Cigarette Tar Content Evaluation Methods: Standards, Procedures, and Laboratory Testing

Tar, formally defined as nicotine-free dry particulate matter (NFDPM), is one of the most tightly regulated constituents of cigarette mainstream smoke, and its accurate measurement underpins regulatory compliance, product labeling, and research worldwide. This article explains the internationally recognized evaluation methods for cigarette tar content, covering sampling, conditioning, machine smoking under ISO 3308 and ISO 4387, chromatographic analysis of nicotine and water, and the final calculation of tar yield in milligrams per cigarette.

Technical Overview

In tobacco science, "tar" is defined as the nicotine-free dry particulate matter (NFDPM) of cigarette mainstream smoke. It is not measured directly; instead, the total particulate matter (TPM) of mainstream smoke is collected on a glass fiber filter pad, the water and nicotine fractions within that condensate are quantified analytically, and tar is obtained by subtraction. Because tar cannot be assessed by simply weighing a burning cigarette, the entire evaluation relies on standardized machine smoking under strictly controlled laboratory conditions.

The core international framework consists of a family of ISO standards, mirrored in many national standards such as the Chinese GB series. The principal documents include ISO 4387 for TPM and NFDPM determination, ISO 3308 for the routine analytical smoking machine, ISO 3402 for conditioning atmospheres, ISO 8243 for sampling, ISO 10315 for nicotine, ISO 10362-1 for water, and ISO 8454 for carbon monoxide in the vapor phase. In China, the corresponding national standards include GB/T 19609 (TPM and tar by routine analytical smoking machine) and GB/T 23355 (nicotine in smoke condensate by gas chromatography).

• ISO 4387: Determination of total and nicotine-free dry particulate matter using a routine analytical smoking machine
• ISO 3308: Routine analytical cigarette-smoking machine, definitions and standard conditions
• ISO 3402: Atmosphere for conditioning and testing of tobacco and tobacco products
• ISO 8243: Sampling of cigarettes
• ISO 10315: Determination of nicotine in smoke condensates by gas chromatography
• ISO 10362-1: Determination of water in smoke condensates by gas chromatography
• ISO 8454: Determination of carbon monoxide in the vapor phase of cigarette smoke
• ISO 9512 and ISO 6565: Determination of filter ventilation and draw resistance, key design parameters affecting tar delivery

All testing described here should be performed by accredited third-party laboratories or in-house laboratories with validated equipment and documented quality systems, since the precision of tar measurements depends heavily on environmental control, machine calibration, and analytical technique.

Testing Samples

Finished Filter Cigarettes

The most common test article is the finished filter cigarette taken directly from retail or production batches. Sample units are selected according to ISO 8243 to ensure statistical representativeness of the lot. Filter design features such as ventilation, activated carbon, or recessed filters are recorded because they strongly influence tar delivery.

Non-Filter Cigarettes

Plain-end cigarettes are tested with the same machine-smoking protocol, the main procedural difference being the butt length at which smoking terminates, which is specified differently for filter and non-filter products in ISO 4387.

Slim, Super-Slim, and Capsule Cigarettes

Narrow-format and flavor-capsule products are evaluated with the same methodology. For capsule products, laboratories typically test both the uncrushed and crushed capsule states, since the physical integrity of the rod and aerosol dynamics can shift particulate yields.

Roll-Your-Own (RYO) Tobacco

RYO tobacco can be assessed after being hand- or machine-filled into standardized tubes with a specified tobacco mass and rod length, so that results are comparable between laboratories. The preparation protocol must be documented in the test report.

Testing Items

A complete tar evaluation package typically includes the following measured and derived quantities, each expressed in milligrams per cigarette unless otherwise stated:

• Total particulate matter (TPM) of mainstream smoke
• Water content of the smoke condensate
• Nicotine content of the smoke condensate
• Tar, i.e., nicotine-free dry particulate matter (NFDPM), calculated as TPM minus water minus nicotine
• Carbon monoxide in the vapor phase, usually reported alongside tar for the standard "tar, nicotine, CO" triad
• Puff count and puff volume parameters recorded during machine smoking
• Supporting physical parameters when required: filter ventilation (ISO 9512), pressure drop (ISO 6565), and cigarette paper permeability (ISO 2965)

Testing Methods

Sampling and Conditioning

Cigarette cartons or packs are sampled per ISO 8243 and allowed to equilibrate in a conditioning atmosphere of 22 °C ± 2 °C and 60 % ± 5 % relative humidity for a minimum of 48 hours (ISO 3402). Proper conditioning is critical because moisture content of the tobacco affects combustion temperature, puff count, and consequently particulate yields. Immediately before smoking, test cigarettes are checked for physical defects, and their mass, circumference, and pressure drop may be recorded.

Routine Machine Smoking (ISO 3308 and ISO 4387)

Conditioned cigarettes are smoked on a linear or rotary smoking machine meeting ISO 3308 specifications. Under the standard ISO regime, each puff is 35 mL in volume, 2 seconds in duration, and taken every 60 seconds, with smoking continuing to a defined butt length. Mainstream smoke is drawn through a pre-weighed Cambridge filter pad (44 mm glass fiber disc) housed in a pad holder held at a controlled temperature. The pad retains the particulate phase while the gas phase passes on for vapor-phase collection. A minimum number of replicate cigarettes (typically at least 20 per sample) is smoked to support statistical validity, and at least two independent series are recommended for verification.

Determination of Water in the Condensate (ISO 10362-1)

After smoking, the Cambridge filter pad is transferred to a vessel and extracted with a suitable solvent, typically isopropanol containing an internal standard. An aliquot of the extract is injected into a gas chromatograph, and water is quantified chromatographically against calibration standards. The water mass is used both in the tar calculation and as a quality control check on the extraction.

Determination of Nicotine in the Condensate (ISO 10315)

Nicotine in the same pad extract is quantified by gas chromatography, typically with a flame ionization detector or a nitrogen-selective detector, using an internal standard such as anethole or quinoline. The method provides the nicotine mass in milligrams per cigarette, which is subtracted from TPM together with water to obtain tar.

Determination of Carbon Monoxide (ISO 8454)

Although not part of the tar calculation, carbon monoxide is almost always determined in parallel. The vapor phase collected in a gas sampling bag is analyzed by non-dispersive infrared analyzers or gas chromatography, and the result is expressed in milligrams of CO per cigarette and converted to microliters per puff where required.

Calculation and Expression of Tar

Tar (NFDPM) is calculated for each cigarette or each smoking series as follows: NFDPM = TPM − water − nicotine, where TPM is the increase in mass of the Cambridge filter pad after smoking. Results are reported in milligrams per cigarette, rounded to the nearest 0.1 mg, together with mean values, standard deviations, and the number of cigarettes smoked. Repeatability and reproducibility limits published in ISO 4387 are applied to judge whether duplicate series agree acceptably.

Intense Smoking Regime

Many regulators and researchers additionally require testing under an intense regime, such as ISO 20778 or the Health Canada Intense conditions (55 mL puff volume, 2 second duration, 30 second interval, and complete blocking of filter ventilation holes). Intense-regime yields are typically substantially higher and are used for comparative product assessment and exposure research rather than for pack labeling.

Quality Assurance of the Determination

Reliable tar data depend on daily verification of puff volume, puff duration, puff frequency, and leak integrity of the smoking machine; monitoring of ambient temperature and humidity; calibrated balances, chromatographs, and gas analyzers; and the use of reference cigarettes or control samples to track method performance over time. Accredited third-party laboratories demonstrate this competence through ISO/IEC 17025 accreditation and regular participation in interlaboratory comparisons.

Applications

Tar content evaluation serves a wide range of regulatory, commercial, and scientific purposes:

• Regulatory compliance: verifying that products meet maximum tar yield ceilings mandated by national legislation and international agreements
• Product labeling: generating the tar, nicotine, and CO yield figures printed on cigarette packs in jurisdictions requiring such disclosure
• Research and development: comparing blend compositions, filter technologies, ventilation levels, and paper permeability during product design
• Manufacturing quality control: monitoring batch-to-batch consistency of deliveries during routine production
• Market surveillance: checking by customs, regulators, or accredited third-party laboratories that marketed products match their declared yields
• Scientific research: supporting toxicology, exposure modeling, and comparative risk studies, including work on modified-risk or next-generation products

It should be noted that machine-measured tar yields are standardized comparative indices. Regulatory agencies worldwide caution that these figures do not directly represent the actual dose any individual smoker receives, because human smoking behavior varies with product design and consumer adaptation.

FAQ

What exactly is "tar" in a cigarette?

Tar is the nicotine-free dry particulate matter (NFDPM) of mainstream smoke. It is the residue of the smoke particulate phase after water and nicotine have been subtracted, consisting of hundreds of condensed organic compounds.

Why is tar not measured directly?

The particulate phase contains water and nicotine, which are quantified separately, so tar is defined operationally as the dry, nicotine-free remainder. The subtraction method under ISO 4387 ensures international comparability of results.

What are the standard smoking machine conditions?

Under the ISO regime, each puff is 35 mL, lasts 2 seconds, and is taken every 60 seconds until a specified butt length is reached. Under intense regimes such as ISO 20778, the puff volume increases to 55 mL, the interval shortens to 30 seconds, and ventilation holes are fully blocked.

How is the tar figure on a cigarette pack obtained?

It comes from laboratory machine smoking under ISO conditions, followed by gravimetric TPM determination and gas-chromatographic analysis of water and nicotine, with tar calculated as TPM minus water minus nicotine and expressed in mg per cigarette.

How reproducible are tar measurements?

When performed under ISO 4387 in a controlled laboratory, tar determinations are repeatable within tight statistical limits defined in the standard. Precision depends on careful conditioning, machine calibration, and analyst technique, which is why accredited laboratories with validated methods are preferred.

Do lower tar numbers mean a safer cigarette?

Machine-measured tar yields are standardized comparative values, not measures of human exposure. Public health authorities emphasize that smokers may compensate by puffing more intensely, so reduced tar figures should not be interpreted as reduced risk.