Particulate Matter
National Ambient Air Quality Standards
Review Process and Status
Tom Moore
WESTAR Council Meeting
September 29, 2010
Portland, OR
Background
• Clean Air Scientific Advisory Committee (CASAC) provides
independent advice to the EPA Administrator on the technical
bases for EPA's national ambient air quality standards
– Established under the 1977 CAA (42 U.S.C. § 7409(d)(2))
– CASAC also addresses research related to air quality, sources of air
pollution, and strategies to attain and maintain air quality standards, and to
prevent significant deterioration of air quality
• There are 7 members of the chartered CASAC
– Appointed by EPA Administrator as Special Government Employees to
serve a 3-year term, may be renewed for an additional 3-year term
– Administered by staff from EPA’s Science Advisory Board
– Members of ad hoc committees or panels are appointed to serve for the
duration of assigned advisory activities
– For this PM NAAQS review, 16 additional panelists were added to the
chartered CASAC, for a total of 23 on the PM Review Panel
Review Status
• Second draft Policy Assessment (June 2010) prepared by OAQPS
staff as part of CAA-required periodic review of PM NAAQS
– Addresses primary (health-based) and secondary (welfare-based) standards
– Reviewed in detail by CASAC PM Panel and discussed at July 26-27 meeting
– September 10th Letter completes this cycle of PM NAAQS review by CASAC
• Presents staff conclusions regarding:
– Adequacy of current suite of PM standards
– Potential alternative standards for consideration in this review
– Uses scientific and technical information assessed in other EPA documents:
• Integrated Science Assessment for Particulate Matter (Final Report) (ISA, 2009)
• Quantitative Health Risk Assessment for Particulate Matter (Final Report) (RA,
2010), and
• Particulate Matter Urban-Focused Visibility Assessment (Final Report) (UFVA,
2010)
Purpose of Policy Assessment
• Intended to “bridge the gap” between relevant scientific
evidence, technical information, and judgments required
of the EPA Administrator in determining whether, and if
so how, to revise the PM NAAQS.
• The current and potential alternative PM standards are
considered in terms of the basic NAAQS elements:
–
–
–
–
Indicator
Averaging time
Form, and
Level
Current PM NAAQS1
Final Rule Indicator Averaging Time
Level
Form
35 μg/m3
98th percentile,
averaged over 3 years
Annual
15 μg/m3
Annual arithmetic
mean, averaged over
3 years2
24-hour
Not to be exceeded
more than once per
150 μg/m3
year on average over
a 3-year period
24-hour
PM2.5
71 FR 61144
October 17,
2006
PM10
1 - Primary and Secondary standards are identical
2 - The constraints on the spatial averaging criteria were tightened by further limiting the conditions under which
some areas may average measurements from multiple community-oriented monitors to determine compliance (see
71 FR 61165-61167)
Adequacy of current annual and 24-hour PM2.5 standards
(Chapter 2)
• Staff concludes currently available information clearly calls into
question adequacy of current standards
• Consider revising standards to provide increased public health
protection
• Alternative PM2.5 standards to protect against both long- and
short-term PM2.5 exposures can rely primarily on the annual
standard, with a 24-hour standard for days with high peak
concentrations
• Alternative PM2.5 Primary NAAQS suggested:
– Annual PM2.5 standard in the range of 13 to 11 μg/m3, in conjunction
with retaining current 24-hour PM2.5 standard of 35 μg/m3, and
– Consideration could also be given to an alternative 24-hour PM2.5
standard of 30 μg/m3 particularly in conjunction with an annual
standard of 11 μg/m3.
CASAC comments: Annual and 24-hour PM2.5 standards
• Supports EPA staff conclusion in Second Draft Policy Assessment
• Increasing uncertainty at lower levels
• No evidence of a threshold (i.e., a level below which there is no
risk for adverse health effects)
• Proposed combinations of annual/daily levels may not be
adequately inclusive
– Not clear why, for example, a daily standard of 30 μg/m3 should only be
considered in combination with an annual level of 11 μg/m3
• Rationale for 24-hour/annual combinations proposed for the
Administrator’s consideration (and exclusion of other
combinations within ranges contemplated) should be more clearly
explained
Adequacy of current primary 24-hour PM10 standard for
thoracic coarse particles (Chapter 3)
• Consider retaining or revising the current standard
– Depends on relative weight placed on evidence supporting
associations with PM10-2.5, and
– Uncertainties associated with this evidence
• Potential alternative primary PM10 standard:
– Retain PM10 indicator and 24-hour averaging time
– Revise form and level
– Consider levels from 85 µg/m3 down to about 65 µg/m3 in
conjunction with a 98th percentile form
CASAC comments: PM10 (thoracic coarse particle) Standard
• Agree with EPA staff recommendation to lower PM10 primary standard
– Current evidence limited, but sufficient to call into question level of protection afforded by
current standard
• Supports EPA staff conclusion - appropriate to change the PM10 standard to a
98th percentile form
– Higher rate of identifying areas in nonattainment while reducing the rate of misclassification
• Do not agree available scientific evidence strongly supports the proposed upper
bound standard level of 85 μg/m3
– Second Draft Policy Assessment demonstrates that a 98th percentile level of 85 μg/m3 would
be less stringent as compared to current standard, protecting a smaller fraction of population
– On a population basis, Policy Assessment results demonstrate a 98th percentile level between
75 and 80 μg/m3 is comparable to degree of protection afforded by current PM10 standard
•
•
Supports lower level for enhanced protection, within range of 75 – 65 μg/m3
Concludes PM10 should continue to be the indicator for thoracic coarse particles
– Preferable to use indicator that reflects coarse PM directly linked to health risks (PM10-2.5)
– Recognizes insufficient data to permit change in indicator from PM10 to direct measurements
of thoracic coarse particles
– Recommend deployment of network of PM10-2.5 sampling systems to expand evidence base
on this indicator and facilitate assessment of whether PM10-2.5 should be used as an
appropriate indicator for thoracic coarse particles
Adequacy of current secondary annual and 24-hour PM2.5 standards to
protect against PM-related visibility impairment (Chapter 4)
• Current secondary annual and 24-hour PM2.5 standards are
identical to primary PM2.5 standards
• Staff concludes currently available information clearly calls into
question the adequacy of current standards
• Suggests revising standards to provide increased public welfare
protection
• Consider alternative secondary PM2.5 standards:
– Establish a new indicator based on using speciated PM2.5 mass and
relative humidity to calculate PM2.5 light extinction
– 1-hour averaging time considering only daylight hours, with relative
humidity no higher than 90 %
– Define a level in terms of PM2.5 light extinction, in the range of 191 to 64
Mm-1 (20 to 30 deciviews)
CASAC comments: Secondary Standard for PM-Related
Visibility Impairment
• Supports EPA staff conclusion that questions adequacy of the
current standards and that PM standards should be revised to
provide increased public welfare protection
– Detailed estimates of hourly PM light extinction under current conditions
(and for assumed scenarios of meeting current standards) clearly
demonstrate current standards do not protect against levels of visual air
quality, which have been judged to be unacceptable in all available urban
visibility preference studies
– EPA staff’s approach for translating and presenting technical evidence and
assessment results is logically conceived and clearly presented. The 20-30
deciview range of levels chosen by EPA staff as “Candidate Protection
Levels” is adequately supported by the evidence presented
CASAC comments: Secondary Standard for PM-Related
Visibility Impairment, continued
• 3 potential indicators were discussed:
– PM2.5 Mass Indicator
– Speciated PM2.5 Mass-calculated Light Extinction Indicator, and
– Directly Measured PM2.5 Light Extinction Indicator
• CASAC would prefer direct measurement of light extinction
– Property of the atmosphere that most directly relates to visibility effects
– Relates directly to demonstrated harmful effect of ambient PM on human
visual perception
– Given time lag associated with implementing Directly Measured
Indicator, CASAC agrees with EPA staff’s preference for Speciated
PM2.5 Mass-calculated Light Extinction Indicator
• To use hourly data from already-deployed continuous PM2.5 mass monitors
• To rely on procedures already been implemented in the Chemical Speciation
Network
Adequacy of current secondary PM standards to protect against
PM-related effects other than visibility impairment (Chapter 5)
• Current secondary PM standards identical to primary PM2.5 and
PM10 standards
– Intended to protect against PM-related effects other than visibility impairment
– Climate, ecological effects, and effects on materials
• Current information supports retaining control of both fine and
coarse particles to address PM-related effects on ecosystems and
materials damage and soiling
• Insufficient information to assess the adequacy of protection
afforded by the current standards
• Also insufficient information at this time to base a national
ambient standard on climate impacts associated with current
ambient concentrations of PM or its constituents.
Remaining Schedule for this PM NAAQS Review Cycle
• Winter 2010-11
– EPA finalizes Policy Assessment
– Proposal package to EPA management and OMB
• February 2011
– Revised/new PM standards proposed
• Fall 2011
– Revised/new PM standards promulgated