Heard D.E. (editor) Analytical Techniques for Atmospheric Measurement

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22 Analytical Techniques for Atmospheric Measurement

good. Commercial instruments will probably be more reliable than research-based

state-of-the-art instruments, but this is not always the case! The detection limits for

commercial instrumentation are improving all the time, although for some species,

especially free-radicals, there are no commercial packages available. For monitoring

networks, where high numbers of devices are needed, low cost, ease of use and

reliability are necessary.

1.3.3 Instruments organised by classiﬁcation of trace species

This book is primarily concerned with the analytical methods and instruments used to

make measurements of atmospheric composition. The chapters are organised according

to analytical technique, and cover many examples of species measured in the atmosphere.

However, if it is desired to determine how to measure a given species in the atmosphere

(or photolysis rates), the structure of the book does not allow for immediate comparison

of the various methods available. The purpose of this section is to provide a single look-

up table, with cross-referencing to individual chapters, to enable such a comparison to

be made quickly. Also, for a given technique, Section 1.3.4 provides in a single table the

range of species that have been measured in the atmosphere, again with cross-referencing

to individual chapters. No attempt is made to suggest whether one method or another is

better suited than another for measurement of a particular species, as the choice is driven

by several criteria (see Section 1.3.2), and the optimum technique may vary according

to the specific application. Individual chapters do provide examples of intercomparisons

for a given species, and so a judgement can be made, for a given platform (e.g. ground-

based), of the merits of particular methods. Section 1.5 discusses methods that are not

covered in other chapters.

Table 1.1 lists analytical methods that have been used to measure individual species

in the atmosphere, organised according to chemical family. The table is not intended to

be exhaustive, and does not contain all the species measured in the atmosphere, and for

each species, may not cover all techniques. It is hoped, however, that all the major species

and how they are normally measured are covered. Satellite measurements and photolysis

frequencies are not included in this table. The optimum technique for a given species is

dependent upon the platform used, conditions encountered (e.g. altitude) and desired

sensitivity, temporal and spatial resolution. The table is restricted to molecules that have

actually been measured under ambient conditions rather than under artificial conditions

in the laboratory, and does not cover methods analysing samples collected onto filters.

Likewise, the methods listed for each molecule are only those that have the required

sensitivity for ambient measurements. Finlayson-Pitts & Pitts (2000) also provide a listing

organised by species measured and cover details of the major methods used.

1.3.4 Instruments organised by analytical technique

Table 1.2 separates analytical techniques used to make composition measurements in the

atmosphere into their major classifications. For each overall classification (e.g. optical),

the individual analytical methods are listed, together with the chemical species that have

Field Measurements of Atmospheric Composition 23

Table 1.2 Analytical techniques for measurement of atmospheric composition and photolysis frequencies

Classiﬁcation Technique Chapter Species measured

Optical Infrared absorption

spectroscopy

2CO

O, N

O, CO, CH

, NO,

, HNO

, hydrocarbons, NH

O, H

, HCl, HBr, HF,

HCN, OCS

Differential optical

absorption spectroscopy

(DOAS)

3NO

, NO, NO

, HONO, NH

, HCHO, CS

, benzene, toluene,

naphthalene, phenol, p-cresol, OH,

ClO, OClO, BrO, OBrO, IO, OIO, I

Cavity ring-down

spectroscopy

2 3 OIO, I

,NO

,CH

, hydrocarbons

(after conversion), elemental

Hg, H

O, O

Fluorescence methods

including laser-induced

ﬂuorescence (LIF)

4 Direct OH, NO, NO

,NO

,SO

O, CO

After conversion: ClO, BrO, ClONO

ClOOCl, HO

O, NO

, peroxy

nitrates, alkyl nitrates, hydroxyl-alkyl

nitrates, HNO

, elemental Hg

Far-infrared emission

spectroscopy

1 OH, HO

Microwave/far infrared

absorption spectroscopy

1 ClO, HO

Mass

spectrometric

Ion impact 5 Universal technique, but in particular

all types of VOCs

Chemical ionisation mass

spectrometry (including

proton-transfer-MS)

5 OH, HNO

, aldehydes,

ketones, DMS, non-methane

hydrocarbons, HO

, alkyl

nitrates, PAN, HO

, sum RO

halocarbons

Aerosol mass spectrometry 6 Chemical composition of aerosols as

function of size

Chemical Peroxy radical chemical

ampliﬁer (PERCA)

7 Sum HO

+RO

Chemiluminescence 7 O

, NO, NO

,NO

, isoprene

Derivatization 7 H

, ROOH, CH

O, HONO

Chromatographic Gas chromatography 8 Permanent gases, CO, CO

, saturated and unsaturated

hydrocarbons (aliphatic and

aromatic), C

, DMS, CH

aldehydes, ketones, alcohols, CFCs,

halocarbons, N

O, PAN, PPN,

organic nitrates

Liquid chromatography 8 PAH, peroxides, aldehydes, ketones,

O, organic acids, biomolecules,

proteins, inorganic ions

24 Analytical Techniques for Atmospheric Measurement

Table 1.2 (Continued)

Classiﬁcation Technique Chapter Species measured

Photolysis

frequencies

Filter radiometry 9 JO

D,JNO



Spectral radiometry 9 JO

D,JNO

, J(HONO), JCH

O,

J value of any species subject

to knowledge of absorption

cross-section and quantum yield

Chemical actinometry 9 JO

D,JNO



Measurements

from space

Satellites (various

techniques)

1 Aerosols, O

O, NO, NO

HNO

,CF

Cl, CF

, CFCl

, other

CFCs, O

, ClONO

,CO

,CH

O, BrO, OClO, SO

,CH

O, HF,

HCl, CO, N

, ClO, O

a

,O

dimer), HOCl

Space shuttle, SpaceLab-3 1 O

, NO, NO

, ClONO

HCl, HF, CH

, CFCs, ClO, H

O, OH

Other Matrix isolation ESR 1 HO

, sum of all RO

,CH

CO ·O

,NO

Solid-state sensors 1 CO, O

, hydrocarbons, NO

Electrochemical 7 O

been measured. For some measurements, only column amounts are measured, rather than

vertically resolved or in situ measurements. Once again, the table is not intended to be

exhaustive, rather indicating commonly used techniques and measured species. Individual

chapters (indicated in the table) should be consulted for more comprehensive tables of

equipment used and species covered. Clemitshaw (2004) provides a very comprehensive

listing of methods organised according to type of analytical technique. For some species,

several methods are available for their detection, with different sensitivities and accuracies,

and a listing in this table does not imply a technique as the optimum method for

detection. The table is restricted to techniques used to make ambient measurements in

the atmosphere, and does not cover techniques that have only been demonstrated to have

excellent sensitivity in the laboratory for specific species.

1.4 Instrument platforms

For many aspiring field scientists (the author included), the transition from ‘the

laboratory’ to ‘the field’ comes as somewhat of a shock. Suddenly, a prized instrument

that has proven itself in the comfortable confines of the laboratory must be exposed to the

harsh reality of the atmosphere in order to make a real measurement. Instruments require

a platform on which to operate, to provide physical support, electrical power, protection

from the elements (in particular the ingress of water), protection from overheating or

distortion due to changes in pressure, and must enable unimpeded sampling which does

not perturb the composition of the surrounding atmosphere. In this section, various types

of platform are discussed, ranging from the ground to space, and both fixed and mobile.

Field Measurements of Atmospheric Composition 25

1.4.1 Ground-based platforms, including vehicle-based

mobile laboratories

The simplest platform is a building or fixed structure on the ground, with an inlet

protruding from the structure or atop a neighbouring tower via a sampling line. There

are many ground-based stations situated around the world. Some are well-established,

highly instrumented, permanent stations, with well-documented meteorological condi-

tions, whereas others are simply a source of power and possibly a few buildings that

provide basic facilities for small, intensive field measurements. There is a trend for larger

instruments to be housed within custom-fitted, air-conditioned, standard size (20 feet,

6 m, in length) shipping containers, with attendant towers or sampling structures, and the

requirements of the site are only a flat area of land together with electrical power (and for

some instruments, running water). This type of arrangement has the added advantage of

faster set-up and tear-down times. The UK Universities Facility of Atmospheric Measure-

ments (UFAM), http://www.env.leeds.ac.uk/ufam/, consists of a distributed set of ground-

based and specialised airborne instruments designed to make in situ measurements of

chemical composition as well as small- and meso-scale measurements of physical param-

eters (e.g. wind profiles, turbulence) in the atmosphere. Many of the instruments are

housed in shipping containers for ease of transportation. Electrical power is usually not

a limiting factor at ground-based sites, with the exception of extremely remote locations

where all power has to be provided through diesel-powered (or possibly wind- or solar-

powered) generators. Often a common sampling height for instrument inlets (e.g. 10 m

above the ground), or a common sampling line (with several ‘Tees’ going to different

instruments), is used during intensive campaigns involving several instruments, although

this is not possible for some bulky instruments with a requirement for short inlets (e.g.

OH measurements).

It is important that there is a good record of the local meteorology, including micro-

meteorological measurements of local mixing or internal boundary layers. Detailed

meteorological measurements are essential during all campaigns, in particular if there

are power-generating diesel generators, whose exhaust must be downwind. To sample

very clean air, which is typical of the background atmosphere free of human influence,

one normally has to travel considerable distances to very remote locations where field

stations are situated. Examples of remote monitoring sites are given in Section 1.7.2.2.

Environments include semi-rural, suburban, urban, desert, coastal, polar, oceanic (island

observatories), forested, mountainous, from sea level up to 3580 m (e.g. the Jungfraujoch

Sphinx Observatory in Switzerland). High-altitude sites are ideal to avoid interference

from water vapour or boundary layer pollution. Figure 1.6 shows photographs of the

Mace Head field site, Ireland, and the Clean Air Sector Laboratory at the Halley Station,

Antarctica, and Table 1.3 contains examples of locations where intensive field campaigns

have been mounted.

A number of ground-based mobile laboratories have been developed for the in situ

measurement of atmospheric composition whilst on the move. There is a requirement of

onboard power to supply to instruments, sufficient air-conditioning to keep instruments

cool, a sampling system able to sample the surrounding air (with the relative velocity of

the vehicle) without contamination from the vehicle’s exhaust, and fast-response (∼1s)

instruments to provide adequate spatial resolution at higher speeds. Applications include

26 Analytical Techniques for Atmospheric Measurement

(a)

(b)

Figure 1.6 (a) The Mace Head Atmospheric Research Station, situated on the west coast of Ireland,

and photographed during the NAMBLEX ﬁeld campaign (July–September 2002). Many of the instruments

brought to the site speciﬁcally for the campaign are housed inside shipping containers. The retro-reﬂecting

mirror for a DOAS system is positioned on the island in the distance. (b) The Clean Air Sector Laboratory

(right), operated by the British Antarctic Survey, and positioned approximately 1.5 km from the main

Halley Base on the Brunt Ice Shelf, Antarctica. The shipping container on the left houses the FAGE

instrument from the University of Leeds, which measures OH and HO

radicals, and which was deployed

next to CASLAB during the CHABLIS (Chemistry in the Antarctic Boundary Layer and the Interface with

snow) summer intensive campaign, January–February 2005. (Photograph courtesy of Dr W.J. Bloss.)

Table 1.3 Major ﬁeld campaigns for the measurement of atmospheric composition (highly selective, since 1991)

Campaign

or acronym

Year Dates Location Type of

environment

Platform Comments

Place Latitude Longitude

MLOPEX-2 1992 April–May Mauna Loa, Hawaii,

USA

20N 156W Free-

troposphere

Ground 3400 m

altitude

TOHPE 1993 Aug–Oct Fritz Peak and Idaho

Hill, Colorado, USA

40N 105W Forested Ground 2687–3070 m

altitude

POPCORN 1994 August Pennewit, Germany 54N 12E Continental,

rural

Ground

ACE-1 1995 Nov–Dec Southwest Paciﬁc

Ocean (South of

Australia)

Aircraft,

ground

ALBATROSS 1996 Oct–Nov North and South

Atlantic

68N–50S various Open ocean

MBL

Ship Aboard ship

R/V Polarstern

EASE97 1997 April–May Mace Head, Ireland 53N 10W Coastal MBL Ground

SONEX 1997 Autumn North Atlantic various various Air-ﬂight

corridor

Aircraft

BERLIOZ 1998 July–August Pabstthum, Germany 53N 13E Rural and

urban plume

Ground

PARFORCE 1998 September Mace Head, Ireland 53N 10W Coastal MBL Ground

1999 June

SOAPEX-2 1999 Jan–Feb Cape Grim, Tasmania 41S 142E Coastal MBL Ground

Table 1.3 (Continued)

Campaign

or acronym

Year Dates Location Type of

environment

Platform Comments

Place Latitude Longitude

PEM-Tropics B 1999 March–April Tropical paciﬁc various various MBL and

free/upper

troposphere

Aircraft

P-3B

and

DC-8

SOS (Nashville) 1999 June–July Cornelia Fort,

Nashville, Tennessee,

USA

36N 88W Polluted

urban

Ground

SOLVE 1999–2000 Winter Polar vortex (from

Kiruna, Sweden)

various various Polar

stratosphere

Aircraft

INDOEX 1999 Feb–March Indian Ocean various various Ship,

aircraft

Rishiri Island 2000 June Rishiri Island, Japan 45N 141E Coastal MBL Ground

PROPHET-2 2000 July–August Pellston, Michigan,

USA

46N 85W Forested Ground

TEXAQS 2000 Aug–Sept Houston, Texas, USA 29N 95W Polluted

urban

Ground

TOPSE 2000 Feb–May USA, Canada, Arctic various various Above

remote

continental

and ice sheet

Aircraft

ISCAT 2000–2001 Nov–Jan South Pole 90S Ice sheet Ground 2800 m

altitude

TRACE-P/

ACE-Asia

2001 March–April Western Paciﬁc various various mainly above

Paciﬁc ocean

Aircraft P-3B

and DC-8

PMTACS-NY 2001 June–August New York City, USA 41N 74W Polluted

urban

Ground

MINOS 2001 August Finokalia Station,

Crete, Greece

35N 26E Coastal MBL Ground

NAMBLEX 2002 July–Sept Mace Head, Ireland 53N 10W Coastal MBL Ground

ANTCI 2003 Nov–Dec South Pole 90S Ice sheet Ground 2800 m

altitude

ECHO 2003 Julich, Germany 51N 6E Forested Ground

TORCH 2003 July–August Writtle, Essex, UK 51N 1E Semi-polluted

rural, London

plume

Ground

2004 May–June Weybourne, Norfolk,

53N 1E Semi-

polluted

rural

Ground

INTEX 2004 June–Aug NE USA, Atlantic various various Aircraft,

ground, ship

ITOP 2004 July–Aug Based at Faial, Azores 38N 28W Mid-Atlantic

ocean

Aircraft

Notes: Special issues of journals were dedicated to the presentation of the results from some of these campaigns. A selected listing of special issues is given in the ‘Further Reading’

section.

Glossary of ﬁeld campaign acronyms used in Table 1.3

Acronym Full name

ACE Aerosol Characterisation Experiment

ANTCI Antarctic Tropospheric Chemistry Investigation

BERLIOZ Berliner Ozone Experiment

EASE 97 Eastern Atlantic Spring Experiment 1997

ECHO Emission and CHemical Transformation of Biogenic Volatile Organic Compounds

INDOEX Indian Ocean Experiment

ISCAT Investigation of Sulphur Chemistry in the Antarctic Troposphere

INTEX Intercontinental Chemical Transport Experiment

ITOP Intercontinental Transport of Pollution

MINOS Mediterranean Intensive Oxidant Study

MLOPEX Mauna Loa Observatory Photochemistry Experiment

NAMBLEX North Atlantic Marine Boundary Experiment

PARFORCE New Particle Formation and Fate in the Coastal Environment

PEM Paciﬁc Exploratory Mission

PMTACS-NY PM2.5 Technology Assessment and Characterization Study – New York

POPCORN Photochemistry of Plant Emitted Compounds and OH Radicals in Northeastern Germany

PROPHET Program for Research on oxidants: Photochemistry, Emissions and Transport

SOAPEX Southern Ocean Atmospheric Photochemistry Experiment

SOLVE SAGE III Ozone Loss Validation Experiment

SONEX Subsonic Assessment, Ozone and Nitrogen Oxide Experiment

SOS Southern Oxidants Study

TEXAQS Texas Air Quality Study

TOHPE Tropospheric OH Photochemistry Experiment

TOPSE Tropospheric Ozone Production about the Spring Equinox

TORCH Tropospheric Organic Chemistry Experiment

TRACE-P Transport and Chemical Evolution over the Paciﬁc

Field Measurements of Atmospheric Composition 31

Figure 1.7 Aerodyne Research Mobile laboratory as deployed in the Mexico City Metropolitan Area

2003 Field Campaign. The facility is equipped to monitor a wide range of trace gas and particle pollutant

concentrations and on-road measurement of in-use vehicle emission ratios (Reprinted with permission

the location of emission plumes, quantifying greenhouse gas emissions (e.g. from natural

gas and landfills), and the spatial distribution of regulated pollutants (O

,NO

, CO,

and particulate matter) in urban centres. Figure 1.7 shows a schematic of a system

operated by Aerodyne Inc., together with the instruments deployed, which is described

in detail in Kolb et al. (2004). An alternative monitoring strategy is to use the laboratory

to temporarily sample at a number of fixed sites (using a battery pack to power the

instruments when the engine is not running) to establish pollutant profiles across an

urban centre (Seakins et al., 2002).

1.4.2 Ship-borne platforms

Ocean-going research vessels are operated by a number of national agencies for the

measurement of atmospheric composition, including ice-breakers for polar regions.

Examples include the Ronald H. Brown, operated by the US National Oceanic and

Atmospheric Administration, the RV Polarstern, operated by the Alfred Wegener Institute,

and the RRS Discovery and Charles Darwin, operated by the UK Natural Environmental

Research Council. Details of the entire worldwide fleet of research vessels, including their

specifications and cruise schedules, are maintained on-line by the University of Delaware,