Volatile Organic Compounds (VOCs) in New Car Interiors
Presented at the 15th International Clean Air & Environment Conference Sydney CASANZ 464-8 26-30nov00
Stephen K. Brown and Min Cheng
CSIRO Building, Construction and Engineering, Graham Road, Highett 3190, Australia
The types of VOCs and their concentrations have been determined in new cars from three different manufacturers, from their purchase on the Australian market to approximately two years later, using a specific test protocol. Total VOC (TVOC) concentrations were initially very high (up to 64,000 µg/m3) in two locally made cars which reached the market one to two months after manufacture. Such TVOC levels have been associated with sensory irritation and impairment of performance and memory in controlled exposure studies. These levels decreased approximately seven-fold in the first month, but still exceeded the NHMRC indoor air goal. The VOCs consisted mostly of substituted benzene compounds and alkanes, as well as some polar compounds. The third car was imported (reaching the market four months after manufacture) and the initial TVOC concentration was 2000 µg/m3. Decays of car VOC concentrations occurred by an exponential process, with TVOC concentrations decreasing by approximately 20% per week after manufacture.
Keywords: Volatile organic compound (VOC), total VOC (TVOC), car, benzene, interior materials.
1.1. VOCs in indoor air
There have been many studies of the types and levels of VOCs in established and new buildings in developed countries, summarised in recent reviews (Brown et al. 1994; Brown 1999). It has been commonly found that 100 or more VOCs can be detected in buildings, covering most compound types such as alkanes, aromatics, aldehydes, ketones and ethers. In established buildings, individual VOCs were generally at concentrations below 50 µg/m3, with most below 5 µg/m3. A measure of the total VOC (TVOC) quantity, total VOC (TVOC) defined as all VOCs in the boiling point range of 50–260°C (WHO 1989), had a mean of 200–1,100 µg/m3, reflecting the large number of VOCs present. VOC concentrations were much higher in new buildings, with TVOC concentrations up to 20,000–40,000 µg/m3 occurring in extreme cases. Recent measurements in some established and new Australian buildings (Brown 2000) have been consistent with these past findings.
1.2. VOC health effects and goals
The health significance of these levels of VOCs is an area of ongoing research. Much of this has focussed around the significance of TVOC exposures, since this appears related to occupant illnesses, such as effects seen in ‘sick building syndrome’, at levels much below those expected to cause illness in occupational exposures. However, the toxicity of individual compounds should also be considered, especially where they have carcinogenic or other significant toxic effects.
Controlled exposures of human subjects to a 22-compound mixture at TVOC concentrations of 7,000–33,000 µg/m3 have observed effects within minutes, such as subjective reactions (odour, discomfort, drowsiness, fatigue/confusion), eye/nose/throat irritation, headache, and (in symptomatic subjects) neurobehavioural impairment. The consensus from the European Commission (1997) working group was that while effects were likely to increase with increasing TVOC, thresholds could not yet be established based on available data. However, it concluded that only sensory effects were likely at concentrations up to 25,000 µg/m3, while other health effects became of greater concern above this level.
In Australia, the NHMRC (1992) recommended the following indoor air goals:
· TVOC not to exceed 500 µg/m3 (1-hour average); and
· any VOC not to exceed 250 µg/m3 (1-hour average).
If these goals were exceeded, it recommended that the ventilation rate to the space be increased or the source of the pollutants be identified and reduced.
1.3. VOCs in car interiors
There have been several investigations into automobile exhaust-related VOCs in car interiors (reviewed in Brown 1999), particularly benzene. These have found car interior benzene concentrations ranging from 10–20 µg/m3 during freeway travel, to 150 µg/m3 in heavy urban traffic. An Australian study by Duffy and Nelson (1996) was consistent with these findings. An environmental goal for benzene has been recommended by the UK Health and Safety Executive as 5 ppb (16 µg/m3) as a one-year average. The impact of car travel to this goal needs to consider the amount of time populations spend in heavy traffic.
Investigation into VOCs in new cars has been limited. Bauhof and Wensing (1999) described a standardised test procedure used in Germany in which VOC concentrations were measured at car interior temperatures of 23–65°C and an unspecified ventilation rate. TVOC concentrations of 35,000–120,000 µg/m3 were reported for six new cars (test temperature not specified), these concentrations decreasing exponentially over a 40-day period to about 10,000–30,000 µg/m3. VOCs consisted of aromatics, glycol ethers and esters, aldehydes, ketones and amines. Grabbs et al. (1999) screened four new cars in the USA, all after being closed for one hour and without temperature control. Three exhibited initial TVOC concentrations of 300–600 µg/m3 and the fourth 7500 µg/m3. The latter decreased exponentially by about 90% within three weeks.
2. Experimental Methods
Three new cars were evaluated from within three days of delivery to the purchaser. All were parked outdoors and were cleaned infrequently and never within a week of air sampling. The age of each car was measured from the middle of the month marked on compliance plates. One was fully imported and the others were locally made, and this was the major influence on the starting age of the cars for assessment.
2.2. Car test protocol
A consistent test protocol was utilised with the cars when sampling the interior air. This protocol was as follows:
(a) The car was moved to a shaded area for the test duration.
(b) It was aired by open windows for approximately 30 minutes before being closed up – doors, windows and vent closed.
(c) it was left closed for two to three hours, assuming it would reach a steady state pollutant concentration in this period.
(d) Air samples were collected at head height in the front of the car and concurrently outside the car at approximately 3–5 m away.
(e) Temperature and humidity outside the car were recorded.
A summary of the test conditions is presented in Table 1.
Table 1. Car descriptions and conditions of testing
Month/year Test conditions . Car Country of of Age Odometer T RH number manufacture manufacture (weeks) (K) (C) (%) . 1 Korea 2/98 16–30 200–3500 13–14 50–80 2 Australia 4/98 10–98 20–27,000 12–20 40–80 3 Australia 7/98 3–91 40–27,000 14–20 40–80
Table 2. VOC measurements in Car 1
Concentrations (mg/m3 at 0°C/101 kPa). Car: Car: Car: Outdoor: 16 24 30 16-30 VOC weeks weeks weeks weeks Acetone + n-pentane 26 18 100 6.0 n-Hexane + MEK 10 6.1 37 <1 Benzene 10 6.5 21 3.0 MIBK 4.0 6.2 14 <1 Toluene 50 32 57 6.3 m+p-Xylene 31 23 37 2.3 Styrene + o-xylene 22 15 23 1.7 Ethylene glycol butyl ether 220 39 39 <1 1,2,4-Trimethylbenzene 34 18 20 0.6 n-Undecane 110 61 73 <1 n-Decane 57 42 60 <1 2-Propylheptanol 29 16 15 <1 n-Dodecane 85 42 44 <1 Other VOCs <50 <30 <30 <1 TVOC 2100 1500 1800 180
Table 3. VOC measurements in Car 2
Concentrations (mg/m3 at 0°C/101 kPa). Car: Car: Car: Car: Outdoor: 10 24 22 115 10–115 VOC weeks weeks weeks weeks weeks Acetone + n-pentane 100 240 180 36 7.5 n-Hexane + MEK 7.4 14 6.0 3.3 <1 Benzene 5.5 20 3.6 12 1.3 Toluene 78 58 21 37 4.0 n-Octane 120 3.1 1.5 0.7 <1 Ethylbenzene 140 7.9 3.6 0.9 <1 m+p-Xylene 220 48 20 20 <1 Styrene + o-xylene 280 51 12 12 2.4 Cyclohexanone 1300 22 12 <3 1.1 Alkene (C10) 480 35 11 7.5 <1 n-Decane 880 160 25 21 <1 1,2,4-Trimethylbenzene 1600 100 37 20 1.3 n-Undecane 520 140 45 2.8 <1 Other VOCs <470 <50 <30 <15 <1 TVOC 20,000 3300 1500 390 50
Table 4. VOC measurements in Car 3
Concentrations (mg/m3 at 0°C/101 kPa). Car: Car: Car: Outdoor: 3 9 95 9-95 VOC weeks weeks weeks weeks Acetone + n-pentane 3700 1000 21 10 n-Hexane + MEK 500 34 5.7 <1 Benzene 84 26 20 2.4 n-Heptane 740 17 1.1 <1 Methylcyclohexane 630 22 0.7 <1 MIBK 590 43 4.1 <1 Toluene 9500 450 57 13 n-Octane 890 35 0.9 <1 Ethylbenzene 880 56 7.5 1.4 m+p-Xylene 2900 230 30 5.5 Styrene + o-xylene 2000 430 16 1.4 Alkene (C10) 1300 130 2.0 <1 n-Decane 3600 610 7.2 1.2 1,2,4-Trimethylbenzene 400 130 15 2.2 n-Undecane 870 310 4.6 <1 Other VOCs <850 <190 <7 <1 TVOC 64,000 9500 410 100
Figure 1. TVOC concentrations in three new cars at different ages since manufacture, fitted to an exponential decay curve c = 128,000 exp(–0.233t).
2.3. Air sampling and analysis
Air sampling was by active sampling using controlled flow pumps at 100–200 mL/minute onto mixed sorbent tubes containing Tenax TA, Ambersorb and activated charcoal. Sample volumes were 0.2–5 L, with the lower volume being used for initial measurements of high concentrations in some cars.
Sorbent tubes were thermally desorbed at 280°C into a GC/FID/MS, with a DB5 column and programmed from 2–240°C. Compounds were identified by MS and quantified by FID, calibrated for each VOC relative to an internal standard of fluorobenzene (injected onto each sample tube). TVOC was estimated from the sum of all FID peaks eluting after 5 minutes (includes pentane and ethanol, but excludes methanol), expressed using the toluene calibration.
Summaries of analytical results for the three cars are presented in Tables 2–4. Generally about 30–40 VOCs were identified in the air samples, but only the more dominant or toxic VOCs are presented here.
3.1. Types and quantities of VOCs
Air samples from Cars 2 and 3 contained mainly substituted benzenes and alkanes, initially at TVOC concentration of 20,000–64,000 µg/m3. Car 1 also contained these types of VOCs plus several alcohols/ethers, indicating different source materials in this imported car. Car 1 exhibited much lower TVOC concentrations, although it is probable that the low TVOC concentration was the result of the long period (16 weeks) to reach the market, while the high TVOC concentration in Car 3 resulted from the short period (3 weeks) to market.
Overall, the more dominant VOCs found in the new cars (highest to lowest concentrations) were toluene, acetone/pentane, o-xylene/styrene, 1,2,4-trimethylbenzene, m,p-xylene, various C7–12 alkanes, ethylbenzene, n-hexane and ethylene glycol butyl ether.
Bauhof and Wensing (1999) reported fewer alkanes and greater numbers of polar VOCs in German cars.
Much greater concentrations were observed in the cars than outdoors, and so clearly the VOCs were emitted from the car interiors. Benzene concentrations in the cars varied from 4–84 µg/m3, while outdoor levels were <1–7 µg/m3. It is unknown if the benzene was emitted from the interior materials of the cars or from leaks from the petrol tanks into the car interior. It is feasible that both factors occurred in Car 3 since the benzene concentration in that car exhibited a large decrease from time of manufacture, similar to that observed for TVOC, and after 95 weeks was still much in excess of outdoor concentrations.
3.2. Toxicity of car VOCs
Benzene is a category 1 IARC carcinogen (known human carcinogen) for which an annual exposure goal of 16 µg/m3 has been recommended (see Section 1.3). Since urban populations spend an average of one hour per day in car travel (Newton et al. 2000), these results indicate that car interiors can be contributors to total exposure to benzene.
Few environmental exposure goals are established for other VOCs. The NHMRC goal of 250 µg/m3 for any compound was exceeded for many VOCs in Cars 2 and 3. Toxic effects of some of these VOCs and ambient air goals (µg/m3 at 0oC/101kPa) based on these effects (Calabrese & Kenyon 1991) are:
· acetone – mucosal irritation (8-hour goal, 39,000);
· cyclohexanone – possible human carcinogen (annual goal, 180);
· ethylbenzene – systemic toxin (24-hour goal, 140);
· MIBK – systemic toxin (8-hour goal, 540);
· n-hexane – neurotoxin (24-hour goal, 540);
· styrene – probable human carcinogen (annual goal, 29);
· toluene – central nervous system dysfunction (8-hour goal, 1600); and
· xylene isomers – foetal development toxins (24-hour goals: o-xylene 310, m-xylene 3100, p-xylene 62).
It is seen that several of these goals may have been exceeded in the cars for several weeks after manufacture TVOC concentrations also occurred at levels that may affect occupants (see Section 1.2) for weeks to months after car purchase, although not for years. The effects that could be caused by this TVOC exposure include eye irritation, and performance and memory factors, all of which may be important car safety issues, as well as occupant health and comfort issues.
Note, however, that all of the above measurements were made in closed cars at low ambient temperatures. Lower concentrations may be expected with greater ventilation of the car interior, while higher concentrations may be expected under higher ambient temperatures. More detailed investigation of VOC concentrations under different operating conditions is needed to decide an appropriate test protocol for simulating occupant exposure to car interior pollutants.
3.3. VOC persistance in new cars
Overall, the VOC concentrations in the cars are seen to decrease with time from manufacture, especially for Cars 2 and 3. The rate of this decrease was estimated for TVOC concentrations by combining the data for all cars. The combined data exhibited good fit to an exponential decay curve, as presented in Figure 1, with a decay rate constant of 0.23 weeks–1. Thus, the TVOC concentrations in new cars is estimated to decrease by a proportion of e–0.23 each week, i.e. a decrease of approximately 20% each week. An overview of the data in Figure 1 shows that the NHMRC TVOC goal will be reached in approximately 24 weeks or 6 months, showing that the pollution of the new car interiors is a transient event to some extent. However, it is clear from long-term measurements in Cars 2 and 3 that after the VOCs from the car interior have depleted, VOCs associated with small fuel tank leaks may be present.
High concentrations of VOCs were found in new cars, especially those reaching the market soon after manufacture, i.e with minimum path-to-market. The total VOC (TVOC) levels found have been observed previously to cause sensory irritation and performance and memory impairment to human subjects, showing that the pollution of new car interiors may be a safety issue. Several of the VOCs observed have potential toxic effects, an aspect that should be explored in further study under simulated conditions of car usage. The decay of TVOC concentrations was found to be exponential, at approximately 20% per week, with the NHMRC indoor air goal being reached after approximately 6 months.
Bauhof H. & Wensing M. 1999, ‘Standard test methods for the determination of VOCs and SVOCs in automobile interiors’, in Organic Indoor Air Pollutants, T. Salthammer (ed.), Wiley–VCH, Weinheim, pp. 105–115.
Brown S.K. 1999, ‘Occurrence of volatile organic compounds in indoor air’, in Organic Indoor Air Pollutants, T. Salthammer (ed.), Wiley–VCH, Weinheim, pp. 171–184.
Brown S.K. 2000, ‘Volatile organic pollutants in new and established buildings in Melbourne, Australia’, Indoor Air (in process).
Brown S.K., Sim M.R., Abramson M.J. & and Gray C.N. 1994, ‘Concentration of volatile organic compounds in indoor air – a review’, Indoor Air 4:123–134.
Calabrese E.J. & Kenyon E.M. 1991, Air Toxics and Risk Assessment, Lew Publishers, Michigan.
Duffy B.L. & Nelson P.F. 1996, ‘Exposure to benzene, 1,3-butadiene and carbon monoxide in the cabins of moving motor vehicles’, Proceedings of 13th International Clean Air and Environment Conference, Adelaide, Clean Air Society of Australia & NZ, pp. 195–200.
European Commission 1997, Total Volatile Organic Compounds (TVOC) in Indoor Air Quality Investigations, Report No. 19, European Commission, Luxembourg.
Grabbs J.S., Corsi R.L. &and Torres V.M. 1999, ‘A screening assessment of volatile organic compounds in the interior of new automobiles’, Proceedings of First NSF International Conference on Indoor Air Health, 3–5 May 1999, Denver, NSF International.
NHMRC 1992, National Indoor Air Quality Goal for Total Volatile Organic Compounds. A Discussion Paper, National Health & Medical Research Council, Canberra.
Newton P.W. et al. 2000, State of Environment 2000 – Human Settlement, Environment Australia (in process).
WHO 1989, Indoor Air Quality: Organic Pollutants, Report on a WHO meeting, EURO Reports & Studies 111, WHO Regional Office for Europe, Copenhagen.
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