014 is 69.6 ppb, in the Denver CBSA, while the highest value of the qu arterly 2015 data is 7 2 ppb , in the New York CBSA.

Finally, t he analysis of the available near

- road NO 2 data from sites having largely a complete years’ worth of data in 2013 and 2014, and the 1 st
, 2 nd , and 3 rd quarter analysis from 2015
, indicate that the larger CBSAs tend generally to have higher measured near

road NO 2 concentrations than their lesser populated CBSA counterparts. This is true for18

both forms of the NO 2 NAAQS, although this correspondence is more strongly manifested and obs ervable in the mean s (i.e., annual averages) of the data

. In light of these results
, the EPA believes the assertion that larger CBSAs generally can expect to have higher measured near

- road NO 2 concentrations than relatively smaller populated CBSAs is valid

.19

Appendix

The first near

- road NO 2 site to begin operation is located in Detroit (AQS ID 26

- 163

- 0093), which start ed as part of an EPA Office of Research and Development research study in 2011

. The next near

- road site to operate is in Boise, Idaho (AQS ID 16

- 001

- 0023), which came online in the spring of 2012 as part of the near

- road NO 2 pilot study
, the details of which can be found at http://www3.epa.gov/ttn/amtic/nearroad.html . While there were nine sites operational for some period of time during 2013, the bulk of sites came online in 2014, as the 1 st phase of the near

- road NO 2 network was due to come online January 1, 2014.

Gantt chart showing the length of operations for 63 near

- road NO 2 sites, as of January 2016 . The list is ordered alphabetically by CBSA name.

Of the nine near

- road NO 2 monitors operational and reporting data in 2013, only four of those sites operated for the full year (sites in Boise, ID ; Des Moines, IA ; Detroit, MI ; and St. Louis, MO). The other five sites (Denver, CO ; Hartford, CT ; Boston, MA ; Minneapolis, MN ; and Kansas City, MO) have data for at least 6 months or so of that year, but not enough for a sufficiently complete annual record. In 2014, 42 near

- road NO 2 sites reported data to AQS. Although Phase 1 near

- r oad NO 2 sites were supposed to begin operations on January 1, 2014, a number of state and local air agencies were not able to20

begin operations on time for various reasons or had interruptions in operations, and as a result, a number of sites had start

- up dates scattered throughout the year or experienced data gaps. In 2015 , the network continued to fill out, and as of January 2016, the EPA estimates that 63 near

- ro ad NO 2 sites are operational, and the remainder of the required network is anticipated to be installed and operational during 2016. The EPA is tracking the installation and detailed characteristics of the near

- road network, and provides these data, which i s periodically updated, at http://www3.epa.gov/ttn/amtic/nearroad.html

.