EPA-600 /R-97-092
September 1997
FIELD METHODS TO MEASURE CONTAMINANT
REMOVAL EFFECTIVENESS OF GAS-PHASE AIR FILTRATION
EQUIPMENT; PHASE 1; SEARCH OF LITERATURE AND PRIOR ART
By
Rea-Tiing Liu
Filtratech Consulting
Rancho Palos Verdes, CA 90275
EPA Cooperative Agreement CR823633-01-1
(American Society of Heating, Refrigerating and Air-Conditioning Engineers)
EPA Project Officer: Russell N. Kulp
Indoor Environmental Management Branch
Air Pollution Prevention and Control Division
National Risk Management Research Laboratory
Research Triangle Park, NC 27711
Prepared for:
U.S. Environmental Protection Agency
Office of Research and Development
Washington, DC 20460
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NOTICE
This document has been reviewed in accordance with
U.S. Environmental Protection Agency policy and
approved for publication. Mention of trade names
or commercial products does not constitute endorse-
ment or recommendation for use.
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FOREWORD
The U. S. Environmental Protection Agency is charged by Congress with pro-
tecting the Nation's land, air, and water resources. Under a mandate of national
environmental laws, the Agency strives to formulate and implement actions lead-
ing to a compatible balance between human activities and the ability of natural
systems to support and nurture life. To meet this mandate, EPA's research
program is providing data and technical support for solving environmental pro-
blems today and building a science knowledge base necessary to manage our eco-
logical resources wisely, understand how pollutants affect our health, and pre-
vent or reduce environmental risks in the future.
The National Risk Management Research Laboratory is the Agency's center for
investigation of technological and management approaches for reducing risks
from threats to human health and the environment. The focus of the Laboratory's
research program is on methods for the prevention and control of pollution to air,
land, water, and subsurface resources; protection of water quality in public water
systems; remediation of contaminated sites and-groundwater; and prevention and
control of indoor air pollution. The goal of this research effort is to catalyze
development and implementation of innovative,, cost-effective environmental
technologies; develop scientific and engineering information needed by EPA to
support regulatory and policy decisions; and provide technical support and infor-
mation transfer to ensure effective implementation of environmental regulations
and strategies.
This publication has been produced as part of the Laboratory's strategic long-
term research plan. It is published and made available by EPA's Office of Re-
search and Development to assist the user community and to link researchers
with their clients.
E. Timothy Oppelt, Director
National Risk Management Research Laboratory
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Abstract
Gas-phase air filtration equipment (GPAFE) has been used in HVAC (heating, ventilating
and air-conditioning) systems for many years. Traditionally it has been used primarily for
controlling odors contained in outdoor air used for building ventilation. Today, because
of the emphasis on good indoor air quality (IAQ), GPAFE is being used more and more
for the control of indoor gaseous and vaporous contaminants that are known or suspected
to affect human health and comfort.
One of the problems facing HVAC design engineers is how to choose a test method to
determine the effectiveness of a gas-phase air filtration device. Many different filter
systems and test methods are available with differing test protocols, instrumentation types
and sensitivities, and costs.
This report, which is the first phase of a two-phase research project, presents the results of
a literature search into existing in-field GPAFE effectiveness test methods including
required instrumentation and costs.
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Contents
Abstract iv
List of tables vil
List of figures viii
Metric Conversions viii
Acknowledgments ix
Executive summary x
1.0 Introduction 1
2.0 Gas-phase air filtration equipment (GPAFE) 3
2.1 Types of GPAFE 3
2.2 Types of Adsorbents 3
2.3 Applications 4
2.4 Performance Variables 5
2.4.1 Bed depth 6
2.4.2 Particle size of adsorbent 6
2.4.3 Void volume 6
2.4.4 Residence time 6
2.4.5 Temperature 6
2.4.6 Relative humidity 7
2.4.7 Flow velocity 7
2.4.8 Contaminant concentration 7
2.5 GPAFE performance under dynamic building operations 8
2.5.1 Relative humidity swing 8
2.5.2 Concentration swing 9
3.0 Existing test methods 9
3.1 Real-time instruments 9
3.1.1 Ozone, sulfur dioxide, and nitrogen dioxide 9
3.1.2 VOCs 10
3.1.3 Corrosive Gases 10
3.1.4 GPAFE test results 10
3.2 Active Sampling methods 12
3.2.1 VOCs . 12
3.2.1.1 Evacuated canister 13
3.2.1.2 Solid adsorbent 13
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3.2.2 Formaldehyde 15
3.2.3 Nitrogen dioxide 16
3.2.4 Sulfur dioxide 16
3.3 Passive sampling methods 17
3.3.1 VOCs 17
3.3.2 Formaldehyde 19
3.3.3 Nitrogen dioxide 21
3.3.4 Ozone 22
3.3.5 Sulfur dioxide & nitrous acid 22
4,0 An application guide 23
4.1 Ozone, sulfur dioxide, and nitrogen dioxide real-time instruments 23
4.1.1 Air sampling 24
4.1.2 Applications 24
4.2 Active sampling methods 24
4.2.1 GPAFE testing 25
4.2.2 Applications 26
4.3 Passive sampling methods 26
4.3.1 GPAFE testing 27
4.3.2 Handling and shipping 28
4.3.3 Applications 28
5.0 Test methods from GPAFE manufacturers 29
5.1 Remaining carbon tetrachloride activity 29
5.2 TVOC loading analysis 29
5.3 KMN04 content analysis 29
6.0 Recommendations 30
7.0 Scope of phase 2 work 31
7.1 Objectives 31
7.2 Targeted gaseous and vaporous contaminants 31
7.3 Type of building 32
7.4 Type of GPAFE 32
7.5 Sampling methods and programs 32
References 34
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List of tables
TABLE 1. GAS-PHASE AIR FILTRATION EQUIPMENT USED IN HVA.C
SYSTEMS 38
TABLE 2. REAL-TIME INSTRUMENTS FOR COMMON GAS-PHASE
CONTAMINANTS IN INDOOR AIR 38
TABLE 3. ACTIVE SAMPLING FOR COMMON GAS-PHASE CONTAMINANTS IN
INDOOR AIR 38
TABLE 4. PASSIVE SAMPLING METHODS FOR COMMON GAS-PHASE
CONTAMINANTS IN INDOOR AIR 39
TABLE 5. FIELD METHODS FOR GPAFE TESTING-APPLICATION GUIDE . .. 39
TABLE 6. PERFORMANCE SPECIFICATION FOR REAL-TIME INSTRUMENT . 40
TABLE 7. STANDARD TEST METHODS FOR ACTIVE SAMPLING-VOCs . ... 40
TABLE 8. STANDARD TEST METHODS FOR ACTIVE SAMPLING -
FORMALDEHYDE 41
TABLE 9. STANDARD TEST METHODS FOR ACTIVE SAMPLING - NITROGEN
DIOXIDE 41
TABLE 10. STANDARD TEST METHODS FOR ACTIVE SAMPLING-SULFUR
DIOXIDE 41
TABLE 11. TEST METHODS FOR PASSIVE SAMPLING - VOCs 42
TABLE 12. STANDARD TEST METHODS FOR PASSIVE SAMPLING -
FORMALDEHYDE 42
TABLE 13. TEST METHODS FOR PASSIVE SAMPLING - NITROGEN
DIOXIDE 42
TABLE 14. TEST METHODS FOR PASSIVE SAMPLING - SULFUR
DIOXIDE 43
TABLE 15. TEST METHODS FOR PASSIVE SAMPLING - OZONE 43
TABLE 16. A LIST OF SUPPLIERS FOR PASSIVE SAMPLERS 44
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List of figures
FIGURE 1. TEST METHODS FOR MEASURING GASEOUS CONTAMINANTS
IN INDOOR AIR 45
FIGURE 2, A MULT ISORBENT TUBE FOR SAMPLING VOCS IN INDOOR AIR
(ACTIVE METHOD) 46
FIGURE 3. AN ACTIVE SAMPLING APPARATUS FOR SULFUR DIOXIDE
(ASTM D-2914) 47
FIGURE 4, A CARTRIDGE FOR PASSIVE SAMPLING OF NITROGEN DIOXIDE
IN INDOOR AIR 48
Metric Conversions
Most measurements in this report are in nonmetric units. Readers
more familiar with metric units may use the following conversion
factors:
Nonmetric
Multiplied bv
Yields Metric
angstrom
0,1
nm
cftn
0.00047
m3/s
°F
5/9 (°F-32)
°C
ipm
0.00508
m/s
ft
0.305
m
in.
2.54
cm
lb
0.454
kg
oz
0.0283
kg
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Acknowledgments
This work was conducted under ASHRAE Research Project 791-RP and EPA
Cooperative Agreement CR82363301-1. The author would like to thank ASITRAE and
the EPA for their funding of this research project. The author would also like to thank the
ASIIRAE research staff, TC 2.3 PMC members, and the EPA for their assistance and
guidance during the course of this research project (phase 1).
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Executive summary
Numerous test methods are commercially available for measuring low level concentrations
of gaseous and vaporous contaminants in ambient and indoor air. With appropriate
sampling procedures, these methods can be readily used to determine the effectiveness of
gas-phase air filtration equipment (GPAFE) in the field.
Categorically speaking, there are three types of test methods; namely, real-time
instruments, active sampling followed with an on-site or off-site analysis, and passive
sampling followed with an off-site analysis. This report describes these test methods and
provides a general guideline regarding the use of these test methods for determining the
effectiveness of installed GPAFE in commercial and institutional buildings.
Although real-time instruments arc very expensive(>S 10,000), they provide continuous
and real-time data to monitor the efficiency and service life of GPAFE The real-time
instruments are commercially available for many gases, including ozone, sulfur dioxide,
nitrogen dioxide, formaldehyde, and hydrogen sulfide. The detection limits are typically in
the low ppb range. For volatile organic compounds (VOCs), the real-time instruments that
can measure a wide range of organic compounds at sub-ppb levels or total VOC at low
ppb levels arc not available at this time.
The real-time instruments have been used to measure the removal efficiencies of GPAFE
against ozone, nitrogen dioxide, sulfur dioxide, and formaldehyde in either laboratory or
field studies. However, the users are limited to those research organizations or companies
who can afford them and have the resources and expertise to operate them. Although
extremely desirable, we do not currently expect that the real-time instruments can be a
cost-effective field method for GPAFE testing from the standpoints of building operation
and maintenance. To fulfill the needs, the instruments must be improved from their present
form (bulky and expensive instruments) to small and low cost sensors with the same or
better detection limits.
Active air samplings are the most common methods used today for air samplings. These
methods are very accurate and sampling time is typically one to eight hours. Active
sampling uses pumps and flow equipment to draw air into sampling tubes. After sampling,
the collected contaminants are either analyzed on-site, or sent back for laboratory analysis.
The typical accuracy of active sampling methods is ±5-10%, and the sensitivity is in a few
ppb range. Active sampling test methods are available for VOCs, nitrogen dioxide, oxides
of nitrogen, sulfur dioxide, formaldehyde, and many other gases. The active sampling and
analysis is usually provided by testing laboratories and consulting firms.
Active sampling methods are recommended for measuring initial efficiency of GPAFE
shortly after the installation (for the purpose of performance verification), or checking its
efficiency when there is a need to do so (e.g., significant changes in pollutant loads or
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design conditions). Since the cost of active sampling and analysis is not inexpensive and
sampling time is relatively short (1-8 hours), a good communication and planning among
building engineer, testing personnel, and GPAFE manufacturer is essential in terms of the
intent of testing, what contaminants should be measured, the expected concentration range
of targeted contaminants, the sampling locations, and the timing for sampling.- In addition,
all the relevant data prior to and during air sampling period should be collected (e.g., flow
rate, relative humidity and temperature of airflow through GPAFE) in order to properly
interpret the test results over such a short sampling time.
Passive air sampling is the most cost-effective, easy-to-operate test method for monitoring
the GPAFE performance. It uses the natural process of diffusion to collect contaminants
in the sampler. This straightforward process requires the placement of the passive sampler
in a location of interest (a minimum of flow velocity of 25 fpm is required) and the
allowance of sufficient time for the sampler to collect an adequate amount of contaminants
for analysis. No external devices such as pumps, tubing, flowmeters, calibration kits, or
power sources are needed. Most passive samples are small badges or cartridges which can
be clipped onto a worker's clothes as a personnel monitor or hung in an indoor space as an
area monitor. After sampling, the sampler is sent back to the manufacturer or laboratory
for analysis. Passive sampler methods for VOCs, nitrogen dioxide, and formaldehyde have
been commercially available for many years. Recently, new techniques have been
developed for measuring ozone and sulfur dioxide concentrations, and they are now
commercially available. The typical accuracy for passive sampling methods is ±20-25% for
VOCs and ±10-15% for ozone, nitrogen dioxide, sulfur dioxide, and formaldehyde. The
sensitivity is typically in a few ppb range.
Passive sampling is recommended as a routine test method used by building engineers to
monitor the removal efficiency and service life of installed GPAFE. Essentially, no
training is required except that the proper procedures should be followed regarding
sampling locations, sampling time, storage (if necessary), and packaging (for shipping the
samplers back to manufacturers and analytical laboratories). In most cases, the shipping
can be done by mail, since the samplers are small enough to fit inside an envelope.
It is important to conduct the passive sampling test on a regular basis and to collect all the
relevant data that can affect the GPAFE performance. In this manner, test data collected at
different periods of service time can be plotted to reliably determine when to change the
media used in GPAFE, and to assess the irregular behavior of GPAFE due to the changes
in pollutant loads and environmental conditions.
As one would expect, literature data on the use of in-field methods for GPAFE testing are
almost non-existent in public domain, especially for passive and active sampling methods.
Therefore, it is necessary to conduct Phase 2 of this research project to obtain actual test
data using selected test methods. These data will be used to prepare a complete
documentation on the test protocols that can be implemented by building engineers to
determine and monitor the GPAFE performance.
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1.0 Introduction
Gas-phase air filtration equipment (GPAFE) has many applications in heating, ventilation,
and air-conditioning (IIV AC) systems. In the past, it was used primarily to remove odors
from outdoor ventilation air and corrosive gases for protecting valuable artwork in places
such as museums. Today, GPAFE has much broader applications. Because of indoor air
quality problems in buildings, the use of GPAFE has been expanded to control gases and
vaporous contaminants that are known or suspected to affect human health and comfort.
Furthermore, the sources of gaseous and vaporous contaminants have been linked more
than outdoor ventilation air. More often they are internally generated from building
materials and furnishings, human-related activities, cleaning agents.
For the last five years, significant progress has been made towards the effectiveness of
GPAFE for IAQ control. Research results from both laboratory and field studies (ref. 1-5)
have shown that a well-designed activated carbon adsorber is effective in removing many
common indoor contaminants found in buildings, including volatile organic compounds,
ozone, sulfur dioxide, and nitrogen dioxide. Furthermore, various chemically-treated and
potassium permanganate-based sorbents (ref. 6-7) are shown to have enhanced removal
capacities for inorganic gases and certain low molecular weight organic vapors such as
formaldehyde and hydrogen sulfide. These research results lead us to believe that
GPAFE, when properly designed and applied, can play an important role in improving
indoor air quality in commercial, institutional, and public buildings.
In spite of this, information regarding the selection and testing of GPAFE has been largely
unavailable. As a result, gas-phase air cleaning is not a control method that can be easily
implemented by HVAC engineers at the present time. Many types of GPAFE are
available, and each of them performs differently depending upon its bed depth, packaging
density, particle size, and extent of bypass. To complicate the subject further, various
types of physical and chemical adsorbents are commercially available for use in any given
GPAFE. Because these adsorbents use different mechanisms to remove contaminants,
they may have different responses to the changes of environmental conditions such as
temperature and relative humidity. Although HVAC engineers do not need to know all of
these effects in details, they do need application guides and standard test methods to
properly select GPAFE in the design stage, and to determine and monitor its performance
before and after the installation.
Recognizing these needs, ASIIRAE now has two research projects directed towards these
efforts. ASHRAE 792-RP (ref. 8) aims towards developing standard laboratory test
methods for full-scale (0.6 x 0.6 m) GPAFE. These methods will allow HVAC engineers
to properly select GPAFE in the building design stage.
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The research project 791-RP has a different purpose. It intends to provide education and
information so that an engineer can properly choose, monitor and implement an in-field
test scheme for GPAFE, The evaluation will determine the capacities of installed GPAFE
to properly benefit the structure and its occupants. The information will be used by
HVAC engineers as a guideline to test for gaseous contaminants in the indoor
environment before and after installation of the gas-phase air filtration equipment. Also,
The research will be used to update the ASHRAE Handbook chapter on contamination
control, and will complement in-field use and interpretation of ASHRAE Standard 62-89
and its future version (ref, 9).
As outlined in the Work Statement (ref. 8), the scope of work for Phase 1 is summarized
as follows:
a. Review and summarize pertinent literature regarding in-field testing schemes and
equipment for determining the efficacy of installed gas-phase air filtration equipment, with
particular emphasis on IAQ.
b. Obtain information from manufacturers, suppliers, and HVAC contractors regarding
available GPAFE, methods of installation, and in-field test methods.
c. Prepare a list of in-field test methods that may be used by HVAC engineers, including
application guideline for each method.
d. Make recommendations for Phase 2 of this project including budget estimate, man
hours, investigator qualifications, and equipment needs for conducting actual testing of
installed GPAFE in office buildings.
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2.0 Gas-phase air filtration equipment (GPAFE)
2.1 Types of GPAFE
There are two types of GPAFE commonly used in HVAC systems, panel and pleated
adsorbers. Their salient features are summarized in Table 1.
The panel adsorber is made of a number of panels arranged in a zigzag configuration
within a housing of standard size (0.6 x 0.6 m). Each panel contains granular or pelletized
adsorbents, typically 4x8 mesh or 3-4 mm in diameter. The bed depth typically is 2.5 or
5.1 cm, and in some designs up to 7.6 cm. Each standard size adsorber is normally rated
at 0.94 mVs (2000 cfm) airflow rate. These adsorbers can be placed in a multiple holding
frame or bolted together to form a bank for handling large air flow rates (up to 22.6 m3/s
for side access housing, and front/rear access housing can be used for flow higher than
22.6 m3/s). There is a large variation among the panel type of adsorbers. They differ in
packing styles, residence time, amount of adsorbent, in-line depth (flow direction),
material of construction, and internal design. It is understood that some of these
differences are design variations, intended to meet different application requirements.
However, many differences truly reflect the product quality. For example, the extent of
adsorbent settling and air leakage between the panel and holder as well as in the housing
are the subtle differences in panel adsorbers. These differences can only be detected by
actual testing. The pleated adsorber is made of fabric materials in which small sizes (20
mesh or smaller) of adsorbent particles are embedded. This type of material is also
available in standard size (0,6 x 0.6 m), typically rated at 0.94 m3/s airflow rate. There is
also a large variation among the pleated type of adsorber in terms of adsorbent particle
size, the amount of adsorbent, and the method of containing the adsorbent particles in the
fabric matrix. Although this type of adsorber does not exhibit adsorbent settling problems,
it has its own potential problems, such as uniformity of adsorbent particles in the fibers
and blockage of adsorbent surfaces from the binders. Again, these effects on GPAFE
performance can not be detected without actual testing.
2.2 Types of Adsorbents
A number of physical and chemical adsorbents are commercially available for use in
GPAFE. Since there is no single adsorbent that is effective for all indoor air contaminants,
the choice of adsorbent depends primarily on the prevailing contaminants in a given
application. In some cases, more than one adsorbent is required.
Activated carbon is the most common adsorbent used in HVAC applications. It uses
physical pore-filling adsorption to store VOCs in its micropores (<20 angstroms). The
pore-filling adsorption is a phenomenon where the adsorbed molecules are packed so
tightly in the micropores that it is in a liquid form. Not all activated carbons have equal
adsorption capacity for VOCs, and the difference can be attributed to their micropore size
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distributions arid internal surface areas. For the control of ppb levels of VOCs, it is
advantageous to use activated carbon that is enriched with micropores and ultrafine
micropores (<10 angstroms). The micropores are useful in adsorbing high boiling point,
large molecular weight VOCs, whereas the ultra fine micropores can adsorb low boiling
point, low molecular weight VOCs. Carbon tetrachloride activity (ref. 10) has been the
most common method for rating activated carbons for VOCs removal. Due to the
anticipated ban of chlorinated hydrocarbons, the ASTM D-28 Committee is currently
developing a butane test for replacing the current carbon tetrachloride test.
Activated carbon has also been shown to be effective in removing ppb levels of ozone and
sulfur dioxide by means of various chemical and catalytic reactions (ref. 3).
With a few exceptions, activated carbon has very little capacity for adsorbing gases that
have boiling points below 0 °C. By impregnating activated carbon with appropriate
agent(s), the capacity for removing such contaminants is drastically increased through
chemisorption and subsequent reactions. For example; caustic-impregnated activated
carbons are used to remove acidic and corrosive gases (e.g., hydrogen sulfides,
mercaptans, hydrochloric acid, and nitrogen oxide), acid-impregnated carbons for
ammonia and amines, and sodium sulfide-impregnated carbon for formaldehyde.
Impregnated carbons are often considered as dual adsorbents because of their ability to
remove VOCs via physical adsorption. However, some loss of VOC capacity is expected
due to the blockage of impregnates in the micropores.
Another class of adsorbent is potassium permanganate-based material. This material has
been used in HVAC industry for years, primarily for odor and corrosion control. It uses
oxidation and catalytic reactions to convert certain low molecular weight, and reactive
compounds into water, carbon dioxide, and other products which are retained on the
interior surfaces. This type of material is known to be effective in removing hydrogen
sulfide, sulfur dioxide, low molecular weight mercaptans, and formaldehyde.
Zeolite can also be used to remove VOCs. It is particularly effective with polar VOCs
such as alcohols and ketones. However, it is not commonly used in HVAC application
because of the cost. Some novel catalysts can be used to remove VOCs and inorganic
gases. However, all of them require high temperatures (>150 °C) to achieve high
conversion levels.
2.3 Applications
For general purpose IAQ in office buildings, GPAFE may be installed in main IIVAC
systems to control common indoor gas-phase contaminants that are either internally
generated or brought in from outdoor ventilation air. To accomplish this, GPAFE is
generally located in the mixed-air position of a main air handler to provide cleaned supply
air for the spaces it serves. In terms of relative locations, GPAFE is generally found
upstream of A/C equipment, and downstream of particulate filters. The GPAFE selection
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can be based on required cleanliness level (concentration methods) or equivalent air
concept (ref, 11), whichever is appropriate for a particular application. The GPAFE sizing
is rather straightforward, and it is commonly based upon airflow rate. That is, one 0.6 x
0.6 m GPAFE for 0.94 m3/s. In some cases, the airflow is derated to enhance the
contaminant removal or accommodate the pressure drop limitation.
GPAFE can also be used for odor control. In most cases, odorous gases or vapors are
brought in from outdoor ventilation air. Buildings near petroleum refineries may have
created additional contaminants such as hydrogen sulfide, chlorine, and mercaptans.
Buildings near combustion sources may experience elevated levels of VOCs, nitrogen
dioxide, and carbon monoxide. These are considered as special IAQ applications. To
eliminate these odors, the solutions often require detailed analysis of contaminants and
concentration, and careful selection and sizing of GPAFE,
Whatever the application, GPAFE seldom relies on single-pass efficiency to control indoor
contaminants (except treating 100% outdoor air). Instead multiple passes are used to
reduce indoor contaminant concentrations in conjunction with recirculation air. It can be
shown from a simple steady-state mass balance (ref. 11) that a low efficiency (single-pass)
can provide significant cleaning of indoor contaminants if adequate recirculation air is
provided. On the other hand, a high efficiency GPAFE may not provide adequate cleaning
if the recirculation airflow is very low. Perhaps, this is one of the reasons that there are so
many types of GPAFE (heavy, medium, light duties). Most of them are useful products if
applied properly.
2.4 Performance Variables
There are many variables that can affect the performance of GPAFE. For the purposes of
discussion, we will divide these variables into two groups; design and application
variables. Design variables are the parameters that filter manufacturers use to design their
GPAFE. These parameters include bed depth, packing density, type of adsorbent, particle
size of adsorbent, and residence time at rated flow. Application variables are the
parameters at which GPAFE is operated in a HVAC system. These parameters include
contaminants and their concentration, temperature, relative humidity, and air flow
velocity.
The breakthrough behavior of adsorber under constant conditions is rather straightforward
and predictable. Depending upon the relative length between bed depth and mass transfer
zone, the adsorber can maintain at near 100% removal levels for a period of time before
contaminants start to break through, or contaminants can immediately break through from
the adsorber as soon as the flow is introduced (ref. 1). If an adsorber is operated at a
condition where the bed depth (L) is shorter than the length of mass transfer zone (L%
initial efficiency (single-pass) will be less than 99%, and continuously decreasing with
time. When the bed depth is somewhere between L'99% for a portion of service time, then decreases with
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the remaining service life. When the bed depth is much larger than the length of mass
transfer zone (say L=5L'), the efficiency is maintained at >99% for most of its service life.
This behavior applies to all types of GPAFE and a wide range of contaminants (with the
exception of ozone). However, air leakage through GPAFE is not taken into
consideration. The mass transfer zone is defined as the length of carbon bed where the
concentration of contaminant decreases to, say 1% of its inlet level. Most GPAFE used in
HVAC systems are designed with bed depth equivalent to or shorter than the length of
mass transfer zone. Therefore, their efficiencies are expected to vary with flow velocity,
temperature, and relative humidity. These effects are summarized as follows:
2.4.1 Bed depth - bed depth affects both efficiency and service life of GPAFE. As
illustrated above, the effect on efficiency can be understood from the concept of mass
transfer zone. The effect on service life is related to the amount of adsorbent in the
GPAFE.
2.4.2 Particle size of adsorbent - smaller particle size has faster adsorption rate.
However, it does not affect the equilibrium (or saturation) adsorption capacity of
adsorbent.
2.4.3 Void volume - void volume is the space between the adsorbent particles in a carbon
bed. A carbon bed with higher void volume will have lower efficiency and shorter service
life.
2.4.4 Residence time - residence time, when properly defined, is a very useful parameter
in characterizing the initial efficiency of an adsorber. It is defined as volume of adsorbent
in an adsorber divided by airflow rate passing through the adsorber. Residence time is a
lumped parameter of three design variables; bed depth, void volume, and total face area of
adsorber. The use of residence time for determining initial efficiency of an adsorber must
take adsorbent particle size into consideration. For panel types of adsorber, a residence
time of 0.1 seconds is required to cover the mass transfer zone for 4x8 mesh coconut shell
activated carbon (ref. 1), which is commonly used in HVAC industry. In general, pleated
adsorbers require less residence time to achieve the same efficiency due to the use of
smaller particles. When the same adsorbent is used, residence time can also be used as an
indicator for service life of an adsorber. An adsorber with longer residence time will have
longer service life. The residence time for panel type of adsorber is 0.02-0.1 seconds, and
0,001-0.03 seconds for pleated type of adsorber.
2.4.5 Temperature - the effect of temperature depends on the removal mechanism of
GPAFE. For physical adsorption of VOCs, an increase of temperature will result in a
decrease of adsorption capacity. On the other hand, temperature can enhance the removal
capacity of contaminants when oxidation or catalytic reactions are the principal removal
mechanisms. In HVAC systems, air temperature itself is not expected to have a significant
effect on GPAFE performance since the variation is generally small. However, a
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corresponding change in relative humidity will have a more pronounced effect on the
GPAFE performance.
2.4.6 Relative humidity - again, the effect of relative humidity depends on the removal
mechanism of GPAFE. For physical adsorption of VOCs, the adsorption capacity of
activated carbon can be significantly reduced in the presence of high relative humidity.
When relative humidity exceeds 50%, significant adsorption of water vapor can occur in
activated carbon. As this happens, the carbon capacity for adsorbing VOCs will be
reduced since both water vapor and VOCs are competing for the same adsorption space,
or micropore volume. However, the extent of this effect depends on the affinity of water
vapor towards the surface of activated carbon relative to VOCs. It has been known that
not all activated carbons have the same affinity for water vapor. Based on the VOC
loading analysis of in-field carbon samples serving HVAC applications (ref. 2), the VOC
adsorption capacity of a coconut shell activated carbon is about 10-15% by weight when
water loading is less than 5% (i.e., <50% relative humidity), and 5-10% when water
loadings exceed 15% (i.e., >60% relative humidity).
For impregnated carbons or other chemical adsorbents, the effect of relative humidity is
specific to the chemistry between impregnate and contaminant. In some systems, relative
humidity has a beneficial effect. For example, the adsorbed water can enhance the
oxidation reaction of potassium permanganate for hydrogen sulfide removal (ref. 12). In
other systems, relative humidity has no effect. For example, the neutralization reaction
between caustic-impregnated carbon and hydrogen sulfide is not influenced by the
presence of water vapor, except in the extreme cases (ref. 13).
2.4.7 Flow velocity - higher flow velocity will decrease the single-pass efficiency of an
adsorber. However, the effect is not a linear relationship. This is a very important point in
recirculation air cleaning. In these systems, the increase of airflow will actually result in a
net increase of contaminant removal rate. This can be understood by the fact that the
contaminant removal rate is determined by the product of recirculation flow rate and
single-pass efficiency of adsorber. In recirculation systems, airflow rate will have no
noticeable effect on adsorber service life. Increasing recirculation rate will result in high
contaminant rate; therefore, lower inlet concentration to the adsorber. The reverse is true
for lowering the recirculation flow rate. In both cases, the net result is the same, that is,
no noticeable change in contaminant load to the adsorber.
2.4.8 Contaminant concentration - all GPAFE will have a longer service life at lower
concentration if all other variables are held constant. However, no GPAFE will have a
proportional increase of service life as concentration decreases. This is because the
adsorption capacity of any adsorbent decreases, but not in a linear relationship, with
decreasing concentration of contaminant. For physical adsorption of VOCs, the extent of
this effect depends .on boiling point of compound, concentration range, and micropore size
distribution of activated carbon (ref. 14). For chemisorption of inorganic gases, the
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adsorption capacity of chemical sorbents also may vary with concentration, the extent of
the effect depends on gases and environmental conditions (temperature and relative
humidity) (ref. 12).
2,5 GPAFE performance under dynamic building operations
We have just discussed the individual effects of various variables on the performance of
GPAFE. This information is useful for understanding the basic behavior of GPAFE;
however, it does not folly describe the actual performance of GPAFE under dynamic
building operations. This is one of the reasons why in-field test methods are needed to
determine and monitor the performance of GPAFE in buildings.
Inevitably, GPAFE, after being installed in a building, will be challenged with the
everlasting changes in pollutant loads and environmental conditions according to ambient
conditions, mode of IIVAC operation, occupant activity, and contaminant sources.
Among these factors, the most noticeable variables are relative humidity and contaminant
concentration. In the following, we will discuss the expected responses of GPAFE under
the swings of these two variables, with particular emphasis on VOCs.
2.5.1 Relative humidity swing - since physical adsorption of VOCs is a reversible
process, activated carbon may continue to adsorb more VOCs from an air stream or
release adsorbed VOCs back to an air stream. This depends on the loading it already has
and its saturation adsorption capacities at various relative humidity levels. To illustrate it,
let us assume that the saturation capacity is 10% at 50% relative humidity (RTI) and 5% at
70% RII. We further assume that a carbon adsorber initially operates at 50% RH, and it
has 2% VOC loading after a period of time. After that, RH is suddenly increased to 70%.
As a result, a decrease of removal efficiency will occur. However, the carbon will
continue to adsorb VOCs since the current VOC loading (2%) is less than its saturation
capacity at 70% RH, which is 5%. Let us assume this adsorber continues to operate at
70% RH until the loading reaches its saturation capacity. At this point the adsorber
efficiency becomes zero (relative to 70%). After that, the relative humidity is back to
50%. As a result, the adsorber will again adsorb more VOCs since the current loading
(5%) is less than the new saturation capacity, which is 10%. Let's say the adsorber
continues to operate at 50% RH until the loading reaches its saturation capacity (10%),
and the adsorber efficiency becomes zero again (relative to 50%). After that, RH
increases to 70%. As a result, the VOCs will desorb, since the current loading (10%)
exceeds the new saturation capacity (5%).
In summary, the adsorber efficiency will respond to the change of relative humidity, but
the effect is reversible. In order to minimize this effect, the residence time of an adsorber
must be long enough so that the mass transfer zone is significantly shorter than the bed
depth of adsorber.
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Certain chemical adsorbents are expected to be affected by the swing of relative humidity.
However, the desorption of contaminants (negative efficiency) is unlikely since
chemisorption is an irreversible process.
2.5.2 Concentration swing - the concentration swing follows the same principle we have
just discussed. However, the effect is expected to be less pronounced as compared to
relative humidity swing, Generally speaking, a significant change in concentration is
required to cause a noticeable effect. However, these conditions may occur during a
building operation. An example of this is high concentration emission of VOCs during a
painting activity. In these situations, a carbon adsorber may work as a capacitor to reduce
the peak concentration. This is to say, a carbon adsorber that has no capacity left for
removing ppb levels of VOCs, can still be very effective to remove ppm of VOCs. On the
other hand, the desorption of VOCs may occur when clean air passes through a carbon
adsorber which is previously saturated with ppm level of VOC. However, the extent of
desorption is highly related to carbon particle size.
3.0 Existing test methods
There is a variety of methods and techniques available to measure the presence and
concentrations of gaseous and vaporous contaminants in indoor environments. Methods
commonly used for indoor air testing include the modified OSHA methods, the EPA test
methods for ambient air quality measurements (ref. 15 and 16), the NIOSH methods for
non-industrial indoor environments (ref. 17 and 18), and ASTM test methods for indoor
environments (ref. 19).
These test methods may be classified into three basic categories; real-time or on-line
instruments, active sampling methods, and passive sampling techniques. Although all of
these methods can be directly applied to the testing of gas-phase air filtration equipment
(GPAFE), the selection of methods often depends on cost of testing and application needs.
The representative equipment used for these test methods are shown in Figure 1.
3.1 Real-time instruments
Table 2 summarizes the real-time instruments for measuring common indoor gaseous
contaminants.
3.1,1 Ozone, sulfur dioxide, and nitrogen dioxide - the real time instruments for
monitoring ppb levels of ozone, sulfur dioxide, and nitrogen dioxide are well-developed.
These instruments provide excellent reliability, accuracy, detection limit, and data
acquisition and communication capability. Since they are contaminant-specific, three
individual instruments are required to measure the concentrations of ozone, sulfur dioxide,
and nitrogen dioxide. The continuous measurement of ppb levels of ozone is based on the
absorption of ultraviolet radiation at 254 nm wavelength. The measurement of sulfur
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dioxide is commonly based on pulsed fluorescence technique, and nitrogen oxides (NOx) is
based on chemiluminescence technique. The operation principles of these real-time
instruments are available from the manufacturers (ref. 20) and will not be discussed here,
3.1.2 VOCs - real-time instruments for measuring a wide range of VOCs at sub-ppb
levels or total VOCs (TVOC) at ppb levels are not available at this time. However, some
real-time instruments can provide excellent detection limits for specific classes of organic
compounds. Semiconductor gas sensors and Fourier transform infrared remote sensing
appear to be the emerging technologies for detecting ppb levels of VOCs. Semiconductor
gas sensor (ref. 21) is a tiny catalytic converter, measuring the change in conductivity as
organic vapors are converted to carbon dioxide and water. These semiconductor-based
sensors are currently marketed as IAQ sensors for building control. However, major
efforts will have to be made before it can be used for GPAFE testing, namely; internal
calibration with a standard VOC, an internal compensation for relative humidity and
temperature effects, and an order of magnitude improvement in detection limit. Fourier
transform infrared remote sensing (ref. 22) has demonstrated its applicability for
measuring ppb levels of many individual VOCs in office buildings.
3.1.3 Corrosive Gases - these wall-mounted or hand-held sensors (ref. 23) were
developed to determine the corrosion potential of controlled environments where
computers and electronic equipment are located to control a manufacturing process. These
sensors measure the film thickness of copper or silver via the change of resonance
frequency on the quartz crystal microbalance (QCM), Each copper or silver-plated crystal
has a natrual resonance frequency based on its mass. As corrosion films form on the
crystal, the mass increases by the reactions between corrosive gases and copper (or silver).
As a result, the resonance frequency decreases. By using proper conversion factors, the
corrosion rates thus can be determined. The amount of corrosion formed film thickness
depends upon the nature of contaminant, concentration of corrosive contaminant,
exposure time, and environmental factors such as humidity and temperature. The ISA
(Instrument Society of America) Standard S71.04 (ref. 24), provides four environmental
classes (Gl, G2, G3, and GX) according to the film thickness on a copper coupon. In
each environmental class the maximum allowable concentration is specified for each
corrosive gas such as hydrogen sulfide, ozone, chlorine, sulfur dioxide, nitrogen dioxide,
and ammonia.
3.1.4 GPAFE test results - Real-time instruments have been used for GPAFE testing.
Battelle (ref. 7) conducted laboratory testing on a full-scale (0.6 x 0,6 m) GPAFE for
ozone, sulfur dioxide, nitrogen dioxide, and formaldehyde. The test was conducted in a
duct under controlled conditions. Before introducing the challenging gases into the test
duct, the test air was cleaned with prefilters, both particulate and gas phase, to establish an
acceptable background level. All of the challenging gases were injected at sample port
upstream of GPAFE at constant concentrations. The sulfur dioxide and nitrogen dioxide
were supplied from high pressure cylinders. Flow of these gases was metered through
mass flow controllers and passed through 0.63 cm teflon tubing to the injection port at
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very low flow rates so that their respective concentrations were in the desired ppb levels in
the test duct. Ozone was introduced by passing a metered flow of approximately 500
cc/min of ultra-high purity air through an electrical discharge ozone source, and then into
the test air. Formaldehyde was introduced as a dilute aqueous solution by means of a
syringe drive, through a heated probe which caused vaporization of the formaldehyde
solution. The standard deviations of challenging concentration generated by the above-
mentioned methods were 6.7-13% for ozone, sulfur dioxide, and nitrogen dioxide, and
24% for formaldehyde.
The flow rate of test air was also maintained at a constant level (0.47 m Vs ±1%) using a
blower with a variable speed motor. The temperature and relative humidity were not
controlled. However, since the room air was used, the variations of temperature and
relative humidity were small (18-20 °C and 50-55%, respectively) during the test period.
The GPAFE tested was of carbon impregnated filter type (contains 3-5 kg 20x60 mesh
impregnated carbon). A total of seven filters arranged in series were used to treat 0.47
m3/s air flow.
The sulfur dioxide concentrations upstream and downstream of the GPAFE were
continuously monitored by Thermo Environmental Model 43-S, which is a high-sensitivity
version of the Thermo Environmental Model 43-A. The detection limit is 0.1 ppbv.
Ozone was monitored by the Thermo Environmental Model 49 with a detection limit of 1
ppbv. Both instruments are designated by the EPA as an equivalent method used for
measuring ambient pollutants (ref. 25). The LMA-3 monitor (ref. 26) was used for
nitrogen dioxide. This is a relatively new instrument which provides extremely high
sensitivity for nitrogen dioxide in a compact and rugged package. Formaldehyde was
monitored by Battelle-developed instrument (ref. 27), which has been used for extensive
sampling of indoor and outdoor air. The performance of the GPAFE was continuously
monitored for 80 hours.
As one would expect, these instruments have proven to be valuable tools in monitoring the
GPAFE performance under dynamic conditions. Since they are real-time instruments, any
effects on GPAFE performance resulting from changes in environmental conditions
(temperature, airflow, and relative humidity) and challenge concentrations, can be
instantaneously detected. For example, about 50 hours into the test, the relative humidity
suddenly dropped to about 40% as a cold front passed through the test site, bringing cold
and dry air into the region. As the relative humidity dropped to 40%, there was a
corresponding increase of S02 concentration downstream of GPAFE. At a later time, the
downstream S02 concentration returned back to the previous level when relative humidity
is adjusted to within the test conditions (50-55%). This instance demonstrates that a real-
time instrument is a valuable tool in monitoring the GPAFE performance, especially in
environments where frequent variations in environmental conditions as well as pollutant
load are expected. If not for the real time instruments, the sudden increase of S02
downstream concentration might have been interpreted as a breakthrough, instead of what
turned out to be a spike as a result of humidity change.
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Since 1990, Weschler et ai, (ref. 3) at Bellcore has been conducting an on-going study to
monitor the performance of GPAFE in a quite large clean room. A total of 12 activated
carbon adsorbers were installed in the air-handling unit servicing the cleanroom. Each
adsorber contains 12 panels arranged in a zigzag configuration within a housing, and each
panel contains 3.4 kg of virgin coconut shell carbon rated at 60% carbon tetrachloride
activity. The air-handling unit treats only outside air; no recirculation air passes through
the unit. The air flow through this unit is 10.2 nvVs. Filters with ASHRAE dust spot rating
of 30% were installed upstream of the carbon adsorbers, and filters with ASHRAE dust
spot rating of 85% were installed downstream of the carbon adsorbers.
Three gas-phase contaminants were monitored: ozone, selected VOCs and sulfur dioxide.
Only the measurements of ozone and sulfur dioxide will be discussed here (the VOCs
measurements will be discussed in Section 4.3). Ozone concentrations were measured
with an ultraviolet (UV) photometric analyzer (254 nm: sensitivity: 1 ppb; precision: ±1%
or 1 ppb, whichever is greater), sulfur dioxide concentrations were measured with a
pulsed flourescent analyzer (range: 0 to 500 ppbv; sensitivity: 1 ppbv; precision: ±1% or 1
ppbv, whichever is greater).
Since ozone and sulfur dioxide are outdoor pollutants in this test site, the indoor and
outdoor concentrations were measured, and the effectiveness of the carbon adsorber is
expressed as indoor/outdoor concentration ratio.
After one year of continuous service, the test results indicate that the I/O concentration
ratio for ozone remains to be 0.1. This ratio was 0.7 prior to the installation of the carbon
filters. After three years service, the ozone I/O ratio increased to 0.2-0.25. For sulfur
dioxide, the I/O ratio is less than 0.1 after 17 months of the installation, and the I/O ratio
is independent of outdoor sulfur dioxide concentration.
3.2 Active sampling methods
Various active sampling methods are available for measuring ppb levels of concentrations
of many inorganic gases and organic vapors. These methods employ sorption tubes or
canisters and pump to collect air samples. Subsequently, the sorbent tubes/canister are
either analyzed at the test site, or sent back to a testing laboratory for contaminant
analysis. Active sampling methods are often used by building researchers, consultants, and
analytical labs for IAQ investigation and diagnostics. Table 3 lists the active sampling
methods for various gases and vapors.
3.2.1 VOCs - there are three basic techniques for active sampling of airborne VOCs;
solvent impingers, evacuated canisters with cryogenic trapping, and solid adsorbents.
Solvent impingers are seldom used due to their lack of sensitivity. Therefore, only the last
two sampling methods will be discussed;
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3.2.1.1 Evacuated canister - ASTM D 5466 (ref. 28) describes a standard testing method
for VOC sampling using evacuated canister technique. The canister sampling can be done
in pressurized or subatmospherie modes. A sample of air is drawn through a sample train
comprising components that regulate the rate and duration of sampling into a precleaned
and pre-evacuated passivated canister. After the air sample is collected, the canister is
transported to a laboratory for analysis. Upon receipt at the laboratory, the canister is
attached to a pressure gauge to measure the final canister pressure. The water vapor
collected in the canister may be removed by a Nafion dryer. Before the analysis, The
VOCs collected in the canister are concentrated in a cryogenically-cooled trap. The
cryogen is then removed and the temperature of the trap is raised. The VOCs are
revolatilized and separated by a GC column, then detected by a mass spectrometer.
This sampling method is applicable to concentration of VOCs ranging from the detection
limits of GC/MS used to 300 ppb by volume. Above this concentration, the sampling
requires dilution with dry ultra high purity nitrogen or air. This sampling method is
particularly well suited for the collection and analysis of complex VOC mixtures and is not
subject to high volatility limitations. Subatmospherie pressure sampling maybe used to
collect grab samples (duration of 10 to 30 seconds) or time-integrated samples (duration
of 12 to 24 hours) taken through a flow-restrictive inlet (for example, mass flow
controller, vacuum regulator, or critical orifice). Pressurized sampling is used when long-
term integrated samples or higher volume samples are required. The sample is collected in
a canister using a pump and flow control arrangement to achieve a typical 103-206 kPa
(15-30 psig) final canister pressure. For example, a 6-L evacuated canister can be filled at
7.1 cm3/min for 24 h to achieve a final pressure of about 144 kPa (15 psig).
For those applications where a membrane dryer is used, difficulties may arise in sample
analysis if moisture accumulates in the dryer. This problem can be eliminated by a
cleaning procedure that periodically heats the dryer to about 100 °C while purging with
high purity air. Contamination may occur in the sampling system if canisters are not
properly cleaned before use. Additionally, all other sampling equipment (for example,
pump and flow controllers) must be thoroughly cleaned to ensure that the filling apparatus
will not contaminate samples. In addition, sufficient system and field blank samples shall
be analyzed to detect contamination as soon as it occurs. Instructions for cleaning the
canister and certifying the field sampling systems are described in ASTM D 5466-93
Section 11.1 and 11.2 (ref. 28). Collection of pressurized samples in humid environments
may result in condensation of water in sampling canisters. This water may prevent the
recovery of polar compounds from the canister.
3.2.1.2 Solid adsorbent - the active sampling of VOCs can be accomplished by means of
adsorption on porous materials such as activated charcoal, tenax, carbon molecular sieves,
or graphitized carbon black using an adsorbent tube and a small portable sampling pump.
The sampling procedure involves the collection of air sample into the adsorbent tube at a
known rate through the pump for a fixed period of time. Then the tube with collected
VOCs is sent back for GC (gas chromatography)/MS (mass spectrometry) analysis.
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The most common adsorbents used in sampling VOCs are activated charcoal and tenax.
The size of charcoal tube ranges from 100/50 to 800/400 mg. which means that the tube is
divided into two sections with the front section containing 100 to 800 mg of activated
charcoal and the back section containing 50 to 400 mg of activated charcoal. The 100/50
mg tube is most frequently used in sampling VOCs. Although activated charcoal is
effective in collecting various VOCs, the collection efficiency can be affected by moisture
present in the air sample. It is known that moisture level (>60% relative humidity) can
reduce VOC adsorption capacity by as much as 50%, especially for low boiling point
compounds. The other problem is sampling polar and reactive organic compounds, some
of which may undergo chemical reactions on the charcoal surfaces to form other species.
In addition, the thermal desorption of high boiling point compounds is not always
quantitative. Tenax, on the other hand, is a chemically inert material and effective in
sampling high boiling point compounds, but ineffective for sampling low boiling point
VOCs (<70-80 °C). Tenax also suffers moisture effect, perhaps to a lesser extent than
activated charcoal.
To collect a wide range of organic compounds in indoor environments, a multisorbent
tube that contains several complementary materials should be used. One such sampler
which contains a combination of Tenax-TA, Ambersorb XE-340, and activated charcoal
has been used to characterize indoor VOCs in office buildings (ref. 29). Another kind of
multisorbent tube (Figure 2) has also been used for sampling VOC in a product emission
study (ref. 30) This multisorbent tube contains carbotrap (graphitized carbon black, 12
m2/g), carbotrap (graphized carbon black, 100 m2/g), and carbonsieve S-l 11 (carbon
molecular sieve, 800 nr/g).
After VOCs are collected in a sorbent tube, the collected VOCs must be recovered before
being injected into GC/MS for analysis. Solvent extraction and high temperature
desorption are the two most common methods used for the recovery of collected VOCs
from the sampler. The identification and quantification of VOCs is done by GC/MS
analysis. For analysis, the GC with a mass-spectrometric detector can be set to operate in
the full scan mode or SIM mode. The GC/MS is set up for automatic and repetitive
analysis. The system is comprised of a GC with a capillary or equivalent column for gas
separation. The system also includes computer and software for data acquisition,
reduction, and reporting. The column equipped in GC separates a VOC mixture as each
compound elutes from the column at different times. This column separation is operated
based on the principle of physical adsorption. As the VOC mixture passes through the
column, the compounds will break through from the column in the order of increasing
boiling point and decreasing order of polarizability of compound. The identification of
compound is done by the retention time of the peak associated with each compound. This
compound identification is often aided by a library database. When operated in full scan
mode, qualitative identification can be confirmed and quantitative identification can be
made for targeted compounds. The presence of other compounds not on the analytical
target list may also be determined qualitatively. Full scan mode limits sensitivity to the
range of 1 to 5 ppb by volume for most applicable compounds. In the SIM mode,
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detection limits can be a factor of 10 or lower, approaching the same sensitivity as a GC
multidetector system. However, SIM flexibility is limited because the MS is programmed
to acquire data for a limited number of ions characteristic of targeted compounds while
disregarding other acquired information. Therefore, the GC/MS-SIM procedure provides
quantitation of a restricted targeted compound list of VOCs.
3.2.2 Formaldehyde - both EPA (ref. 31) and ASTM (ref, 32) provide standard test
methods for determination of formaldehyde and other carbonyl compounds in air. Both
methods are similar and use active sampler methodology. The method, specific to
formaldehyde, can with some modifications, also detect many other types of aldehydes and
ketones. This method uses an absorbing agent, 2,4-dinitro-phenylhydrazine (DNPH) to
collect formaldehyde. By reacting with DNPH in an acidic environment, formaldehyde is
readily converted to a stable DNPH derivative. This derivative is analyzed using high
performance liquid chromatography (HPLC), equipped with an ultraviolet (UV)
absorption detector operating at 360 nm. Formaldehyde or other carbonyl compounds in
the sample are identified and quantified by comparison of their retention time and peak
height, or peak areas with those of standard solutions.
The test begins with drawing a known volume of indoor air through a prepacked silica gel
cartridge coated with acidified DNPH, at a sampling rate of 0.5 -1.2 L/min. for an
appropriate period of time. After sampling, the sample cartridges are capped and placed
in borosilicate glass culture tubes with polypropylene caps. The capped tubes are then
placed in a friction-top can containing a pouch of charcoal and returned to the laboratory
for analysis. Alternatively, the sample vials can be placed in a thermally-insulated box with
appropriate padding for shipment to the laboratory. The cartridges may either be placed in
cold storage until analysis, or immediately washed by gravity fed elution of 6 cm3 of
acetonitrile from a plastic syringe reservoir to a graduated test tube or a 5 cm3 volumetric
flask. The elute is then diluted to a known volume and refrigerated until analysis.
The DNPH method is suitable for determination of formaldehyde in the concentration
range of low ppb to low ppm. It can be used for long-term (1-24 hour) or short-term (5
to 60 min) sampling of indoor air for formaldehyde. The sampling flow rate usually ranges
between 0.5 and 1.2 L/min.
This test method has been used by two different laboratories to make over 1500
measurements of formaldehyde and other aldehydes in ambient air for the EPA Urban Air
Toxics Program (UATP), conducted in 14 cities throughout the Unite States. The
precision of 45 replicate HPLC injections of a stock solution of formaldehyde-DNPH
derivative over a two-month period has been shown to be 0.85% relative standard
deviation. Triplicate analysis of each of twelve identical samples of exposed DNPH
cartridges provided formaldehyde measurements that agreed within 10.9%. The absolute
percent differences between collocated duplicate sample sets from the 1988 UATP
program were 11.8% for formaldehyde.
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3.2.3 Nitrogen dioxide - the active sampling of nitrogen dioxide in indoor or ambient air
is often accomplished by a colorimetric method based on the Griess-Saltzman reaction,
ASTM D 1607 (ref. 33) describes such an active method.
For air sampling, assemble a fritted-tip bubbler (absorber) along with a mist eliminator,
flow meter, pump, and mist eliminator. The fritted-tip bubbler contains 10 mL of
absorbing agents (prepared by dissolving 5 g of anhydrous sulfanilic acid in one liter of
water containing 149 mL glacial acetic acid). Draw an air sample through it at the rate of
0.4 L/min, long enough to develop sufficient color (about 10 to 60 min.). Measure the
total air volume sampled, temperature and pressure (for air volume correction, if
necessary). After sampling, development of the red-violet color is complete within 15 min
at room temperature. Transfer to a stoppered cuvette and read in a spectrophotometer at
550 nm, using distilled water as a reference. If colors are too dark to read, unexposed
adsorbing agent may be used to dilute the colors. Then multiply the measured absorbance
by the dilution factor.
When sampling is conducted with fritted-tip bubblers, this test method is valid for
determining nitrogen dioxide concentrations between 4 and 10 mg/m3 (0.002 and 5 ppm).
The standard deviation of results obtained from a single analyst on separate samples from
the same flowing air stream is 0.524 C 1/2 (C from 10 to 400 pg/m3). Where C is
concentration of nitrogen dioxide in pg. The standard deviation of single analyses, obtained
from different laboratories taking separate samples from the flowing air stream is 0.517 +1.27
C m (C from 16 to 400 pg/nf).
For high concentration applications (>5 ppm), the active sampling of nitrogen dioxide can
be accomplished using the phenol-disulfonic acid colorimetric procedures (ref. 34).
3.2.4 Sulfur dioxide - the active sampling for sulfur dioxide is also commonly carried out
by colorimetric methods (see Figure 3). Sulfur dioxide is absorbed by aspirating a
measured air sample through a tetrachloromercurate (TCM) solution, resulting the
formation of a dichlorosulfonatomercurate complex. After the absorption is completed,
any ozone in the solution is allowed to decay. The liquid is treated first with a solution of
sulfamic acid to destroy the nitrite anion formed from the absorption of oxides of nitrogen
present in the atmosphere. It is treated next with solutions of formaldehyde and specially
purified acid-bleached pararosaniline containing phosphoric acid to control pH.
Pararosaniline, formaldehyde, and bisulfite anion react to form the intensely colored
pararosaniline methyl sulfonic acid.
In a 1-hour sampling, add 10 mL of TCM solution to a midget impinger and insert it into
the sampling system (see Figure 3). Collect the sample at approximately 0.5 L/min for 1
hour, using either a critical orifice or a needle valve to control flow. Shield the absorbing
reagent from direct sunlight during and after sampling by covering the impinger to prevent
deterioration. Keep the temperature of the absorbing solution below 25 °C. If the sample
must be stored before analysis, maintain the temperature at 5 °C in a refrigerator. The 24-
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hour sample procedure is similar to 1-hr sampling, except for the difference in amount of
TCM solution (50 mL) and flow rate (0.2 L/min).
This test method is applicable in determining sulfur dioxide concentrations ranging from
approximately 25 ftg/m3 (0.01 ppm) to 1000 ng/m3 (0,4 ppm). The limit of detection,
corresponding to twice the standard deviation, is 4 pg/m3 in a 24-hr sample, or 7 pg
S02/m3 in a 1-h sample.
3.3 Passive sampling methods
Passive sampling techniques use a natural process called diffusion to collect air
contaminants into the sampler. This collection process is done without any external
devices such as pump, battery or tubes. Driven by the concentration difference, diffusion
brings gaseous or vaporous contaminants from air into the sampler, and the contaminants
are collected by the adsorbent or chemical reagent in the sampler. After a period of
sampling time, the samplers are sent to testing laboratories and the collected contaminants
are recovered and analyzed. Table 4 summarizes the passive sampling methods for
various gaseous and vaporous contaminants.
The passive sampling methods were originally developed for monitoring the worker's
exposure in industrial settings, and the sampling guidelines provided by manufacturers are
geared towards OSHA and ACGIH (American Conference of Governmental Industrial
Hygienists) standards. However, with some modifications in sampling time, these passive
sampling methods are equally applicable to indoor air quality applications in commercial
and institutional buildings.
3.3.1 VOCs - the passive VOC sampler generally consists of a diffusion screen (white
film), a spacer, and a charcoal (activated carbon) sorbent pad assembled in a disk shaped
plastic holder. The sampler can be clipped to the worker's lapel or pocket near the
breathing zone to measure personal exposure, placed in a particular location to measure
the VOC concentration in that space, or placed upstream and downstream of GPAFE to
measure the removal efficiency.
Each VOC sampler comes sealed in an aluminum can. Sampling begins by removing the
monitor from the can and recording the time. After sampling, the white film on the face of
the monitor is removed and replaced with an impermeable cap; the time is again recorded.
Samplers are typically analyzed soon after sampling. During the sampling period, the
monitor should be placed at a location with adequate air movement (at least 25 fpm).
Stagnant air at the face of the sampler will result in nonrepresentative sampling.
The sampling time of VOC passive monitor depends upon the VOC concentrations in air.
For the compliance of OSHA or ACGIH standards in industrial environments, typical
sampling time is 8 hours, chosen to be consistent with the TWA values (8-hour work day).
However, for indoor air quality applications in commercial and institutional buildings, the
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sampling time is typically extended to one-four weeks. The reason for this is that the
VOC concentration is at least three orders of magnitude lower than the concentrations
encountered in industrial applications.
After the completion of sampling, the collected VOCs in the samplers are desorbed using
the extraction method. In most cases, carbon disulfide is used. Typically, this extraction
procedure is conducted by placing the charcoal pad in a vial into which 1-2 mL carbon
disulfide is added, then the vial is gently vibrated for 30-60 mins to desorb VOCs from the
charcoal pad. After the extraction, a 1 or 2 pL aliquot is injected into GC/MS for VOC
analysis.
The VOCs data from the GC/MS analysis are reported as the weights (ug) of individual
organic compounds that are collected during air sampling. By knowing the sampling rate,
sampling time, recovery coefficient, and the weight collected, the concentration of a
particular compound can be calculated .
The validity of passive organic monitors for indoor air applications has been studied
extensively. Cohen et al.(ref. 35) conducted a set of controlled chamber experiments to
validate the passive samplers (3M OVM (Organic Vapor Monitor) 3500) for five
compounds (chloroform, benzene, heptane, perchlorethylene, and dichlorobenzene), two
concentration levels (10 and 100 pg/m3) and two relative humidity levels (20 and 70%).
Shield and Weschler (ref. 36), conducted a field study by using passive sampler (3M OVM
3500) to monitor VOCs concentrations in telephone switch offices (New Jersey). The
results of these two studies indicated that the accuracy of passive VOC samplers is
typically ± 25% with 95% confidence level. One interlaboratory study was conducted in
Europe by De Bortoli et al.(ref. 37), where the OVMs were exposed for four days to
concentrations ofbutanol, xylene, pinene, and decane from 25 to 1500 jig/m3. Except for
butanol and pentanol all deviations between the passive and active measurement were less
than 21 percent. The deviation between the predicted value and the passive measurement
ranged between -34 and +15 percent for all compounds except butanol and pentanol. The
errors arise from the loss of contaminants during collection and recovery. The study
conducted by Seifert and Abraham (ref. 38) has shown that the 3M OVM passive
samplers can be used as valid sampling techniques for a wide range of VOCs. This group
exposed the samplers in a chamber for a 2-week period and measured concentration that
varied from predicted by between 1 and 22 %.
Based on the analysis of blank sample, Shield and Weschler (ref. 36) assessed that the
detection limit would be 0.06 pg/m3 for compounds with boiling point higher than 175 °C.
This is based on the assumption that a value three times the blank value is required for
unambiguous detection. This detection is low enough to allow passive sampling
technique to measure the indoor concentration of most organic compounds .
Passive VOC samplers have been used to monitor the removal efficiencies of GPAFE in
the field. In the Weschler study (ref. 3), selected VOCs were measured using passive
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samplers (3M OVM 3500, accuracy: 25%, reproducibility: 13% of the mean value,
sensitivity: 0,06 jig/m3).
For measuring VOCs removal efficiencies, three replicate passive samplers were placed
upstream of the carbon adsorber, and another three samples downstream of the carbon
adsorber. The single pass efficiency of adsorber is calculated from the difference in
concentration measured upstream and downstream of the carbon adsorber. For subsequent
collection periods, the samplers were positioned identically. The sampling time is 4-6
weeks , Prior to the VOC analysis, each passive sampler was spiked with an internal
standard and then extracted with 1 mL of carbon disulfide solution. Organic compounds
contained in the extract were separated and identified using standard GC/MS procedures.
The single-pass efficiencies of the carbon adsorber for selected VOCs are in the range of
60-90% after one year of continuous service (ref. 36).
3.3.2 Formaldehyde - ASTM D 5014-94 (ref. 39) describes a standard test method for
measurement of formaldehyde in indoor air using passive sampler methodology. In this
method formaldehyde is collected in a diffusion tube and analyzed by a colorimetric
method using 3-methyl-2-benzothiazolinone hydrazone hydrochloride (MBTH).
During sampling, formaldehyde is absorbed into a 0.05% aqueous solution of MBTH
contained in a glass vial, which comes with a septum cap that retains a Knudscn disk.
During air sampling the vial is inverted to establish contact between the absorbing liquid
and the Knudsen disk. Formaldehyde diffuses from the ambient atmosphere into the
MBTH solution through the Knudsen disk at a constant rate. After collection, the
resulting azine is oxidized by a ferric chloride-sulfamic acid solution to form a blue
cationic dye in acidic medium. The concentration of the blue cation is measured by
colorimetry at 628 ran. The concentration of formaldehyde is computed from the amount
of formaldehyde collected divided by the product of the diffusion rate and the time of
exposure.
At heart of this test method lies the Knudsen disk, which provides a constant sampling rate
of formaldehyde. This disk is also a gas barrier that prevents the interference of other
aldehyde compounds. The Knudsen disk is made of polytetrafluoroethylene membranes
of 0.07 mm thickness and 0.02 jim pore sizes. Using the prescribed sampler, the Knudscn
disk allows the ambient atmosphere to be sampled for formaldehyde at a constant rate of
approximately 11,6 mL/min independent of air flow velocity ranging from 0.13 to 1.3 m/s
(25 to 250 ft/min). The sampling rate normally is provided by the supplier of the Knudsen
disks, but may also be determined experimentally in accordance with the procedures
described in ASTM D5014-94, Section 10.3.
This test method allows field measurement of formaldehyde in indoor air at concentrations
from 0.01 to 17 mg/m3 (0.008 to 14 ppm) using sampling times between 15 mins and 24
hours. A 24-hour sampling time is recommended to measure time-weighted average
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formaldehyde concentration ranging from 0,01 to 0.2 mg/m3 (0.008 to 0.16 ppm, v/v) in
offices and residences. An 8-h sampling time allows measurement ranging from 0.03 to
0.6 mg/m3 (0,025 to 0.5 ppm, v/v). The test method is suitable for both area and personal
monitoring. In addition, this test method allows sampling and quantification of
formaldehyde under field conditions with the aid of a portable field colorimeter, without
any laboratory support.
The MBTH method of analysis was checked for reproducibility by three different
laboratories. The results agreed within ±5%. During the development of this test method,
five independent sets of ten samplers were each exposed to laboratory test atmospheres of
formaldehyde between 0.1 and 1 mg/m3 for 4-h periods. A linear relationship between the
formaldehyde concentration and the amount collected by the sampler was observed. The
mean coefficient of variation and bias determined for the five sets of data were 5.0 and
1.2%, respectively. Additional experiments examined the effect of air velocity impinging
upon the sampler. Four independent sets of twenty devices were each exposed to face
velocities between 0.13 and 1.3 m/s (25 and 250 fpm). The MCV (mean coefficient of
variation) and the mean bias for these data were 4.1% and 2.1%, respectively.
This test method has also been checked in field study (ref, 39). In this study, the samplers
were exposed to formaldehyde concentrations between 0.05 and 0,5 mg/m3 for 5-hr
periods in a carpeted room with gypsum board walls, Reference samplers were collected
over 30-min periods at approximately 45 min intervals following the procedure
recommended in NIOSH P&CAM 125. The mean bias and MCV were -4.8 and 7.3%,
respectively, leading to an OS A (overall system accuracy) of ±19.8%.
There is another type of passive test method for formaldehyde. This formaldehyde
sampler is a badge-shaped device used for either personal or area monitoring. Bisulfite-
impregnated adsorbent is used to collect formaldehyde (convert formaldehyde to a less
volatile product). It is known that this test method is liable to humidity effects since the
reaction between formaldehyde and bisulfite is sensitive to water vapor. For this reason, it
will be advisable to use the badge equipped with an additional section for controlling
relative humidity during sampling.
This passive method, with the incorporation of humidity control, has been tested to
determine the interference effect of other compounds such as isopropyl alcohol and .
phenol. The test results indicated that isopropyl alcohol does not interfere with the
formaldehyde measurements. However, the presence of phenol will interfere with the
formaldehyde measurements. At similar concentrations, the presence of phenol causes
approximately a 20% reduction in the level of formaldehyde reported by the monitors.
This interference effect can be corrected by increasing the concentration of chromotropic
acid in the analytical procedure from 1% to 5%. It is recommended that the 5%
chromotropic acid be used in the analysis whenever phenol is suspected of being present
during the formaldehyde sampling period. The reliable quantitation level in the analytical
procedure is 3.6 pg. With the sampling rate of this monitor at 4.52 pg per ppm-hr, this is
equivalent to sampling 0.1 ppm in 8 hours.
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3.3.3 Nitrogen dioxide - the nitrogen dioxide passive sampling method was first
developed by Palmes in 1976 (ref. 40), and the sampling tube he developed is often
referred to by others as the Palmes Tube. As a matter of fact, Dr, Palmes pioneered the
passive sampling techniques for sulfur dioxide in 1973 (ref. 41), then developed the
technique for nitrogen dioxide.
The Palmes tube is made of acrylic tubing with a length of 7.1 cm and an inside diameter
of 0.95 cm (the area/length ratio is 0.1 cm). The collecting media is triethanolamine
(TEA), which is coated on stainless steel grids (40 x 40 per inch mesh and 0.25 mm
diameter wire). Three of these wafer-shape stainless steel grids coated with TEA were
stacked at the bottom of a 1.27 x 1.27 cm sleeve type low density polyethylene cap. This
cap was then fixed at one end of the tube, holding the TEA coated screens in position.
The device is designed simply to be used in the field, light weight (7 g) and unbreakable.
It is designed to be worn with the exposed end of the tube in downward position since
diffusion is independent of gravity. In addition, wearing the sampler open end down
would keep dust or water from falling into the open end of the tube. A schematic diagram
of a personal N02 sampler is shown in Figure 4.
The TEA coating involves three steps; cleaning of stainless steel (dipping into ultrasonic
bath, rinsing with distilled water, and drying in an oven at 125 °C), dipping into a 50%
volume/volume solution of TEA in acetone, and evaporating of acetone (first, excess
TEA/acetone solution was removed by placing on absorbent paper, then acetone was
evaporated by allowing 15 minutes waiting time). This procedure gave an average TEA
loading of 0.95 mg/screen. This is equivalent to 6.4 pmole TEA per screen or 19 umole
for the three screens used in each sampler. This represents a very large amount capacity
for N02 collection considering that quantities of N02 to be collected are often less than
100 nanomoles.
The amount of N02 collected in a TEA-coated screen was determined by a colormetric
method. After the sampling, the TEA-coated screen is transferred from the sampling tube
to a glass-stoppered graduate in which the adsorbing solution was added to a volume of
55 mL. After vigorous shaking for about 30 seconds (allows a few minutes for solid to
settle), 10 mL of the solution was then transferred to another glass-stoppered graduate.
Before the absorbance measurements, 10 minutes was allowed for complete color
development. The amount of NO ion was measured using the standard curve prepared
from a standard N02 ion solution. The absorbing solution was made of sulfanilamide,
NED A, and hydrogen peroxide. The standard solution was produced by dissolving 0.15
grams of reagent-grade sodium nitrite in distilled water, and diluted to 1 liter. This
solution contained 100 |ig of N02 (ion) per milliliter.
The accuracy of this method is about ±10-15%, and the sensitivity is in a few ppb range.
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3.3.4 Ozone - the passive method for sampling indoor ozone has been developed recently
(ref. 42-43), and is now commercially available . This technique is based on the oxidation
reaction of nitrite (N02) to form nitrate (N03"). The passive ozone sampler is a barrel-
shaped device with a clip. The sampler contains two glass-fiber filters coated with
potassium carbonate (K2C03) and sodium nitrite (NaNG2). After nitrate is formed from
the oxidation reaction of nitrite, the amount of nitrate is determined by using ion
chromatography. The average ozone concentration is calculated from the measured
nitrate concentration and a known sampling rate. This technique has been validated by
controlled laboratory tests at typical ambient ozone concentrations (40 ppb to 100 ppb)
under relative humidities and temperatures varying from 10 to 80% and 0 and 40 °C,
respectively. The limit of detection for the passive sampler is 17 ppb for 12 hour
measurements and the precision is ±9.8% at lower concentration and ±7% at higher
concentrations (ref. 42).
This sampling method has also been verified in a field study (ref. 42). In this study, indoor
and outdoor samples were collected from 23 non-smoking households. All homes were
located within residential neighborhoods. Monitoring was conducted at each home for 5-
day period. In each home, indoor samples were collected over 12 hours for all daytime
periods at various locations, such as main activity rooms (at least 1 meter from walls),
window air conditioners, and other ventilation devices, (1.2 meter above the floor to avoid
effects from turbulence). Outdoor ozone concentrations were measured using passive
samplers placed outside homes, at least 1 meter from walls, trees, and other large subjects.
Outdoor ozone sampling time was 24 hours.
For method validation purposes, ozone concentrations were also measured at a stationary
ambient monitoring (SAM) site using an UV photometric ambient ozone analyzer, in
addition to the passive ozone samplers. The UV analyzer is designated as an equivalent
method for ambient ozone measurements by the U.S. EPA. The lower detection limit for
the UV analyzer is 2 ppb with a precision of 2 ppb. Daytime ozone concentrations
measured by the continuous monitor at the SAM site ranged from 28 to 92 ppb, with a
mean of 55+15 ppb. The collected daytime passive samplers measured ozone at levels
ranging from 31 to 95 ppb, with a mean being 56+16 ppb. Nighttime ozone
concentrations measured by the passive samplers also ranged from 3 to 40 ppb, with a
mean of 19+9 ppb. The relative error of the passive sampler measurements was calculated
to be 15% for daytime and 25% for nighttime samples. The higher relative error for
nighttime samples may be due to the low nighttime ozone concentrations; it represents an
absolute uncertainty of only 5 ppb.
3.3.5 Sulfur dioxide & nitrous acid - the monitor consists of a polystyrene cartridge closed
on one end and covered on the other by a diffusion barrier made of Gore-tex membrane. The
cartridge is 3.8 cm in diameter and attaches to surfaces by a metal clip. The passive monitors
are assembled in a clean air hood. The cartridge contains a 37 mm sodium carbonate treated
glass fiber filter which is the collecting medium for the nitrous acid (1IONO) and sulfiir dioxide
(SO,). After the sampling, the monitor is analyzed by ion chromatography.
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This passive monitor (ref. 44) was tested in an environmental chamber for the effect of
humidity (25-80%), and over a limited range of HONO (40-110 ppb), S02 (180-250 ppb)
concentrations, and sampling times (2-43 hours). To validate this passive sampling
technique, continuous monitoring (EPA equivalent test protocols) instruments were used
as reference to compare the concentration measured by the passive monitor.
For nitrous acid, the sampling rate is 100 mL/min (±14 .8), and the limit of detection based
on the ion chromatography analysis is 7.1 nmoles HONO, equivalent to 29 ppb-hr. For
sulfur dioxide, the sampling rate is 41 mL/min (+3.4), and the limit of detection is 52.6
ppb-hr. (requires at least one hour sampling time if the concentration is 52.6 ppb, and 10
hours if the concentration is 5.26 ppb). For both gases, excellent agreement was found
between concentrations measured by the reference instrument and passive sampling
technique, although the accuracy is higher for sulfur dioxide than nitrous acid (±20% for
nitrous acid and ±10% for sulfur dioxide). Relative humidity was found to have no
significant effect on the sampling rate of either gas.
4.0 An application guide
The selection of field methods for GP AFE testing depends largely upon the application
needs and cost. For this purpose, Table 5 compares various types of test methods in terms
of capability, sampling requirements, availability, and cost. Furthermore, information
regarding the sampling procedures for GPAFE testing, accuracy, and detection limit for
each test method will be provided in this section. It must be stressed that with the
exception of real-time instruments, the methods outlined in this section have not been
verified or demonstrated for GPAFE testings.
4.1 Ozone, sulfur dioxide, and nitrogen dioxide real-time instruments
As discussed previously, the unique advantage of using real-time instruments for GPAFE
testing is that they provide near real-time data. This is especially useful if users would like
to investigate the effects of contaminant concentration and environmental conditions (e.g.,
relative humidity, airflow rate, and temperature) on the removal efficiency of GPAFE
under dynaimic conditions.
The real-time instruments for ozone, sulfur dioxide, and nitrogen dioxide are well-
developed, and these monitors provide excellent reliability, accuracy, detection limit, and
data acquisition and communication capability. The continuous measurements of ppb
levels of ozone are based on the absorption of ultraviolet radiation at 254 nm wavelength
The measurements of sulfur dioxide are commonly based on pulsed fluorescence
technique. NO-N02 is based on chemiluminescence technique. The performance
specifications of these real-time instruments can be obtained from the manufacturers, and
should meet the performance specifications in Table 6,
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4.1.1 Air sampling - sampling of outdoor or indoor air should be conducted in
accordance with the guidelines provided by EPA and ASTM (ref. 44-47). For ozone
sampling, special attention should be given to ensure accurate measurements. The
sampling tubes should be made of inert material (e.g., PTFE fluorocarbon), and the
sampling line should be short and direct, preferably not more than 5 m in length. Since
ozone in ambient air can easily be created and destroyed under direct exposure to bright
sunlight via a series of photochemical reactions, the air sampling points should be in a
shady location or protected from direct exposure to bright sunlight. When the sampling
air is hot and humid, neither the sample line nor its path through the instrument should be
cooled to the condensation point, since ozone is soluble and rapidly destroyed by
condensate. Situations in which the analyzer will be exposed to rapid and frequent
changes of ambient temperature should be avoided. Many instruments compensate for
slow changes in ambient temperature, but do not respond well to the rapid changes often
found in small air monitoring stations, which may exceed 1 °C/min.
The removal efficiency of GPAFE can be determined by sequential sampling upstream and
downstream of GPAFE through the use of a three-way valve. Due to the concentration
differences before and after GPAFE, adequate purging should be provided to prevent
memory effect before switching the sampling valve, or the initial data after switching the
sample valve should be ignored. The upstream location should be 2-3 inches from the
GPAFE and the downstream location should be 8-10 feet away from GPAFE.
4.1.2 Applications - although real-time instruments are ideal for monitoring the removal
efficiency and service life of GPAFE, the cost is prohibitive for building engineers to use
for general purpose IAQ applications.
These instruments are primarily used for ambient air quality monitoring (e.g., EPA), for
laboratory evaluation of GPAFE, and for monitoring of a critical environment or process.
Although not used extensively, these instruments have been used as a reference to validate
active or passive sampling techniques. They have also been used to control the
concentration of targeted contaminants in conjunction with building DDC control and the
use of appropriate GPAFE.
4.2 Active sampling methods
Active air samplings are the most common methods used today for air sampling. These
methods are very accurate and sampling time is relatively short, typically one to eight
hours. This method provides integrated concentration data over the sampling period of
time. Therefore, one can not use this method to investigate the performance of GPAFE
under dynamic conditions.
Active sampling uses pump and flow equipment to draw air into the sampling tubes. After
sampling, the collected contaminants are either analyzed on the test sites, or sent back to
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laboratories for analysis. Active sampling test methods are available for VOCs, nitrogen
dioxide, oxides of nitrogen, sulfur dioxide, formaldehyde, and many other gases. These
methods are summarized in Tables 7-10. The active sampling and analysis are usually
provided for by testing laboratories and consulting firms.
4.2.1 GPAFE testing - since the sampling time of active methods is rather short, it is
essential to have a good communication and planning among building engineer, testing
laboratory, and GPAFE manufacturer in terms of the intent of testing, the contaminants to
be measured, an expected concentration range of targeted contaminants, sampling
locations, and timing for sampling. In addition, all the relevant data prior to and during air
sampling period should be collected (e.g., flow rate, relative humidity and temperature of
airflow through GPAFE) in order to properly interpret the test results over such a short
period of sampling time.
A guide for GPAFE testing is suggested as follows:
a. Prior to the sampling, calibrate the sampling system including pump, flow regulator,
tubing to be used.
b. Follow manufacturer's instructions on air sampling procedures,
c. For measuring removal efficiency of GP AFE, the sampling points, both upstream and
downstream of GPAFE, should be in the locations where the airflow is well mixed, and as
close to GPAFE as possible. Generally, the distance is 5-15 cm upstream of GPAFE, and
2.4-3 m downstream of GPAFE. For large GPAFE installation, duplicate samplings may
be required to obtain a good average upstream and downstream concentration.
d. For measuring removal efficiency of GPAFE, simultaneous air sampling should be
conducted at upstream and downstream location of GPAFE, especially when sampling
time is short.
e. Sampling volumes (or time) - The minimum sample volume (time) is governed by the
detection limit of the analytical method, and the maximum sample volume is determined by
the capacity of media used to collect the contaminants. Due to the concentration
difference between upstream and downstream of GPAFE, larger sampling volume (higher
flow rate or longer sampling time) may be required at downstream locations to ensure the
amount of contaminant collected is well above the detection limit of the analytical method.
f. A sample flow rate ofless than 10 mL/min should not be used. Calculations based upon
diffusion coefficient for several compounds indicate that sampling at less than 10 mL/min
may not give accurate results.
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g. It is recommended that at least one sampling tube should be presented for analysis as a
field blank with every 10 or 15 samples. The purpose of the field blank is to check if the
sampling tubes are contaminated prior to and during the sampling. If a field blank shows
contamination, results from the field blank should not be used to correct sample results,
and the samples taken during the test must be assumed to be contaminated.
h. During air sampling, collect all the relevant data that can affect the GPAFE performance
such as temperature, relative humidity and airflow rate.
4.2.2 Applications - since the cost of active sampling and analysis is expensive and
sampling time is relatively short (1-8 hours), active sampling methods are recommended to
be used for measuring initial efficiency of GPAFE shortly after the installation (for the
purpose of performance verification), or checking its efficiency when there is a need to do
so (e.g., significant changes in pollutant loads or design conditions). The active sampling
method should also be used when there is a reason to believe that the installed GPAFE is
no longer working (e.g.,smelling odors). Active sampling is unsuitable for use as a routine
field method for monitoring the service life of GPAFE due to the number of tests required
and associated cost over the life time of GPAFE. The cost of a single test is at least a few
hundred dollars.
4.3 Passive sampling methods
Passive air sampling is the most cost-effective, easy-to-operate test method for air sampling.
Since this technique uses a natural process called diffusion to collect contaminants on the
sampler, all that is required is to place the passive sampler in a location of interest and allow
sufficient time for the sampler to collect an adequate amount of contaminants for analysis. It
does not require any external devices such as pump, tubing, flow meter, calibration kit, or
power source. The passive sample is often in the form of a badge or cartridge, which can be
clipped onto a worker's clothes as a personnel monitor or hung in an indoor space as an area
monitor. After sampling, the sampler is sent back to the manufacturer or laboratory for
analysis.
Passive sampling is generally less accurate than either real-time instruments or active
sampling methods due to the loss in contaminant collection and recovery. In addition, the
required sampling time is longer. In spite of this, passive sampling appears to be the most
attractive method for monitoring GPAFE performance due to its low cost and ease of
sampling.
It is important to conduct the passive sampling test on a regular basis and to collect all the
relevant data that can affect the GPAFE performance. By doing so, test data collected at
different periods of service time can be plotted to reliably determine when to change
GPAFE, and to assess the irregular behavior of GPAFE due to the changes in pollutant
loads and environmental conditions.
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The passive sampling methods for VOCs, nitrogen dioxide, and formaldehyde have been
available for many years. New techniques have been developed for measuring ozone and
sulfur dioxide concentrations, and they are now commercially available. These methods
are summarized in Table 11-15. A list of manufacturers and suppliers for passive samplers
are given in Table 16.
Most test protocols developed for passive sampling of low levels of inorganic gases
(ozone, sulfur dioxide, formaldehyde, and nitrogen dioxide) in indoor air may be directly
applied to measure VOC efficiency of GPAFE without significant modifications.
However, for VOCs, the test protocol must be simplified in terms of compound selection
for analysis since it is impractical to track down all the individual compounds in a complex
VOC mixture. To simplify the analysis and reduce the cost, compound selection for
VOCs will be discussed in Section 7.
4.3.1 GPAFE testing - a guide for GPAFE testing is suggested as follows:
a. Open the sampler container at the time sampling is to be initiated.
b. Follow the manufacturer's instruction for air sampling procedures.
c. Ensure that the air velocity at the sampler position is above the minimum velocity
recommended by the manufacturer (typically 0.13 m/s). Avoid sampling stagnant areas
such as against walls or in corners of rooms.
d. Follow manufacturer's instruction for sampling time. The minimum sampling time is
governed by the sampling rate and the sensitivity of the analytical method. The maximum
sampling time is determined by the sampling rate and the removal capacity of media used
to collect contaminants. Due to the concentration difference between upstream and
downstream of GPAFE, larger sampling volume (higher flow rate or longer sampling
time) may be required at downstream locations to ensure the amount of contaminant
collected is well above the detection limit of the analytical method.
e. Since the accuracies of passive sampling for concentration measurements typically are
±15 - +25% depending upon type of gases to be measured, a minimum of two samplers
should be placed both upstream and downstream of GPAFE in order to obtain a good
average value. Theoretically, the errors in efficiency measurements could be as large as
±50%. However, the use of the duplicate samplers should minimize the errors to some
extent.
f. At the end of the sampling period, the sampler should be removed and the sampling time
recorded. The sealed samples should be send to the laboratory for analysis.
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4.3.2 Handling and shipping - the chemical species collected on passive samplers may
be exposed to a variety of handling, shipping, and storage conditions. Certain precautions
should be taken to minimize the losses and extraneous contamination.
a. Samples should be sealed securely and identified clearly.
b. Samples collected should be kept at room temperature or below and not exposed to
direct sunlight (especially for VOCs and ozone samplers).
c. If samplers are to be shipped in aircraft cargo holds, the preferred procedure is to carry
the samples on board. The individual carrying the samples should be cognizant of federal
regulations limiting or prohibiting the transport of certain materials aboard aircraft and
take the appropriate action to ensure compliance.
d. Samplers should be shipped as soon after sampling as possible, and analyzed as soon as
possible (not to exceed five working days),
e. Bulk solvent samples should never be shipped or stored directly with the collected air
samples.
4.3.3 Applications - For indoor air sampling, the passive sampling technique is ideal for
large scale field studies since the use of active samplers may be out of the question due to
the potentially high variability of contaminant concentrations. It is also ideal for use to
investigate the effect of contaminant exposure on chronic health effect, since it would
require a sampler with much longer exposure duration than the typical 8-12 hours in active
sampling.
For GPAFE testing, the passive sampling technique is recommended to be used as a
routine test method used by building operation & maintenance personnel to monitor the
removal efficiency and service life of installed GPAFE. Essentially, there is no training
required except that the proper procedures shall be followed regarding sampling locations,
sampling time, storage (if necessary), and packaging (for shipping the samplers back to
manufacturers and analytical laboratories). In most cases, the shipping can be done by
mail, since the samplers are small enough to fit inside an envelope.
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5.0 Test methods from GPAFE manufacturers
Several air filter manufacturers provide test methods for determining the remaining life of
GPAFE. Instead of measuring the contaminants in the air, the methods determine what is
in the filter. These methods are outlined as follows:
5.1 Remaining carbon tetrachloride activity - this method is intended for assessing the
remaining life of activated carbon for VOCs removal. In summary, the method includes
the following steps:
a. The in-service carbon sample is taken out of the installed GPAFE and sent back to the
manufacturer for analysis.
b. The carbon tetrachloride (CC14) activity test (ref. 10) is used to measure the remaining
CC14 activity of the in-service carbon sample.
c. The manufacturer reports the remaining life (%) of activated carbon based on the
difference of CC14 activities between the new and in-service carbon. Some manufacturers
use this test method only as an indicator for carbon changeout.
Obviously, this is an over-simplified method for estimating the remaining life of activated
carbon for VOCs. If the remaining life is to be reported, the conclusion should be as
conservative as possible. Nevertheless, it is still a useful method for determining the
saturation life of carbon if the test is conducted on a regular basis. It can be stated with
caution that the in-service carbon is saturated with respect to VOCs when the remaining
CC14 activity decreases to a constant level. However, the effect of relative humidity has to
be considered in the interpretation of test data.
5.2 TVOC loading analysis - this is an improved method for determining the saturation
life of activated carbon for TVOC. Instead of using a surrogate compound, this method
directly measures the TVOC loading from the field conditions. The TVOC loading of in-
service carbon sample is measured from the difference of two ASTM test methods. The
total volatile test (ref. 48) determines TVOC plus moisture contents, and the xylene
extraction test (ref. 49) determines the moisture content. A reliable decision on carbon
changeout can be made by monitoring of TVOC loadings on a regular basis.
Furthermore, with a database it is possible from a single TVOC loading test to predict the
remaining adsorption capacity for TVOC. Unfortunately, such database does not exist at
this time.
5.3 KMNO4 content analysis - this method is intended for use as a routine test method
for determining the remaining activity (e.g., impregnate content) of KMN04-based
material. The test method is available from various manufacturers. For the purpose of
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adsorbent changeout, many manufacturers provide useful commentary recommendations
(e.g., safe, borderline, change, change immediately) based on the range of the KMN04
content.
6.0 Recommendations
As discussed in this report, there are three types of test methods that can be used to
determine the effectiveness of installed GPAFE in commercial and public buildings for
indoor air quality purposes.
Although real-time instruments are ideal for monitoring the removal efficiency and service
life of GPAFE, the cost prevents building engineers from such use.
Active sampling is an accurate, short term test method. It is most suitable for building
engineers to validate the removal efficiency of GPAFE shortly after the installation, or at
any time when there is an urgent need to check its removal efficiency. Such situations may
occur when there is an anticipated increase in pollutant loads (e.g., building renovation or
painting activity) or there is reasonable doubt that GPAFE is no long working (e.g.,
worker complaints of poor air quality or odors).
Passive sampling, because of its low cost and ease of operation, has the potential to be the
most attractive field method for GPAFE testing. Although certain limitations may apply,
this technique in general has the capability of sampling air over a very large time span, say
from a few hours to a few weeks, without sacrificing its accuracy. This flexibility makes it
ideal for both short term and long term monitoring of a wide range of GPAFE. Passive
sampling methods are available for a wide range of contaminants including VOCs, ozone,
nitrogen dioxide, formaldehyde, and sulfur dioxide. In order to reliably determine when to
change GPAFE, it may be necessary for building engineers to set up a GPAFE monitoring
program in which passive sampling for targeted contaminants is conducted on a regular
basis. This sampling program can be very cost effective, since the cost of each sampling
(including analysis) is considerably less than $100, and the shipping of samplers (for
analysis) can be done by mail.
As pointed out in this report, both active and passive sampling methods have been widely
used for ambient and indoor air sampling. However, the use of these methods for field
testing of GPAFE is still a new application, and this kind of test data is almost non-
existent in public domain. Therefore, it would be necessary to conduct a field study to
collect actual test data for various contaminants under representative use of GPAFE,
particularly in office buildings, and use these data to prepare a complete document on the
test protocols that can be implemented by building engineers.
To properly apply these technigues for field testing of GPAFE, several key issues need to
be addressed in Phase 2 of this research project as follows:
30
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Sampling time - The sampling time must be long enough to collect adequate amount of
sample for subsequent analysis. This would depend upon the sampling rate of a particular
method and contaminant concentrations. A guideline must be provided with respect to
each method and concentration range.
Sampling location - Ideally, the sampling locations shall be such that they measure the
representative upstream and downstream concentrations of GPAFE. We recommend
sample locations 5-15 cm in front of GPAFE for upstream sampling and 2.4-3 m for
downstream sampling (this distance is a conservative estimate for achieving uniform
mixing of air flow). However, in many instances, the air flow may not be well mixed right
before entering the GPAFE due to the improper installation, or simply there is no 2.4-3 m
duct space for downstream sampling. For these situations, the traverse sampling is
required to obtain a good average of concentration. The guideline shall identify such
installations and the protocols for traverse sampling.
Effect of flow velocity - The duct velocity in GPAFE installations is typically in the range
of 0.19-0.28 m3/s. Currently, there are no test data available to assess the effect of such
high velocity on the accuracy of both active or passive sampling. This issue needs to be
fully investgated. If such effect does exist, the corrections shall be given to account for
duct velocity.
7.0 Scope of phase 2 work
7.1 Objectives - the objectives for phase 2 of this research project will focus on the
following:
a. Conduct a field test program to determine and monitor the effectiveness of GPAFE
used in buildings for indoor air quality purposes.
b Based on the collected test results, validate and refine the test protocols and application
guide outlined in the Phase 1 report.
c. Prepare documentation that allows building engineers to implement the cost-effective
test protocols for determining or monitoring the performance of installed GPAFE for
indoor air quality applications.
7.2 Targeted gaseous and vaporous contaminants - for any air sampling, one must first
determine what contaminants are to be measured. For general purpose IAQ in office
buildings, it has largely been agreed that volatile organic compounds, ozone, formaldehyde,
sulfur dioxide, and various forms of oxides of nitrogen (N02-N0) are the most common or
prevailing contaminants in terms of their abundance in buildings and health effect on
occupants.
31
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For VOCs, there is a long list of compounds of measurable concentrations in indoor air.
Even with passive sampling, this may significantly increase the analysis cost and create
difficulty and confusion in data interpretation and management if all the individual
compounds are to be measured. As discussed in this report, the adsorption capacity of
activated carbon is primarily determined by the boiling point of compounds. Therefore,
the breakthrough behavior of a VOC mixture on a carbon bed is such that low boiling
point compounds will break through first, followed by compounds with medium boiling
points. The carbon bed is near complete saturation when high boiling point compounds
start to break through. Compounds with similar boiling points will break through at about
the same time period. This predictable behavior makes it possible to select three
compounds with distinctly different boiling points to represent the breakthrough of a
whole VOC mixture. In this regard, three compounds, heptane, toluene, and ethyl benzene
are recommended. The service life can be based on heptane removal efficiency if one
elects to use complete removal of all VOCs as a criterion for GPAFE changeout, toluene
efficiency if the criterion is based on TVOC, or ethylbenzene if one elects to change
GPAFE when it is completely saturated and no longer can remove any VOCs. We
recommend the use of toluene as most indoor air guidelines for VOCs are based on the
concentration of TVOC.
7.3 Type of building - this program will select office buildings as the main test sites.
However, other building environments such as airports, hospitals, museums, archives, and
schools should also be included. Indoor air quality in these environments is an important
issue as well. Furthermore, these environments are more motivated to maintain acceptable
indoor air quality and are likely to have gas-phase air filtration equipment in the HVAC
systems. A good mixture of building selection will be three office buildings with different
pollutant loads (new, renovated, and existing) and HVAC systems (VAV and CAV), and
three buildings selected from airports, hospitals, museums, archives, and one school,
7.4 Type of GPAFE - the program will include various types of GPAFE that have
representative use in buildings for indoor air quality purposes. Although this may have no
significant impact on the test method itself, the data obtained may help engineers to
evaluate and select GPAFE for their applications. Furthermore, these data may serve as a
baseline or frame work for engineers to estimate removal efficiency and service life of
various GPAFE in field conditions.
The GPAFE selection can be based on type (panel or pleated type), type of adsorbent,
amount of adsorbent, and particle size of adsorbent.
7.5 Sampling methods and programs - the objective of this research project is to come
up with a cost-effective and reliable field test method for GPAFE testing. In this regard,
the program shall include both active and passive sampling methods for GPAFE testing,
with particular emphasis on passive sampling techniques. Several specific programs are
suggested as follows:
32
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a. Establish test protocols for using passive sampling methods to determine the service
life of GPAFE (long term). All the test sites will be monitored with passive sampling
methods for at least twelve months or until GPAFE shows no remaining capacity left to
remove these contaminants. The sampling should be conducted on a regular basis. Four to
six samplings and analysis for each selected contaminant should be carried out at different
time intervals during this program,
b. Establish test protocols for using active sampling methods to determine the removal
efficiency of GPAFE (short term). Active sampling should be conducted at several
selected sites to determine the removal efficiency of GPAFE for various contaminants.
The timing for conducting such tests would be, for instance, to determine the removal
efficiency of GPAFE shortly after the installation, when there is an anticipated increase of
pollutant load, or simply at different time intervals.
c. Determine the representative sampling locations for large GPAFE installation.
d Based on the collected VOC data, recommend a few compounds that can be used to
determine the service life of GPAFE.
e. Monitor TVOC loading analysis and correlate the results with those obtained from
passive VOC sampling.
33
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34
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November 1990.
35
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28. 1994 Annual Book of ASTM Standards D-5466: Volatile organic chemicals in
atmosphere (canister sampling method), Vol. 11.03, p. 577, 1994.
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1986.
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symposium on air sampling for volatile organic compounds, Philadelphia, PA, June 1992.
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compounds in ambient air, Method TO-11," EPA Report No. EPA-600/4-89-017 (NTIS
PB90-127374), 1989.
32. 1994 Annual Book of ASTM Standards D-5197: Standard test method for
determination of formaldehyde and other carbonyl compounds in air (active sampler
methodology), Vol. 11.03, p. 493, 1994.
33. 1994 Annual Book of ASTM Standards D-1607; Standard test method for nitrogen
dioxide content of the atmosphere (Griess-Saltzman reaction), Vol. 11.03, p.11, 1994.
34. 1994 Annual Book of ASTM Standards D-1608: Standard test method for oxides of
nitrogen in gaseous combustion products (phenol-disulfonic acid procedures), Vol. 11.03,
p. 16, 1994.
35. Cohen, M, A,, P.B. Ryan, and Yukio Yanaglsawa " The validation of a passive sampler
for indoor and outdoor concentrations of volatile organic compounds." Journal of Air and
Waste Management, Vol. 40, No 7, pp. 993-997, 1990.
36. Shield, H.C. and C.J. Weschler "Analysis of ambient concentration of organic vapors
with a passive sampler." APCA Journal, Vol. 37, No. 9, pp. 1039-1045, 1987.
37. DeBortoli, M., H. Knoeppel, L.Molhave, B. Seifert, and D. Ulrich "Interlaboratory
comparison of passive samplers for organic vapors with respect to their applicability to
indoor air pollution monitoring: A pilot study," Report EUR 9450 EN, Commission of the
European Communities, Joint Research Centre, Ispra, Italy, 1984.
38. Siefert, B. and H.J. Abraham " Use of passive samplers for the determination of
gaseous organic substances in indoor air at low concentration levels." Int. J. Environ.
Anal. Chem. Vol. 13, p. 237, 1983.
39. 1994 Annual Book of ASTM Standards D-5014: Standard test method for
determination of formaldehyde in indoor air (passive sampler methodology). Vol. 11.03, p.
411, 1994.
36
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40. Palmes, E.D., A.F. Gunnison, J. Dimattio, and C. Tomczylk" Personal sampler for
N02." Am, Ind. Hyg, Assoc. Journal. Vol. 37, p. 570, 1978.
41. Palmes, E.D. and A.F. Gunnison " Personal monitoring device for gaseous
contaminants." Am. Ind. Hyg. Assoc. Journal. Vol. 34, p. 78, 1973.
42. Liu L-J S., P. Koutrakis, and H.H. Suh " Use of a personal monitoring technique to
assess indoor ozone concentrations - a pilot study." Proceedings of Indoor Air'93, Vol. 2.
p. 305, 1993.
43. Grosjean, D. and M.W. Hi sham "A passive sampler for atmospheric ozone," Journal,
Air and Waste Management Association, Vol. 42, pp. 169-173, 1992.
44. Leaderer, B P., J. Sullivan, P. Koutrakis, and J.M. Wolfson "A passive monitor for the
measurement of nitrous acid & sulfur dioxide." Proceedings of Indoor Air '93, Vol. 2,
p. 233, 1993.
45. EPA, Ambient monitoring guidelines for prevention of significant deterioration, EPA-
450/4-87-007 (NIIS PB90-168030). Environmental Protection Agency, Office of Air
Quality Planning and Standards, Research Triangle Park, NC, May 1987.
46. EPA, Quality assurance handbook for air pollution measurement systems, Vol. II,
Environmental Protection Agency, Washington, DC, 1987b.
47. Annual Book of ASTM Standards, ASTM D1357: Standard Practice for Planning the
Sampling of the Ambient Atmosphere, Vol. 11.03, pp. 6-9, 1994.
48. Annual Book of ASTM Standards, ASTM D3175-88: Standard Test Method for Total
Volatile Content of Activated Carbon, Vol. 15.01, 1988.
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Moisture Content of Activated Carbon, Vol. 15.01, 1988.
37
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TABLE 1. GAS-PHASE AIR FILTRATION EQUIPMENT USED IN HAVAC SYSTEMS
Type of adsorber
Residence time
Amount of
adsorbent
Particle size of
adsorbent
Depth
Panel type
0.035-0.1 seconds
20-90 lbs
4x6 or 4.8 mesh
12"-3P
Pleated type
0.001-0.03 seconds
a few ounces
to 15 lbs
-20 mesh
r-12"
Adsorbents: Activated carbons, impregnated activated carbons, potassium permanagnate-based sorbent, and
zeolites
TABLE 2. REAL-TIME INSTRUMENTS FOR COMMON GAS-PHASE CONTAMINANTS IN
INDOOR AIR
Gases and vapors
Method of detection
Sensitivity
o,
UV photmetic
1 ppb
NOfc Nox, and NO
chemiluminescence
0.1-0.5 ppb
S02
pulsed fluorescence
I ppb
Corrosive gases film
thickness of copper and silver
NA
VOCs
catalytic oxidation (TVOC)
high ppb-low ppb
Specific VOCs
infrared spectroscopy
5-11 ppb
TABLE 3. ACTIVE SAMPLING FOR COMMON GAS-PHASE CONTAMINANTS IN INDOOR
AIR
Gases and vapors
Sampling method
Analysis
Sensitivity
VOCs
adsorption tube with porus
solids (tenax, charcoals, or
multisorbents)
GC/MS
ppb-ppt
no2
wet impinger
with absorbing agent
(sulfanilic acid)
coloriinetric
2ppb
S02
wet impinger with
absorbing agent (TCM)
eolorimetric
10 ppb
HCHO
wet impinger with
absorbing agent (DNPH)
HPLC with
UV detector
low ppb
38
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TABLE 4 PASSIVE SAMPLING METHODS FOR COMMON GAS-PHASE CONTAMINANTS
IN INDOOR AIR
Gases and vapors Collection method Analysis Sensitivity
VOCs
diffusion and adsorption
solvent extraction
GC/MS analysis
ppb-ppt
no2
diffusion and adsorption
eolorimetry
low ppb
HCHO
diffusion and adsorption
colorimetiy
lowppb
S02
diffusion and adsorption
ion chromatography
low ppb
o,
oxidation of nitrite
ion chromatography
low ppb
TABLE S. FIELD METHODS FOR GPAFE TESTING-APPLICATION GUIDE
Methods Capability Operation Availability Cost
Real-time
Continuous data
Unattended opertion
Ozone, sulfur
dioxide
>$10,000
Instruments
Accuracy: ± 1% or less
Detection limit: <; 1 ppb
Response time: s 100 sec
Power source required
Nitrogen dioxide
Active sampling
1 -24 hr time-averaged data
Sampling time: 1-24 hr
Accuracy: ± 5-10%
Detection limit:
-------
TABLE 6. PERFORMANCE SPECIFICATION FOR REAL-TIME INSTRUMENT
Ozone
Nitrogen dioxide
Sulfur dioxide
Range:
0-1 ppm
0-1 ppm
0-1 ppm
Noise
0.5 ppb
0.2 ppb
0.5 ppb
Lower detection limit
lppb
0.4 ppb
1 ppb
Zero drift
<1 ppb/24 hour
<0.4 ppb/24 hour
<1 ppb/24 hour
<2 ppb/week
Span drift
± 1%/month
± l%/24hour
± 0.5%/week
Response time
20 seconds
80 seconds
110 seconds
Precision
1 ppb
1 ppb
1 ppb
Operating temperature
15-35 °C
15-35 °C
15-35 °C
TABLE 7. STANDARD TEST METHODS FOR ACTIVE SAMPLINC-VOCs
ASTMD 5466-93
ASTMD 3686/3687
Sampling method
evacuated canister
charcoal tube
Analysis method
GC/MS
GC/MS
Sampling time
10-30 sec (subatmosphcric)
1-24 hours (pressurized)
1 -24 hours
VOCs
Works well for a wide range of
stable compounds (-30-180 °C
boiling point)
Does not work well with low
boiling point compounds, but
this can improve with the use of
multisorbent tube
Low detection limit
<1 ppb
1
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TABLE 8. STAND AMD TEST METHODS FOR ACTIVE SAMPLING-FORMALDEHYDE
ASTMD 5197-92
Sampling media
silica gel coated with DNPH
Analysis method
HPLC with UV detector
Sampling time
5-60 min. (short term)
1 -24 hours (long term)
Low detection limit
low ppb
High detection limit
low ppm
Accuracy
±5-10%
TABLE 9. STANDARD TEST METHODS FOR ACTIVE SAMPLING-NITROGEN DIOXIDE
ASTMD 3608-91
Sampling media
absorption agent (sulfonic acid)
Analysis method
colorimetry
Sampling time
1-24 hours
Low detection limit
2 ppb
High detection limit
5 ppm
Accuracy
< 10%
TABLE10. STANDARD TEST METHODS FOR ACTIVE SAMPLING-SULFUR DIOXIDE
ASTMD 2419-91
Sampling media
absorption agent (TCM)
Analysis method
colorimetiy
Sampling time
1 -24 hours
Low detection limit
10 ppb
High detection limit
0.4 ppm
Accuracy
<5%
41
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TABLE 11. TEST METHODS FOR PASSIVE SAMPLING - VOCs
Sampler personal badge
Sampling media charcoal pad
Analysis method GC/MS
Sampling time 1 -8 weeks (ppb levels) 1 -24 hours (ppm levels)
Low detection limit 0.02 ppb
High detection limit high ppm
Accuracy ±15-25%
Cost <$ 100 (including analysis)
TABLE 12, STANDARD TEST METHODS FOR PASSIVE SAMPLING - FORMALDEHYDE
ASTMD 5014-94
Sampler
Sampling media
Analysis method
Sampling time
Low detection limit
High detection limit
Accuracy
Cost
tube
absorbing agent (MBTH)
colorimetry
15 mill - 24 hours
9 ppb
14 ppm
±10-15%
<$100 (including analysis)
TABLE 13. STANDARD TEST METHODS FOR PASSIVE SAMPLING - NITROGEN DIOXIDE
Sampler
cartridge
Sampling media
TEA coated stanless steel screen
Analysis method
colorimetry
Sampling time
1-24 hours
Low detection limit
2 ppb
High detection limit
low ppm
Accuracy
±10-15%
Cost
<$100 (including analysis)
42
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TABLE 14. TEST METHODS FOR PASSIVE SAMPLING - SULFUR DIOXIDE
Sampler
Sampling media
Analysis method
Sampling time
Low detection limit
High detection limit
Accuracy
Cost
cartridge
sodium carbonate treated filter
ion chromatography
1-24 hours
1 -2 ppb
low ppm
±10-15%
<$100 (including analysis)
TABLE 15. TEST METHODS FOR PASSIVE SAMPLING - OZONE
Sampler
cartridge
Sampling media
potassium carbonate and sodium nitrite coated filter
Analysis method
ion chromatography
Sampling time
1-24 hours
Low detection limit
1-2 ppb
High detection limit
low ppm
Accuracy
±10-15%
Cost
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TABLE 16. A LIST OF SUPPLIERS FOR PASSIVE SAMPLERS
Supplier
pollutants
GMD 570 Formaldehyde Dosimeter
Bacharach, Inc.; 625 Alpha Drive
Pittsburgh, PA 15238
Tel: (412) 963-2200
DOA Passive Monitors
4526 Telegraph Road, Ste, 205
Ventura, CA 93003
Tel: (805) 644-0125
3 M Passive Monitors
3M Center Bldg, 275-6W-01
St. Paul, MN 55144
Tel: 800-666-6477
SKC 575-001 Passive Sampler
SKC West; P.O. Box 4133
Fullerton, CA 92634-4133
Tel: 800-752-9378
Ogawa Passive Samplers
Ogawa & Co.; 1230 SE 7th Avenue
Pompano Beach, FL 33060
Tel: (305) 781-6233
Air Quality Research
2800 7th St.
Berkeley, CA 94710
Tel: (415)644-2097
Microfiltration Systems
6800 Sierra Ct.
Dublin, CA 94568
Tel: (415) 828-6010
formaldehyde
formaldehyde
sulfur dioxide
ozone
volatile organic compounds
formaldehyde
ethylene oxide
mercury vapor
volatile organic compounds
sulfur dioxide
nitrogen oxide
nitrogen dioxide
ozone
formaldehyde
nitrogen dioxide
nitrogen dioxide
44
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Real-time instruments for ozone, nitrogen dioxide, and sulfur dioxide
Active sampling method
Figure 1 - Test methods for measuring gaseous contaminants in indoor air
45
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Composite Sorbent Cartridges
Stainless steel cartridge
Weakest Stronger Strongest
Adsorbent Adsorbent Adsorbent
Carbotrap C Carbotrap Carbosieve S-ll
Carboxen 1001
Car boxen 1003
Figure 2. A multisorbent tube for sampling VOCs in indoor air
(active method)
-------
Membrane
filter
Needle
valve
\J/ . To air pump
Figure 3. An active sampling apparatus for sulfur dioxide (ASTM D-2914)
-------
-Cs>
00
5 4
"i
L
f i
I 9
I f
I I
I %
\ %
1. Teflon disk
2. Teflon ring
3. Stainless screen
4. Coated collection filter
5. Stainless Screen
6. Diffuser end cap
Figure 4. A cartridge for passive sampling of nitrogen dioxide in indoor air
------- |