CHAPTER 22
ANALYTICAL TECHNIQUES USED IN MONITORING
OF ATMOSPHERIC AIR AND STACK GASES
Waldemar Wardencki, Jacek Namieśnik
Chemical Faculty, Gdańsk University of Technology
80-952 Gdańsk-Wrzeszcz, 11/12 Narutowicza Str.
ABSTRACT
In the paper, on the basis of literature data and our experience, the classification of
methods and techniques used in investigations of atmospheric gases, the examples of
determined substances and types of obtained information have been presented.
Furthermore, the schematic diagrams of typical designs of systems applied in such
studies have been presented. The sytems for continuous monitoring of stack gases are
also characterized.
Chapter 22
1 INTRODUCTION
The activities of nature, including humans, produce a great number of different
substances, which are introduced (emitted) into environmental compartments (air, water
and soil) causing their pollution. The interest in air pollution is related to the fact, that
air contains oxygen essential for life and, what is even more important, that its quality
has a direct influence on human health due to human basic function such as breathing. It
was calculated that man consumes daily about 16 kg of air.
As air pollution are considered:
- substances which change the qualitative composition of air in relation to the
called average composition of troposphere,
- natural components of air (e.g. carbon dioxide, nitrogen oxide and methane)
appearing at higher levels than results from their contribution in the average
composition of troposphere.
Protection against detrimental effects of polluted air should be handled with reliable
information on the level at which particular pollutions are present. Such information can
be achieved by measurement of the particular substances using proper analytical
techniques.
The use of appropriate methods and analytical techniques in practices for air studies
provides information necessary for:
- estimation of qualitative and quantitative composition of pollutants,
- knowledge of composition variability in time and space,
- estimation of emission sources and their intensity,
- studies of processes in the atmosphere and interaction range of particular
pollutants,
- estimation of exposure rate and accumulation of pollutants by living organisms,
- evaluation of technical effectiveness of undertaken protective measures.
In practice, a great number of techniques and instruments, both for sampling and
determination of the concentration levels of different components of air pollution are
used.
2 INTERACTION RANGE OF AIR POLLUTANTS
It is estimated that in human history over 6 million chemical compounds have been
produced, most of them in the 20th century. Furthermore, more than a thousand of new
compounds are created every year. Many of these compounds can be emitted from point
or diffuse sources to the environment and depending on their toxicity may cause
different diseases.
Air pollution can influence especially human health due to the fact that the atmosphere
is a good carrier of pollutants, starting from gases, such as SO2, NOx, volatile and
semivolatile organic compounds, aerosols to particulate matter. Depending on their
interaction range the pollutants may effect on a different scale (local, regional or
global). It is related not only with geographical and meteorological conditions but also
with their stability characterized by their lifetime. Figure 1 shows the interaction range
of typical air pollutants with their effects.
447
Chapter 22
Figure 1. Range of air pollutants actions
3 GENERAL CLASSIFICATION OF TECHNIQUES AND METHODS
APPLIED IN AIR STUDIES
Generally, the techniques and methods used to study atmospheric air can be classified
according to the following parameters:
- pollutant state (gaseous, liquid, aerosols, particulate matter),
- compound type and its concentration level,
- aim of measurements ( estimation of emission, deposition),
- period of measurement (long- or short-term),
- manner of measuring (direct or with sample preconcentration) and measurement
site ( in situ, in laboratory),
- automation level of measurements.
In Table 1 the classification of methods applied in air studies on the basis of different
parameters is presented.
448
Chapter 22
TABLE 1.
Parameters used for classifications of techniques and instruments applied in
atmospheric air studies
No
Parameter
1
Pollutant state
2
Analyte type
3
Aim of measurements
4
Type of desired information
5
Manner of measurement
6
Analyte concentration
7
Measurement site
8
Type of used instruments
9
Level of automation
Additional information
Gaseous componets
Suspension matter components
Organic components
Inorganic components
Estimation of:
- emission
- imission
- deposition
Instantaneous concentration
Short-term concentration
Averaged weigted concentration
Averaged weigted concentration for total
measuring time
Direct
After preconcentration step
Main components
Minor components
Trace components
In situ
In laboratory
Stationary instruments
Mobile instruments
Manual instruments
Automatic instruments
The division based on the level of automation is important from a practical point of
view. According to this criteria two groups of methods are distinguished – manual and
automatic. The manual methods, usually labour- and time-consuming, need the proper
laboratory equipment. Furthermore, it is difficult to obtain good precision and the
results are obtained after some hours or even days. Such measurements are applied
mainly for immediate and periodic assessment of pollutants and air quality and also for
calibration of measuring devices.
Automatic methods, demanding self-acting, usually expensive equipment, enable
continuous recording of the concentration of measured substances delivering the results
almost immediately. In such case the obtained results refer to real time.
4 DETERMINED SUBSTANCES AND TYPES OF INFORMATION
OBTAINED FROM ANALYSIS OF ATMOSPHERIC AIR SAMPLES
Typical air samples in which pollutants are determined include ambient (outdoor) air,
indoor airworkplace atmospheres, stack gases, exhaust gases from vehicles, air from
soils over and around landfill waste sites, industrial gases from open and closed
instalations (including leaks), exhaled breath and air from special atmospheres (e.g.,
caissons, submarines, emergency capsules). The pollutants (both organic and inorganic
types) may be present in different forms as gases, aerosols (liquid, solid) and sorbates
and in a very broad range of concentration.
449
Chapter 22
Special awareness of analysts is focused on compounds which are on the list of
hazardous substances established by the Environmental Protection Agency of United
States (U.S EPA) ) (Table 2).
TABLE 2.
Classes of chemical compouds on the list of hazardous air pollutants (HAP’s) according
to U.S. EPA
Abbreviation
VVOC
VVINC
VOC
VINC
SVOC
SVINC
NVOC
NVINC
Group name of
compounds
Very Volatile
Organic
Compounds
Very Volatile
Inorganic
Compounds
Volatile Organic
Compounds
Volatile Inorganic
Compounds
Semivolatile
Organic
Compounds
Semivolatile
Inorganic
Compounds
Nonvolatile
Organic
Compounds
Nonvolatile
Inorganic
Compounds
Total
Vapour pressure
(mm Hg) at 250C
Number of
compounds
belonging to
particular group
>380
15
>380
6
from 0.1 to 380
82
from 0.1 to 380
3
from 1 10-7 to 0.1
64
from 1 10-7 to 0.1
2
<1x10-7
5
1x10-7
12
189
The different toxicity of pollutant causes that analysts are interested in are most
often found in compounds in mixtures containing from several to tens components. The
congeners of polichlorinated dibenzodioxins and dibenzofuranes are examples of such
compounds (Table 3).
450
Chapter 22
TABLE 3.
Mixtures of chlorinated organic compounds in environment
Group name of compounds
Polychlorinated
dibenzodioxins
Polychlorinated dibenzofurans
Polychlorinated biphenyls
Chlorinated bornanes
(toxafen’s derivatives)
Polychlorinated terphenyls
Polychlorinated
diphenyloethers
Polichlorinated naphtalenes
Polychlorinated alkanes
Polybrominated biphenyls
Polibrominated
diphenyloethers
Acronim
Number of analytes
PCDD
135
PCDF
PCB
75
209
CHB
32768
PCT
81149
PCDE
209
PCN
PCA
PCB
75
Not determined
209
PBDE
209
The obtained information concerns different types of concentration of investigated
pollutants depending on applied sampling techniques and measuring period. The results
of measurements may be referred to real time (instantaneous concentrations) or to a
selected period of time (e.g., 30 days, twenty-four hours, month, year). Final
measurements represent an averaged concentrations.
Considering the frequency of sampling discrete, periodic and instantaneous
measurements are distinguished. Taking into account space, parameter measurements
are divided to a point , averaged along a defined part of space and averaged on the
selected area. Final measurements enable of determination of weighted average
concentrations over the sampling period. Figure 2 presents schematically different
forms of concentration obtained in the function of sampling time.
451
Chapter 22
Figure 2 Schematic diagram of different sampling techniques used for getting
information on concentration of analytes in determined measuring time
5 GENERAL CLASSIFICATION OF METHODS AND EQUIPMENT USED
FOR SAMPLING AND ANALYSIS OF GAS SAMPLES.
Figures 3 presents general classification of techniques used for air sampling and
analysis [1].
Figure 3. General classification of methods and devices used for sampling and analysis
of gas samples [1]
452
Chapter 22
Frequently, in analysis of air, due to low and very low concentrations of analytes it is
necessary to use analytical techniques combined with simultaneous preconcentration of
analytes. Generally, three sampling techniques are used:
- dynamic techniques,
- passive techniques,
- denudation techniques.
- The operating principles of particular sampling devices belonging to each group
are schematically presented in Figure 4.
Figure 4. Schematic representation principle of operation of sampling devices using
passive, dynamic and denuder techniques [1], C – concentration of pollutant,
Q – flow rate of sample, t – sampling time, d – tube diameter, L – height of
stagnant air
The detailed divisions of dynamic techniques, passive dosimeters and denuders are
presented in Figures 5, 6 and 7.
453
Chapter 22
Figure 5. Classification of air sampling techniques based on passive dosimetry [1]
Figure 6. Classification of air sampling techniques with simultaneous dynamic
enrichment of analytes [1].
454
Chapter 22
Figure 7. Classification of denudation techniques of analytes sampling from air stream
[1]
6 SELECTED EXAMPLES OF THE SYSTEMS USED
IN AIR POLLUTION STUDIES
Scientific literature describes a great number of analytical methods and instruments
which can be applied for determination of different pollutants in atmospheric air. In this
chapter some examples of typical sytems are presented. They are based on
preconcentration of analyte before the final determination. Two approaches are the most
frequently used for these purposes: adsorptive and/or cryogenic preconcentration.
The system presented in Figure 8 enables continuous, automatic determination
of ambient atmospheric levels of ammonia [2]. The combination of an adsorbent
(Porasil B) and analysis with extremely sensitive gas chromatograph using flame
thermionic detector allows determination of ammonia concentrations as low as 0,1 ppbv
with a resolution of 15 or 30 min. The obtaining of good precision (relative standard
deviation was better than 5% in the range of 2-106 ppbv of ammonia) was possible due
to using of a Curie-point thermal desorption device.
455
Chapter 22
Figure 8. Schematic diagram of the system for preconcentration of atmospheric
ammonia with gas chromatography equipped with a flame thermionic
detector [2]
The system for measurements of methyl halides in the marine atmosphere
(Figure 9) is based on canister sampling and capillary GC/MS. A 500 ml of air sample
in a canister is drawn through two traps. The first, filled with glass beads and cooled at
– 150 0C, collects CH3Cl and less volatile compounds [3]. The analytes are desorbed at
20 0C (low enough to prevent water vapour desorption but high enough to desorb target
compounds) and transferred to the second trap with Tenax TA, which is kept at – 20 0C
(high enough to prevent CO2 trapping but low enough to collect target compouds). The
compounds after desorption from the second trap at 180 0C are transferred to the
capillary trap cooled at – 180 0C for cryofocusing. GC/MS analysis is started when
capillary trap reaches 100 0C. Stability tests of samples collected in two types of
canisters (electro-chemical buffing and fused-silica lined) with smooth surfaces showed
that both could hold methyl halides for long periods (even up to 6 weeks) without
significant change in gas concentration.
Figure 9.Schematic diagram of the system for preconcentration of methyl halides and
the GC/MS unit for air samples collected in canisters [3]
456
Chapter 22
Preconcentration using cryogens (liquid nitrogen or argon) is technically more
complicated but generally is more versatile. It can be applied for collecting compounds
with a broad range of boiling points and especially for volatile analytes. Futhermore, it
enables cryofocusing of chromatographic zones which makes separation easier.
The arrangement presented in Figure 10. [4] permits measurement of C2-C10
hydrocarbons at the sub-ppb level. Air samples of 400-ml collected in canisters were
preconcentrated in an open nickel tube (80 cm x 0.5 mm) cooled with liquid argon.The
moisture in air samples was removed using a Nafion dryer inserted between sample
inlet and cryotrap. The transfer line (70 cm x 0.16 cm), between valve and column, is
kept at 60 0C. The FID was calibrated using standard reference material, propane in air
at 3 ppm. The standard was diluted to ppbC levels using a dynamic dilution system. The
trapped analytes were desorbed by heating with 900C hot water and determined
chromatographically. More than 50 ambient hydrocarbon, including C2-C10 alkanes, C2C6 alkenes, some alkylated aromatics and isoprene were determined wit an estimated
accuracy of +-20%.
Figure 10. Flow diagram of the system for preconcentration of C2-C10 hydrocarbons
from air sample [4]
The second system uses two-liter canisters with electropolished internal
surfaces [5]. The canisters before using were cleaned under high-vacuum condition and
tested by connecting them to a high-vacuum pump system (10-9 Torr). Air samples
(100-2000 ml) were passed through a cryotrap U-tube cooled by liquid nitrogen to
preconcentrate nonmethanes hydrocarbons (NMHC’s). Next, the cryotrap was heated
with an electric heater and analytes were tranferred to a cryofocusing unit (-175 0C).
After liberation analytes were analysed using the gas chromatography with an
Al2O3/KCl PLOT column. A total of 52 of NMHC’s were found. The detection limits
were typically in the 10pptv range and the reproducibility was 5-7% precision at the 110 ppb level.
457
Chapter 22
Figure 11. Schematic diagram for preconcentration and cryofocusing trap for
determination of C2-C8 hydrocarbons in background air samples [5]
Sampling of air containing semi-volatile compounds (pure compounds vapour
pressure in the range 10-8-10-2 Torr), e.g. polyaromatic hydrocarbons (PAH’s) and
polychlorinated biphenyls (PCB’s), should take into account the fact that these
compounds may be present to a significant degree in two phases; in the gas phase and as
sorbates on the suspended particles. In such cases filter/sorbent samplers are used. The
particles are collected on filters and analytes from the gas phase are adsorbed on
properly chosen adsorbent.
Two high-volume filter/sorbent samplers used for simultaneous collection of
particulate matter and gaseous species are presented in Figure 12 [6].
Figure12 Schematic diagrams of samplers for particle and gas sampling [6]
458
Chapter 22
In the first sampler the main (front) and backup filters are made of quartz fibers.
In the second filter the main filter is in form of a Teflon membrane. The backup filter
providing two estimates of the amounts of gas phase adsorption to the front quartz filter
in the first sampler allow corrections for gas adsorption to that quartz fiber filter. The
losses from the filter due to volatilization during a sampling can be minimized by
shortening the sampling time and maintaining constant temperature of the filter. The
main stream of air (1.4 m3/min) passes trough both filters and two 1.27 cm-thick
poliurethane foam (PUF) sheets. The more volatile compounds are sorbed on PUF’s
and volatile compounds from the stream of 600 cm3/min are sorbed on Tenax-TA.Both
samplers were used for determination of PAH’s in air giving the similar results.
7. SYSTEMS FOR CONTINUOUS MONITORING OF STACK GASES
Continuous monitoring requires automatically acting systems, which are usually a
multielemented, integrated and co-operated set of measuring devices, auxiliary
equipment and calibration appliance [7,8]. Continuous monitoring systems can be
classified on the basis of different criteria. Depending on the way in which measurement
is made, and especially on the applied sampling mode, extractive and in situ systems are
distinguished [9].
In extractive systems, as the name implies, the sample is extracted continuously
from a duct or stack from a representative volume of stack gases and sent by transfer
line to analyzers (one or more single component analyzers or one multicomponent
analyzer). The two main types of extractive systems are fully extractive (sometimes
called simply “extractive”) and dilution-extractive (also known as “dilution”).
Figure 13. Schematic diagram of fully extractive system for continuous emission
monitoring of stack gases [9]
A typical extractive system (Figure 13) has a stainless steel probe, with a filter to
remove coarse particulates. After filtration, a heated, unchanged sample is transferred to
a sample conditioner located in the system enclosure. Calibration gas is delivered from
the enclosure to the probe and back through the sample tubing to calibrate the system.
The simplest sampling conditioning method is cooling the sample and allowing the
moisture to condense and drain out of the system.
For monitoring of CO, CO2, NOx and SO2 instruments based on spectroscopic
techniques (mainly infrared), paramagnetic properties and with solid electrolytes
(zirconium dioxide) for oxygen determination are frequently used. For low
concentration of NOx and SO2 a chemiluminescent method can be applied. Fully
extractive systems can be sometimes used without moisture removal, especially when
sample contains components are easily soluble in water.
459
Chapter 22
Fully extractive systems are recommended for monitoring of pollutants in stack
gases with different physicochemical parameters of compounds. Another advantage of
such systems is the possibility of monitoring of several locations using one analyzer
(time-share systems).
Dilution of the sample gas (Figure 14) with clean, dry air to the sample (usually
from 50:1 to 250:1) considerably facilitates the sample handling and reduces the dew
point of the sample gas so the sampling line can be unheated. Furthermore, the diluted
sample is similar in respect of pollutants concentration to ambient air enabling the using
ambient analyzers. Relatively small amounts of sampled gases increases the time
between cleaning the filters. Because most dilution-extractive systems are affected by
changes in temperature and barometric pressure it is recommended to install at the
sampling location temperature and pressure sensors for compensating these effects. The
dilution systems are recommended for plants fueled with carbons when high levels of
particulates are present in stack gases (0.1 g/m3) and corrosive substances (e.g., HCl or
SO3).
Figure 14. Schematic diagram of dilution-extractive system for continuous emission
monitoring of stack gases [9]
In situ systems (Figs.15 and 16) are mounted at the sampling location allow
monitoring the sample without removing it from the source and do not require sample
conditioning or transport of the sample gas. It minimizes the measurements errors
during sampling, transferring and conditioning the sample.
Figure 15. Schematic diagram for point-type in situ system for continuous emission
monitoring of stack gases (sensor mounted at the end of the probe) [9]
460
Chapter 22
Figure16. Schematic diagram for point-type in situ system for continuous emission
monitoring of stack gases (sensor mounted in the box with the sensor
electronics) [9]
In practice, two types of in situ systems are used: point and path monitoring
systems. In point monitoring systems sample probe and analyzer are installed in side the
stack. They are also called in stack monitors and measure gas at a single point.
Therefore, it is important to choose a location that is representative in terms of the
components of interest. As analyzers in such systems spectroscopic instruments are
used (based on absorption of UV and IR radiation) and electrochemical devices. In situ
monitoring systems are recommended for locations with easy stack access and for
measuring SO2 and O2 in combustion sources because point monitors are very costeffective for measuring only one or two components.
Figure 17. Schematic diagram of single-path type in situ system for continuous emission
monitoring of stack gases [9].
461
Chapter 22
Figure 18. Schematic diagram of dual-pass stack gases in situ system for continuous
emission monitoring of stack gases [9]
Path monitoring systems minimize errors that can arise when location of
measuring point is not representative and due to the disturbances in the flow of stack
gases. They measure gas concentration along a path, usually across the diameter of the
stack or duct. A light source is mounted on one side of the stack and a beam is passed
through to the other side. A single-pass system measures the light that reaches the other
side of stack, whereas a double-pass system uses a reflector and passes the light back
across the stack before performing the measurements. Two parameters are limited in
these systems: the length of the measuring path (no less than 0.5 m , no more than 8-10
m) and temperature of stack gases (no more than 300 0C).
In situ systems are usually mounted in the ducts after electrostatic precipitators
or in chimney ducts.
8 SUMMARY
A great number of analytes and the broad range of concentrations in which they can be
present means that there is no universal method for air sampling . The different aims of
analysis and the necessity of getting the desired information require the application of
specific sampling techniques and methods for final determination. This can be
confirmed by literature concerning the analysis of air in which many different systems
for air sampling and analysis are presented. In this paper some exemplary solutions
have been presented. Many review papers deal with these problems [1,10-16]
REFERENCES
[1.] J. Namieśnik, W. Wardencki, Pol. J. Environ. Stud., 11, 211-218 (2002)
[2.] N. Yamamoto, H. Nishiura, T. Honjo, Y. Ishikawa, K. Suzuki, Anal. Chem., 66,
756-760 (1994)
[3.] H-J. Li, Y. Yokouchi, H. Akimoto, Atmos. Environ., 33, 1881-1887 (1999)
[4.] Liaw, T-L. Tso, J-G. Lo, Anal. Sci, 10, 325-331 (1994)
[5.] Q. Gong, K.L. Demerjian, J. Geophys. Res., 102, 28059-28069 (1997)
[6.] K. M. Hart, J.F. Pankow, Environ. Sci. Technol., 28, 655-661 (1994)
[7.] J.A. Jahnke, Continuous Emissions Monitoring, Van Nostrand Reinhold, New
York, 1993
[8.] J.R. White, Pol. Eng. 27(6), 46-50 (1995)
[9.] K. Walker, Chem. Eng. Progress, 28-34 (1996)
[10.] D. Helmig, J. Chromatogr. A, 843, 129-146 (1999)
462
Chapter 22
[11.] K. Peltonen, T. Kuljakka, J Chromatogr. A, 710, 93-108 (1995)
[12.] Sampling and analysis of airborne pollutants (eds: E.D. Winegar, L.H. Keith),
Lewis Publ. Sci., Boca Raton-Ann Arbor-London-Tokyo, 1993
[13.] K. Des Tombe, D.K. Verma, L. Stewart, E.B. Reczek, Am. Ind. Hyg. Assoc. J.,
53, 136-144 (1991)
[14.] R. Mukund, T.J. Kelley, S.M. Gordon, H.J. Hays, W.A. Mc Clenny, Environ. Sci.
Technol., 29, 183A-187A (1995)
[15.] T.J. Kelly, M.W. Holdren, Atmos. Environ., 29, 2595-2608 (1995)
[16.] J. Dewulf, H. Van Langenhove, Atmos. Environ., 31, 3291-3307 (1997)
463