POWER June 2012 - 38

AIR QUALITY
Particulate Matter Air Quality
Standards Continue to Evolve
The U.S. Environmental Protection Agency has regulated particulate matter as
an air pollutant for more than 40 years. Over time, PM regulations and
testing methodologies have become more complex, with the focus shifting
to smaller particle size fractions and the inclusion of the condensable
form of PM. New developments make navigating the permitting and compliance
process efficiently more important than ever.
By Louis A. Corio and Robert P. Newman PE, Zephyr Environmental Corp.
P
articulate matter (PM) is a term used to
define an air pollutant that consists of a
broad class of chemically and physically
diverse substances that exist as discrete particles
(liquid droplets or solids). PM can include a
number of components such as acids (for example,
nitrates and sulfates), organic chemicals,
metals, and soil or dust particles.
The U.S. Environmental Protection
Agency (EPA) regulates " particulate matter "
(originally referenced as total suspended particulate
or TSP) as PM10 (particles with an
aerodynamic diameter of less than or equal
to 10 micrometers) and PM2.5 (particles
with an aerodynamic diameter of less than or
equal to 2.5 micrometers). PM10 consists of
coarse and fine size fractions; PM2.5 is categorized
as fine PM. Also, in some cases, the
EPA regulates certain species of PM as separate
air pollutants (including lead, beryllium,
fluorides, and sulfuric acid).
PM may be emitted directly from a source
( " primary " PM) or formed in the atmosphere
as a result of complex reactions involving gaseous
precursors emitted from distant sources
( " secondary " PM). Gaseous precursors that
contribute to the formation of secondary PM
include sulfur dioxide (SO2
), nitrogen oxides
(NOx), and volatile organic compounds.
PM that is captured in-stack on the emission
sampling equipment filter is referred to
as the filterable component of primary PM
emissions ( " filterable " PM). Solid or liquid
particles that condense from gaseous emissions
within seconds of exiting a stack (at
ambient conditions) are referred to as the
condensable component of primary PM emissions
( " condensable " PM). Condensable PM
emissions can be as much as 90% of total PM
(condensable plus filterable PM) emissions,
depending on fuel type, emission control
systems, combustion temperatures, and other
source-specific conditions. All condensable
PM, if emitted by a source, is in the PM2.5
size fraction; therefore, all condensable PM
38
is a component of both primary PM2.5 and
primary PM10 emissions.
The particle size category is directly linked
to its potential to adversely impact human
health and welfare. PM10 is small enough
to easily pass through the throat and nose
and enter the lungs, and it can cause serious
respiratory and cardiovascular health effects;
therefore, this PM size fraction is sometimes
referenced as " inhalable " particulate. In addition
to human health effects, fine PM is a main
contributor to visibility impairment (regional
haze) in many urban areas of the country.
Regulatory History of PM
The regulation of PM air pollution under the
Clean Air Act (CAA) began in 1971 with
the establishment of the National Ambient
Air Quality Standard (NAAQS) for TSP. A
summary of the most prominent regulatory
milestones for the PM NAAQS and related
compliance assessment procedures are shown
in the table.
Over the next 40 years, the regulatory requirements
evolved to address smaller particle
sizes and physical characteristics of PM. For
example, condensable PM was recently included
as a regulated component of PM air
pollution alongside filterable PM. Moving
forward, for PM10 and PM2.5, State Implementation
Plans (SIPs) and regulations, General/Transportation
Conformity, New Source
Review (NSR, which includes both nonattainment
NSR, or NNSR, and Prevention of
Significant Deterioration, or PSD, review),
and annual emissions statements all must address
condensable PM emissions. This recent
regulatory requirement, along with anticipated
regulatory updates and federal guidance in
2012, creates a variety of new challenges, esRegulatory
milestones for PM NAAQS and related compliance assessment
requirements. Source: EPA
Year
1971
1987
1997
2006
2008
2010
2011
2012
(expected)
Regulatory action
TSP NAAQS promulgated
PM NAAQS revision; PM10 standards introduced
PM NAAQS revision; PM2.5 standards introduced; PM10 Surrogacy Policy established whereby permit
applicants are allowed to use compliance with PM10 NSR requirements (including PM10 NAAQS)
as a surrogate approach for meeting PM2.5 NSR requirements
PM2.5 24-hour NAAQS revised/lowered; PM10 annual NAAQS revoked
PM2.5 NSR rules finalized; significant emission rates established for primary PM2.5 emissions (10
tpy); and the PM2.5 precursors, SO2 and NOx (40 tpy each)
Final PSD increments, SILs, and SMC for PM2.5 promulgated
PM10 Surrogacy Policy ended; PSD compliance demonstrations required for PM2.5 emissions, including
accounting of direct PM2.5 emissions and secondarily formed PM2.5 from precursors; states must
establish limits taking into consideration the condensable fraction of PM2.5 emissions
Revision/lowering of the annual PM2.5 NAAQS; EPA's release of PM2.5 modeling guidance; SIP integration
of PM2.5 NSR rules
Notes: TSP = total suspended particulate; NAAQS = National Ambient Air Quality Standards; NSR = New Source
Review (a federal air permitting program); PSD = Prevention of Significant Deterioration; SIL = significant impact level;
SIP = state implementation plan; SMC = significant monitoring concentration; SO2 = sulfur dioxide; NOx = nitrogen
oxides; tpy= tons per year.
www.powermag.com
POWER | June 2012

http://www.powermag.com

POWER June 2012

Table of Contents for the Digital Edition of POWER June 2012