FTIR CEMS systems for Cement plants 

 Luc Sevrette 

 to: 

 Keith Barnett 

 05/20/2010 05:54 PM 

 Cc: 

 Jeff Ryan, Barrett Parker 

 Show Details 

Hello Keith, 

 

I left you a voice message yesterday and understand you’re away today. I 

hope we can talk together tomorrow (I’ll be in Europe next week). 

 

As per my earlier email to Jeff Ryan (cc to you) on 04-24 and similar 

e-mail to Barrett Parker last week during EPRI CEM User Conf, Gasmet 

Technologies has available for many years commercial solutions (not R&D) 

for accurately monitoring HCl and many other HAPs or std pollutants in 

stack gases. Our FTIR CEM systems are able to measure 12-16 components 

and 

are not much more expensive compared to traditional good NOx/SO2 CEMS 

designed for cement applications. 

 

Because of the evolution of the regulations in Europe (Haz waste, inc 

Cement), most of those Gasmet turn-key FTIR CEM systems have been sold 

over there. The experience Gasmet has in North America is more with 

portable systems (probably more than 50 units in use currently). 

 

In addition of the spec sheet and other info I sent few weeks ago, here 

is 

report from European Authorities approving the use of Gasmet FTIR CEM 

system. As you can see the overall measured performances are well below 

the 2% of range we are stating in our spec sheets. For HCl in particular, 

our min full range is 15mg/m3 = 10ppm, therefore our detection limit is 

below 0.2ppm. While it is certainly appropriate for the 2ppm limit as 

indicated in the proposed Cement MACT (for existing plant), this may not 

sufficient for new plants 0.1ppm proposed limit. We are currently working 

on this (0-5ppm HCl range is certainly achievable in time) but we can’t 

justify more development effort should this limit not being part of the 

final regulation. 

 

Gasmet is aware there is “lobbying” from several North American FTIR gas 

analyser manufacturers trying to convince the community that the low 

resolution system (that Gasmet manufactures) would not be appropriate to 

measure low level of pollutants (HCl or other HAPs). This is generally 

not 

true, FTIR spectral resolution is not directly tied to detection limit 

and 

accuracy. As support to this statement, I’m including independent report 

sponsored by UK Enviro Agency comparing various commercial CEM 

technologies for measuring low level HCl. Among the various techniques, 

Low resolution FTIR (GASMET) and medium/high resolution FTIR are compared 

and results show in general better performance of low resolution 
instrument. You will notice results from instrumental methods are 

compared 

to EPA TM 26A and EN 1911. 

 

As an example of the use of Gasmet portable (low-resolution) FTIR 

instrument in the USA, I have attached copy of paper presented at AWMA 

2001 by T. Dunder from Entropy (one of the stack testing company at that 

time the most experienced with FTIR). Results were very comparable to EPA 

TM (3A, 6C, 7E, 10) for std pollutants, but in one simple lightweight 

package compared to full extractive CEM a stack tester would normally 

used. 

 

While capital investment of FTIR CEMS may be slightly higher than 

conventional cold-dry extractive CEMS, operational cost are much lower 

(no 

water condensation and associated maintenance issues, no need for 

frequent 

recalibration, simpler overall packages). Therefore, on a 5-10 year 

lifetime, overall cost of ownership for FTIR CEMS are generally lower 

than 

for other technologies. 

 

FTIR is now a mature technology for stack gas analysis (for waste 

incinerators, cement and power plants). Altogether with other European 

FTIR CEMS suppliers, there are probably more than 1,200 full FTIR CEMS in 

operation (mostly in Europe). 

 

Gasmet Technologies has 17 years experience in providing FTIR stack gas 

analysis and certainly is one of the largest supplier of this technology 

worldwide. We foresee no issue to meet the Performance Specification 15 

(nor PS-2, PS-3, PS-4, PS-4A, PS-8) has required by US EPA and look 

forward to engage communisation with EPA representatives on this matter. 

 

Best regards 

 

Luc Sevrette 

Gasmet Technologies Inc. 

Manager CEM Products 

luc.sevrette@gasmet.com 

(514) 292 4925 

www.gasmet.com 

 
 

This certificate may only be reproduced in its entirety and without change 

Page 1 of 11 

PRODUCT CONFORMITY CERTIFICATE 

This is to certify that the 

GASMET MULTI-GAS ANALYSER 

CX4000 with Oxitec 500 E SME 5 Oxygen Analyser, 

DX4000 & EN4000 Multi-gas Analyser

manufactured by: 

Gasmet Technologies OY 

Pulttitie 8 A 1 

FIN-00880 Helsinki 

Finland 

has been assessed by Sira Certification Service 

and for the conditions stated on this certificate complies with: 

MCERTS Performance Standards for Continuous Emission 

Monitoring Systems, Version 3.1 dated July 2008, 

EN15267-3:2007, 

& QAL 1 as defined in EN 14181: 2004 

Certification Ranges : 

 CO 0 to 75 mg/m3 0 to 300mg/m3 

 SO2 0 to 75 mg/m3 0 to 500mg/m3 

 HCl 0 to 15 mg/m3 0 to 90mg/m3 

 NO 0 to 200 mg/m3 0 to 600mg/m3 

 NO2 0 to 200 mg/m3

 N2O 0 to 100 mg/m3

 NH3 0 to 15 mg/m3

 

 CO2 0 to 25 % vol 

 O2 0 to 25 % vol* 

 H2O 0 to 30 % vol 

* Certification range only applies to CX4000 analyser with Oxitec 500 E SME 5 oxygen analyser option. 

Project No: 674/0062 & 674/0334 

Certificate No: Sira MC 030014/04 

Initial Certification: 04 July 2003 

This Certificate Issued 16 March 2010 

Renewal Date: 03 July 2013

 Technical Director 

MCERTS is operated on behalf of the Environment Agency by 

Sira Certification Service 

12 Acorn Industrial Park, Crayford Road, Crayford 

Dartford, Kent, UK, DA1 4AL 

Tel: 01322 520500 Fax: 01322 520501 
 

Certificate No: Sira MC 030014/04 

This Certificate Issued: 16 March 2010

This certificate may only be reproduced in its entirety and without change 

Page 2 of 11 

Approved Site Application 

Any potential user should ensure, in consultation with the manufacturer that the emission 

monitoring system is suitable for the process on which it will be installed. 

For general guidance on stack emission monitoring techniques refer to Environment Agency 

Technical Guidance Note M2: Monitoring of stack emissions to air. Operators with installations 

falling under the Large Combustion Plant Directive or Waste Incineration Directive must refer 

to Technical Guidance Note M20: Quality Assurance of Continuous Emission Monitoring 

Systems, for guidance on the suitability of CEMS for their installations. M2 and M20 are 

available on the Agency’s website at www.mcerts.net

On the basis of the assessment and the ranges required for compliance with EU Directives 

this instrument is considered suitable for use on waste incineration and large coal-fired 

combustion plant applications. This CEM has been proven suitable for its measuring task 

(parameter and composition of the flu gas) by use of the QAL 1 procedure specified in 

EN14181, for LCPD and WID applications for the ranges specified. The lowest certified range 

for each determinand must not be more than 1.5X the emission limit value (ELV) for WID 

applications, and not more than 2.5X the ELV for LCPD and other types of application. 

Basis of Certification 

This certification is based on the following Test Report(s) and on Sira’s assessment and 

ongoing surveillance of the product and the manufacturing process: 

 TÜV Köln Report Number: 936/21203240/B, dated 3rd September 2007 

TÜV reports are accepted on the basis of the Environment Agency’s document ‘MCERTS – 

Guidance on the acceptance of German type approval test reports for CEMS’ Version 2 

(October 2003) 

Product Certified 

The measuring system consists of the following parts: 

 Gasmet FT-IR Gas Analyser 

 Gasmet Sampling Unit 

 Enotec Oxygen analyser Oxitec 500 E SME 5 (optional) 

 M&C Probe 

This certificate applies to all instruments fitted with software version 4.42.2 and with serial 

numbers 305 onwards* (which have been fitted with a GICCOR interferometer). 

*except model numbers; 440, 456, 457, 460, 463, 464, 468, 471, 490, 491, 506, 507, 509, 532, 535-537, 548-551, 

562-568, and 587-595 
 

Certificate No: Sira MC 030014/04 

This Certificate Issued: 16 March 2010

This certificate may only be reproduced in its entirety and without change 

Page 3 of 11 

Certified Performance 

The instrument was evaluated for use under the following conditions: 

Ambient Temperature Range: +5oC to +40oC 

Instrument IP rating: IPX4 

Note: If the instrument is supplied with an enclosure then the ambient temperature shall be monitored 

inside the enclosure to ensure that it stays within the above ambient temperature range. 

Unless otherwise stated the evaluation was carried out on the certification range CO 0 to 75 mg/m3

, SO2 0 to 75 mg/m3, HCl 0 to 

15 mg/m3

, NO 0 to 200 mg/m3, NO2 0 to 200 mg/m3, N2O 0 to 100 mg/m3, NH30 to 15 mg/m3, CO2 0 to 25 % vol, O2 0 to 25 % vol, 

H2O 0 to 30 % vol 

Test Results expressed as % of the 

certification range 

Other results MCERTS 

specification 

 <0.5 <1 <2 <5 

Response Time (Note 1) 

 O2 20 <200s 

 CO, NO, NO2, N2O, CO2, H2O 120 <200s 

 SO2, HCl, NH3 180 <400s 

Repeatability standard deviation at zero 

point 

 O2 0.16 <0.2% 

 CO 0.07 <2.0% 

 NO 0.23 <2.0% 

 NO2 0.26 <2.0% 

 N2O 0.05 <2.0% 

 SO2 0.14 <2.0% 

 HCl 0.10 <2.0% 

 NH3 0.40 <2.0% 

 CO2 0.08 <2.0% 

 H2O 0.17 <2.0% 
 

Certificate No: Sira MC 030014/04 

This Certificate Issued: 16 March 2010

This certificate may only be reproduced in its entirety and without change 

Page 4 of 11 

Test Results expressed as % of the 

certification range 

Other results MCERTS 

specification 

 <0.5 <1 <2 <5 

Repeatability standard deviation at 

reference point 

 O2 0.0 <0.2% 

 CO 0.0 <2.0% 

 NO 0.0 <2.0% 

 NO2 0.0 <2.0% 

 N2O 0.0 <2.0% 

 SO2 0.0 <2.0% 

 HCl -1.0 <2.0% 

 NH3 0.2 <2.0% 

 CO2 0.0 <2.0% 

 H2O 0.0 <2.0% 

Lack-of-fit 

 O2 0.16 <0.2% 

 CO -1.9 (-1.7 over range 

0 to 300 mg/m3

) <2.0% 

 NO -1.3 (1.7 over range 

0 to 600 mg/m3

) <2.0% 

 NO2 -0.6 <2.0% 

 N2O 0.6 <2.0% 

 SO2 -1.3 (1.6 over range 

0 to 500 mg/m3

) <2.0% 

 HCl -1.6 (-1.1 over range 

0 to 90 mg/m3) <2.0% 

 NH3 -1.7 <2.0% 

 CO2 1.3 <2.0% 

 H2O -1.9 <2.0% 
 

Certificate No: Sira MC 030014/04 

This Certificate Issued: 16 March 2010

This certificate may only be reproduced in its entirety and without change 

Page 5 of 11 

Test 

Results expressed as % of the 

certification range 

Other results MCERTS 

specification 

 <0.5 <1 <2 <5 

Influence of ambient temperature zero 

point 

 O2 -0.02 <0.5% 

 CO -0.12 <5.0% 

 NO 1.5 <5.0% 

 NO2 0.3 <5.0% 

 N2O -0.1 <5.0% 

 SO2 -1.3 <5.0% 

 HCl 0.9 <5.0% 

 NH3 1.0 <5.0% 

 CO2 0.1 <5.0% 

 H2O 0.1 <5.0% 

Influence of ambient temperature 

reference point 

 O2 -0.24 <0.5% 

 CO -0.12 <5.0% 

 NO 1.8 <5.0% 

 NO2 0.6 <5.0% 

 N2O 0.6 <5.0% 

 SO2 -1.9 <5.0% 

 HCl 3.2 <5.0% 

 NH3 -1.9 <5.0% 

 CO2 -1.3 <5.0% 

 H2O -1.0 <5.0% 
 

Certificate No: Sira MC 030014/04 

This Certificate Issued: 16 March 2010

This certificate may only be reproduced in its entirety and without change 

Page 6 of 11 

Test Results expressed as % of the 

certification range 

Other results MCERTS 

specification 

 <0.5 <1 <2 <5 

Influence of sample gas flow for 

extractive CEMS 

 O2 0.15 <0.2% 

CO, NO, NO2, N2O, SO2, HCl, 

NH3, CO2 , H2O <1 <2.0% 

Influence of voltage variations 190 to 

250V 

 O2 0.03 <0.2% 

 CO -0.87 <2.0% 

 NO -2.0 <2.0% 

 NO2 -0.83 <2.0% 

 N2O -0.60 <2.0% 

 SO2 1.79 <2.0% 

 HCl -1.19 <2.0% 

 NH3 -1.73 <2.0% 

 CO2 1.6 <2.0% 

 H2O 0.71 <2.0% 

Cross-sensitivity at zero (Note 2) 

 O2 0.09 <0.2% 

 CO 0.5 <2.0% 

 NO -0.6 <2.0% 

 NO2 0.6 <2.0% 

 N2O 0.5 <2.0% 

 SO2 0.5 <2.0% 

 HCl 1.3 <2.0% 

 NH3 0.5 <2.0% 

 CO2 0.5 <2.0% 

 H2O 0.5 <2.0% 
 

Certificate No: Sira MC 030014/04 

This Certificate Issued: 16 March 2010

This certificate may only be reproduced in its entirety and without change 

Page 7 of 11 

Test Results expressed as % of the 

certification range 

Other results MCERTS 

specification 

 <0.5 <1 <2 <5 

Cross-sensitivity at reference (Note 2) 

 O2 0.09 <0.4% 

 CO 1.7 <4.0% 

 NO -2.0 <4.0%

 NO2 3.1 <4.0%

 N2O 2.7 <4.0%

 SO2 3.1 <4.0%

 HCl 3.1 <4.0%

 NH3 3.6 <4.0%

 CO2 -2.0 <4.0%

 H2O 3.9 <4.0%

Measurement uncertainty 

 O2 0.709% vol.-% 

 CO 2.84mg/m3

 NO 9.82 mg/m3

 NO2 10.39 mg/m3

 N2O 3.73 mg/m3

 SO2 4.41 mg/m3

 HCl 1.32 mg/m3

 NH3 0.99 mg/m3

 CO2 1.07 vol.-% 

 H2O 1.90 vol.-% 

Guidance - at 

least 25% 

below max 

permissible 

uncertainty 
 

Certificate No: Sira MC 030014/04 

This Certificate Issued: 16 March 2010

This certificate may only be reproduced in its entirety and without change 

Page 8 of 11 

Test Results expressed as % of the 

certification range 

Other results MCERTS 

specification 

 <0.5 <1 <2 <5 

Calibration function (field) 

 O2 0.99 >0.95 

 CO 0.96 >0.95 

 NO 0.99 >0.95 

 NO2 0.99 >0.95 

 N2O 0.97 >0.95 

 SO2 0.99 >0.95 

 HCl (Note 3) 0.95 (Note 3) >0.95 

 NH3 0.95 >0.95 

 CO2 0.99 >0.95 

 H2O 0.99 >0.95 

Response Time (Field) 

 O2 20 <200s 

 CO, NO, NO2, N2O, CO2, H2O 120 <200s 

 SO2, HCl, NH3 180 <400s 

Lack of fit (field) (Note 4) 

 O2 <0.2 <0.2% 

CO, NO, NO2, N2O, SO2, HCl, 

NH3, CO2 , H2O <2 <2.0% 

Maintenance interval 

 28days >8 days 

Availability 

 

 

FTIR 97 

 O2 99.9 

>95% 

>98% for O2
 

Certificate No: Sira MC 030014/04 

This Certificate Issued: 16 March 2010

This certificate may only be reproduced in its entirety and without change 

Page 9 of 11 

Test Results expressed as % of the 

certification range 

Other results MCERTS 

specification 

 <0.5 <1 <2 <5 

Zero and Span drift requirement 

The following is recommended by the manufacturer: 

- Automatic zero calibration with nitrogen once per 

day 

- Water calibration once per year or after any 

analyser service. 

Clause 

6.13 & 10.13 

Manufacturer 

shall provide a 

description of 

the technique to 

determine and 

compensate for 

zero and span 

drift. 

Change in zero point over maintenance 

interval 

 O2 0.06 <0.2% 

 CO 0.25 <3.0% 

 NO 0.39 <3.0% 

 NO2 -0.18 <3.0% 

 N2O 0.19 <3.0% 

 SO2 0.72 <3.0% 

 HCl 0.31 <3.0% 

 NH3 0.37 <3.0% 

 CO2 0.19 <3.0% 

 H2O 0.25 <3.0% 
 

Certificate No: Sira MC 030014/04 

This Certificate Issued: 16 March 2010

This certificate may only be reproduced in its entirety and without change 

Page 10 of 11 

Test Results expressed as % of the 

certification range 

Other results MCERTS 

specification 

 <0.5 <1 <2 <5 

Change in reference point over 

maintenance interval 

 O2 0.18 <0.2% 

 CO 0.3 <3.0% 

 NO 0.0 <3.0% 

 NO2 2.5 <3.0% 

 N2O 0.7 <3.0% 

 SO2 2.4 <3.0% 

 HCl 2.7 <3.0% 

 NH3 2.1 <3.0% 

 CO2 0.4 <3.0% 

 H2O -0.9 <3.0% 

Reproducibility 

 O2 0.09 <0.2% 

 CO 1.23 <3.3% 

 NO 0.82 <3.3% 

 NO2 1.18 <3.3% 

 N2O 1.23 <3.3% 

 SO2 0.56 <3.3% 

 HCl 2.70 <3.3% 

 NH3 0.93 <3.3% 

 CO2 0.80 <3.3% 

 H2O 1.93 <3.3% 

Note 1 Results obtained from field trial 

Note 2 Cross-sensitivity to the following interferents; O2, H20, CO, CO2, CH4, N2O, NO, NO2, NH3, SO2, HCl 

Note 3 Average value reported, overall results taken into account. 

Note 4 Data derived from the analysis function test 
 

Certificate No: Sira MC 030014/04 

This Certificate Issued: 16 March 2010

This certificate may only be reproduced in its entirety and without change 

Page 11 of 11 

Description: 

GASMET CX-4000 FTIR multicomponent gas analyser uses the Fourier Transform Infrared technique 

to measure several gaseous components including water vapor using sample extraction without dilution 

or drying of the sample gas. The FTIR instrument operates in the wave number range of 4200 to 900 

cm-1. The heated measuring cell has a pathlength of up to 5 meters and the temperature is set to 

180oC. The sample extraction system is heated throughout and the sample is transferred through 

electrically heated sample lines. Sample line length in the field test was 20 meters. 

The Gasmet CEM system tested for MCERTS consists of: 

× Gasmet CX-4000 FTIR gas analyser 

× Gasmet Industrial Computer running Calcmet software 

× Enotec Oxygen analyser Oxitec 500 E SME 5 (optional) 

× Gasmet sampling system with the following functional parts 

Heated pump: Charles Austen Pumps Ltd model L2 HH 230; Heated particle filter: Headline 

filters model HRS 211 201; Heated lines; Heated probe: M&C Products model SP 2000 

GASMET DX-4000 is a portable version of the CX-4000 and is used in the following configuration: 

× Gasmet DX-4000 portable FTIR gas analyser 

× Portable Computer running Calcmet software 

× Gasmet portable sampling system with the following functional parts 

Heated pump: Air Dimensions Inc. B161; Heated particle filter: Headline filters model HRS 

211 201; Heated lines; Heated probe: M&C Products model PSP 4000

GASMET EN-4000 model is produced for incorporation in other manufacturer's equipment and is sold 

including the Gasmet FTIR gas analyser, GASMET Industrial computer, and the GASMET Sampling 

system. 

General Notes 

1. This certificate is based upon the equipment tested. The Manufacturer is responsible for 

ensuring that on-going production complies with the standard(s) and performance criteria defined 

in this Certificate. The Manufacturer is required to maintain an approved quality management 

system controlling the manufacture of the certified product. Both the product and the quality 

management system shall be subject to regular surveillance according to ‘Regulations Applicable 

to the Holders of Sira Certificates’. The design of the product certified is defined in the Sira 

Design Schedule for certificate No. Sira MC 030014/02. 

2. If certified product is found not to comply, Sira Certification Service should be notified 

immediately at the address shown on this certificate. 

3. The Certification Marks that can be applied to the product or used in publicity material are 

defined in ‘Regulations Applicable to the Holders of Sira Certificates’. 

4. This document remains the property of Sira and shall be returned when requested by the 

company. 
1

AN INTERCOMPARISON BETWEEN AUTOMATIC AND MANUAL METHODS OF

MEASURING HYDROGEN CHLORIDE CONCENTRATIONS IN STACK RELEASES

 M J Lewandowski

1 ABSTRACT

The Environment Agency is involved in independent monitoring programmes at a variety of industrial processes

where the permits require the measurement of hydrogen chloride (HCl) concentrations in stack releases. The

programmes have revealed a number of difficulties associated with the currently used HCl monitoring techniques.

Significant differences have been observed between results obtained using manual testing methods and those

obtained using continuous emission monitoring systems (CEMs).

Consequently the Agency commissioned a project to compare and assess various measurement techniques

under controlled and repeatable laboratory conditions. The work has been carried out by the UK’s National

Physical Laboratory (NPL). The inter-comparison consisted of a series of tests involving CEMs and Standard

Reference Methods (SRMs) using a test chamber developed for the purpose of instrument certification under

the Agency’s Monitoring Certification Scheme (MCERTS). The facility delivered controlled traceable test gases

to the analysers either in across-stack or in an extractive monitoring set-up.

The instrumental methods covered included the gas filter correlation (GFC), differential optical absorption

spectroscopy (DOAS), tunable diode laser (TDL), Fourier transform spectroscopy (FTIR)- medium and low

resolution , and ion mobility mass spectrometry (IMMS). The two manual methods tested were SRMs as

specified by EN1911 and US EPA method 26A.

The tests have demonstrated that in general the instrumental techniques perform well and produce much more

repeatable results than SRMs. No major interferent effects were observed across all techniques. The SRMs were

not challenged with gaseous chlorides which would have caused much greater discrepancies between the

automatic techniques and the manual ones. The performance of SRMs puts a question mark over their use as a

principal means of calibration of CEMs especially in view of possible interfering effect of gaseous chlorides.
2

2 LABORATORY TESTING PROGRAMME

2.1 Scope of the tests

A series of laboratory tests were carried out to assess the HCl monitoring techniques. The tests performed on the

CEMs were:

• Accuracy;

• Accuracy in the presence of interfering species;

• Linearity;

• Linearity in the presence of interfering species;

• Cross sensitivity to interfering species (including water);

• Detection limit;

• Effect of ambient temperature on zero and span readings.

It was not practical to subject the SRMs to the same testing programme as the CEMs, due to the comparatively

long time period required for one SRM measurement. The SRMs sampled a series of test gases, containing a

range of HCl concentrations, some with interferents present. The test gases were chosen to enable an

assessment of :

• Accuracy;

• Linearity;

• Cross Sensitivity

In addition, parallel measurements were made using a subset of the CEMs during the SRM tests to provide a

direct comparison of results.

2.2 Testing facilities

The test facility was developed to carry out laboratory testing for the Environment Agency’s MCERTS scheme

for continuous emission monitors and was used to deliver controlled traceable test gases and simulate relevant

features of a stack environment.The test facility used for testing the HCl monitoring techniques in the laboratory

comprised of a number of components ; a probe chamber, water vapour generator, interferent blender unit,

environmental chamber and binary network gas blender.

The probe chamber is a 1 metre long gas-tight chamber mounted in an oven. It was used to simulate the

environment that an analyser may be exposed to in a stack. Traceable concentrations of gas mixtures were

maintained at controllable temperatures and pressures.

The water vapour generator was used to generate accurate concentrations of water vapour. It mixed known flows

of water and dry air and raised the temperature of the mixture to ensure total vaporisation.

The interferent blender unit is a dynamic dilution system comprising nine mass flow controllers, one of which

was used to control the flow of the diluent gas and the remainder controlled the flows of the interferents gases.

The environmental chamber was used to control the ambient environment that cross stack analysers were

exposed to. During these tests, the probe chamber, including its oven, was located inside the environmental

chamber. Only those components of the CEMs that are mounted on stacks were subjected to the ambient

temperature tests.

The binary network is a facility that was used to produce the required, accurate and traceable, gas mixtures. The

gas mixtures were produced dynamically using several mass flow controllers (MFC) that were connected in

parallel. During the tests the total flow of the gas mixture and the concentration of HCl injected into the probe

chamber were kept constant. This was achieved by adjusting the diluent gas flow to the appropriate settings
3

when each additional interferent was injected, enabling the settings for the HCl, generated using the binary

network, to remain stable. The configuration is illustrated in Figure1.

Figure 1. Schematic diagram of facility generating test gases

2.3 Test gases

The accuracy test was carried out using a commercially manufactured HCl standard, which was calibrated by

NPL, directly and traceably to UK national standards. This gas had a nominal concentration at 90% of the testing

range. The testing range was nominally 0 to 100 μmol/mol of HCl.

The zero gas used was obtained from a compressed air line. This was scrubbed by a catalytic converter to reduce

the hydrocarbon content to less than 0.1 μmol/mol, dried to remove water at a dew point of -70°C and filtered to

remove particulate matter of diameter greater than 3 micrometres.

The uncertainties of gases used are summarised in Table 1.

Output to probe

chamber

HCl ~ 80 μmol/mol

NO2 ~ 10 μmol/mol

CO2 ~ 200

mmol/mol

CH4 ~ 30 μmol/mol

H2O ~ 100 mmol/mol

 13.5 l/m

4.5 l/m

Interferent

Blender

Binary

Network

Water Vapour

Generator

HCl. ~ 550 μmol/mol

Diluent Air

MFC. 0 ~ 2.0 l/m

MFC. 4.5 ~ 2.5

l/m

NO2 ~

100μmol/mol

CO2. ~

100μmol/mol

Diluent Air

MFC. 0 ~ 0.5

l/m

MFC. 0 ~ 1.0

l/m

MFC. 4.5 ~ 1.5

l/m

 4.5 l/m

H2O. 1 mol/mol

Diluent Air

MFC. 0 ~ 1.5 l/m

 (vapour)

MFC. 4.5 ~ 3.0

l/m

4.5l/m
4

Table 1 Uncertainty of Source Test Gases

GAS SUPPLIED NOMINAL

CONCENTRATION

NPL MEASURED

CONCENTRATION AND

UNCERTAINTY

NO2: Bulk (103 ± 5.15) μmol/mol -

CO2: Bulk 1 mol/mol -

CH4: Bulk (915 ± 18.3) μmol/mol -

Water 1 mol/mol -

HCl: Bulk 1

Bulk 2

Bulk 3

Bulk 4

532.8 μmol/mol

540.2 μmol/mol

541.1 μmol/mol

542.3 μmol/mol

(587 ± 20)μmol/mol

(580 ± 20)μmol/mol

(493 ± 17) μmol/mol

(621 ± 21)μmol/mol

Air 1 mol/mol Water < 500 μmol/mol

Particulate < 3 micron

.

3 TEST RESULTS

3.1 Gas filter correlation (GFC)

The gas filter correlation technique uses a narrow bandpass interference filter to isolate the appropriate region

within the infrared spectrum at which the determinand has absorption features. The analyser uses two

hermetically sealed gas filled cuvettes on a rotating chopper to modulate an infrared beam that has been passed

through a cell containing the sample gas. Normally one of the cuvettes is filled with nitrogen and the other with

the determinand gas (in this case HCl). The infrared beam then falls onto a detector. The detector receives two

alternating signals: one, the ‘sample’ signal, is unattenuated through the nitrogen cuvettes, the other, the

‘reference’ signal, is attenuated by the specific fine absorption bands produced by the HCl cuvette. When the

analyser is exposed to the sample gas the ‘sample’ signal is attenuated due to the presence of any HCl in the

sample gas removed. The analysis function obtained during the tests is shown in Figure 2.

Figure 2 GFC response to HCl corrected for accuracy-test result, interferents present

Actual CEM Response

y = 0.9792x

R

2

= 0.9996

Corrected CEM Response

y =0.9988x

 R2=0.9996

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60 70 80 90 100

Applied Concentration in μmol/mol

CEM Response in μmol / mol
5

3.2 Differential optical absorption spectroscopy (DOAS)

Differential Optical Absorption Spectroscopy is used to measure the concentration of gases by determining the

gradient of an absorption peak. This is achieved by measuring the difference between the absorbance at a

wavelength where the sample gas has produced a distinctive absorption peak, and at one or more wavelengths

on either side of the peak.

The technique uses white light produced from a continuous light source, (in this case a high pressure Xe lamp),

to form a parallel beam using a focusing mirror. The parallel light passes through the sample cell, then reflects off

a mirror which focuses the light into the entrance of a monochromator. The grating of the monochromater

disperses the light so that the spectrum is projected on to a mask. This allows the segments of the dispersed

spectrum to fall on to a rotating wheel, with the central wavelength set by the monochromator wavelength

setting. The rotating wheel contains a number of narrow slits, which scan the portion of the spectrum dispersed

across the monochromator exit slit and pass it to a detector. The signal, detected using a photomultiplier, is

measured at numerous locations across the exit aperture, and these signals are stored in different channels and

are analysed to determine the HCl concentration. The analysis function obtained during the tests is shown in

Figure 3.

Figure 3 DOAS response to HCl corrected for accuracy-test result, interferents present

The data processing of the DOAS analyser incorporated a correction for the presence of water. Therefore, the

concentration of HCl should not have been affected by water vapour. However, when the analyser was exposed

to 80 μmol/mol of HCl with 10pph of water vapour, the observed concentration of HCl decreased by

approximately 10 μmol/mol. A plausible explanation for this effect is related to the calibration of the water channel

in the analyser. When the analyser was exposed to 10pph of water vapour it measured the concentration of the

water vapour to be between 15-20pph. This suggests that the calibration of the water channel in the analyser may

have drifted, decreasing the concentration of HCl by approximately 10 μmol/mol in the presence of water. This is

not an inherent fault with the DOAS technique, but it does highlight potential problems with analysers which

correct for intereferent effects.

Actual CEM Response

y = 0.8792x

R 2= 0.9978

Corrected CEM Response

y = 0.9583x

 R2= 0.9978

-10

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60 70 80 90 100

Applied Concentration in μmol/mol

CEM Response in 

μmol / mol
6

3.3 Fourier transform infrared spectroscopy (low 

 resolution FTIR) - automated data analysis

An FTIR spectrometer consists of an infrared source that emits a broad band of wavelengths of infrared

radiation. The infrared radiation is passed through an interferometer which modulates the signal. The

interferometer performs an optical inverse fourier transform on the signal, then passes the modulated infrared

beam through the gas sample. The intensity of the infrared beam is measured by a detector, the signal is

digitalised, and Fourier transformed by a computer to obtain the infrared spectrum of the sample gas.

The low resolution FTIR analyser extracted the gas sample through a 5 metre long heated line. The calibration

was carried out by the manufacturer. The analyser gave a digital output that displayed its readings in μmol/mol.

The resolution of the analyser used was 8 wavenumbers. ( A wavenumber is a spectroscopic unit. It is an inverse

wavelength, one wavenumber is equal to 1cm-1).

Figure 4. Low resolution FTIR response to HCl corrected for accuracy-test result, interferents present

Actual CEM Response

y = 0.9923x

R

2

= 0.9972

Corrected CEM Response

y = 1.0419x

R

2

= 0.9972

-20

0

20

40

60

80

100

0 10 20 30 40 50 60 70 80 90

Applied Concentration in μmol/mol

CEM Response in μmol/mol
7

3.4 Fourier transform infrared spectroscopy ( medium

resolution FTIR) automated data analysis

The medium resolution FTIR system used the same technique as the low resolution system, but with a higher

spectroscopic resolution (1 wavenumber).

The medium resolution FTIR analyser extracted the gas sample through a heated line that was 5 metres long. The

calibration used was carried out by the manufacturers. The analyser gave a digital output that displayed readings

in μmol/mol. The analysis function obtained during the tests is shown in Figure 5.

Figure 5. Medium resolution FTIR response to HCl corrected for accuracy-test result, interferents present.

The medium resolution FTIR analyser initially had a problem related to the sampling system. This became

apparent when the analyser was exposed to 80 μmol/mol of HCl in the presence of 10pph of water vapour, The

concentration of HCl decreased to 38.1 μmol/mol in the presence of water. The problem was identified as the

sample line particulate filter. The purpose of the filter was to eliminate any particulate matter with a diameter

greater then 3 microns. However, the filter appeared to remove a significant proportion of HCl in the presence of

water vapour. The heated line was removed from the inlet to the sampling system, and attached directly to the

sampling cell. When the test was repeated, the concentration of HCl increased to 83.9 μmol/mol in the presence

of water. This higher value can be explained by a spectral broadening effect that many of the optical analysers

appeared to experience.

In order to resolve any doubts relating to the data processing of the automated FTIR analysers, the raw data

obtained from the Medium Resolution FTIR spectra were manually re-processed, and the results noted, enabling

a direct comparison between the automated and manual results.

Corrected CEM Response

y = 1.0046x

R

2

 = 0.9973

Actual CEM Response

y = 1.0465x

R

2

 = 0.9973

0

20

40

60

80

100

120

0 10 20 30 40 50 60 70 80 90 100

Applied Concentration in μmol/mol

CEM Response in 

μmol / mol
8

3.5 Ion mobility mass spectroscopy (IMS)

 Ion Mobility Mass Spectrometry, (IMS), operates in a similar way to an atmospheric pressure time of flight mass

spectrometer. All mass spectrometers consist of: an ion source which ionises the sample molecule, a mass

analyser that differentiates the ions according to their mass-to-charge ratio, and finally a detector which

measures the ion beam current.

In the analyser tested, an IMS cell was used to detect the sample gas. The sample was indirectly ionised using a

Ni63 ring, a beta ionisation source, within the sample cell. The resultant ion clusters were separated in the

presence of an electrical field to generate spectra which were measured on the detector. The concentration of the

sample gas could then be determined.

The IMS analyser extracted the gas sample through a heated line that was 5 metres long. The calibration was

carried out by the manufacturer. The analysis function obtained during the tests is shown in Figure 6.

Figure 6 Ion mobility Spectroscopy response to HCl corrected for accuracy test results,

 interferents present.

A number of problems were encountered which affected the performance of the IMS analyser in the laboratory

environment. However, these problems would not necessarily be relevant if the analyser was operated in a

typical industrial environment, where it would normally be operated with a dilution facility. In order to operate

the analyser with the test facility it was necessary to set it up in an atypical configuration.

The problems encountered were:

ß the analyser signal went off scale (below zero) when exposed to zero gas;

ß a lack of insulation around the internal cell;

ß significant analyser noise;

ß pressure effects on the flow rate.

Actual CEM Response

y = 0.5378x

R

2

= 0.9323

Corrected CEM Response

y = 0.8444x

R

2

 = 0.9323

0

5

10

15

20

25

30

35

40

45

0 10 20 30 40 50 60

Applied Concentration in μmol / mol

CEM Response in

μmol / mol
9

3.6 Tunable diode laser (TDL)

Tunable diode laser spectroscopy is used to measure the concentration of gases via an optical method using the

principle of selective infrared absorption by the gas molecules. The TDL operates in the near infrared spectral

range (NIR) producing narrow linewidth light, that is tunable over a small wavelength range. The analyser is

capable of operating at a single frequency, which can be tuned by temperature and/or current. Several different

modulation techniques can be adopted to increase the signal to noise ratio. This involves modulating the output

of the laser by modulating the current, and thus temperature of the diode, to measure the concentration of the

sample gas. Due to the wide range of gases that have a single absorption line in the NIR, the TDL analyser can

select multiple absorption lines at different frequencies. The lines produced are generally the overtone lines from

the fundamental absorption lines due to the rotational and vibration modes of the molecules.

The basic technique behind the TDL involves scanning the laser over the absorption line. To improve the

detection sensitivity the technique applies a modulation of the laser frequency. The modulation frequency used

is significantly less than the width of the absorption line, so that the formation of the second harmonic

component of the signal produced can be used to quantify the concentration of the sample gas. The analysis

function obtained during the tests is shown in Figure 7.

Figure 7. TDL response to HCl corrected for accuracy-test result, interferents present

A number of problems were experienced with the TDL analyser:

ß a decrease in transmission due to ambient vibrations;

ß spectral broadening of the sample gas absorption line when exposed to interferents;

ß miss-identification of HCl when exposed to methane;

ß loss of sensitivity in the presence of water vapour.

In addition the technique, in common with other purely spectroscopic techniques, was incapable of monitoring

molecules bound in complex compounds.

The TDL analyser was found to be very sensitive to the alignment of the optical beams, and this caused the

instrument to be sensitive to vibration. If the analyser were to be subjected to typical vibrations on a stack it is

possible the transmission, and hence the sensitivity, might be affected. This is a potential problem with cross

stack instruments in general.

Corrected CEM Response

y = 0.9422x

R

2

= 0.9903

Actual CEM Response

y = 1.1491x

R

2

 = 0.9903

0

20

40

60

80

100

120

0 10 20 30 40 50 60 70 80 90 100

Applied Concentration in μmol / mol

CEM Response in

μmol / mol
10

The spectral broadening of the absorption line caused the analyser to read the concentration of the sample gas

incorrectly when simultaneously exposed to interferents. The broadening was due to absorption lines from the

interferent gases overlapping with the HCl absorption lines. This gave an apparent decrease in the HCl

concentration. This was caused by the base of the HCl absorption peak being broadened by the absorption peak

of the interferent gas and in turn causing the baseline reading to be too high, resulting in a reduced HCl reading.

This effect is a feature of the choice of spectral region used to detect HCl and in principle is not an inherent

problem with the technique. However, this does highlight an area of potential concern in any spectroscopic

technique.

When the analyser was exposed to methane as one of the individual interferents a further problem emerged. The

analyser ‘locked’ on to the methane absorption feature and identified this as HCl. This would appear to be a

feature of the data processing software within the analyser. In the presence of HCl the analyser had correctly

identified the HCl peak, however when the HCl was removed and replaced with methane this was incorrectly

identified as HCl. Due to both the HCl and methane absorption peaks having relatively close wavelengths the

analyser detected the methane peak as an HCl peak. A further complication was that when the analyser was

subsequently exposed to HCl it did not respond, which implies that the lock to the incorrect, methane,

wavelength had been maintained.

The analyser also exhibited an apparent loss in sensitivity in the presence of water vapour. A possible

explanation for this is hydrogen bonding. The water molecules that are injected into the probe chamber tend to

form a very strong dipole-dipole attraction to the HCl molecules, known as a hydrogen bond. This means the

hydrogen atom serves as a bridge between two electro-negative atoms, holding one by a covalent bond and the

other by an electrostatic force. When 10pph of water vapour is injected into the probe chamber with 80 μmol/mol

of HCl, the water molecules start to form hydrogen bonds with the hydrogen atoms in HCl. The HCl atoms in a

hydrogen bond will have broader absorption spectra than free atoms. Therefore, the analyser will detect a

broader spectral band than that seen under calibration conditions, resulting in a decrease in the sensitivity of the

analyser when exposed to water.

3.7 Manual sampling method EPA 26A.

The manual testing methods measure the emissions of hydrogen halides and halogens from a stationary source.

The basic principle involves extracting the sample gas isokinetically from the source then passing it through a

heated line and a filter, into an absorbing solution that collects the gaseous hydrogen halides and halogens. The

filter is used to collect particulate matter such as halide salts. The hydrogen halides form ions in the solution.

The manual testing used a set of ‘mini’ impingers to collect the HCl. Two separate techniques were compared:

method 26A and EN1911-1.

The methods were each used to sample the test gas from the probe cell over 12 hourly sampling periods. The

concentration of the test gas was kept constant for each hourly sample. Some samples had water vapour present,

the rest used dry gas. The sampling system used to perform the manual method 26A is shown in Figure 8.

Figure 8 Sampling System for ManualMethod 26A.
11

The results obtained with manual extractive method 26A are shown in table 2.

 Table 2

The graph shown in Figure 9 illustrates the CEM response of the manual testing method 26A in comparison to

the applied concentrations.

Figure 9. Response of manual Method EPA 26A to HCl

Applied Sample Gas Applied Concentration

μmol/mol

Result

μmol/mol

HCl 2.2 0.4

HCl 4.4 3.6

HCl 54.4 43.9

HCl 60.4 54.1

HCl 13.0 10.6

HCl 71.6 64.8

HCl + NO2 4.4 + 9.9 3.3

HCl 60.4 50.8

HCl + H2O 60.4 + 11.1 pph 53.5 + 12.2 pph

HCl 63.1 54.7

HCl + H2O 71.6 +13.2 pph 56.1 + 14.6 pph

HCl 37.0 29.3

Manual Method 26A

y = 0.8945x

R

2

 = 0.987

Ideal Response

0

10

20

30

40

50

60

70

80

0 10 20 30 40 50 60 70 80

Applied Concentration in μmol/mol

Manual Method 26A Concentartion in 

μmol/ mol
12

3.8 Manual sampling method EN 1911

The sampling system used to perform the manual method EN 1911 is shown in Figure 10.

Figure 10 Sampling System for Manual Method EN 1911-1

The results obtained for the manual testing method EN1911 are summarised in table 3.

 Table 3

Applied sample gas Applied concentration

(μmol/mol)

Result

(μmol/mol)

HCl 2.3 2.3

HCl 4.6 4.2

HCl 55.2 52.2

HCl 59.8 56.6

HCl 11.5 10.7

HCl 72.8 66.4

HCl + NO2 4.6 + 9.9 4.8

HCl 61.4 65.4

HCl + H2O 61.4 + 11.1 pph 47.7

HCl 64.4 63.0

HCl + H2O 72.8 +13.2 pph 92.8

HCl 36.8 18.4
13

The graph shown in Figure 11 illustrates the CEM response of the manual testing method EN 1911-1 in

comparison to the applied concentrations.

Figure 11 Response of manual method EN 1911 to HCl

Ideal Response Modified Response

of EN1911

y = 0.9956x

 R2= 0.9863

0

10

20

30

40

50

60

70

80

90

0 10 20 30 40 50 60 70 80

Applied Concentration in μmol / mol

Response of Method EN 1911 in 

μmol/ mol

EN 1911

EN 1911-1

modified

Outlying points

EN 1911 - 1
14

4. A SUMMARY OF THE HYDROGEN CHLORIDE INTERCOMPARISON

RESULTS

Table 4 Summary of the results obtained for automatic analysers

Performance Characteristic DOAS TDL GFC Low Res.

FTIR

High Res

FTIR

Automated

Data

High Res

FTIR

 Manual

Data

IMS

CEM Range

(μmol/mol)

-10-100 -10 - 100 0 - 100 0 - 100 0 - 100 0 - 100 0 - 70.69

Response Time (sec) 245 32 216 180 180 180 180

Accuracy of Response ( %

of applied concentration)

7.5 (6.0)1

13.1

2.7 -4.6 -4.4 - -13.9

Accuracy of Response in

the Presence of a Mixture

Interferents (% of applied

concentration)

-9.4 (18.0)1

5.3

-2.0 2.2 4.4 - -57.2

Linearity Error (% of full

scale)

0.2 -0.3 -0.2 -2.4 -1.1 - 0.4

Linearity Error in the

Presence of a Mixture of

Interferents (% of full

scale)

-0.2 -0.7 0.1 2.3 2.5 - -0.3

Cross Sensitivity Tests

Applied Conc. of HCl for

span reading (mmol/mol)

80.4 80.4 80.4 80.6 80.6 80.6 50.6

( The following sensitivity results are presented as % of full scale)

NO2:- The effect on zero -0.1 0.2 -1.1 0.02 1.6 - 1.8

NO2:- The effect on span 0.3 1.9 -0.5 0.2 1.3 - -11.6

CH4:- The effect on zero -0.5 0.1 -1.0 0.3 2.3 - -0.7

CH4:- The effect on span -1.1 2.1 -0.1 0.8 1.6 - 0.3

CO2:- The effect on zero 0.7 0.7 -1.2 0.3 2.1 - -0.4

CO2:- The effect on span -0.9 -0.4 -1.0 3.3 4.3 - 3.2

H2O:- The effect on zero -0.3 0.2 0.5 1.1 2.5 1.8 -1.0

H2O:- The effect on span -10.0 -8.4 -5.1 7.3 -31.2 -30.6 -3.7

H2O:- The effect on zero - - - - 0.8 0.6 -

H2O:- The effect on span - - - - 7.8 7.5 -

(without sampling system)

Sum of single component

interferents 2 The effect on

zero

-0.2 1.2 -2.8 1.7 8.5 - -0.3

Sum of single component

interferents 2 The effect on

span

11.7 -4.8 -6.7 11.6 -24.0 - -11.8

Cocktail:- The effect on

zero

-0.7 0.3 1.6 3.4 2.1 - 1.2

Cocktail:- The effect on the

span

-8.0 -6.0 -5.2 7.7 -27.6 - -27.0
15

5 CONCLUSIONS

The results of the tests show that in general the CEM techniques performed well, and gave more representative

results than the manual techniques. Some of the problems which occurred with the CEMs were due to analyser

design, while others were due to faults with the particular equipment being tested. While these are not indicative

of problems with the techniques themselves, they do highlight the importance of good design, reliable

manufacture and adequate testing and calibration of installed equipment. A number of the faults observed would

not have been evident had they occurred in equipment installed on a stack. The Monitoring Certification Scheme

(MCERTS) introduced in the UK by the Agency is aimed at demonstration of fitness for purpose of equipment

and helps to avoid the kind of problems that came to light in the present study.

The various problems observed have also highlighted a number of issues with spectroscopic techniques in

general. The potential for overlapping absorption bands means that these techniques may be particularly

sensitive to interferents. In addition, reference and zero spectral measurements must be free from interferent

absorption peaks. The performance of systems using such techniques will depend upon the correct choice of

spectral region by the manufacturer. Accurate calibration of such analysers is also fundamental, and care should

be taken to ensure that no assumption is made by the manufacturer as to the matrix within the gas (for example

presence of water vapour).

CEMs should also be used within the range of conditions specified by the manufacturer, and it is important that

they are installed and configured correctly. The effect of operating an analyser outside its normal operating

conditions can be seen in the results obtained from the IMS system. In this case operating the analyser in a

configuration which delivered a concentration of water vapour which was above that recommended for the

analyser caused significant errors.

All analysers had response times of less than 4 minutes, which for most stack applications is well within

requirements.

The results of the accuracy test were within 15 % of measured value for all analysers. The IMS had an error of

13.5%, which may have been due to the configuration in which it was operated, as discussed above. The TDL

initially gave a response which was 6% in error. After recalibration by the manufacturer this changed to 13%, but

the response to water vapour changed after this recalibration, and it appears the analyser was recalibrated with

wet gases. The accuracy errors were in general due to the calibration artefacts used by the manufacturers. The

results from the tests have been quoted as ‘corrected results’ when they have been scaled to take account of the

accuracy test results. This allowed for better comparison between different techniques. No major systematic

interferent effects were observed across all the techniques. Some analysers were susceptible to water vapour

interference. This manifested itself as a quenching effect in all techniques apart from the low resolution FTIR

which gave a positive response to water vapour. It is worth noting that the TDL analyser initially gave larger

positive response to the accuracy test in the presence of interferents than it did to HCl alone. However, after the

analyser had been returned to the manufacturer for recalibration its response to HCl alone was higher than its

response to HCl in the presence of interferents. Examining the analyser’s response to individual interferents it is

clear that this was mainly due to a relatively high sensitivity to water vapour.

The manual methods are known to be sensitive to total chlorides rather than HCl specifically. This response,

which is an inherent part of the methods, was not challenged in these tests. It should be noted however that

under field conditions, chloride ions might well be present in a number of forms other than HCl.

In general, the manual methods performed less consistently than the CEMs. The linearity of the manual methods

was acceptable but not as good as most of the CEMs. The manual methods showed no consistent systematic

effect due to the presence of water vapour or NO2. Two results from EN 1911 had to be treated as outliers, as

shown in Figure 11.

All the tests were performed under laboratory conditions. The techniques were presented with test gases which

had a more uniform matrix than would often be found under real conditions. The overall performance of the

techniques was encouraging. The largest source of error in most cases was due to the calibration of the system.

The tests of manual methods have shown a baseline for the performance of these techniques under close to ideal
16

conditions. They have shown that under these conditions the techniques are capable of producing reasonably

consistent results, and inconsistencies of the magnitude observed under field conditions have not been seen.

BIOGRAPHICAL DETAILS : MACIEK LEWANDOWSKI

Environment Agency

National Compliance Assessment Service

Lancaster, LA1 4XQ, UK

Phone: 01524 581931 Fax: 01524 842709 E-mail: maciek.lewandowski@environment-agency.gov.uk

Maciek Lewandowski is a Technical Manager in the National Compliance Assessment Service of the

Environment Agency. His responsibilities include technical guidance on monitoring of stack emissions and

ambient air quality. His main area of work is the implementation of the MCERTS scheme for ambient air quality

monitors. He participates in the work of three working groups of CEN TC 264. Before joining the Agency he

worked in the field of environmental consultancy dealing with environmental impact assessments, stack

monitoring exercises, operation of ambient air quality monitoring networks and development of calibration

systems for automatic analysers.
1

For Presentation at the Air & Waste Management Association’s 94th Annual 

Meeting & Exhibition, June 24-28, 2001, Orlando, Florida 

Abstract 276 Session AO-2a 

FIELD EVALUATIONS OF A PORTABLE, LOW RESOLUTION 

FTIR ANALYZER FOR MEASUREMENT OF AIR POLLUTANTS 

IN STATIONARY SOURCE EMISSIONS AND AMBIENT AIR 

Thomas A. Dunder, Ph.D. 

Entropy, Inc. 

PO Box 90067 

Research Triangle Park, NC 27675-0067 

ABSTRACT 

A portable, low resolution FTIR (Fourier Transform Infrared) analyzer designed for stationary 

source testing, continuous emissions monitoring, and ambient air testing was evaluated in several 

field settings. The Gasmet Analyzer is manufactured by Temet Instruments Oy (Helsinki, Finland). 

The analyzer is designed for multi-component, real-time measurement of criteria air pollutants, 

gaseous hazardous air pollutants (HAPs), and volatile organic compounds (VOCs). Three separate 

field test studies are described where the analyzer was used to measure different gas matrices. 

Ambient air measurements were performed at several locations in a manufacturing and warehousing 

facility to identify the cause of product discoloration. Stack measurements were performed at pilotscale coal combustion research facility where a novel NOx removal system was being tested. Ozone 

slip from the ozone-injection NOx control system was monitored in comparison with ozone 

instrumental analyzers. The FTIR also quantified NO, NO2, N2O, HNO3, and SO2 emissions at the 

coal combustor. In the third study, simultaneous measurements were made between the FTIR and a 

CEM system at a glass melter furnace. Comparisons were made with single component 

instrumental analyzers using the EPA Test Methods 3A (CO2), 6C (SO2), 7E (NOx), and 10 (CO), 

with a relative accuracy test audit (RATA) performed for NOx and CO2 measurements at the glass 

melting furnace. NOx emissions a glass melting furnace were speciated to determine the relative 

emissions of NO, NO2, and N2O. The paper summarizes the evaluation results. 

Key Words: FTIR, NOx, Nitrogen Oxides, CEM, ambient, emissions 
2

INTRODUCTION 

Environmental field testing for gaseous components presents a significant challenge because of the 

diversity of analytes, sample matrices, and test conditions that are encountered. A similar diversity 

of techniques are available for sample collection and analysis. Traditionally this has meant a choice 

between manual (impinger- or adsorbent-based) methods, single component gas analyzers (e.g., 

NOx, SO2, CO), and a representative, but non-speciated measurement, such as a total hydrocarbon 

(THC) analyzer. There are drawbacks to each of these options. For example, manual test methods 

require off-site laboratory analysis with data typically not available until several weeks after testing. 

These methods collect an integrated sample and yield average concentrations, providing neither 

temporal information nor any indication of the variation in emissions over the test period. 

Single component analyzers do provide real-time and time-resolved data, but are available for a 

limited subset of analytes. These analyzers generally require sample conditioning (for moisture 

removal and gas cooling) in source-level testing applications which are often characterized by high 

gas temperature and moisture content. Single component analyzers also must be calibrated 

frequently during a test, requiring several gas cylinders per analyzer. Finally, the data from a total 

hydrocarbon analyzer, while yielding time-resolved organic emissions data that is proportional to 

the source emission rate, provides no information on the gas composition. Since the response from 

a hydrocarbon analyzer is based upon the response to a selected hydrocarbon (usually methane or 

propane), the resulting measured concentration can be considerably less than the true concentration 

for hydrocarbons that give poor response in a flame ionization measurement. 

In recent years, several types of multi-component analyzers have been developed for field testing 

applications. These analyzers, which include Fourier Transform Infrared (FTIR) spectrometers, gas 

chromatographs (GC), and gas chromatograph-mass spectrometers (GC-MS), overcome the 

limitations described above by providing real-time, time-resolved data for multiple components. 

The last decade can be characterized as the time when these well-established laboratory instruments 

made the transition from the lab to the field. Initially, testing firms went to great lengths to design 

mobile laboratories with adequate environmental control (temperature, vibration) to allow existing 

lab instruments to be transported and operate under field conditions. More recently, instrument 

manufacturers have responded to the market need by designing true field instruments. The lab 

analyzers were re-engineered and re-born as field portable analyzers, simultaneously made smaller, 

more rugged, less susceptible to variation in temperature and vibration, and lower in cost. 

Entropy, Inc. (Raleigh, NC) was one of the first environmental testing companies to conduct field 

testing using FTIR spectroscopy, having constructed an FTIR mobile laboratory in 1992. Entropy 

chose to focus on FTIR because it has the most broad applicability of the modern, multi-component 

analytical techniques. This is because all gaseous molecules, with the exception of homonuclear 

diatomics (N2, H2, Cl2, etc.), absorb infrared radiation and can, in principle, be detected. Recently, 

Entropy has been evaluating the GASMET, a field portable FTIR analyzer. The GASMET FTIR 

offers significant advantages in portability, ruggedness, and ease of use that hold the potential to 

allow FTIR to be used more extensively in air emissions and ambient air testing than the current 

laboratory-type instruments now in use. This paper describes three cases studies where the 

GASMET was used in different field testing applications. 
3

GASMET ANALYZER 

The GASMET FTIR is manufactured by Temet OY (Helsinki, Finland) and marketed in the United 

States by Air Quality Analytical (Austin, Texas). Several instrument configurations are available 

depending upon the measurement application. The GASMET DX-4000 model is a portable (35 

pounds, 8”x20”x20” dimensions), low resolution (7.7 wavenumber resolution) spectrometer that is 

capable of performing real-time simultaneous analysis for multiple gas phase components. The 

analyzer evaluated in these field tests was outfitted with an adjustable temperature (ambient - 180 

o

C) gas cell of 2.4 meter pathlength and a Peltier-cooled MCT detector; other detector and cell 

options are available. Unlike most FTIR analyzers, neither liquid nitrogen nor a continuous 

instrument purge with gaseous nitrogen is required, though an instrument purge is recommended 

when measuring low concentrations of water or CO2. The analyzer is operated with a laptop 

computer via a RS-232 cable. The spectrometer operates at a scan rate of 8 scans/second, or 540 

scans per averaged spectrum collected using a typical one minute integration time. Integration 

times as short as 1 second may be used to capture data with improved time resolution, while 

integration times up to 5 minutes are an option for optimal signal-to-noise and sensitivity. 

Analysis is performed using an algorithm based on CLS (classical least squares). This analytic 

routine compensates for cross-interference encountered when species absorb in the same spectral 

region. Besides reporting the measured concentration for each compound, a spectral residual is also 

calculated that is indicative of the analytical accuracy. The FTIR analysis is optimized by the user, 

by selection of reference standards and analytical regions, to minimize spectral residuals. 

The Temet CALCMET software is Windows-based and mouse operated, with pull-down menus to 

control instrument functions. Measured concentrations are displayed in either bar graph and trend 

plot format. For each measurement, the residual associated with the measured concentration is 

reported on-screen, and the data is flagged if residuals exceed defined limits. The residual values 

provide immediate feedback on measurement accuracy, indicating, for example, if a new 

background spectrum should be measured or the presence of an unknown compound in the gas 

sample. 

A library of quantitative reference spectra for over 200 compounds is provided with the instrument, 

and the user can measure additional reference standards as needed. For certain compounds (in 

particular, water vapor) the analytical results are improved if the reference standards are measured 

on the spectrometer being used for measurement. The library standards are generally measured at 

either low (40 o

C) or high (180 oC) temperature, depending upon the application. Conditioned or 

other low moisture gas streams can be analyzed with cell temperature set high enough to prevent 

condensation (40-50 o

C) while hot, wet gas streams are analyzed at high (180 oC) temperature. The 

CALCMET software can be configured to automatically compensate for differences in cell 

pathlength, temperature, or pressure when utilizing library spectra. 

The reference standards listed in Table 1 were used in the field test projects detailed in this paper. 

All reference spectra were measured at cell temperatures of 40 or 50 o

C. Additional reference 

standards are provided in the GASMET spectral library beyond those listed below. 
4

hTABLE 1 

GASMET FTIR CALIBRATION STANDARDS

Component Formul

a 

Concentration Pathlength Source 

Benzene C6H6 35 ppm 420 cm Temet Spectral Library 

Carbon Dioxide CO2 1000 ppm 420 cm Temet Spectral Library 

 11.0 % 250 cm Entropy Protocol 1 Gas Standard 

 18.0 % 250 cm Entropy Protocol 1 Gas Standard 

Carbon Monoxide CO 29 ppm 250 cm Entropy Protocol 1 Gas Standard 

 64 ppm 250 cm Entropy Protocol 1 Gas Standard 

 90 ppm 250 cm Entropy Protocol 1 Gas Standard 

 950 ppm 420 cm Temet Spectral Library 

Ethane C2H6 425 ppm 180 cm Temet Spectral Library 

Ethyl Benzene C8H10 26 ppm 420 cm Temet Spectral Library 

Methane CH4 4 ppm 250 cm Entropy Protocol 1 Gas Standard 

 100 ppm 420 cm Temet Spectral Library 

Nitric Acid HNO3 100 ppm 180 cm Temet Spectral Library 

Nitric Oxide NO 2 ppm 854 cm Temet Spectral Library 

 100 ppm 420 cm Temet Spectral Library 

 201 ppm 420 cm Temet Spectral Library 

 450 ppm 250 cm Entropy Protocol 1 Gas Standard 

 1014 ppm 250 cm Entropy Protocol 1 Gas Standard 

Nitrogen Dioxide NO2 1 ppm 854 cm Temet Spectral Library 

 48 ppm 420 cm Temet Spectral Library 

 117 ppm 420 cm Temet Spectral Library 

Nitrous Oxide N2O 1 ppm 420 cm Temet Spectral Library 

 99.9 ppm 250 cm Entropy Gas Standard 

Ozone O3 1 ppm 250 cm Entropy Lab (Ozone Generator) 

Propane C3H8 9 ppm 420 cm Temet Spectral Library 

Sulfur Dioxide SO2 54 ppm 250 cm Entropy Protocol 1 Gas Standard 

 94 ppm 250 cm Entropy Protocol 1 Gas Standard 

 480 ppm 250 cm Entropy Protocol 1 Gas Standard 

Toluene C7H8 43 ppm 420 cm Temet Spectral Library 

Water H2O 0.01 % 250 cm Entropy Lab (Moisture Generator) 

 0.05 % 250 cm Entropy Lab (Moisture Generator) 

m-Xylene C8H10 26 ppm 420 cm Temet Spectral Library 

o-Xylene C8H10 26 ppm 420 cm Temet Spectral Library 

p-Xylene C8H10 26 ppm 420 cm Temet Spectral Library 
5

Case Study 1: Ambient Air Testing in a Manufacturing/Warehouse 

Environment 

A major personal care products company had encountered a problem with discoloration of a nonwoven material between the time of manufacturing and shipment from the warehouse. The client 

had theorized that the discoloration could be caused by exposure to gases such as SO2, NOx, or CO 

that may be present in either the manufacturing facility or the storage warehouse. An indoor air 

testing program was conducted to quantify these and other compounds in the ambient air at several 

locations inside the manufacturing plant and a nearby warehouse. 

The client manufactures several types of non-woven sheet. A polymer material is extruded, cut, and 

pressed into a sheet in a web process. For some products, the material is dried during production 

using heated air from a natural gas burner. The manufacturing plant is divided into several large 

rooms for production, conversion, and storage. Electric fork lifts and other vehicles are used in the 

plant area, with no vehicular emissions anticipated. In the warehouse, however, the fork lifts are 

fueled by propane. The dryer burners and the warehouse fork lifts were the only recognized source 

of gas emissions. Testing was performed at the several locations in the plant and a nearby 

warehouse. 

Sample Collection 

An unheated sampling system consisting of a stainless steel probe, 1/4” Teflon tubing, and a headhead diaphragm pump was used to transport gas samples to the FTIR system. Depending on the 

test location, between 5’ and 30’ of 1/4” diameter head tubing was used to transport the gas. A 0-10 

lpm rotameter mounted on the FTIR cell outlet was used to measure the gas flow rate through the 

cell, which was maintained at 2 lpm. The FTIR gas manifold also allowed calibration gases 

(nitrogen, 99.9 ppm nitrous oxide (N2O)) to be directed to the FTIR cell for background, zero, and 

calibration transfer standard (CTS) measurements. The gas cell was maintained at 50 o

C during the 

testing. 

The FTIR system was mounted on a rolling cart and operated using a laptop personal computer. At 

the start of the test, the FTIR was allowed to warm up for about 1 hour before commencing 

sampling. The FTIR optical bench was purged with nitrogen at all times during the testing. As an 

initial calibration check, a CTS test was performed with 99.9 ppm nitrous oxide (N2O) to verify 

system operation, followed by a zero measurement using nitrogen gas. The zero measurement was 

conducted to verify that no components are detected at greater than 1 ppm concentration. 

The FTIR system was powered down when it was moved between test locations and powered up 

once it was set up in the next location. Once it was powered up it was allowed to warm up before 

commencing sampling by using the system software to verify that the cell and spectrometer 

temperature had equilibrated. Generally, the system was only powered down for a few minutes 

between location changes, so the internal temperature usually had not changed significantly and 

measurements could be performed almost immediately. Zero measurements were conducted at each 

test location to ensure no cross-contamination had occurred and verify the spectrometer was 

maintaining a stable baseline. Measurements were performed for several minutes at each location, 

with data collected until at least three consecutive one minute spectra gave consistent results. 
6

Test Locations 

A total of six test locations were sampled, including manufacturing areas, dryer ducts, storage areas, 

conversion and packaging areas, and a warehouse. The test locations are described below: 

Location 1: A manufacturing area near the production web. FTIR set up in close 

 proximity to the web dryer. Ambient air outside the dryer was tested. 

Location 1 Dryer: The FTIR probe was inserted inside the natural gas-fired dryer duct 

just downstream from the burner flame. 

Location 2: A storage area separate from the manufacturing area for finished rolls 

 of material. Ambient air in the storage room was tested. 

Outside Air: While the FTIR system was in Location 2, a long (~30’) sample line 

 was used to collect outside air. 

Location 3: FTIR moved into adjoining production room to test ambient air. 

Location 4 Dryer: Heated air from the natural gas dryer described above was blown onto 

 the moving web of material under production. The FTIR probe was 

 inserted into the web dryer vent outlet close to the web. 

Location 4: FTIR probe moved ~15’ from web dryer location. Ambient air tested. 

Location 5: FTIR moved into adjoining conversion/packaging room. Ambient air 

 was tested. 

Location 6 Warehouse: FTIR transported to a nearby warehouse where ambient air was tested. 

TABLE 2 

FTIR Ambient Air Test Results: Multiple Locations Inside Plant 

Test Location Average 

CO 

(ppmv) 

Average 

NO 

(ppmv) 

Average 

NO2

(ppmv) 

Average 

N2O 

(ppmv) 

Average 

CH4

(ppmv) 

Average 

SO2

(ppmv) 

System Zero (Nitrogen) 0.2 0.0 -0.2 0.0 0.0 -0.1 

Location 1 -0.4 2.2 1.7 0.0 2.8 2.4 

Location 1 Dryer 207.1 32.2 5.3 1.7 116.7 7.56 

System Zero (Nitrogen) 0.1 1.2 -0.1 0.0 0.5 0.2 

Location 2 -0.4 3.1 0.3 0.1 2.8 3.5 

Outside Air -0.5 2.7 0.3 0.1 2.8 3.4 

Location 3 -0.7 1.0 0.3 0.1 2.6 2.6 

System Zero (Nitrogen) 0.1 0.2 0.0 0.0 0.4 0.4 

Location 4 Web Dryer 22.4 18.5 0.7 0.1 12.4 5.4 

Location 4 Ambient Air 3.0 2.6 0.3 0.0 4.1 3.2 

System Zero (Nitrogen) 0.2 0.0 0.0 0.0 0.1 0.5 

Location 5 2.7 2.0 0.3 0.0 3.9 3.1 

System Zero (Nitrogen) 0.1 0.3 0.0 0.0 0.1 0.0 

Location 6 (Warehouse) 5.8 4.3 0.5 0.0 2.5 2.1 

System Zero (Nitrogen) 0.1 -0.2 0.0 0.0 0.2 0.1 
7

Spectral Analysis. 

The FTIR spectra were analyzed using the classical least squares routine incorporated in the 

GASMET software and the reference standards listed in Table 1. Based on a review of the spectra 

and the spectral residuals, it could be concluded that additional species are not present at significant 

concentrations (> 5 ppm). 

Measurable differences were detected in the air composition at different test locations. The highest 

measured concentrations were from the natural gas fired dryer, as measured in the Location 1 dryer 

and at the Location 4 web dryer. Typical combustion gases (high levels of CO2 and above ambient 

levels of CO, NO, and CH4) were detected at these locations, with the highest readings within the 

dryer itself. Slightly higher levels of SO2 were measured in these two locations as well. Methane 

readings were on the order of 1.5 ppm higher in Locations 4 and 5 compared to other locations, and 

CO2 levels were likewise higher in this area. Insignificant amounts of NO2 and N2O were detected 

in all locations, excepting within the dryer. The warehouse showed enhanced concentrations of 

CO2, CO, and NO due to the propane-powered fork lifts used in this facility. Propane itself was not 

detected in any test location. No analytes were detected in zero gas measurements performed at 

each test location. 

The GASMET system had not been optimized for ambient-level measurements, with low-ppm level 

calibration standards for all species, but gave very reasonable results. The test demonstrated the 

portability and ease with which the system could be moved between locations to commence testing. 
8

Case Study 2: Ozone, NOx, and Organic Testing at a Coal Combustion Facility 

A major diversified company requested a testing program to quantify ozone and other emissions 

associated with a novel NOx pollution-control system. Testing was conducted at a pilot-scale coal 

combustion facility at a research institute where the client was testing the system. The NOx control 

system employs ozone injection to convert NO to NO2, which is subsequently removed in a packed 

bed caustic scrubber. The pilot coal combustor system was designed for research activities, such as 

co-firing with other fuels and evaluation of pollution control equipment. The combustor is 

equipped with a lime slurry injection system for SO2 removal, a fabric filter baghouse for control of 

particulate emissions, and a packed bed caustic scrubber for acid gas and NO2 removal. 

Optimal operation of the NOx control system requires that the ozone injected into the system be 

controlled to maximize NOx removal and minimize ozone slip. The client had attempted to monitor 

ozone slip using ambient level ozone monitors. Several instrumental ozone analyzers (API Model 

450, API Model 265A, TECO Model 49C, Monitor Labs Model 9810) had been installed to monitor 

ozone slip. Agreement between the ozone analyzers was poor, most likely due to measurement 

interferences from other flue gas constituents, and reliability was also an issue. The monitors were 

designed for ambient-level measurements and so could be adversely affected by flue gas 

components, and high concentrations, not encountered in ambient air. The test program was 

conducted to measure the ozone concentration for comparison with the ozone analyzers, to identify 

interfering species that potentially cause the analyzer bias, and to monitor speciated NOx

concentrations. 

Organic (methane, benzene, toluene, ethyl benzene, o-xylene, m-xylene, and p-xylene) and 

inorganic (CO, CO2, H2O, NO, NO2, N2O, HNO3, O3, SO2) compounds were measured by FTIR. 

The ozone calibration was performed prior to the field test using a Dasibi Model 1003-RS ozone 

analyzer which has a built-in ozone generator for internal calibration with an output of 1 ppm 

ozone. Reference spectra were obtained for this 1 ppm ozone standard. A second ozone calibrator 

(API Model 401) was at the test site, and the FTIR measurement accuracy was evaluated by 

measuring a 1 ppm ozone sample from this calibrator. A total of 14 consecutive measurements 

were made, yielding an average reading of 1.00 ppm and a standard deviation of 0.19. It should be 

noted that ozone at 1 ppm concentration has a maximum absorbance of 0.0012 at 1057 cm-1, while 

the peak-to-peak signal to noise in this spectral region is ~0.0002 absorbance units. Based on this 

peak intensity, the FTIR detection limit for ozone was approximately 0.5 ppm, using a 3:1 S/N ratio 

as a detection limit. 

Testing was conducted at the coal combustor stack, downstream of the outlet of the packed bed 

scrubber. The ozone injection rate was varied on a scale of 0 (no ozone) to 10 (maximum ozone) 

throughout the test in order to obtain a range of ozone emission rates. As seen in Figure 1 and 

Table 3, in the absence of ozone NO was emitted at about 180 ppm. As the ozone injection rate 

increased the NO concentration would be progressively reduced and NO2 would increase. Ozone 

slip was only detected at injection rates greater than 9, and when ozone was detected NO2 would 

decrease. Under the same condition where ozone slip was detected, nitric acid (HNO3) would also 

be detected, possibly resulting from reaction between O3 and NO/NO2 in the sampling system. 

BTEX (benzene, toluene, ethyl benzene, and xylenes) compounds were analyzed by FTIR 

throughout the test, as these species had been identified as potential interferents for the ambient 
9

ozone monitors. With the exception of p-xylene (detected up to 2 ppm, though likely a false 

positive), none of these species were detected at concentrations exceeding 1 ppm during the test 

program. 

TABLE 3: FTIR TEST RESULTS DURING VARIABLE OZONE INJECTION 

COAL COMBUSTOR STACK (ALL CONCENTRATIONS PPMVD) 

Ozone Setting 

(Relative) 

Average 

Ozone 

Average 

NO 

Average 

NO2 

Average 

N2O 

Average 

HNO3 

Average 

SO2 

0 <0.5 183.1 17.5 3.8 0.8 19.1 

7.28 <0.5 14.3 140.1 3.3 <0.5 35.9 

8.01 <0.5 13.7 119.3 3.3 <0.5 39.8 

8.46 <0.5 13.2 116.1 3.2 <0.5 39.0 

8.82 <0.5 12.0 110.8 2.8 <0.5 31.0 

9.11 1.0 7.5 33.3 3.3 15.2 9.2 

9.36 2.0 7.4 27.5 3.6 17.6 10.2 

9.50 3.1 7.8 22.1 3.8 17.8 10.5 

9.55 3.6 6.4 16.5 1.6 3.0 13.5 

9.70 2.0 6.9 14.6 1.6 3.4 15.1 

9.85 1.9 7.0 15.4 1.7 3.2 25.2 

Sample Collection 

An existing sampling system at the pilot facility extracted gas from the PVC stack using unheated 

teflon tubing. The extracted gas was conditioned for removal of moisture using a condenser 

immersed in an ice bath located a few feet from the stack. Approximately 50’ of 0.5” diameter 

teflon tubing transported the stack gas to the ozone analyzers, and an additional 25’ of teflon tubing 

connected to the FTIR sampling manifold. An unheated, teflon diaphragm pump was used to draw 

sample gas through the sampling system and on to the FTIR analyzer. A 0-10 lpm rotameter 

mounted on the FTIR cell outlet was used to determine the gas sampling rate. The FTIR gas 

manifold also allowed gases to be directed to the FTIR cell for background, zero, and calibration 

transfer standard (CTS- 99.9 ppm nitrous oxide (N2O)) measurements. 

Ozone is a reactive molecule that will not be successfully sampled unless appropriate precautions 

are taken. Consequently, the sampling system was entirely teflon, with the exception of a stainless 

steel valve. The FTIR gas cell is metal, but ozone was successfully measured by replacing the steel 

cell inlet fitting with a teflon fitting and maintaining an adequate flow rate. Experiments were 

conducted to verify that optimal sampling conditions were employed. Sampling flow rates ranging 

from 2 to 10 lpm were examined, and it was determined that flows exceeding 5 lpm were required 

to transport ozone without significant losses. High flow rates can impact accuracy by pressurizing 

the gas cell, and so flow rates of 5 lpm were subsequently used. Measurements with the nitrous 

oxide CTS gas indicated that this flow rate caused a slight (~2%) high bias in the FTIR analysis; the 

FTIR data was not corrected for this bias. A second experiment was conducted to determine 

whether ozone was lost in the pump by alternately placing the pump upstream and downstream of 

the FTIR. No difference was found between these two configurations, and the pump was set up 

upstream of the FTIR. 
10

The FTIR analysis was optimized, by selection of reference standards and analytical regions, to 

minimize spectral residuals. The residuals were also used to infer the presence of other species in 

the spectra; nitric acid (HNO3) was detected and added to the analysis based on the observation of 

high residuals for several other compounds. Given the NOx control system process chemistry, the 

most likely compounds to be present may be N2O4 and N2O5, for which infrared reference standards 

are not currently available.
Stack Emissions Versus Ozone Generator Setting

0

50

100150200

0.0 7.3 8.0 8.5 8.8 9.1 9.4 9.5 9.6 

Ozone Setting (Relative)

NO, NO2, HNO3 (ppm)

NO NO2HNO3 O3

Figure 1: FTIR Measurement of NO, NO2, HNO3, and O3 at Coal Combustor Stack 
12

Case Study 3: NOx Speciation and CEM Comparison at a Glass Melting Furnace 

A glass manufacturer was interested in determining the relative proportions of NO, NO2, and N2O 

in their glass furnace stack emissions. FTIR measurements were conducted as part of a larger test 

program, which included CEM testing for CO, CO2, SO2, and NOx, The GASMET FTIR was 

connected to the CEM sampling manifold, where it measured the same sample (stack effluent, local 

and system calibration gases) as the CEM system. Hot, wet stack gas was extracted at the furnace 

stack, conditioned for removal of moisture, and transported to the mobile laboratory for analysis. 

EPA methods 3A (O2, CO2), 6C (SO2), 7E (NOx), and 10 (CO) were performed for a total of 6 runs 

of one hour duration. 

In addition to performing NOx speciation tests, the FTIR system was used as a CEM system, subject 

to the requirements of the EPA method requirements. Local and system calibrations were 

conducted, and the FTIR data was corrected in an identical fashion as the CEM system for 

calibration bias, system bias, and calibration drift. Table 4 shows the calibration results for the 

FTIR data; the succeeding five runs also passed all method calibration requirements. 

Simultaneous FTIR and CEM measurements for CO2, SO2, and NOx over a 1 hour time period are 

shown in Figure 2. CO was measured by both systems, but was never detected at greater than 1 

ppm. The measured emissions were varied in concentration during all of the test runs for all three 

analytes, reflecting the affect of various process operations. Comparison of the measurements for 

SO2 and CO2 shows excellent agreement between the FTIR and CEM monitors, both in terms of the 

absolute concentrations and the temporal variation in emissions. The NOx measurements, by 

comparison, show a distinct difference in the FTIR and chemiluminesence readings. Both monitors 

show the spikes and dips in the NOx emissions, but the FTIR readings are consistently higher in 

magnitude. 

Relative accuracy test audit (RATA) calculations were performed for CO2 and NOx as shown in 

Table 5. Unfortunately, an SO2 relative accuracy audit could not be conducted because SO2 CEM 

data was not collected beyond the first hour run, as the span gas cylinder had been consumed and 

the data could not be corrected for bias and drift. The CO2 and NOx RATA results are consistent 

from the trends seen in Figure 2, with excellent agreement for CO2 and a measurable bias for NOx. 

This striking difference between FTIR and chemiluminesence analyses for NOx has been previously 

observed. For example, in an EPRI study of FTIR CEM analyzers conducted by Entropy in 1993-

94, FTIR systems from Bomem and KVB-Analect both yielded higher concentrations than a 

standard NOx monitor. Several RATA tests were conducted in conjunction with that project and 

presented in Paper 94-TP298.02 at the 1994 AWMA Conference. Relative accuracies ranging from 

3 to 22 % were calculated, with the best accuracy at low NOx levels (< 250 ppm) and worst 

accuracy at high NOx levels (>800 ppm). The current RATA result of 13.2% relative accuracy is 

consistent with the previous data. 
TABLE 4 

TYPICAL FTIR CALIBRATION DATA 

Calibration Gas Standards: CO2 (11.04, 17.91%), CO (29.83, 64.1, 89.7 ppm), NOx (449.7, 1014 ppm), SO2 (5

Span Ranges: CO2 (20 %), CO (100 ppm), NOx (1000 ppm), SO2 (100 ppm) 

 CO2 (%) % ERROR CO (ppm) % ERROR NOx

(ppm) 

% ERROR SO

Initial Cal Error Zero 0.0 0.0 % 0.2 0.2 % 2.7 0.3 % 0.(Direct Calibration) Low NA NA 29.8 -0.6 % NA NA NCriteria:<2% Error Mid 11.0 -0.3 % 64.4 0.3 % 451.3 0.2 % 53

High 18.0 0.3 % 89.8 0.1 % 1018.5 0.4 % 93

 Result PASS PASS PASS Run 1 CO2 (%) % BIAS CO (ppm) % BIAS NOx

(ppm) 

% BIAS SO

Initial System Bias Zero 0.4 -1.8 % -0.9 1.1 % 0.5 0.2% 1.System Calibration High 17.9 0.4 % 29.0 0.8 % 445.4 0.6 % 92Criteria:<3% Bias Result PASS PASS PASS Run 1 CO2 (%) % BIAS CO (ppm) % BIAS NOx

(ppm) 

% BIAS SO

Final System Bias Zero 0.0 0.0 % -0.4 0.6 % 1.6 0.1 % 0.System Calibration High 18.3 -1.7 % 28.8 0.9 % 441.3 1.0 % 92Criteria:<3% Bias Result PASS PASS PASS  CO2 (%) % DRIFT CO (ppm) % DRIFT NOx

(ppm) 

% DRIFT SO

 Zero 0.0 -1.8 % -0.4 0.5 % 1.6 0.1 % 0. High 18.3 2.1 % 28.8 -0.1 % 441.3 -0.4 % 92Criteria:<3% Drift Result PASS PASS PASS 
170240310380450

10:19:12 10:29:17 10:39:22 10:49:26 10:59:31 11:09:3

NOx (ppm) NOx (FTIR)

NOx (CEM)

1725334149

10:19:12 10:29:17 10:39:22 10:49:26 10:59:31 11:09:3

SO2 (ppm) SO2 (CEM)

SO2 (FTIR)

1.62.12.73.2

10:19:12 10:29:17 10:39:22 10:49:26 10:59:31 11:09:3

CO2 (%)

CO2 (FTIR)CO2 (CEM)

Figure 2: Comparison of FTIR and CEM Analyzer Measurements of CO2, SO2, and NOx at a Glass Melter 
16

There are several conceivable explanations for the difference in FTIR and chemiluminescent NOx

measurements. It should be noted that the FTIR and chemiluminescent analyzers pass all 

calibration checks, and are demonstrably able to measure a known mixture of NO in nitrogen. One 

explanation could be that all three FTIR systems are similarly incorrect and yield a high bias in 

measuring NOx. This would present an unlikely coincidence, because each FTIR system had its 

own reference spectra and independently programmed quantitative analysis. Another possibility is 

that either the FTIR or chemiluminescent analyzers are not measuring NO and NO2, the two 

primary components of NOx, correctly. It is an unlikely coincidence that the three independent 

FTIR systems would have the same measurement bias, and chemiluminescent analyzers are required 

to undergo a NO2→NO converter efficiency test that should ensure proper measurement. 

Another potential explanation is a negative bias in the chemiluminescent measurement. It is well 

known that these analyzers are subject to an effect termed “chemiluminescent quenching”. A 

chemiluminescent analyzer operates by reacting ozone (O3) with NO to form an exited NO2

molecule, which then spontaneously emits a photon. The analyzer measures the emitted photons to 

quantify NOx. If another molecule, in particular CO2 or H2O which have relatively high quenching 

coefficients, collides with the excited NO2 molecule before it has chemiluminesced, it can 

“collisionally deactivate” the NO2 and no photon is emitted. Therefore a NOx analyzer can be 

expected to measure NO calibration gas (a mixture of NO and nitrogen) properly while having some 

negative bias in a combustion gas matrix. This difference between FTIR and chemiluminescent 

analyzer results is certainly deserving of further study. A dynamic matrix spiking experiment, 

where known amounts of NO and NO2 are injected into a gas matrix with appropriate 

concentrations of CO2, CO, H2O, SO2, and so forth, would be the optimal way to test this 

hypothesis. 

TABLE 5 

RELATIVE ACCURACY TEST AUDIT RESULTS: FTIR VERSUS ENTROPY CEM SYSTEM 

Run 

(30 Minute Average) 

CO2 (%) 

FTIR 

CO2 (%) 

CEM 

Differenc

e 

NOx (ppm) 

FTIR 

NOx (ppm) 

CEM 

Differenc

e 

1 2.83 2.85 -0.020 370.15 326.99 -43.16 

2 2.99 3.00 -0.015 382.40 340.00 -42.40 

3 2.96 2.95 0.015 396.54 360.74 -35.81 

4 2.98 2.97 0.014 399.09 359.39 -39.70 

5 2.51 2.55 -0.047 330.68 292.29 -38.39 

6 2.44 2.51 -0.065 330.27 293.96 -36.31 

7 2.51 2.57 -0.060 334.56 293.36 -41.20 

8 2.40 2.49 -0.085 333.49 292.05 -41.37 

9 2.46 2.52 -0.059 330.49 290.28 -40.21 

10 2.43 2.49 -0.060 332.92 292.88 -40.04 

MEAN 2.652 2.691 -0.038 354.05 314.19 -39.86 
17

Relative Accuracy 2.3% 13.2%

The NOx measurements were speciated into NO, NO2, and N2O concentrations. Nitrous oxide was 

not detected at concentrations exceeding 0.5 ppm. Nitrogen dioxide ranged from 3.3 to 6.0 percent 

of the total NOx. Overall, the test demonstrated the capability for speciating emissions, and the 

utility of FTIR for CEM applications at industrial sources. 

CONCLUSIONS 

Although FTIR is now an accepted technique, with promulgated EPA test methods, for compliance 

air pollutant measurements, it is not yet in widespread use for several reasons. From the testers’ 

prospective it is due to the reputation of high instrument cost, complexity, and insufficient 

ruggedness for field applications. Industrial testing clients often do not have confidence in using 

new measurement technologies to characterize emissions. Regulators have not mandated using the 

technology, or included it as a testing option, when writing facility permits. The GASMET system 

design and CALCMET software are a step forward for bringing this technology into widespread use 

for air emission and ambient testing measurements. The case study projects described in this paper 

illustrate the wide variety of applications where the analyzer can be employed, the accuracy in 

comparison with accepted methods, and the cost effectiveness of simultaneously analyzing, in real 

time, for multiple components.