Cigarette sidestream smoke tar determination quantifies the nicotine-free dry particulate matter (NFDPM) released from the smoldering cone of a cigarette into the surrounding environment, providing essential data for product development, regulatory submission, and secondhand smoke assessment. This analysis is performed on linear smoking machines equipped with fishtail chimney collection systems in accordance with ISO 20778, CORESTA Recommended Method No. 55, and related ISO test procedures. This article explains the sample requirements, measured parameters, analytical workflow, quality controls, and typical applications of sidestream smoke tar testing.
Technical Overview
Sidestream smoke is the aerosol and gas mixture emitted from the lit end of a cigarette between puffs, produced by smoldering combustion of the tobacco column and diffusion of smoke through the cigarette paper. Together with exhaled mainstream smoke, it forms the principal source of environmental tobacco smoke, and it typically contributes the majority of the total particulate matter released by a burning cigarette into ambient air. Quantifying the tar content of sidestream smoke is therefore a key element of tobacco product characterization, harm-reduction research, and indoor air quality studies.
In cigarette smoke analysis, "tar" is defined as nicotine-free dry particulate matter (NFDPM), calculated as total particulate matter (TPM) minus water minus nicotine. For sidestream smoke, this determination is performed using a linear smoking machine fitted with a fishtail chimney that encloses the burning cigarette and continuously draws the emitted smoke through a Cambridge filter pad, while puffing is simultaneously carried out at the butt end. The collected particulate matter is quantified gravimetrically, and nicotine and water are measured by gas chromatography. The procedure is governed by ISO 20778 (definitions and standard conditions for sidestream smoking) and CORESTA Recommended Method No. 55, supported by ISO 10315 for nicotine, ISO 10362-1 for water, and ISO 3402 for sample conditioning, with corresponding national standards such as the GB/T series applied in domestic testing programs.
Testing Samples
Combustible Cigarettes
Standard filtered and non-filtered cigarettes in king-size, regular, slim, and super-slim formats are the primary test articles. Samples are drawn from production lots in accordance with ISO 8243 sampling principles, and a typical full determination requires several hundred cigarettes to support replicate runs, sample selection, and retained specimens.
Cigarillos and Small Cigars
Cigarillos, small cigars, and other combusted tobacco products can be evaluated using the same collection principle, with adjusted butt lengths, puff counts, and mounting arrangements to accommodate different product geometries and burn behaviors.
Reference and Monitor Cigarettes
Certified reference or monitor cigarettes are smoked alongside test samples as in-run controls. Their sidestream tar values are tracked on control charts to verify that the smoking machine, chimney flow, and analytical system remain within statistical control across test campaigns.
Testing Items
The core deliverable of the test is sidestream smoke tar, reported in milligrams per cigarette, together with the supporting parameters required for its calculation:
- Sidestream total particulate matter (TPM), mg/cigarette
- Sidestream water content, mg/cigarette
- Sidestream nicotine content, mg/cigarette
- Sidestream tar (NFDPM) = TPM − water − nicotine, mg/cigarette
- Puff count, static burn time, and other combustion characteristics
- Optional gas-phase indicators such as sidestream carbon monoxide per ISO 8454, where a comprehensive emission profile is required
Testing Methods
Sample Conditioning and Selection
Cigarettes are conditioned in a controlled atmosphere of 22 °C ± 2 °C and 60 % ± 5 % relative humidity for a minimum of 48 hours in accordance with ISO 3402. Prior to smoking, test pieces are screened by weight and, where applicable, by draw resistance per ISO 6565 so that only cigarettes within specified tolerance bands are used, reducing variability in the final result.
Sidestream Smoke Generation and Collection
Each cigarette is mounted vertically inside a fishtail chimney installed on a linear smoking machine meeting ISO 3308 and GB/T 19609 requirements. The machine puffs the cigarette at the butt end under the standard ISO regimen (35 mL puff volume, 2 second duration, 60 second interval), or under an intense regimen (55 mL, 2 seconds, 30 seconds, with ventilation blocking) when a more aggressive comparison is required. Simultaneously, a constant exhaust flow specified by the method continuously sweeps the sidestream smoke rising from the lit end through a preconditioned Cambridge filter pad, which retains the particulate phase until the cigarette is smoked to the prescribed butt length.
Gravimetric Determination of Total Particulate Matter
The Cambridge filter pads are equilibrated and weighed to the nearest 0.1 mg before and after exposure. The mass gain, divided by the number of cigarettes smoked per determination, yields sidestream TPM in mg/cigarette. Pad blanks are carried through the procedure to correct for environmental moisture and handling effects.
Instrumental Analysis of Nicotine and Water
The particulate matter on each pad is extracted with isopropanol containing a suitable internal standard. An aliquot of the extract is analyzed for nicotine by gas chromatography with flame ionization detection in accordance with ISO 10315, and for water by gas chromatography in accordance with ISO 10362-1. Calibration standards, procedural blanks, and spiked recoveries are run with each batch to confirm analytical accuracy.
Calculation of Tar and Quality Control
Sidestream tar is calculated on a per-cigarette basis as TPM minus water minus nicotine. A complete determination typically comprises at least 20 valid replicate cigarettes distributed across machine ports to cancel positional bias. Results are validated through monitor cigarette control charts, blank corrections, replicate agreement, and documented measurement uncertainty, ensuring that reported values are defensible for regulatory and scientific use.
Applications
Sidestream smoke tar data support a wide range of scientific, regulatory, and commercial objectives across the tobacco industry and public health research:
- Product registration and regulatory submissions in jurisdictions where sidestream emission data are required
- Research and development of reduced-sidestream products, including low-diffusion cigarette papers and modified blend designs
- Assessment of contributions to environmental tobacco smoke and evaluation of secondhand smoke exposure scenarios
- Indoor air quality modeling and ventilation studies in laboratories and accredited third-party testing environments
- Comparative benchmarking of competing products and retrospective comparison with historical or published datasets
- Academic research on combustion behavior, smoke chemistry, and tobacco control policy evaluation
FAQ
What is the difference between sidestream and mainstream smoke?
Mainstream smoke is drawn through the cigarette and out of the mouth end during puffing, whereas sidestream smoke is emitted from the lit end between puffs during natural smoldering. Because smoldering occurs at lower temperatures and under different oxygen conditions, sidestream smoke has a distinct chemical profile and normally accounts for the larger share of the total smoke released into a room.
Why are nicotine and water subtracted from total particulate matter?
Regulatory convention defines tar as nicotine-free dry particulate matter. Water is a major condensation component and nicotine is reported as a separate analyte, so both are measured and deducted from TPM to give a consistent, comparable tar figure.
What smoking conditions are used for sidestream tar testing?
The standard ISO machine-smoking regimen of a 35 mL puff lasting 2 seconds taken every 60 seconds is the baseline condition under ISO 20778 and CORESTA Recommended Method No. 55. Intense regimens with a larger puff volume, shorter interval, and blocked ventilation may be applied when a worst-case emission profile is needed.
How many cigarettes are needed for a determination?
A single full campaign generally requires several hundred conditioned cigarettes, since a valid result depends on replicate determinations, weight and draw-resistance screening, monitor cigarettes, and retained archive samples. The exact quantity is defined in the study plan.
Can heated tobacco products or e-cigarettes be tested for sidestream tar?
The fishtail chimney method is designed for combusted cigarettes. Products that do not sustain combustion generate little or no true sidestream smoke, so their assessment relies on dedicated aerosol collection protocols rather than the sidestream tar procedure described here.
How should results be interpreted?
Sidestream tar values are machine-generated comparative indices under standardized laboratory conditions. They are not direct predictions of human exposure, but they provide a reproducible basis for product comparison, trend monitoring, and research when the specified conditions, quality controls, and reporting conventions are strictly followed.