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62 Analytical Techniques for Atmospheric Measurement

Table 1.4 (Continued)

Species

measured

Analytical technique Temporal

resolution

Detection limit Chapter

CO Gas chromatography/ﬂame

ionisation detector

40 min 8

(in situ) Non-dispersive infrared

spectroscopy

2hr 2

CFCs, HCFCs,

HFCs

Gas chromatography/electron

capture detector/mass

spectrometer

2hr 5, 8

Gas chromatography/hot

mercuric oxide reduction gas

detector coupled with UV

detection

40 min 8

Gas chromatography/Flame

ionisation detector

40 min 8

the European Centre for Medium Range Weather Forecasting (ECMWF), which can be

downloaded from the website http://badc.nerc.ac.uk/data/ecmwf-trj/. It was possible to

observe the formation of an internal boundary layer during the transition from the ocean

to the land (where the surface roughness increases), and also to identify when sea-breeze

effects dominated, periods when trajectory calculations used to deduce air mass origins

are unreliable. This information is critical for the correct positioning of instruments

relative to one another, and to interpret long time-series of composition measurements.

1.9 Instrumented chambers for the study of simulated

atmospheres

The atmosphere is not very accommodating. Extended bad weather or simply not

sampling air masses with the desired history during a campaign can be highly frustrating,

and the scientific impact of what is usually an expensive operation is seriously compro-

mised. Being able to choose the composition of the atmosphere that is sampled offers

many advantages, especially when stable conditions are required over long periods,

perhaps in order to perform instrument intercomparisons or test the zero response of

an instrument. In more polluted environments, it is not possible to study the oxidative

degradation of a single VOC via field measurements, in order to compare with model

calculations, as many thousands of VOCs may be present. Atmospheric chambers with

simulated atmospheres are ideal if it is desired to study the mechanism for degradation

of one species at a time. It is possible to systematically vary individual parameters under

controlled conditions, and to remove the vagaries of the meteorology.

There are a number of highly instrumented outdoor atmospheric chambers worldwide,

which use the sun’s radiation to initiate photochemistry. Excluded in this section are

indoor smog-chambers which use artificial light sources, such as black lamps or xenon

lamps, to initiate photochemistry. Indoor environmental chambers are discussed in some

Field Measurements of Atmospheric Composition 63

detail by Finlayson-Pitts & Pitts (2000). Two examples of large outdoor chambers are

the EUPHORE (European Photoreactor Program) community facility, which consists of

two hemispherical chambers at CEAM (The Mediterranean Centre for Environmental

Studies), Valencia, Spain, and the SAPHIR (Simulation of Atmospheric Photochemistry

in a Large Reaction) chamber at Forschungszentrum Jülich, Germany. Photographs of the

chambers are shown in Figure 1.11. Both chambers are highly instrumented, containing

a wide variety of in situ instruments, using most of the techniques described in this book.

A feature of both chambers is the ability to measure free-radical species, for example OH

and HO

radicals. The chambers are equipped with motorised shutters and hence can

also be operated in the dark. A useful feature is the ability to quickly switch on or off

the solar radiation, and monitor the rise or fall of radical precursors or the free-radicals

themselves. It is found that the walls of the chamber are sources of free-radicals, and

this must be characterised thoroughly. The Jülich SAPHIR chamber can accommodate

several standard-sized shipping containers underneath it, with sampling probes entering

from beneath, and has been used for a number of intercomparisons, providing stable

conditions that can be altered at will over long periods.

An EU-funded project EUROCHAMP (Integration of European Simulation Chambers

for Investigating Atmospheric Processes) aims to provide a grid of environmental trace

gas and aerosol chambers designed for the scientific investigation of atmospheric chemical

processes.

1.10 Future directions

In recent years there has been an increase in the number of species monitored, the type of

platform on which measurements are possible, and, importantly, an improvement in the

accuracy and precision of reported measurements. Important questions are the following:

Which species do we really need to measure but are not currently being measured?

Which species already measured need to be measured better? Are there emerging and

promising techniques in the laboratory, that may enable new or better measurements?

Which regions of the atmosphere are still poorly characterised and merit further study?

In the following chapters the authors have each highlighted current developments and

future needs for specific analytical techniques, and these points are not repeated here.

Research grant funding for future development of analytical techniques is largely driven

by the scientific needs with respect to the individual species in the atmosphere. Thus,

although in individual chapters there are discussions regarding the future directions for

that particular technique (e.g. in Chapter 2, discussions that an improvement in IR laser

sources will lead to a better measurement of formaldehyde, CH

O), the future direction

for a particular species may not involve that type of technique at all. Common to all

techniques, there is a need to make instruments much smaller and portable, requiring

advances in electronics. Intercomparisons and the sharing of calibration standards have

no doubt led to improved confidence in atmospheric measurements, but further work is

needed. The flow of air into sampling inlets varies from technique to technique, and so a

calibration method that works well with one instrument may be unsuitable for another.

A possible way forward is to agree a standard inlet type so that calibration sources can

be circulated amongst several groups.

64 Analytical Techniques for Atmospheric Measurement

(a)

(b)

Figure 1.11 (a) One of the two EUPHORE atmospheric simulation chambers at Valencia, Spain.

Further information on this facility, including instruments, can be obtained from http://www.gva.es/ceam/

index_i.htm. (b) The SAPHIR atmospheric simulation chamber at Jülich, Germany. For further information,

see http://www.fz-juelich.de/icg/icg-ii/saphir.

Field Measurements of Atmospheric Composition 65

In a chapter on field measurements within the IGAC Synthesis Book (Tyndall et al.,

2003), which was completed in April 2001, the authors (25 in total) speculated about the

future of measurement techniques, and considered (a) the evolution of the techniques

themselves, and (b) the needs of the atmospheric community. A summary is included here.

For (a), the anticipated trends included a wider application of mass spectrometric methods

(see Chapter 5), improvements in optical spectrometry (see Chapters 2–4), miniaturised,

automated gas chromatographs (see Chapter 8), and continued development of satellite

instrumentation (see also below). For (b), there was seen to be a need for more compact,

universal instruments that can be readily calibrated. The measurement techniques for

some free-radicals were seen to be unsatisfactory, for example RO

radicals, or too difficult

for routine measurements. A shortlist of requirements included (Tyndall et al., 2003) the

following: techniques for high-frequency hydrocarbon and other VOC measurements;

rapid, reliable measurements of water vapour, NH

and NO

; an international OH/HO

instrument intercomparison; instrumentation for unstable N reservoirs N

 HO

;

the development of single-particle instruments with molecular speciation (see Chapter 6);

measurement techniques for X, XO, OXO, HOX (where X = Cl , Br and I); additional

monitoring stations in the Tropics; sondes and LIDARS to measure vertical profiles of

a wider variety of trace (especially short-lived) gases; and satellite-based instruments for

global three-dimensional distributions of trace gases in the troposphere (see also below).

Since 2001, some of these requirements have been realised. For example, an inter-

national OH/HO

intercomparison involving German, British and Japanese groups was

performed in the summer of 2005 at the Jülich SAPHIR chamber (see Section 1.9); aerosol

mass spectrometers capable of analysing single particles have been developed and deployed

(see Chapter 6); further short-lived halogen species have been detected, including I

using DOAS (see Chapter 3); and new satellite instruments, for example SCIAMACHY

and those on the AURA satellite, are providing high quality tropospheric measurements.

The use of mass spectrometry is certainly on the increase, for example there are signif-

icant numbers of proton-transfer-reaction mass spectrometers (using quadrupole and

time-of-flight mass spectrometers, see Chapter 5) being used by the community for

real-time measurement of a wide range of VOCs (in particular oxygenated species),

and two-dimensional chromatography combined with flame-ionisation detection or mass

spectrometry (see Chapter 8) is being used to speciate and quantify ever larger numbers

of VOCs in polluted air. Future improvements in sensitivity and time-resolution are still

necessary, and there is a need for the detection of water soluble, thermally labile and

polar organic species which are readily taken up into the condensed phase.

At present, free-radical concentrations in the troposphere are only measured using

in situ techniques at selected locations, and for short periods, usually during intensive

field campaigns (although there is a five-year study of OH concentrations at a rural site

in southern Germany (Berresheim et al., 2005)). There is a need for long-term trends

for short-lived reactive molecules in the troposphere, such as ozone and free-radicals,

in particular OH (which controls the oxidising of the daytime troposphere), and also

global-scale measurements of a wide range of tropospheric free radicals, including OH,

,RO

,XO(X= I, Br and Cl) and NO

. Continuous measurements of tropospheric

OH from a geographically diverse range of ground-based instruments, or from satellites

would, for the first time, enable any long-term trends in global or regional OH levels to

be monitored directly. Satellite measurements of free-radicals in the troposphere would

66 Analytical Techniques for Atmospheric Measurement

be a major advance, but are probably not likely in the near future. Instruments must

become more reliable, be capable of unattended operation over longer periods, and

require lower levels of operator expertise. There are some very compact instruments

undergoing development in the laboratory, for example cavity ring-down spectrometers

or locked cavity absorption techniques using small continuous diode lasers, that may

become suitable for measurements of free-radicals (Bakowski et al., 2002; Brown, 2003).

The idea of intracavity laser spectroscopy for ultra-sensitive detection of atmospheric OH

was first suggested in 1991 (McManus & Kolb, 1991) but only around 2000 have suitable

continuous wave laser sources at 308 nm become available (Barry et al., 2000).

One of the main reasons for the measurement of short-lived free-radicals is to provide

a target species to test the accuracy of chemical mechanisms. However, in order to

adequately constrain the model, it is necessary to know the co-measured concentrations

of longer species whose reactions are either sources or sinks for the free-radical being

investigated. In the case of OH, there are thousands of species in polluted air, mainly

VOCs, which remove OH, and despite developments in instrumentation to measure ever

larger number of VOCs, it will never be possible to measure all the OH sinks, and

therefore completely constrain the model. In polluted environments, modelled OH levels

sometimes exceed the measurements, consistent with missing sinks. Another approach is

to measure the atmospheric lifetime of OH, 

, which is the reciprocal of the total loss

rate by reaction with its sinks, and is given by





X



(1.7)

where X

represents a sink for OH, and k

is the rate coefficient for the reaction X

+OH.

One measurement therefore defines the rate of removal of OH by reaction with all

its sinks, and several groups worldwide have now developed field instruments for the

measurement of 

directly (see Chapter 4). Measurement of the lifetime of other

short-lived intermediates could also aid in the quantification of their budgets.

Considerable improvements in satellite products can be expected in the near future

(Brasseur et al., 2003). The global distribution of aerosols is highly variable and vertically

resolveddistributions with goodsensitivity arenecessaryto quantifytheir contribution tothe

radiative budget of the atmosphere and for comparison with models. New methods under

development include the LIDAR in-space technology experiment (LITE), which uses lasers

atseveral wavelengths operating from satellites. Improvements inlaser technology may allow

more reliable operation of lasers in space, and differential absorption LIDAR (DIAL), which

is well proven on the ground, may prove feasible from satellites.

Observations from geostationary orbits ∼36 000 km will enable horizontal resolutions

of 10 km or less, and temporal resolutions of ∼10–15 min. In contrast to instruments

on satellites in low earth orbit, it will be possible to view the same spot continuously,

and obtain a full diurnal profile with good temporal resolution. With good spatial and

temporal resolution it will then be possible to perform process studies, monitoring the

evolution of shorter-lived species within pollution events, in a similar way to ground-

based intensive field campaigns. Several satellites in geostationary orbit would provide

a full coverage of the earth, except for the polar regions. New technology, in the form

of detectors, communication and data handling, is being developed for geostationary

satellites. It is important to validate any new satellite product via carefully planned

Field Measurements of Atmospheric Composition 67

ground- or aircraft-based measurements. However, it is not always straightforward to

compare in situ measurements with satellite observations.

Acknowledgements

I would like to thank Professor Ulrich Platt from the University of Heidelberg for

supplying information about the measurement of atmospheric composition from space

using DOAS instruments on satellite platforms (Platt & Stutz, 2006).

Further reading

Books and other general reviews

Brasseur, G., Orlando, J.J. & Tyndall, G. (1999) Atmospheric Chemistry and Global Change, OUP,

Oxford.

Brasseur, G.P., Prinn, R.G. & Pszenny, A.A.P. (2003) Atmospheric Chemistry in a Changing World.

An Integration and Synthesis of a Decade of Tropospheric Chemistry Research, 300 pp., Springer-

Verlag, Berlin.

Calvert, J.G. (1994) The chemistry of the atmosphere: Its impact on global change, Chemistry for

the 21st Century, Blackwell Scientific Publications, Oxford.

Clemitshaw, K.C. (2004) A review of instrumentation and measurement techniques for ground-

based and airborne field studies of gas-phase tropospheric chemistry, Critical Reviews in Environ-

mental Science and Technology, 34, 1–108.

Finlayson-Pitts, B.J. & Pitts, J.N. (2000) Chemistry of the Lower Atmosphere. Theory, Experiments

and Applications, Academic Press, San Diego.

Holton, J.R., Pyle, J.A. & Curry J.A. (2003) Encyclopaedia of Atmospheric Sciences, Elsevier.

Newman, L. (1993) Measurement challenges in atmospheric chemistry, in Advances in Chemistry,

M.J. Comstock (ed.), 407 pp., American Chemical Society, Washington DC.

Platt, U. & Stutz, J. (2006) Differential Optical Absorption Spectroscopy, Springer, Heidelberg.

Ravishankara, A.R. (2003) Atmospheric chemistry: Long-term issues, Chemical Reviews, 103 (12),

4505–5262.

Roscoe, H.K. & Clemitshaw, K.C. (1997) Measurement techniques in gas-phase tropospheric

chemistry: A selective view of the past, present and future, Science, 276, 1065–1072.

Sievers, R.E. (1995) Selective detectors. Environmental, industrial and biomedical applications,

Chemical Analysis: A Series of Monographs on Analytical Chemistry and Its Applications,

J.D. Winefordner (ed.), 261 pp., John Wiley & Sons, New York.

Wayne, R.P. (2000) Chemistry of Atmospheres, Oxford University Press Inc., New York.

Journal special sections for some major ﬁeld campaigns

(selective)

(in chronological order of the campaign dates)

The Tropospheric OH Photochemical Experiment (TOHPE, 1993) J. Geophys. Res., 102 (D5), 1997.

Photochemistry of Plant-emitted Compounds and OH Radicals in Northeastern Germany

(POPCORN, 1994) J. Atmos. Chem., 31 (1–2), 1998.

68 Analytical Techniques for Atmospheric Measurement

Aerosol Characterisation Experiment. Radiative Effects of Aerosols in the Remote Marine

Atmosphere (ACE 1, 1995) J. Geophys. Res., 103 (D13), 1998, 104 (D17), 1999.

Subsonic Assessment Ozone and Nitrogen Oxides Experiment (SONEX, 1997) Geophys. Res. Lett.,

26 (20), 1999.

North Atlantic Regional Experiment (NARE, 1993, 1996, 1997) J. Geophys. Res., 103 (D22), 1998,

104 (D11), 1999.

International Photolysis Frequency Measurement and Modelling Intercomparison Study (IPMMI,

1998) J. Geophys. Res., 108 (D16), 2003.

Berliner Ozone Experiment (BERLIOZ, 1998) J. Geophys. Res., 108 (D4), 2003.

New Particle Formation and Fate in the Coastal Environment (PARFORCE, 1998, 1999) J. Geophys.

Res., 107 (D19), 2002.

Southern Oxidants Study – Atlanta Supersite Project (SOS, 1999) J. Geophys. Res., 108 (D7), 2003.

Indian Ocean Experiment (INDOEX, 1999) J. Geophys. Res., 107 (D19), 2002.

Pacific Exploratory Mission Tropics B (PEM-Tropics B, 1999, 2000) J. Geophys. Res., 101 (D23),

2001, 108 (D2), 2002.

Southern Africa Regional Science Initiative (SAFARI, 2000) J. Geophys. Res., 108 (D13), 2003.

SAGE III – Ozone Loss and Validation Experiment and Third European Stratospheric Experiment

on Ozone (SOLVE-THESEO, 1999, 2000) J. Geophys. Res., 107 (D20), 2002, 108 (D5), 2003.

Investigation of Sulfur Chemistry in the Antarctic Troposphere (ISCAT, 2000) Atmos. Environ.,38

(32), October 2004, pp. 5363–5373.

Tropospheric Ozone Production about the Spring Equinox (TOPSE, 2000) J. Geophys. Res., 108

(D4), 2003.

Intercontinental Transport and Chemical Transformation 2002 (ITCT 2K2, 2000) J. Geophys. Res.,

109, 2004.

Mediterranean Intensive Oxidant Study (MINOS, 2001) Atmos. Chem. Phys., 3, 2003.

Transport and Chemical Evolution over the Pacific – Aerosol Characterisation Experiment Asia

(TRACE-P, ACE-Asia, 2001) J. Geophys. Res., 108 (D20 and D21), 2003, 109 (D16), 2004.

Characterization of Asian Aerosols and Their Radiative Impacts on Climate (ACE-Asia, 2002 J.

Geophys. Res., 108 (D23), 2003, 109 (D19), 2004.

North Atlantic Marine Boundary Layer Experiment (NAMBLEX, 2002) Atmos. Chem. Phys., 5, 2005.

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