Effect of Ventilation and Sampling Time on Environmental Tobacco Smoke Component Ratios Paul R. Nelson," David L. Heavner, Barbara B. Collle, Katherine C. Malolo, and Mlchael W. Ogden R. J.
Reynolds Tobacco Company, Bowman Gray Technical Center, Wlnston-Salem, North Carolina 27 102
rn Several environmental tobacco smoke (ETS) markers were evaluated in a controlled environment test chamber. Ratios of the markers were determined at ventilation rates of 0-4 air changes/h and sampling durations of 30-360 min. Solanesol, ultraviolet particulate matter, and fluorescent particulate matter were good predictors of respirable suspended particle concentrations. 3-Ethenylpyridine concentrations correlated well with concentrations of gas-phase ETS components. The ratio of nicotine to both gas- and particulate-phase components is highly variable. As a result, the sole use of nicotine as an ETS marker may lead to significant errors in ETS exposure assessment. Introduction Determining actual exposure to environmental tobacco smoke (ETS) poses complex problems. Many common indoor air contaminants have sources other than ETS. For example, respirable suspended particles (RSP) are commonly attributed to ETS; however, many additional sources for particles are present in most indoor environmenta. Such alternate sources include infiltration of particles from outdoor air, combustion byproducts, cooking, and normal human activity (1-4). When gravimetric RSP samples are obtained in the field, it is not possible to apportion the particulate matter to each of its sources from weight or size alone. In order to determine exposure to indoor air contaminants from ETS, it is necessary to monitor tobacco-specificcompounds which are present in definite proportion to compounds with many possible origins. A report by the National Research Council identified four characteristics which an ETS marker should possess (5). The marker should be (1) unique or nearly unique to tobacco smoke, (2) present in sufficient quantity to facilitate detection at low smoking rates, (3) emitted at similar rates for a variety of tobacco products, and (4) in consistent ratio to the contaminant or category of contaminants of interest for a wide range of tobacco products under a wide range of environmental conditions. Several markers for the particulate phase of ETS have been proposed. Among them are solanesol, ultraviolet particulate matter (UVPM), and fluorescent particulate matter (FPM). Solanesol is a primary trisesquiterpenoid alcohol associated with the lipid fraction of tobacco leaves (6, 7). Relatively large quantities of this compound have *Send correspondence to this author at R. J. Reynolds Tobacco Co., BGTC 611-13, Winston-Salem,NC 27102. 0013-938X/92/0926-1909$03.00/0
been detected in the particulate fraction of ETS (7). Several methods for the determination of solanesol in atmospheric samples have been described (6-9). UVPM and FPM are techniques based upon the ultraviolet absorbance and fluorescence, respectively, of methanol extracts of filters used to obtain gravimetric RSP determinations (IO,11). Although the latter two techniques are not unique for ETS particles, they provide good specificity and place an upper limit on the fraction of RSP due to smoking (10). Nicotine and 3-ethenylpyridine are two potential vapor-phase markers for ETS. Nicotine is an alkaloid which occurs naturally in the leaves of tobacco. When tobacco is burned, some of the nicotine is transferred to the mainstream smoke and some is pyrolyzed. The pyrolysis products can be found in both mainstream and sidestream smoke. Between 3 and 4 mg of nicotine also may be associated with sidestream emissions (12). Although mainstream and sidestream nicotine are found in the particulate phase, ETS nicotine is found primarily in the vapor phase (12-15). Many methods for its quantitation in ETS have been described (16-19). 3-Ethenylpyridine,formed by the pyrolysis of nicotine when tobacco is burned, was first detected in mainstream smoke of cigars (20)and cigarettes (21)and was found later in sidestream smoke (22). Thome (23)was the first to report 3-ethenylpyridine concentrations in ETS by real-time analysis with a mass spectrometer. Since that time, methods for determining 3ethenylpyridine by analysis of treated benzenesulfonic acid-coated denuders (24) and XAD-4 sorbent tubes (25) have been developed. A study was undertaken to evaluate several ETS markers for their consistency in ratio to compounds in ETS which are not specific to tobacco smoke. Three particulate-phase markers (solanesol, UVPM, FPM) and two vapor-phase markers (nicotine, 3-ethenylpyridine) were evaluated to determine whether their ratios to other ETS constituents remained constant when sampling was performed under different conditions of ventilation and when samples were collected for different lengths of time following the smoking of two University of Kentucky 1R4F reference cigarettes. Experimental Section The experiments were performed in an 18-m3stainless steel test chamber in which temperature, humidity, and ventilation rate were controlled. A physical description of the chamber and its operating modes is given elsewhere (26). During this set of experiments, the chamber was
0 1992 American Chemical Society
Environ. Sci. Technol., Vol. 26, No. 10, 1992
1909
operated in conditioned make-up mode. That is, fresh building air was dehumidified, filtered through high-efficiency particulate absolute (HEPA) and charcoal filters, rehumidified, and then thermally conditioned prior to its introduction to the chamber. No air from the chamber was recirculated. The chamber was ventilated at nominal rates of 0, 0.5, 1, 2, and 4 air changes per hour (ACH). These air exchange rates were chosen to simulate a large fraction of the air exchange rates typically found in indoor environments. The static (0 ACH) condition was included to compare results expected in other environmental chambers under static conditions with results obtained under conditions of ventilation that would typically be found in the real world. With the exception of runs made at 0 ACH, the temperature was controlled at 22 "C and relative humidity was maintained at 50%. Temperature and relative humidity were not controllable at 0 ACH due to the lack of input of cooled air into the chamber, During the runs at 0 ACH, the chamber temperature typically increased by 2-3 "C, and the relative humidity decreased proportionally. During the experiments, CO, total volatile organic compounds (VOCs) (estimated by FID response), NO,, and particle mass concentrations were determined in real time with commercial analyzers described elsewhere (27). Each of the chemical analyzers was calibrated prior to each run, and real-time data were collected on an IBM PC running ASYST software. Nicotine and 3-ethenylpyridine were determined in real time by atmospheric pressure chemical ionization mass spectrometry ( 2 3 , B ) . Gravimetric RSP, UVPM, and FPM were determined by the methods of Conner (10) and Ogden (11). Solanesol was determined by the method of Ogden (7) as were nicotine and 3ethenylpyridine (17,25). Each run during the decay rate studies lasted a total of 384 min. The first 12 min of the run was used to determine background concentrations. A smoker then entered the chamber and smoked two University of Kentucky 1R4F cigarettes in 10.5 min. The two cigarettes were lit in succession 30 s apart. The smoker puffed once per minute on each cigarette. Each cigarette lasted for an average of 10 puffs. At 24 min into the run (=1.5 rnin after completing smoking), the smoker exited the chamber, which was subsequently resealed for the final 360 min of the experiment. In order to examine the effect of sampling duration on ETS component ratios, a segmented sampling protocol was developed. Discrete samples were collected for the periods 0-30,30-60,60-120,120-240, and 240-360 min following smoking. In order to calculate the time-weighted average (TWA) concentration for periods such as 0-240 rnin following smoking, the amounts of anal@ collected from the four samples covering this period were summed, and the sum was divided by the total volume of air sampled. This calculation was repeated for each analyte determined by discrete sampling. TWA concentrations for the periods 0-30,0-60,0-120,0-240, and 0-360 min were calculated. An attempt was made to gather at least three data points for each analyte at each air exchange rate. Due to the presence of missing data points, it was necessary to repeat experiments at some air exchange rates more than three times. The number of replicate runs follows the air exchange rates in parentheses: 0 ACH (3); 0.5 ACH (3); 1 ACH (4);2 ACH (5); 4 ACH (5). Over the course of the 384-min measurement period, the ambient CO concentration frequently decreased by as much as 0.2 ppm. As a result, concentrations of CO near the end of the experiment were frequently negative relative to concentrations 1910 Envlron. Scl. Technol., Vol. 26, No. 10, 1992
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Flgure 1. Average of five real-time nicotine determlnatlons (solM line) measured in a controlled envlronment test chamber ventllated at 2 ACH. The values have been normalized to their lnltial concentration of 285 pg/m3. The dashed llne represents the concentration predlcted by a flrstorder decay process.
at the beginning. When this occurred, negative concentrations were treated as missing values. Consequently, only one sample was obtained for the 240-360-min CO sample at 4 ACH.
Results and Discussion Decay of ETS Components. When the decay characteristics of each component measured in real time were analyzed, they were found to follow firsborder kinetics with a rate proportional to the air exchange rate. Nicotine and 3-ethenylpyridine provided exceptions to this trend. The decay rates of the other components relative to the air exchange rate were as follows: NO,, 0.95; CO, 0.93; VOC, 1.00; RSP, 1.14. This trend in relative rate of decay is similar to that described by others (29,30). At each of the air exchange rates studied, nicotine initially decayed more rapidly than other ETS constituents. However, as sampling time increased, the decay of nicotine slowed. Eventually, the concentration of nicotine remained at a near-steady-state concentration which was elevated above the original background concentration in the chamber. This observation is probably due to a reversible adsorption onto chamber surfaces followed by a slower subsequent desorption from these surfaces. 3-Ethenylpyridine followed a first-order decay for the first 2-3 h after smoking. Its decay then slowed, suggesting that an adsorption/desorption phenomenom similar to, but not as pronounced as, that observed for nicotine was taking place. The measured decay of this compound was slower than the decay of other compounds, a result which was contrary to the observations of Tang (30). The difference may be due in part to an artifact of the real-time measurement technique used for this investigation (31). A plot of nicotine concentration vs time obtained by averaging real-time concentrations during each of the five runs at 2 ACH is shown in Figure 1. The solid line is the actual nicotine concentration observed in the ETS chamber, normalized to the initial value (285 pg/m3). The dashed line indicates the predicted concentration vs time dependence that would be expected if nicotine had decayed by a first-order process. It can be seen from this figure that the concentrations of components (such as VOCs and RSP) which decay by a first-order process will decrease
Table I. Ratios between ETS Nicotine and Total VOCs (As Estimated by FID Response) at 1 ACH
ratio
30 min
total sampling time 60 rnin 120 rnin 240 rnin
absolute relative”
105.1 1.42
101.1 1.36
~
107.8 1.45
123.6 1.67
~~~
360 rnin 130.4 1.76
“Ratios normalized to the ratio obtained for a 30-min sample taken at 0 ACH (74.1 jtg/m3 nicotine per ppm FID response).
to their background concentrations long before nicotine decays to its background level. As a result, it would be possible to detect nicotine in the absence of other ETS components. This behavior of nicotine has been confirmed in a number of studies (32-36). Due to differences in surface characteristics, it can be difficult to make generalizations between results obtained in a stainless steel chamber and those found in “real-world” environments. Studies of the adsorption and desorption of VOCs on a number of surfaces have revealed that it is difficult to generalize the behavior of different VOCs across a variety of substrates (37,381. Investigations performed by others suggest that, in general, adsorption of VOCs on stainless steel surfaces is lower than would be expected on architectural materials (39). The extent of nicotine adsorption on walls of the chamber (flat surface) and the observation of similar behavior in field and other studies (32-36) suggest that the behavior observed here for nicotine is typical across a wide range of surfaces. However, ratios between specific VOCs and marker compounds may be more variable under typical sampling conditions as a result of differing sink/source characteristics associated with various building materials. Nicotine Ratios. In effect, the time-weighted average concentration of an analyte is equal to the integrated real-time concentration divided by the measurement time. As a result, when ratios between ETS component concentrations are determined, they may be sensitive to the decay kinetics of the compounds being studied. In order to obtain a constant ratio which is applicable across a wide range of sampling conditions, the two compounds must decay similarly across the range of sampling conditions. Ratios between nicotine and ETS components which exhibit first-order decay kinetics will be variable due to differing rates of removal from indoor air. From Figure 1, it is clear that the ratio of the areas under the nicotine curve (solid line) and first-order decay curve (dashed line) do not remain constant as measurement time is increased. Assuming that the first-order decay curve represents the decay of a second ETS component in the chamber, the ratio of nicotine to the other component initially will be less than predicted by fiit-order decay kinetics due to the more rapid decay of nicotine. After approximately 1 h, the decay of nicotine is slow relative to the decay of the other component. At this point, the ratio of nicotine to the other component will gradually increase as the sampling time is lengthened. Data illustrating this trend are shown in Table I. During the first hour after smoking, the ratio of nicotine to total VOC concentration decreased slightly to 101.1. As the sampling time was increased beyond 1h, the ratio increased to 130.4 due to the presence of residual nicotine desorbing from chamber surfaces after the VOCs had decayed due to the effect of ventilation. Furthermore, the data in Figure 1 demonstrate that if nicotine is measured some time after smoking, then its ratio to another component can be strongly affected by the differential decay of nicotine and the second component. For example, a ratio determined for the period 2-3 h after
Flgure 2. Normallzed ratio between XAD nicotlne and VOC concentratlons estimated with a FID detector. The values have been normalized to the ratio obtalned for a 30-mln sample at 0 ACH (74.1 pg/m3 nicotlne per ppm VOC). Llnes of Constant ratio have been drawn at Intervals of 0.3333, beginning at a ratio of 0.6667.
smoking will be very large because the second component will have been swept out of the environment while nicotine
is still present in relatively large concentrations. Normalized ratios such as those in the second data line of Table I were used to generate the plots shown in Figures 2-8. In each of these plots, normalized ratios between ETS components are plotted (2)as a function of sampling duration ( X ) and ventilation rate (Y). For each of these plots, the value of the ratio between the two ETS components for a 30-min sample obtained at 0 ACH was used as a reference point for normalization. Ratios between the components at all other sampling time/ventilation rate combinations were divided by the normalization factor. For the data illustrated in Table I, the ratio between nicotine and FID response at 60 rnin was 36?’% greater than the ratio obtained a t the reference point. Normalization of the data in this manner allows the variation in ratio between different ETS markers to be shown on the same scale. The exact ratio can be determined by multiplying the relative or normalized ratio determined for each sampling time/ventilation rate combination by the normalization factor. The variation in the nicotine to ETS VOC (estimated by FID response) ratio is illustrated in Figure 2 as a function of sampling time and ventilation rate. The normalization factor used for this plot is 74.1 ~ g / m nic-~ otine per ppm FID response. In order to clarify differences in ratio, lines of constant ratio are drawn at intervals of 0.3333, beginning a t a ratio of 0.6667. When the Y line corresponding to ventilating at 2 ACH is examined as a function of measurement time, the previously described variation in ratios can be easily observed. While nicotine is decaying more rapidly than VOCs in the chamber, the relative ratio of these two components decreases. At approximately 1h, the minimum ratio for this air exchange rate is attained. At longer measurement times, the ratio increases. The observed trends are different a t other air exchange rates. At 4 ACH, the relative difference in the decay of nicotine and VOC concentrations is much less than it is at lower air exchange rates. As a result, the initial dip in ratio is not observed. However, at this higher air exchange rate, there was still some residual nicotine in the chamber after the VOCs had been removed by ventilation; Envlron. Scl. Technol., Vol. 26,
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Flguro 3. Normalized ratio between XAD nicotine and resplrable suspended particle (RSP) concentrations. The values have been normalized to the ratio obtained for a 30min sample at 0 ACH (0.108 pg/mS nicotine per pg/m3 RSP). Llnes of constent ratio have been drawn at Intervals of 0.3333, beginning at a ratlo of 0.6667.
as a result, the ratio of nicotine to FID response increased with time. At low air exchange rates, a different trend was observed. Due to the relatively high concentration of nicotine in the chamber, loss of nicotine by surface adsorption occurred at a much faster rate than loss of nicotine by ventilation. As a result, nicotine concentrations decayed more rapidly than the VOC concentration throughout the experiment. This led to a continuing decline in the ratio of nicotine to FID response as the sampling time was increased. In most "real-world" studies, air exchange rate is an uncontrolled and unmeasured variable and a fixed ampling time is used in a variety of environments. The trends in ratio as a function of air exchange rate (constant X lines) are important for understanding variations in component ratios in field sampling studies. Although variations in ratio as a function of sampling time are relatively small, the ratio varies greatly as a function of air exchange rate. The largest variations in ratios were typically observed between 0 and 2 ACH. The ratio between nicotine and VOC concentrations typically increased over the entire range of air exchange rates examined. The largest relative increases were observed for ratios determined for long measurement times. A >550% increase in ratio is seen for a 6-h sample as the air exchange rate is increased from 0 to 4 ACH. Even for the relatively short measurement time of 2 h, the ratio increased by more than 280% over the same range of air exchange rates. It is also notable that, at all measurement times, the minimum ratio was obtained in an unventilated chamber. If a ratio involving nicotine is defined in a chamber operated with no ventilation, field measurements apportioned using that ratio will overestimate the concentration of other ETS components. The ratio of nicotine to RSP is illustrated in Figure 3. The absolute ratios were normalized to 0.108 pg/m3 nicotine per pg/m3 RSP. At an air exchange rate of O/h, the ratio is seen to decrease consistently for sampling times up to 4 h. This is due to the adsorption of nicotine onto the walls of the chamber. Eventually, the nicotine ceases ita rapid decay and the ratios become more constant. This behavior appears to be limited to low air exchange rates (2 h) sampling times. Between the lowest and highest ratios, a spread of 350-600% is observed. The large spread in values as a function of sampling time and air exchange rate is consistent with the large range of values reported in the literature: RSP to nicotine ratios are reported to vary from =4.5:1 to 260:l (27, 40-43). The variation in ratios observed in both the chamber and field studies is probably influenced most strongly by differences in smoking rates and surface characteristics of the environment sampled. Both of these factors would be expected to have a significant influence on the decay of nicotine relative to other ETS constituents. It may be possible to generalize ratios within certain microenvironments with similar air exchange rates and surface characteristics; however, global generalizations of ratios between nicotine and other ETS Constituents are inappropriate. Such attempts will result in crude estimates at best. Additional problems occur if an ETS marker has a variable background concentration. Figure 4 shows the ratio of nicotine to CO. The values have been normalized in the same manner as the RSP and FID ratios (24.44 m 3 nicotine per ppm CO). FID response, RSP, and CO all exhibited first-order decay in the chamber. The relationships shown in Figures 2 and 3 are similar to each other and other components with fiist-order decay. The anomalously high ratio observed for a 6-h sample at 4 ACH shown in Figure 4 waa caused by small changes in ambient CO concentration. Over the course of the day, ambient CO concentrations would decrease by as much as 0.2 ppm. When this occurred, the true background concentration late in the experiment was lower than the initial background concentration. As a result, CO averages taken over a long averaging time were biased low, which caused the ratio between CO and compounds with an unchanging background to be artificially inflated. The effect is exacerbated at higher air exchange rates because the CO concentration in the test room is closer to the actual ambient CO concentration. This problem demonstrates that a marker with a variable background concentration may
Figwe 5. Nmnalized ratk between solanesol and RSP concentratlons. The values have been normalized to the ratlo obtained for a 30-min sample at 0 ACH (0.032 pg/m3 solanesol per pg/m3 RSP).
Flgure 6. Normalized ratio between UVPM and RSP concentratlons. The values have been normalized to the ratio obtained for a 30-min sample at 0 ACH (1.08 m/m3 WPM per m/m3 RSP). A line has been drawn at a constant ratlo of 0.6667.
lead to misleading relationships among ETS Components. Particulate Matter Ratios. Three markers specific to the particulate phase of ETS were evaluated in the same manner as nicotine. UVPM and FPM gave similar results, so only ratios of UVPM and solanesol to RSP will be discussed here. In Figure 5, the relationship between solanesol and RSP is plotted on the same scale as Figures 2 and 3. The ratio was normalized to a value of 0.032 pg/m3 solanesol per pg/m3 RSP. When compared to nicotine, solanesol is a superior marker for ETS RSP. The greatest variation in ratio is -50%. Although this is larger than one might ideally hope, the relative variation in ratios between solanesol and RSP is nearly 1order of magnitude smaller than that for nicotine. Furthermore, if the ratio is standardized to a constant sampling time obtained in a static chamber for sampling times less than 2 h, the error due to unknown air exchange rate is predicted to be
