Influence of filter ventilation on the chemical composition of cigarette mainstream smoke

Abstract

Total yields of cigarette smoke constituents are greatly influenced by smoking behaviour, the tobacco blend as well as a variety of cigarette design parameters. Thereby, filter ventilation, i.e. diluting the smoke by providing a zone of microscopic holes around the circumference of the filter is one method to reduce the yield of ‘tar’ and other smoke compounds. However, little is known how these design variations influence the combustion conditions, and therefore, the overall chemical pattern of the smoke. In this paper single photon ionization-time-of-flight mass spectrometry (SPI-TOFMS) is used to characterize and compare cigarettes on a puff-by-puff basis, which differ only in filter ventilation magnitude. The research cigarettes investigated were made from Virginia tobacco and featured filter ventilations of 0% (no ventilation), 35%, and 70%. The cigarettes were smoked under two different puffing regimes, one using the puffing parameters of the conventional International Organization for Standardization (ISO) smoking regime and a more intense smoking condition. Results show that every variation entails a change of the chemical pattern, whereby, in general, cigarettes with 0% filter ventilation as well as the intense smoking regime lead to a more complete combustion compared to the ISO smoking conditions and the high ventilated cigarettes. Changes in the overall patterns can also be observed during the smoking for individual puffs. Some substances dominate the first puff, some species are more pronounced in the middle puffs, whereas others are preferably formed in the last puffs. This demonstrates the high complexity of the occurring processes. Results might help to understand the formation and decomposition reactions taking place when a cigarette is smoked and offer scope for targeted reduction strategies for specific toxicants or groups of toxicants in the smoke.

Introduction

Cigarette smoke is a highly dynamic and very complex matrix, in which over 4800 compounds have been identified. About 400–500 species are present in the gas phase; approximately 300 of them can be classified as semi-volatiles [1], [2]. Most of these smoke constituents are at trace levels; some are very reactive, resulting in a continuously changing mixture [3].

Tobacco type and blend mixture greatly influence the chemical composition and yields of smoke constituents. In addition, cigarette design parameters such as dimensions and type of filter, cigarette paper, and ventilation systems also play an important role. Ventilation is defined as air entering any point of an unlit cigarette other than through its lighting end. Filter or tip ventilation is defined as the amount of air entering the cigarette through the portion of tipping paper that is not overlapping the tobacco rod. In contrast, paper ventilation is the air entering the whole length of the tobacco rod. Ventilation is usually expressed as the degree of ventilation, i.e. the ratio of ventilation air flow to the total flow exiting the cigarette mouth-end, expressed as a percentage. A detailed description on how ventilation rates of cigarettes are technically determined can be found in ref [4].

In this study, filter ventilation is provided by a zone of microscopic holes, perforated by an on-line machine laser system, around the circumference of the filter [5]. Fig. 1A illustrates the filter end of three research cigarettes. The cigarettes differed in ventilation rates of 0%, 35% and 70% with ‘tar’ yields on smoking to an ISO regime of 13.9, 10.7, and 5.3 mg nicotine free dry particulate matter (NFDPM) respectively. Fig. 1B–D show close-ups of the respective filters with 0% ventilation, i.e. no holes present (Fig. 1B), holes entailing a ventilation rate of 35% (Fig. 1C), and holes leading to a ventilation of 70% (Fig. 1D).

During a puff, a fraction of the puff volume enters through the filter ventilation holes, effectively reducing the portion of the puff volume coming from the lighting end. As a consequence, less tobacco is burnt and the generated smoke is diluted with the incoming air as it passes through the filter. Accordingly, total yields of gas phase and particulate phase compounds are reduced roughly in proportion to the degree of ventilation. However, yields of gas phase smoke constituents are reduced to a greater degree than for particulate matter. This is due to diffusion of the gaseous species out of the tobacco rod as the smoke travels through it. Increasing ventilation levels decrease the smoke flow rate through the rod, which, in turn, increase smoke residence time within the rod and allow greater opportunity for gaseous diffusion to occur. In contrast, the reduced flow rate entails increased filter efficiency for particulate matter (‘tar’). ‘Tar’ is a collective term for the particulate phase material in cigarette smoke; specifically total particulate matter minus nicotine and water (PMWNF). In the UK, there has been a progressive reduction of the sales-weighted average ‘tar’ yield from about 38 mg in the mid-1950 to below 10 mg today, driven by recommendations of the Independent Scientific Committee on Tobacco and Health. Since 2004 the European Union has applied a ‘tar’ maximum value of 10 mg PMWNF for all cigarettes sold, when measured under the International Organization for Standardization (ISO) smoking regime [5], [6]. Filter ventilation has been one of the tools widely used in order to reduce machine-smoked yields of ‘tar’ and other compounds [4] and references therein.

The degree of reduction of total smoke yields (smoke from a complete cigarette) due to dilution, diffusion, filtration, etc. is well characterized [4], [5]. However, little is known how these cigarette design alterations may affect the chemical composition during the smoking process due to changed burning conditions. With increasing ventilation, burning conditions and heating rates may be less harsh due to smaller portions of air entering the burning zone, and these different amounts of air may influence chemical reactions occurring in the combustion and pyrolysis zones of the cigarette. This may lead to fluctuations and short-time variations of individual compounds and compound classes respectively. It is also anticipated that increased residence time of the smoke in the rod at increasing ventilation, will allow more time for coagulation, yielding a smoke with fewer larger particles with increasing ventilation.

Since smoke is a continuously changing mixture it is important to investigate relatively fresh smoke (not older than one second), rather than smoke that has aged over a few minutes [7]. Furthermore, the analytical technique used must be fast and simultaneously address a wide range of chemical substances. In addition, it should interfere as little as possible with the complex and often interrelated combustion and pyrolysis processes occurring in the cigarette. Recently, single photon ionization-time-of-flight mass spectrometry (SPI-TOFMS) has proven to be well suited for real-time analysis of gaseous and semi-volatile compounds of the cigarette smoking process [8]. Therein it has been demonstrated that the yields of many smoke constituents of cigarette mainstream smoke differ from puff to puff. Mainstream smoke is the smoke which emerges from the mouth-end of the cigarette during a puff and is usually inhaled by the smoker [3]. Thereby, most compounds feature an increase in yield from the first to the last puff, whereas other substances are in exceptionally high amounts in the first puff compared to the following puffs. Different formation mechanisms of these species are most likely responsible for these behaviours. Therefore, it is possible that varying ventilation rates may also alter the overall chemical composition of cigarette smoke during the smoking process. Hints for this have been found in a previous study of a combined set-up of on-line photoionization TOFMS and an on-line fast particle sizer [9]. In the framework of this study focus is on unraveling the influence of ventilation on the chemical pattern of the gas phase. In doing so, we analyzed three types of research cigarettes, which only differed in filter ventilation rate. The filter ventilation rates of the cigarettes were 0%, 35%, and 70%, respectively. The cigarettes were otherwise of a standard construction in a King Size format with Virginia tobacco and a cellulose acetate filter. The aim was to determine the influence of ventilation rate on the chemical pattern for the total amount of smoke per cigarette as well as on a puff-by-puff basis. Moreover, besides the usual puff dimensions of the ISO smoking conditions (35 mL puff volume, 1 puff per minute, 2 s puff duration – defined as STD here) a more intense smoking regime (INT) was also applied (70 mL puff volume, 1 puff per minute, 2 s puff duration) and yields as well as chemical patterns were compared. Results might help to unravel the complex formation and decomposition reactions taking place when a cigarette is smoked, and offer insight into selective reduction mechanism for toxicants within the smoke.