  SEQ CHAPTER \h \r 1 UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

REGION 1

5 Post Office Square, Suite 100

Boston, MA  02109-3912

Memorandum

	Date:     	January 24, 2011

	Subject: 	Technical Support Document for Revision to the Carbon
Monoxide Maintenance Plan for Lowell, Massachusetts

	From: 		Anne K. McWilliams, Environmental Scientist

			Air Quality Planning Unit, Office of Ecosystem Protection

 	 To: 		Anne Arnold, Manager

			Air Quality Planning Unit, Office of Ecosystem Protection 

On April 14, 2010, the State of Massachusetts submitted a formal
revision to its State Implementation Plan (SIP).  The SIP revision
consists of a modification to Massachusetts’s carbon monoxide (CO)
maintenance plan for Lowell.

Background

The City of Lowell, Massachusetts was designated nonattainment for the
CO National Ambient Air Quality Standard (NAAQS) in 1978 (43 FR 9003). 
In 1991, following passage of the 1990 Clean Air Act Amendments, the
city retained this designation by operation of law (56 FR 56694),
although ambient monitoring showed attainment at that time. On May 25,
2001, the State of Massachusetts submitted a formal CO redesignation
request for Lowell (and Springfield, Waltham, and Worcester).  On
February 19, 2002, the U.S. EPA redesignated the City of Lowell
nonattainment area to attainment for the CO standard and approved the
Massachusetts maintenance plan for this area (and for Springfield,
Waltham, and Worcester) (67 FR 7272).  Since that time, there have been
no violations of the CO NAAQS of 9 ppm (8 hour average) or 35 ppm (1
hour average) in Lowell, and CO is trending downward to a level less
than 30% the NAAQS. 

Evaluation of Massachusetts’s Submittal

Massachusetts would like to discontinue monitoring for CO in Lowell. 
Lowell is a “sole pollutant” site, monitoring only CO.  The
Massachusetts Department of Environmental Protection (DEP) allocates
considerable resources each year to cover the lease agreement with the
property owner, maintenance of the monitoring and support equipment,
phone and electricity, travel to and from the site from the main office
in Lawrence, and staff time to conduct routine and emergency
maintenance, all of which are resources that could better be used
elsewhere in the state’s monitoring program. 

As previously stated, CO levels have been falling in Lowell since the
early 1980s.  (See attached Figure 1 of Lowell CO levels.)  The NAAQS of
9 ppm (8 hour average) has not been violated since 1984, and current
readings of the 8 hr 2nd high design value are in the 2 to 3 ppm range,
and have been for the past nine (9) years. During this period, the daily
vehicle miles traveled (VMT) in the Lowell area continued to increase.
(See attached Table 1 for the Northern Middlesex County  Daily VMT
trend.)  Most of the CO reduction has been due to “fleet turnover,”
with newer, cleaner motor vehicles making up an increasing share of the
fleet, and this trend is unlikely to change. 

On October 17, 2006, EPA published a final monitoring rule revising
minimum monitoring requirements.  That rule explicitly recognized that,
in some cases where measured levels of pollutants are low, shutting down
certain CO monitors may be allowed.  The rule, however, also explicitly
provides that if a monitor is the only monitor in the area, and it
serves as a trigger to implement a contingency measure in an
EPA-approved maintenance plan, the maintenance plan would need to be
revised, and the trigger replaced. (See 71 FR 61250 and 71 FR 61301.)

Based on the downward CO trend, Massachusetts revised the contingency
threshold or “trigger” in its Lowell CO maintenance plan.  The state
plans to cease monitoring for CO in Lowell, and instead, will continue
monitoring for CO in nearby Worcester, and to use these data as a
surrogate for Lowell CO levels. (See attached Figure 2 comparing CO
levels in the two cities.)  Lowell and Worcester are located 42 miles
apart.  Worcester (population 175,011) is somewhat larger than Lowell
(population 103,615) so its CO concentrations can be expected to be
slightly higher due to greater motor vehicle emissions.  Both were
designated nonattainment in 1991 for CO “by operation of law” though
both had design values below the standard at that time.  In both cases,
only the city itself was designated nonattainment since data did not
support an expansion of the nonattainment area.  Both were redesignated
to attainment in 2001, and both measure CO concentrations well below the
standard at this time.  

Massachusetts DEP will continue to collect and review CO monitoring data
from nearby Worcester, MA on an on-going basis.  In the event the second
highest CO concentration in any calendar year monitored in Worcester
reaches 75 percent of the federal 1-hour or 8-hour national ambient air
quality standard for CO (35 and 9 ppm, respectively), Massachusetts
will, within 9 months of recording such concentrations, re-establish a
CO monitoring site in Lowell consistent with EPA siting criteria, and
resume analyzing and reporting those data.  Massachusetts will continue
to commit to implement its contingency program in Lowell in the event
that a CO violation (the ‘contingency trigger’) is monitored at the
re-established Lowell monitoring site at any time during the maintenance
period and to consider one or more of the other EPA-approved measures
listed in the 2001 Maintenance Plan for Lowell if necessary to reduce CO
levels.

If the Worcester CO monitor measures a violation of either the federal
1-hour or 8-hour NAAQS for CO prior to the re-establishment of a Lowell
CO monitor, the contingency measures in 2001 Maintenance Plan for Lowell
will be implemented in Lowell, as well as triggering contingency
measures in Worcester under the terms of the existing Maintenance Plan
for Worcester.  The contingency measures in Lowell will continue until a
re-established Lowell CO monitor shows that the area is attainment of
the CO standard.  Worcester contingency measures would continue until
the Worcester CO monitor shows that the Worcester area is in attainment
of the CO standard.

When implementing contingency measures, Massachusetts will review and
implement the measures necessary to remedy the violation, including
transportation control measures (TCM) or other additional vehicle or
fuel controls.

Recommended Action

This SIP revision should be approved.

For the reasons outlined above, EPA agrees that the criteria
Massachusetts DEP will utilize represent a reasonable plan modification
and approach for shutting down a CO monitor that is currently measuring
concentrations well below the existing 1- hour and 8- hour CO national
ambient air quality standards.  The revisions represent an acceptable
alternative contingency triggering mechanism as part of a CO maintenance
plan.  Under this plan, we believe air quality goals can be maintained,
and State monitoring resources, conserved.

Attachment

ATTACHMENT

Figure 1: Carbon Monoxide Trend for Lowell, Massachusetts

Table 1: 5-Year Average Daily Vehicle Miles Traveled from 1990 – 2009

Northern Middlesex Region:

Daily Vehicle Miles Traveled (VMT)



% change over

        Year	                VMT	5-yr period

1990	         6,329,000 	n/a

1995	         6,763,000 	6.9%

2000	         7,261,000 	7.4%

2005	         7,842,000 	8.0%

2009	         7,990,000 	1.9%



Figure 2: Lowell, MA CO Compared to Worcester, MA CO

 U.S. Census Bureau, 2008 Population Estimates

 Ibid

 Data provided by Bob Frey from the Massachusetts Department of
Transportation via e-mail.  The figures are estimated from the Federal
Highway Administration’s Highway Performance Monitoring System and the
Massachusetts Department of Transportation’s travel demand model, and
represents total daily travel on all roads in the region.  2009 is the
latest year available. 

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