USE OF THE EMISSION ISOLATION FLUX CHAMBER TO DETERMINE AREA
SOURCE EMISSIONS
CE Schmidt1 , David Ranum2
1
CE Schmidt, PhD,Environmental Consultant, 19200 Live Oak Road, Red Bluff, CA 96080,
(530) 529-4256, SCHMIDTCE@aol.com.
2
David Ranum, Project Manager, Sage Environmental Consulting, LP. 4611 Bee Caves Road,
Suite 100, Austin, Texas 78746 (512) 327-0288, davidr@sageenviornmental.com
ABSTRACT
This paper introduces the Emission Isolation Flux Chamber, an USEPA-referenced method for
determining mass emission rates from land or liquid area sources. The paper describes the flux
chamber design, its theory of operation and its ability to quantify mass emission rates from a
wide variety of volatile organic and inorganic emission sources including landfills, land farms,
lagoons, surface impoundments, heap piles, compost piles, agricultural heaps, silage,
uncontrolled hazardous waste facilities, controlled hazardous waste treatment and disposal
facilities, and spill sites. The paper concludes with a brief discussion of the downhole flux
chamber, a related technology developed for assessing subsurface contaminant sources
including groundwater plumes.
1.0
Introduction
Suppose you need to determine the emission rate of pollutants from a waste water lagoon or a
land farm located on your facility. How do you do it? At first you might consider measuring the
concentration of the air above the surface or perhaps analyzing a sample of the soil or liquid, but
neither method provides you with a mass emission rate. You might also consider modeling or
some form of transect monitoring. But these are both expensive, time-consuming approaches and
may not provide representative data. A proven methodology does exist however for directly
determining mass emission rates from area sources. The emission isolation flux chamber (flux
chamber) is a flux measurement technology that can provide accurate results for many different
types of area sources. This paper explains what a flux chamber is, how it works, and its use in
different applications to determine mass emission rates.
2.0
What is a Flux and What is a Flux Chamber?
In the study of transport phenomena (for example, heat transfer, fluid dynamics and mass
transfer) flux is defined as the rate of flow of a property per unit area. In the context of air
emissions from area sources, flux means the mass transfer of gas compounds from an area source
to the atmosphere. The gas compounds of interest include both volatile and semi-volatile
pollutants. An area source is a defined locale which emits pollutants into the air. There are many
types of area sources. Common examples include land farms, animal feed lots, large spills of
volatile materials, garbage dumps, waste water treatment lagoon, gas stations, compost piles, etc.
The emissions or flux of pollutants from an area source are expressed in engineering units as
mass per time per surface area, or milligrams/meter2, minute-1.
Since it is usually infeasible to directly measure the flux from an entire area source, individual
flux measurements are made from small portions of the area source. These individual results are
combined to produce a representative flux which is then applied to the overall area source,
The emission isolation flux chamber is designed to make individual flux measurements possible.
When positioned on a section of the area source it effectively isolates that section so that a
specific flux measurement from a defined area can be made.
Figure 1, from the U.S. Environmental Protection Agency’s (USEPA) flux chamber user’s guide
(U.S. EPA. Measurement of Gaseous Emission Rates From Land Surfaces Using an Emission
Isolation Flux Chamber: User's Guide. February, 1986) illustrates the standard flux chamber
together with support equipment. The flux chamber consists of a clear plexiglas dome mounted
on a circular, sixteen (16) inch diameter stainless steel base. Ports in the plexiglas cover provide
access for sweep air inlet and outlet ports as well as temperature measurement. The sweep air is
introduced into the chamber from a compressed gas cylinder of ultra high purity air at a
controlled flow rate of five (5) liters/minute. The flux emission, combined with the sweep air, is
sampled at the outlet port. Note that the flux chamber can be operated with or without sweep air
(that is, in dynamic or static mode). The dynamic method is generally preferred since it produces
little or no 'wall effects' making it more suitable for the assessment of fairly reactive gas species
including compounds like hydrogen sulfide, a common interest at many sites.
Figure 1. Emission Isolation Flux Chamber
Figures 2 and 3 illustrate the flux chamber being used to measure emissions from both solid and
liquid surfaces.
Figure 2. Flux Chamber Measuring Soil Emissions
Figure 3. Flux Chamber Measuring Petroleum Waste Stream Emissions
3.0
Theory of Operation
The flux chamber is a dynamic 'mixed tank reactor' with a residence time of six (6) minutes.
Residence time is the time required for one chamber atmospheric exchange and equals the
chamber volume (30 liters) divided by the sweep-gas flow rate (typically 5 liters/minute). Design
testing has determined that it takes between four and five residence times or 24 to 30 minutes for
the contents of the standard flux chamber to reach equilibrium. In field tests, grab and/or
integrated samples are typically collected therefore, 30 minutes after the test’s start time.
The flux emission from a test site is calculated according to the equation:
𝐹𝑙𝑢𝑥 = (𝐶 ∗ 𝐹)/𝐴
Where:
Flux
C
F
A
= Flux emission (mg/m2*min)
= Concentration (mg/m3)
= Sweep Air Flow (m3/min)
= Surface Area (m2).
Concentration can be determined in several ways. The sweep air output can be measured directly
with a handheld analyzer. Or, if a speciated analysis of the flux emissions is desired, then a
sample of the output stream can be collected in an evacuated canister or a tedlar bag for off-site
laboratory analysis. Concentrations of semi-volatiles can be obtained in similar fashion using
other appropriate sample collection media such as polyurethane foam (PUF) for example.
As mentioned, characterization of emissions from an area source often requires more than a
single flux measurement. Multiple flux chamber tests are usually needed in order to properly
account for spatial variability in a medium to large area source. The number of individual tests
depends on several factors: the size of the area source, the number of predetermined grid points,
the number of samples necessary to provide a statistically representative sampling of the
population of grid points and, of course, the test budget. Following completion of the testing, the
area source maximum, minimum and average flux emission values, can be calculated.
In addition to spatial changes, temporal changes of flux emissions must also to be considered.
Diurnal flux changes are typically characterized by including 'control point testing' over the
course of a test day; that is by re-testing a designated sampling point several times during a
single day. Day-to-day variability is assessed by conducting re-testing in repeat locations over
the course of several days. Seasonal testing is conducted to define flux variation over the course
of a year.
The development of the emission isolation flux chamber proceeded from field studies carried out
in the 1950s and 60s. An EPA study in the 1980’s led to the standard design shown in Figure 1
and to the USEPA User’s Guide, previously referenced. The standard USEPA design meets the
following performance criteria:

The flux chamber must have minor impact upon the flux event.





The flux chamber test method must demonstrate acceptable accuracy, precision, and
background levels.
The chamber must be constructed from non-reactive materials.
The chamber must be easily portable.
Test surfaces in contact with flux emissions must be accessible and easy to clean.
Reasonable sample collection times.
Flux chamber validation studies have included compound recovery tests (average of 103%
recovery of EPA target compounds), mixing tests using carbon monoxide (97% mixed at five
residence times), precision studies (typically <20%) and accuracy studies (typically >90%).
Specialty applications have also included recovery studies for semi-volatile compounds.
4.0
Why Use A Flux Chamber?
There are several good reasons supporting the use of flux chamber technology to quantify area
source emissions:
1. The flux chamber is an USEPA recognized test method. The EPA has published a flux
chamber protocol document which provides flux chamber construction details and flux
chamber operational procedures.
2. Unlike other area source assessment technologies, the flux chamber measures flux
emissions directly without the use of modeling or estimation techniques. This greatly
improves the accuracy and representativeness of the resulting data.
3. Critical parameters such as background concentration, isolation from external biases,
sample volume, and sweep air flow rate are measured and controlled. This ensures
measurement results of known accuracy and precision per application.
4. Flux chamber testing is cost-effective compared to other area source assessment
technologies (for example, indirect assessment, fence line measurement and modeling).
5. The flux chamber works as well at complex area sources as it does at relatively simple
sources. At a complex area source where other air emission sources are present, the
ability of the flux chamber to isolate a small portion of the area source from upwind
interferences greatly simplifies data collection and interpretation.
6. Extensive documentation on flux chamber performance characteristics is available.
Validation studies have been conducted on land surfaces (solid surfaces) and liquid
surfaces (aqueous, petroleum, sludge). These studies, together with site-specific quality
control results, reinforce the quality of the data generated.
5.0
Typical Flux Chamber Applications
The standard flux chamber can be used on many types of area sources, provided that the chamber
can effectively seal off and isolate a small portion of the area source. This is usually
accomplished by inserting the bottom circumference of the chamber about ¼-inch into the solid
or sludge surface. Sometimes, however, the surface will be impenetrable and external sealing
will have to be used (earthen soil, a fabricated collar adapter, or sandbags for instance). For
liquid surfaces the most efficient way to position the chamber is to suspend it from overhead
structure so as to control the chamber’s placement and depth of penetration into the liquid (water,
wastewater, or petroleum).
Some examples of the variety of area sources tested with the flux chamber include the following:

Petrochemical and refining facilities -- landfills, land farms, stockpiled materials, open
tanks, seams and leaks on storage tanks, passive vents, active vents, surface spills,
lagoons, storage ponds, and waste treatment facilities.

Municipal and industrial waste water treatment facilities -- dissolved air flotation tanks,
open storage tanks, head works, primary and secondary municipal waste water treatment,
filtration and tertiary treatment units, and discharge points.

Waste storage and remediation sites -- Treatment, Storage, Disposal Facilities (TSDFs),
hazardous waste sites, sites subject to the Comprehensive Environmental Response,
Compensation, and Liability Act (CRCLA), and Superfund sites. Air emission studies of
various control agents and approaches have also been studied using flux chamber
technology in support of compliance monitoring and site clean-up activities.

Agricultural sites -- animal husbandry farms and dairies with particular focus on air
emissions from manure handling and disposal, and emissions from feed sources.

Building interiors -- to assess indoor air quality affected by vapor intrusion from
subsurface sources.
6.0
Advantages and Disadvantages
It's important to know both the pros and cons of the emission isolation flux chamber before
launching into a site assessment, especially when the assessment is compliance-driven or due to
litigation.
ADVANTAGES OF THE FLUX CHAMBER TECHNOLOGY

The flux chamber represents the only direct assessment technology with an established
USEPA protocol for area source emission assessment.

Flux chamber technology has been well studied and documented, and reference papers on
most area source applications are available, along with the validation studies, as reference
material.

Flux chamber technology, when coupled with the appropriate sample collection media
and analytical techniques is selective and sensitive.

Flux chamber technology is spatially and temporally selective.

The flux chamber can characterize area source emissions from a complex site where
upwind interferences would complicate assessment by any other area source technology.

The resulting units of measurement or 'flux' are the preferred inputs to dispersion
modeling (for assessing off site impacts) and compliance reporting (mass per unit of
time).
DISADVANTAGES OF THE TECHNOLOGY

Access to the area source is required for the assessment. For some sites, this may involve
additional site safety requirements.

The source must be essentially planar. Three-dimensional sources such as large spillways or surface mixers cannot be measured with the flux chamber.

The technology requires the equipment exactly as specified in the USEPA User's Guide.
The flux chamber specifications and procedures must be followed in order for the
performance specifications and QA/QC data of the User’s Guide to be applicable.
Deviations from these protocols may negate the validity of the data.

The technology requires staff trained in air measurement sciences, proficient in the
operation of the flux chamber according to the protocols described in the USEPA User’s
Guide, and who are able to make informed selections of analytical techniques.
7.0
A New Flux Chamber Application
A downhole flux chamber technique has been developed
to investigate subsurface contamination including spills,
contaminated groundwater, underground plume detection
and plume migration mapping. The downhole assessment
flux chamber is a small (0.6 liter) acrylic chamber that is
designed to fit into a hollow stem auger. With it, flux can
be determined as a function of depth. Data from the
downhole flux chamber can provide diagnostic
information useful for a variety of purposes, including
subsurface plume identification, source apportionment,
support for engineering analysis, and Phase 3 site
assessment. A schematic diagram of the downhole flux
chamber is shown in Figure 4. A complete description of
this technology can be found in the USEPA document,
User's Guide for the Measurement of Gaseous Emissions
from Subsurface Wastes Using a Downhole Flux
Chamber.
8.0
Summary
The emission isolation flux chamber is a uniquely useful
tool for assessing air emissions from a wide variety of area
sources including landfills, land farms, lagoons, surface
impoundments, heap piles, compost piles, agricultural
heaps, silage, uncontrolled hazardous waste facilities,
controlled hazardous waste treatment and disposal
facilities, and spill sites. Its light weight and small size
make it easily adaptable to a variety of test locations. The
flux chamber requires a minimum of support equipment
to operate and, if constructed and operated in compliance
with the USEPA User’s Guide, provides representative
data of known quality.
Figure 4. Downhole Flux Chamber
9.0
References
REFERENCES
USEPA, "Measurement of Gaseous Emission Rates from Land Surfaces Using an Emission
Isolation Flux Chamber- User's Guide," EPA 600/8-86-008 (NTIS PB86-223161), February
1986.
USEPA, "Procedures for Conducting Air Pathway Analysis for Superfund Activities, Interim
Final Documents, Volume 2- Estimation of Baseline Air Emissions at Superfund Sites", EPA450/1-89-002a (NTIS PB90-270588), August 1990.
USEPA, "Validation of Flux Chamber Emission Measurements on Soil Surface", Radian
Corporation, EMSL-LV, June 1986.
USEPA, "User's Guide for the Measurement of Gaseous Emissions from Subsurface Wastes
Using a Downhole Flux Chamber," EPA, Office of Research and Development, Cincinnati,
Ohio EPA Contract No. 68-CO-0003, Work Assignment No. 0-13, May, 1986.
USEPA, "Validation of the Flux Chamber Method for Measuring Air Emissions from Surface
Impoundments", Final Report, EPA Contract No. 68-02-3889, Work Assignment #2, January
1988.