UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
REGION III
1650 Arch Street Philadelphia, Pennsylvania 19103

DATE: May 12, 2015

SUBJECT: Supplemental Technical Support Document

– Determination of Attainment for

the Balitmore, MD 2008 8

- Hour Ozone Nonattainment Area

RE: Response to Comments Concerning Baltimore Area Invalidated and Missing Monitoring Data

FROM: Irene Shandruk, Physical Scientist /s/

Office of Air Program Planning

TO: EPA

- R03

- OAR

- 2014

- 0884

THRU: Cristina Fernandez, Associate Director /s/

Office of Air Pro gram Planning

I. Background

On March 18, 2015, EPA proposed to determine that the Baltimore, Maryland Moderate Nonattainment Area (Baltimore Area) has attained the 2008 8

- hour ozone National Ambient Air Quality Standard (NAAQS) (hereafter referred to as “NPR”) . 80 FR 14041. EPA received adverse comments on the proposed determination of attainment. The commenter state d that Baltimore’s ozone monitors do not fully and accurately capture all maximum ozone exposures and asserted there we re many instance s where ozone monitors “ shut off ” for at least a day during a heat wave when ozone levels were rising. The commenter claim ed that had the monitors collected data during those periods, ozone exceedances would likely have occurred whi ch may have altered the Baltimore Area’s ozone design value and adversely affected any “clean” data for the Baltimore Area which might delay EPA’s determination of attainment for the Baltimore Area with the 2008 ozone NAAQS

.
EPA consulted with the Marylan d Department of the Environment (MDE) concerning the monitors questioned by the commenter

, including the monitors at Davidsonville, Padonia, and Aldino. MDE reviewed the monitoring data at these monitors for the dates alleged by the

commenter as “shut ting off.” MDE provided information to EPA supporting the conclusion that these monitors did not “shut off” as the commenter alleges but that MDE invalidated data from these monitors for brief periods of time due to extenuating circumstances such as condensat ion build up and power failures.

II. Respons ive Information for Comments Concerning Monitor Operation 1. Comment regarding Davidsonville data from 7/17/1 2

- 7/19/1 2 (page 27 of comments on EPA’s NPR )2

a. In a Number of Instances, Ozone Monitors Shut Off a s Ozone Concentrations Increased, Nearing an Exceedance When examining just the past five years of hourly data from these ozone monitors, it is clear that there were many instances of ozone concentrations increasing and nearing an exceedance, and then shutting off and not reporting any data. These instances oft en happened during peak ozone season and/or a summer heat wave.

The monitor at the Davidsonville Recreation Center (#240030014), which had a 2012

- 2014 design value of 74 ppb, displayed this phenomenon numerous times. For example, July 17, 2012

was a very hot day, with a maxim um temperature of 100 degrees, and very high hourly ozone values, starting at 10 am, of 83 ppb, 93 ppb, 95 ppb, 91 ppb, 91 ppb, 95 ppb, and 102 ppb, but, at 5 pm, the monitor shut off.

The monitor did not record any data for July 18 , 2012, an even hotter day up to 104 degrees, and did not come back online until noon on July 19, 2012, which was a relatively cooler day with a maximum of 95 degrees. The monitor’s first recorded values when it came back online were, chronologically, 74 p

pb, 82 ppb, 90 ppb, 90 pp b, 93 ppb, 92 ppb and 93 ppb.

It is likely that the monitor missed a tremendously high ozone exceedance when it was shut off for the entirety of July 18, 2012, as the preceding day’s 8

- hour maximum average ozone level was 94 ppb ( the monitor’s 3rd highest value that year) and the following day’s was 87 ppb (the monitor’s 4th highest value.) Given July 18 was an even hotter day, it is reasonable to infer that the ozone maximum would have been in between 87 and 94 ppb, and most likel y at the upper end of that range. If the monitor had recorded a level even just in the middle of this range at 91 ppb or above, it would have been the monitor’s 4th highest value, changed the 2012

- 2014 design value to 76 ppb, and continuously kept the Balt imore area in nonattainment, thus precluding EPA from even proposing this CDD.

Response : MDE disputes that this monitor was “shut off.” The data was simply invalidated. From the station log notes: During the 4pm hour on 7

- 17

- 12, the window AC unit in the shelter failed . By 5pm the shelter temperature was 94.8°F, the next hour it was 100°F. The analyzer really shouldn't run over 86°F, per the manual. By the afternoon of 7

- 18

- 12, we had replaced the AC
unit and started to cool down the shelter. Even th ough a note was left about a PC passing on the afternoon of 7

- 18

- 12 (it did pass), the values were invalidated in Envista through 11:30am on 7

- 19

- 12 because of instability on the minute readings.

Second, upon MDE review, MDE asserted it is highly unlikely that the monitor missed a tremendously high ozone exceedance and it is not reasonable to infer that the max would have
been between 87 a nd 94 parts per billion ( ppb ) unless one assumes that ozone concentrations are solely dependent on temperature and beha ve somewhat linearly from day to day to day at each
monitor . MDE also asserted this ignores the meteorology and the behavior of the other ozone monitors in Maryland on 7/18/1 2

. On 7/17/1 2 , there were 13 monitors registering exceedances in Maryland, 5 in the Baltimore area, 5 in the Washington area, 1 in the Philadelphia area and 2
on the eastern shore. On 7/18/1 2 , even though the max temperature was higher, there were only3

5 monitors regi stering exceedances, 2 in the Baltimore area, 2 in the Washington area and 1 on
the eastern shore. On 7/19/1 2 , there were 7 monitors registering exceedances, 1 in the Baltimore area (Davidsonville , tied for daily max in Maryland with PG Equestrian Center ), 5 in the Washington area and 1 on the eastern shore. On 7/18/ 2 , thunderstorms were initiating around 3

PM between Beltsville and Davidsonville and they swept through the area between 5 and 6 PM

. There also was appreciable cloud cover by 3 PM. Ozone conc entrations at the PG Equestrian Center (the closest monitor to Davidsonville and the site that most closely correlates with Davidsonville) had early morning (10 AM ) concentrations in 90 ppb range but decreased after that due to boundary layer mixing, as eviden ced by the preconvective cumulus field which developed between noon to 1 PM (per analyses b y MDE meteorologist )

.
The highest 8

- hour ozone max in Maryland on 7/18/1 2 was 84 ppb, measured at Edgewood, well
north of the isolated thunderstorms that occu rred at Davidsonville. Even if one were to substitute the Edgewood max at Davidsonville (which has no sound technical basis) it would have no impact on the 2012

- 2014 design value at Davidsonville. The max at the PG Equestri a n Center (again, the closest mon itor to Davidsonville and most closely correlated) on 7/18/1 2 was 76 ppb, a more likely candidate for subst i t ution (and technically defensible).

2. Commenter regarding Davidsonville 6/29/1 2

- 7/1/1 2 (page 27 of comments on EPA’s NPR ) Another example, from the same monitor, begins on June 29, 2012. The maximum 8

- hour average for that day was 102 ppb but the monitor shut off at 10 pm and does not report data again until July 1, 2012 at noon, at which point the first values are 78 ppb, 78 ppb , 73 ppb, 73 ppb, and 77 ppb. The monitor did not record any data for the entirety of June 30, 2012, which was during peak ozone season and a heat wave, with maximum temperatures of 103, 95 and 97 respectively for the three days.

Response : According to MDE, t he re was a power failure at the Davidsonville monitoring station which began 6/29/12 at 10:33 PM. Power was not restored until 7/1/12 at 11:37 AM (from the site’s datalogger power f

ailure log). This was a direct result of the passage of a derecho which caused considerable damage throughout Maryland with many downed trees and power lines a nd extensive power outages that lasted for extended periods throughout Maryland and many other

states.

Excerpted from the preface of the January 2013 NOAA Service Assessment “The Historic Derecho of June 29, 2012” ( http://www.nws.noaa.gov/os/assessments/pdfs/derecho12.pdf ):

On June 29, 2012, a derecho of historic proportions struck the Ohio Valley and M id

- Atlantic states. The derecho traveled for 700 miles, impacting 10 states and Washington, D.C. The hardest hit states were Ohio, West Virginia, Virginia, and Maryland, as well as Washington, D.C. The winds generated by this system were intense, with seve ral measured gusts exceeding 80 mph. Unfortunately, 13 people were killed by the extreme winds, mainly by falling trees. An4

estimated 4 million customers lost power for up to a week. The region impacted by the derecho was also in the midst of a heat wave. The heat, coupled with the loss of power, led to a life

threatening situation. Heat claimed 34 lives in areas without power following the derecho.

Excerpted from the Executive Summa ry of the January 2013 NOAA Service Assessment “The Historic Derecho of June 29, 2012”:

On June 29, 2012, a devastating line of thunderstorms known as a derecho (deh REY cho) moved

east

- southeast at 60 miles per hour (mph) from Indiana in the early aftern oon to the Mid

Atlantic region around midnight. The states most significantly impacted were Indiana, Ohio, Kentucky, Pennsylvania, West Virginia, Maryland, Virginia, Delaware, New Jersey, and North Carolina, as well as Washington, D.C. Nearly every county impacted by this convective system suffered damages and power outages. Winds were commonly above 60 mph with numerous reports of winds exceeding 80 mph. Some areas reported isolated pockets of winds greater than 100 mph. The storm resulted in 13 deaths, ma inly a result of falling trees. One major impact from the derecho was widespread power outages. More than 4 million customers were without power, some for more than a week after the storms moved through. To make matters worse, the area affected was in the midst of a prolonged heat wave. There were 34 heat

- related fatalities in areas without power because of the derecho.

In addition to the Davidsonville monitoring station , the ozone monitoring stations at Edgewood, Rockville, Southern Maryland, PG Equestria n Center and Calvert all lost power. Edgewood’s power was restored at 4:00 AM on 6/30/12 and all the other Baltimore area monitors were fully operational during the 6/29/12

- 7/1/12 period while Davidsonville was without power. Despite the heat, n one of the other Baltimore area monitors registered exceedances during that period

, again demonstrating that temperature alone is a poor indication of expected ozone levels

. The derecho effectively swept out much of the ozone in the upwind area to the west all the w ay to Chicago.

3. Comment regarding Padonia monitor 7/22/11 (page 28 of comments to EPA’s NPR ) This phenomenon is prevalent in not just this most recent design value time period, but before then as well. For example, the monitor at Padonia Elementary School (#240051007) recorded a maximum 8

- hour average of 86 ppb on July 20, 2011, which included hourly values as high as 95 ppb, 98 ppb, 103 ppb, 96 ppb, and 81 ppb. The next day on July 21, 2011, the monitor records consistently high hourly values starti ng at 2 pm of 81 ppb, 86 ppb, 83 ppb and then shuts off at 5

pm. The monitor did not start reporting again until July 23, 2011 at 11 am, missing the entirety of July 22, 2011, which was an extremely hot day conducive to ozone formation.

Response First, M DE and EPA find this issue irrelevant to the NPR which proposed to determine the Baltimore Area attained the 2008 8

- hour ozone standard based on 2012

- 2014 design values. This is only presen ted to bolster the commenter’s claims that these type s of “phenomena” are “prevalent” and that they discovered “many instances” of these occurring over a five year period. If that were the case, the completeness criteria would not have been met.5

Second, it is also irrelevant because the 2011

- 2013 design val ue for Padonia was 78 ppb without collecting any data on 7/22/11. The site was already out of attainment and any data collected on 7/22/11 would not have changed that fact.

Thir d, according to MDE, the monitor did not shut off. The data was invalidated du e to condensation in the sample line which actually got into the monitor resulting in erroneous readings . There were temperature control issues in the shelter , with the shelter eventually reaching 50 o F before being noticed early 7/22/11. It took until noon on 7/23/11 to dry out the monitor and bring it back on line.

4. Comment regarding Davidsonville monitor 5/23/13

- 5/31/13 (page 28 of comments on EPA’s NPR ) There were also several instances in which ozone monitors shut off and did not report data for several days, sometimes for even over a week, during ozone season. These are times when many exceedances may have occurred, and thus could have significantly inc reased design values, but were not recorded because the monitors were not recording data.

For example, the Davidsonville Recreation Center’s monitor, which is on the cusp of nonattainment at 74 ppb, turned off and did not report data for over one week during ozone season, from noon on May 23, 2013 through 8 am on May 31, 2013. During this time period when the monitor was off, daily maximum temperatures reached 80, 89, 92 and 90 degrees, which are at and well above the threshold for ozone exceedances in Baltimore. Thus, the monitor may well have missed exceedances that would have kept the monitor in nonattainment for 2012

- 2014.

Response This is another instance of temperature control issues in the shelter. According to MDE, the temperature in the shelt er was turned down for operator comfort on the morning of 5/23/13 and was inadvertently not readjusted when the operator left the shelter. The temperature reached 60 o F and stayed there until 5/29/13 at 11:00 AM. Condensation had formed in the sample line a nd got into the monitor. The monitor was dried out and put back online on 5/31/13.

During the period from 5/23/13 through 5/28/13, the highe st 8

- hour max in the Baltimore A rea was 59 ppb and there were no exceedances reg istered anywhere in Maryland . On 5/ 29/13 an 8

- hour max of 80 ppb was measured at Fair Hill in the Philadelphia nonattainment area , but no exceedances we re registered in the Baltimore Area (max 68 ppb), Washington A rea, or the eastern shore. No exc e edances were measured anywhere in Maryland on 5/30/13 (Baltimore
A rea max 71 ppb). On 5/31/13, the Pad onia monitor, in the Baltimore A rea, was the only monitor in Maryland to register an exceedance at 76 ppb. Given the overall low regional ozone concentrations, this definitely was not a time when many exceedances may have occurred or when the monitor may well have missed exceedances. Even if you substitute the max exceedance in Maryland during that entire time period (the 80 ppb at Fair Hill), the 2012

- 2014 design value at Davidsonville would rema in unchanged. The likelihood of an exc e edance of 88 ppb or greater (the value needed to change the Davidsonville design value to 76 ppb) occurring at Davidsonville during the period in question is extremely rare.6

5. Comment regarding Aldino monitor 8/17/12

- 8/20/12 (page 28 of comments on EPA’s NPR ) Similarly the Aldino monitor (#240259001), which has a 2012

- 2014 design value of 73 ppb, is missing data from 8 pm on August 17, 2012 through 1 pm on August 20, 2012.50 The daily maximum temperatures durin g the time period included 92, 94 and 80 degrees. 51

Response There was a power failure at the Aldino monitor beginning at 7:46 PM on 8/17/12, a Friday. The power came back on at 7:47 PM but went back out at 8:54 PM. When the operator returned to the site Monday 8/20/15 at 12:25 PM, it was noticed that 2 circuit breakers had tripped. They

wer e reset at that time and the site came back online.

During this entire period, there were no exceedances registered anywhere in Maryland. A cold front came through the evening of 8/17/12 (probably triggering the power outage). There were clouds and rain throughout the area on 8/19/12 and 8/20/12. It is highly unlikely that any exceedances were missed at Aldino during the time the power was out.

III. EPA Analysis
EPA finds MDE’s explanations for inoperable monitor s during the periods in question by the commenter to be reasonable and supported by the technical evidence as discussed above. A variety of technical issues, such as power failures or condensation build

- up in the monitors, led to missing or invalidated monitoring data and are supported by monitoring station log notes.

Ozone monitors are sophisticated analytical instruments which mostly operate quite reliably

. However , there are many possible ways for the m onitors to malfunction or to produce erroneous or compromised data. It is unreasonable to expect any ozone monitor to operate continuously 24 hours a day for seven days a week over the seven month ozone season without experiencing any operational issues. For instance, ultraviolet lamps can burn out , vacuum pumps can fail, leaks can develop, particulate filters can clog and water vapor can condense in the sample manifold and be drawn into the monitor, among other possibilities.

The monitors also must be operated in environmentally controlled buildings or instrument shelters . I f the air conditioning fails and the monitors overheat, unstable readings may occur. If the temperature gets too cold in a shelter on a hot and humid day, condensation can occur and affect the ozone readings. Monitoring stations frequently house additional monitoring equipment and require a high electrical current draw. Ozone exceedance days are often observed on very hot and humid days. These conditions contribute greatly to conde nsation issues and high demand creates stress on the electrical grid which can lead to power failures. Thunderstorms also frequently occur under these conditions, which can also cause power failures.

A strict schedule of preventative maintenance, operatio nal checks, daily zero and span challenges, periodic audits and a minimum of bi

- weekly precision checks are in place to insure7

that any problems are addressed in a timely manner and that the highest possible quality data is being produced.

Since MDE prod uces daily ozone forecasts, monitoring site operators are alerted ahead of time when they can expect ozone exceedance days and extra efforts are taken to insure, to the best of their ability, that the monitors are operating properly and to avoid any instru ment downtime or loss of data due to preventative maintenance, audits or other quality control checks during those periods when high ozone levels are forecast.

In conclusion, Appendix P of 40 CFR part 50 formally recognizes the potential issues that can be encountered in monitoring ozone concentrations by allowing for some missing data. Each ozone monitor must produce daily maximum 8

- hour average concentrations for at least 90% of the days within the ozone monitoring season, on average for the 3

- year design value period, with a minimum data completeness requirement in any one year of at least 75% of the days within the ozone monitoring season for a design value to be considered valid. All of the Balti more A rea ozone monitors meet these requirements for the period in question.