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.

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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.

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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.

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TABLE 1. Parameters used for classifications of techniques and instruments applied in atmospheric air studies

No Parameter Additional information

1 Pollutant state Gaseous componets Suspension matter components

2 Analyte type Organic components Inorganic components

3 Aim of measurements

Estimation of: - emission - imission

- deposition

4 Type of desired information

Instantaneous concentration Short-term concentration

Averaged weigted concentration Averaged weigted concentration for total

measuring time

5 Manner of measurement Direct After preconcentration step

6 Analyte concentration Main components Minor components Trace components

7 Measurement site In situ In laboratory

8 Type of used instruments Stationary instruments Mobile instruments

9 Level of automation 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.

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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 Group name of compounds

Vapour pressure (mm Hg) at 250C

Number of compounds belonging to

particular group

VVOC Very Volatile

Organic Compounds

>380 15

VVINC Very Volatile

Inorganic Compounds

>380 6

VOC Volatile Organic Compounds from 0.1 to 380 82

VINC Volatile Inorganic Compounds from 0.1 to 380 3

SVOC Semivolatile

Organic Compounds

from 1 10-7 to 0.1 64

SVINC Semivolatile

Inorganic Compounds

from 1 10-7 to 0.1 2

NVOC Nonvolatile

Organic Compounds

<1x10-7 5

NVINC Nonvolatile Inorganic

Compounds 1x10-7 12

Total 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).

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TABLE 3. Mixtures of chlorinated organic compounds in environment

Group name of compounds Acronim Number of analytes

Polychlorinated dibenzodioxins PCDD 135

Polychlorinated dibenzofurans PCDF 75 Polychlorinated biphenyls PCB 209

Chlorinated bornanes (toxafen’s derivatives) CHB 32768

Polychlorinated terphenyls PCT 81149 Polychlorinated diphenyloethers PCDE 209

Polichlorinated naphtalenes PCN 75 Polychlorinated alkanes PCA Not determined

Polybrominated biphenyls PCB 209 Polibrominated diphenyloethers 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.

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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]

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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.

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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].

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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.

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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]

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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, C2-C6 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 1-10 ppb level.

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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]

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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.

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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]

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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 cost-effective 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].

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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)

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[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)