SOURCE MONITORING

An Overview of VOC sampling

methods and reporting in South

Africa

Presented by

Gerald Woollatt

LEVEGO

Stationary Source Emission Measurement

Specialists

Overview

Volatile Organic Compounds (VOC’s) what are they?

Classification of VOCs – as per UK, EA - TGN: M16

Relevant standards and legislation regarding VOC’s monitoring-for stack gas emissions - a South African perspective

An overview of the sampling methodology /techniques

Reporting criteria

Current challenges in South Africa

Question and answer session

VOCs what are they?

Volatile organic compounds (VOCs) are organic chemicals that

have a significant vapour pressure at room temperature and as a

result have a low boiling point

Typically classified as organic compounds that have a boiling

point lower than 250oC

They are organic compounds that easily release vapours or gases

into the air we breathe

VOCs what are they? contd.

Significant build up in the atmosphere can harm

human health and cause damage to the receiving

environment

Common examples of VOCs that may be present in

our daily lives are: benzene, ethylene glycol,

formaldehyde, methylene chloride,

tetrachloroethylene, toluene, xylene, and 1,3-

butadiene.

Classification of VOCs

Classification of VOCs as per the United Kingdom

Environment Agency, technical guidance note M16 –

Monitoring volatile organic compounds in stack gas emissions

Classified according to potential harmfulness namely:

– Highly harmful – examples; benzene, vinyl chloride. These

substances are known to be carcinogenic, mutagenic or toxic.

– Class A compounds – Carry a lower albeit a significant risk,

suspected carcinogens, contribute substantially to photochemical

ozone. Examples; trichloroethylene, benzyl chloride

– Class B compounds – Remaining majority of VOCs are considered as

having a lower degree of harm examples; butane and ethyl acetate

Relevant legislation and methods

in South Africa

National Environmental Management: Air Quality Act (Act No. 39 of 2004) sets out the relevant VOC emission limits for new and existing plants under the section 21 regulations for listed activities.

The current limits vary significantly per subcategory described in the regulations

A variety of methods are currently utilised and contained under the section 21 regulations namely:

– US EPA Methods 18, 25A and 25B

How do we specify the

concentration of VOCs?

There are three commonly used ways of reporting the

concentrations of VOCs:

– The concentration of the individual VOCs – currently defined in

NEMA as the TO14 suite of compounds, USEPA Method 18 as

reference method

– The sum of the concentrations of specific, individual VOCs in the

samples, USEPA Method 18 as reference method

– As total organic carbon (TOC), which is the concentration of

organic carbon in the gas stream, USEPA Method 25A as reference

method

VOCs vs TOCs

– Volatile organic compounds - speciated

Volatile organic compound (VOC) measurements are typically

determined using sampling and testing procedures as described in US

EPA Method 18 “Measurement of Gaseous Organic Compound

Emissions by Gas Chromatography”

Samples are collected in Tedlar, or similar bags, charcoal tubes or gas

canister's and the major organic components of the gas mixture are

separated by gas chromatography (GC) and individually quantified by

mass spectrometry. The retention times of each separated component

are compared with those of known compounds in the TO14 VOC suite

under identical conditions. Commercially available standard mixtures

are used to calibrate the GC under the same conditions as those of the

samples

VOCs vs TOCs

– Total organic carbon

Total organic carbon (TOC) concentration measurements are typically

determined using sampling and testing procedures as described in US

EPA Method 25A “Determination of Total Gaseous Organic

Concentration Using a Flame Ionization Analyser”. This method is

applicable for the determination of total gaseous organic concentration

of vapours consisting primarily of alkanes, alkenes, and/or arenes

(aromatic hydrocarbons). The concentration is expressed in terms of

propane (or other appropriate organic calibration gas) or in terms of

carbon

A gas sample is extracted from the source through a heated sample line

and glass fibre filter to a flame ionisation detector (FID). Results are

reported as volume concentration equivalents of the calibration gas or

as carbon equivalents.

Sampling techniques for

monitoring TOC – FID

Flame Ionisation Detectors – SRM USEPA 25A

• This technique works by a gas being passed into a

measurement chamber which uses a flame to create ions

from VOCs

• FIDs do not differentiate between different compounds

since they respond to the total charge generated from the

ions produced by this technique and will include all

organic compounds reported as total organic carbon as

propane or methane (standard reference/calibration gas)

Sampling techniques for

monitoring TOC

Other techniques for measuring total organic carbon

include:

Photo Ionisation Detection (PID) and catalytic oxidation

- these techniques have limitations and are not widely

used for compliance monitoring for stack emissions

Sampling techniques for

monitoring VOCs

1: VOCs are collected on Sorbent tubes (activated carbon)

followed by gas chromatography – SRM USEPA 18

• The GC is calibrated as per the specific suite required, in

the South African context this would be suite TO14 as

defined in the section 21 regulations of NEMA

• Individual species are quantified and a total sum of the

TO14 suite compounds identified can also be reported

Sampling techniques for

monitoring VOCs1: VOCs are collected on Sorbent tubes (activated carbon)

followed by gas chromatography – SRM USEPA 18

Sampling techniques for

monitoring VOCs2: Non – dispersive infrared– (NDIR) detection – SRM

USEPA 25B

• All VOCs absorb infrared radiation, different

compounds will absorb energy at different frequencies

• This means that VOCs have an electromagnetic

fingerprint which is known as a spectrum

• VOCs may be identified by quantifying the peak or

peaks in a compounds spectrum

• It should however be noted that if there is a mixture of

VOCs in the gas stream then the spectra may overlap.

This technique is therefore more suitable for identifying

single compounds or simple mixtures where there are no

interferences

Sampling techniques for

monitoring VOCs

2: Non – dispersive infrared– (NDIR) detection

Sampling techniques for

monitoring VOCs3: Fourier transform infrared (FTIR) detection

• The FTIR uses the same basic principle as simple infra

red analysers, but resolves interfering spectra by

splitting the beam in two

• A fourier transform calculation is then utilized to

identify distinct compounds

• The technique is not routinely utilized for periodic

monitoring. It is most commonly utilized in fixed

installations for continuous emission monitoring

• Portable units are available but are expensive

VOC Reporting Criteria

Different requirements for different listed processes

Various reporting requirements:

TOC – as per NEMA

TVOC – as per NEMA

TVOC –Thermal and Non thermal - as per NEMA

Methane and non methane VOCs - as per various

AELs

Current Challenges Facing South

Africa

Current Legislation does not define VOCs

sufficiently

Different methods / techniques listed in the

regulations will provide potentially different

results which may be misleading or lead to

misinterpretation of results

The licensing authority needs to provide

guidance in this respect

Current legislation specifies TO14 suite which

is out of date and has been replace by TO15

Current Challenges Facing South

Africa Contd.

South Africa has to establish its own criteria for

sampling and reporting “Reporting needs to be

standardised”

Skilled and qualified sampling personnel are in

short supply

Reporting, sampling and analytical techniques

need to be standardised across the board

The much anticipated norms and standards must

seek to address these regulatory short comings

Question and Answer Session