[] TL: THE EXPOSURE OF CAR DRIVERS AND PASSENGERS TO VEHICLE EMISSIONS: COMPARATIVE POLLUTANT LEVELS INSIDE AND OUTSIDE VEHICLES SO: Greenpeace UK (GP); Earth Resources Research DT: August 1992 Keywords: greenpeace reports cars air pollution smog safety transportation atmosphere / Paul Jefferiss Andrew Rowell Malcolm Fergusson Earth Resources Research 6 August 1992 Acknowledgements The authors would like to thank Adrian Fernandez- Bremauntz, Penny Carey and Claire Holman for their assistance in the preparation of this review. Responsibility however, for what follows remains entirely that of the authors. Executive Summary Studies from Britain, continental Europe and the United States conclude that in-vehicle levels of the vehicle-derived pollutants benzene (and other hydrocarbons), carbon monoxide, and nitrogen dioxide are substantially higher than those found in air about 50- 100 metres from the road. Levels of benzene have been found to be from 2 to 18 times higher than those in ambient air; levels of carbon monoxide (CO) from 2 to 14 times higher; and of nitrogen dioxide (NO2) from 1.3 to 2.5 times higher. Exposure to elevated levels of benzene and CO is highest on urban roads, in dense slow-moving congested driving conditions, and especially in stable air conditions. The in-vehicle levels of nitrogen oxides, on the other hand, seem to be worse during motorway driving, and levels of NO2 in particular seem to rise later in the day. Interestingly, in most studies the level of ventilation did not significantly alter interior concentrations, although conditions tended to be worse with the heater on and somewhat better with air conditioning in use. This is due primarily to the fact that pollutant levels are also high immediately outside the vehicle, and the air above the road itself is like a 'tunnel' of high concentrations of pollution, with levels decreasing rapidly as one moves away from the centre of the road. Recent data from the US, where the majority of vehicles now use catalytic converters, reveal absolute and relative levels of these pollutants comparable with those in Europe, suggesting that catalysts alone may not solve the problem. 1. Introduction Previous studies of air pollution from vehicle traffic have concentrated on ambient air quality and its effects on people outside vehicles. However, drivers and passengers in vehicles are also exposed to potentially higher levels of air pollution. This paper reviews recent studies which compared the levels of vehicle-derived pollutants found inside and outside motor vehicles. The main pollutants examined were benzene (and other hydrocarbons), carbon monoxide (CO), and nitrogen dioxide (NO2). Of these, benzene and CO are primary by-products of the combustion of petrol, whereas NO2 is a secondary pollutant formed when nitric oxide (NO), another primary by-product, is oxidised in air. (See Appendix II for detailed definitions and explanations of exposure limits of these pollutants.) Most of the studies determined the absolute levels of these gases inside cars and then compared them relative to the levels found in a variety of different environments outside. This review focuses mainly on the relative levels, although the absolute levels on which the relative values were based have been provided for the sake of completeness. Unless otherwise indicated, Taverages' are mean averages taken across the whole experiment and Tmaximum levels' are the highest values recorded at specific moments during the test. The term 'ambient air' refers to the air tested simultaneously at fixed monitoring stations located in the vicinity of test- vehicle operation, normally at a distance of between 50 and 100 metres. The term 'roadway air' refers to the 'tunnel' of polluted air extending several metres above the road surface and dropping off sharply either side of the road. The term 'exterior of the car' means the exterior surface of the car. Where the term 'microenvironment' is used, this denotes certain specific localities within the general environment. These are, for example, inside buildings, inside cars, inside homes, and on the street. Some of the studies discussed below considered the effect of three types of in-vehicle air management systems on pollutant concentrations. These are 'ventilation', denoting the use of open windows, vents or electrical fans to increase the air change rate in the vehicle; and heaters and air-conditioning systems which, although they are also means of ventilation, are usually specified separately in the studies. Where the term 'vehicle-derived pollutants' is used, this means any pollutant which has either been emitted directly from a vehicle through exhaust or evaporation, or derives from such emissions. TNon vehicle-derived' pollution, on the other hand, denotes emissions or secondary pollutants from all other sources. 2.Volatile Organic Compounds Q Benzene and Others Volatile organic compounds (VOCs), or hydrocarbons, are emitted from automobiles through the exhaust, as uncombusted and partly combusted fuel and by evaporation from the engine and fuel tank during running. This results in higher concentrations of VOCs from vehicle sources in roadway air than in the surrounding ambient atmosphere. Recent studies have found that VOCs from vehicle sources, including benzene, also penetrate the interior of cars at levels which can exceed those found in ambient air by two to eighteen times. Benzene is a proven carcinogen for which the World Health Organization recommends no safe levels for humans. A study by Weisel et al (1992) of commuters in suburban New Jersey and New York City found that in the winter mean levels of benzene in car interiors (12 5g/m3) were twelve times higher than levels in the ambient air of the suburbs (1 5g/m3) and three times higher than in the city (4 5g/m3), whereas non-vehicle hydrocarbons were not. Concentrations increased as traffic density rose and travel and wind speed dropped. Concentrations did not vary significantly according to location within the car, but varied by a factor of four on a day to day basis, and were slightly reduced by increasing ventilation. Levels during idling were higher in summer (3.4 - 12 5g/m3) than in winter (1.1 - 3.4 5g/m3), probably due to increased evaporation. On the basis of figures provided by other studies Weisel et al (1992) calculated that benzene levels in automobiles in California (16 5g/m3 in winter and 9.8 5g/m3 in summer) were also two or three times higher than in the ambient air outside (8.6 5g/m3 in winter and 3.1 5g/m3 in summer), whereas non-vehicle hydrocarbons were not. Levels of formaldehyde, a probable human carcinogen, were also twice as high inside as out. Wallace (1989), too, in four experiments carried out in New Jersey and Los Angeles calculated the mean exposure of drivers to benzene (40 - 60 5g/m3) to be seven to ten times the mean concentration in a variety of outdoor environments (6 5g/m3) and three to four times the mean exposure of his subjects in all tested environments (15 5g/m3). Refuelling at a petrol station led to far higher exposure levels, estimated at 3000 5g/m3 (= 1 part per million [ppm]), a figure confirmed in another study (Bond, 1986, cited by Wallace, 1989). These findings support work by Chan et al (1989 and 1991b) who found that the mean concentrations of benzene inside cars in Raleigh, North Carolina in 1988 (11.6 5g/m3) were the same as those on the exterior of the vehicle, but six times higher than those in ambient air (1.9 5g/m3). Concentrations were higher in cars on urban routes than in those on country roads, in a ratio of about 10 to 1. Concentrations were lowest with the air conditioning on, highest with the vent open and the fan on, irrespective of whether windows were open or shut. No difference was observed between morning and afternoon commuting trips. Urban pedestrians, too, were exposed to higher concentrations of benzene (6.8 5g/m3) than those in ambient air. In a study of Boston commuters in the winter of 1989, Chan et al (1991a) found average levels of benzene in cars to be about 17 5g/m3, almost twice as high as those for urban cyclists (9.2 5g/m3) and pedestrians (10.6 5g/m3); and four to seven times as high as those in the home (3.9 5g/m3) or office (2.5 5g/m3). Concentrations were lower on motorways than on urban roads, where they could reach levels of 64 5g/m3, and were generally higher with the heater turned on. These levels were higher than Chan et al (1989 and 1991b) had found in Raleigh in the summer of 1988 (mean 11.6 5g/m3; maximum 42.8 5g/m3) but lower than in Los Angeles in the winter of 1988 (mean 50 5g/m3; maximum 266.6 5g/m3). In an earlier study, Petersson (1979) had already discovered that concentrations of benzene and other hydrocarbons inside cars were Tconsiderably higher' than those found at roadsides. Like Weisel et al (1992) and Chan et al (1991a), Petersson (1979) found that concentrations increased with traffic density. Figures for the concentrations of hydrocarbons inside taxis were given by Otterlin (1979) who found mean levels of 58 5g/m3 of benzene. These concentrations were about three times higher than those inside other public transport vehicles in an urban environment. Concentrations were 2-5 times greater in high, rather than in low, density traffic and were closely dependent on atmospheric conditions. Because this study was carried out in Sweden, where taxis are petrol driven, the results may not be directly relevant to diesel driven taxis in the UK. However, they probably reflect conditions for petrol driven mini cab drivers in the UK. 3.Carbon Monoxide The following studies from the United States and Britain have placed the mean concentrations of CO inside cars in urban environments at between 8 and 14 ppm, commonly rising to peaks of 60 ppm or even higher. These levels are 2 to 14 times higher than those in ambient air. In the US, the National Ambient Air Quality Standard for carbon monoxide mandates that the daily maximum 1- hour ambient air concentration shall not exceed 35 ppm, and the maximum 8-hour concentration 9 ppm, more than once a year. An early study by Borst (1975) found that if the exhaust or heating system of a car is defective, carbon monoxide might enter the vehicle, and he suggested that periodic inspections be undertaken, especially in cars with air-cooled engines. Chaney (1978) found that carbon monoxide emissions which entered cars from individual passing vehicles could be accurately measured. The car itself, therefore, seems to offer incomplete protection from such emissions. A 1978 study by Hickman and Hughes of eleven cars in London revealed interior carbon monoxide levels of 12 to 60 ppm, which represented 30 to 80 per cent of levels on the surface exterior of the cars. These concentrations were calculated to result in blood carboxy-haemoglobin levels of 1.5 to 3.0%. Concentrations inside did vary according to conditions outside, but were buffered by the ventilation systems, and differed from vehicle to vehicle . In a later study of eight subjects Hickman (1989) found that, at 7.72 ppm, average levels of carbon monoxide inside cars were higher than in any other of drivers' normal microenvironments, inside or outside. They were almost twice as high as the levels encountered when cycling or motorcycling, and about five times higher than when walking near roads. Peak exposure too, at 62 ppm (minute average), was twice as high when driving cars as when motorcycling or walking by roads. This meant that even though it occupied less than 5% of their time, for non-smokers, driving in cars was the largest single source of exposure to carbon monoxide, constituting about 25% of their total intake (5.1 ppm hours/day). Concentrations were much higher when driving on urban than on rural roads, where concentrations could be as low as ambient air levels, and owing to the rapid exchange of air, concentrations varied widely and quickly according to traffic conditions. A study by Petersen et al (1982) of Los Angeles passenger vehicle commuting determined that mean interior CO levels (13 ppm) were fractionally lower than levels on the exterior of the car (0.92:1). But even with the vents and windows closed, they ranged from 1.4 to 11.2 times higher than those in ambient air and were on average 3.9 times higher. Interior CO levels rose in slow or heavy traffic, frequently exceeding 40 and even 60 ppm for short periods. On motorway slip- roads one subject was exposed to mean interior levels of 23.6 ppm. A study by Johnson (1984) of Denver Colorado residents in the winter of 1982-3, showed mean in-vehicle levels of CO were twice as high as those for pedestrians, and three or more times as high as those in a variety of local ambient air environments. Mean levels were 13.46 ppm for enclosed car parks, 9.79 ppm for motorcycles, 8.52 ppm for buses, and 8.2 ppm for cars, but only 3.88 ppm for pedestrians, and 0.69 - 3.17 ppm for a variety of other outdoor locations, ranging from a local park to an outdoor car park. However, the use of petrol-driven buses in the US may limit the relevance of Johnson's and Flachsbart's data on buses (discussed in greater detail below) in a British context where most buses have diesel engines. In another study of Washington and Denver commuters in the winter of 1982-3, Hartwell et al (1984) found that the average interior concentration of CO in commuting vehicles of all types tested was 4.51 ppm, more than two and a half times the average exposure level for a variety of outside activities tested (1.74 ppm). Even higher mean levels (6.93 ppm) were found in multi-storey car parks. In a study of Washington DC commuters in the winter of 1983, Flachsbart et al (1987) found median in-car CO levels of 9 - 14 ppm for 40 - 60 minute trips, in-bus levels of 4 - 8 ppm for 90 - 110 minute trips, and in-train levels of 2 -5 ppm for 30 - 45 minute trips. This compared with mean ambient CO levels of 2.3 ppm, indicating average in-car levels 4 to 6 times higher than outside. Flachsbart et al (1987) comment that these figures correspond to those found by others for Stamford, Connecticut; Los Angeles, California; Phoenix, Arizona; and Denver, Colorado. Traffic speed and density, type of route, and meteorological conditions were significant determinants of concentrations. Mean levels of CO for different parking garages ranged from 20.9 to 94.0 ppm. Chan et al's (1989 and 1991b) studies of commuting in Raleigh, North Carolina (see above) found mean in-vehicle concentrations of carbon monoxide (11.3 ppm) to be slightly lower than those on the exterior (11.7 ppm) but almost four times the level found in ambient air (3.0 ppm), with maximum levels inside (32 ppm) six times higher than maximum levels in ambient air (5.5 ppm). [] TL: THE EXPOSURE OF CAR DRIVERS AND PASSENGERS TO VEHICLE EMISSIONS: COMPARATIVE POLLUTANT LEVELS INSIDE AND OUTSIDE VEHICLES SO: Greenpeace UK (GP); Earth Resources Research DT: August 1992 Keywords: greenpeace reports cars air pollution smog safety transportation atmosphere / [part 2] 4.Nitrogen Dioxide Tonkelaar (1983) found levels of nitrogen dioxide inside cars commuting to Delft to be 1.3 - 2.5 times higher than those in ambient air. The levels on motorways (92 5g/m3) on the inward journey were higher than those on roads in the city itself (77 5g/m3), in distinction from the other pollutants in which the situation was reversed. Levels of NO2 were also higher in the afternoon rush hour than in the morning, unlike the other pollutants, perhaps because levels of NO2 are more dependent on background levels, and on the availability of ozone which typically increases later in the day as a result of photochemical activity. The level of NO2 exceeded that recommended by the Dutch Health Council. A study by Rudolf (1990) confirmed Tonkelaar's discovery that for motorway driving, nitrogen oxides are more significant in- vehicle pollutants than carbon monoxide. That is, although absolute levels of NO2 were less than those for carbon monoxide, the effective exposure to NO2 is more acute in relation to both ambient levels and health guidelines. Chan et al's studies (1989 and 1991b) of commuting in Raleigh, NC found mean (87.4 ppb) and maximum (196 ppb) levels of in- vehicle NO2 slightly higher than those on the exterior (71.2 ppb and 183 ppb respectively), but provides no data for ambient air. They also found higher levels in the afternoon than in the morning and higher levels for rural driving. The fact that Hickman (1989) found no NO2 inside or outside cars is probably attributable to the inadequacy of his monitoring instrumentation for NO2 (as he himself acknowledged). 5.General A comprehensive study of in-vehicle pollutants in the south coast air basin of California by Shikiya et al. (1989) was in broad agreement with the studies cited above for specific pollutants. Mean in-vehicle concentrations of carbon monoxide (8 ppm) and benzene (24 5g/m3) at peak commuting times were 2.5 times higher than ambient air during the same periods and up to four times higher than average 24-hour ambient air levels. Concentrations of formaldehyde, toluene, and xylene, too, were 'much higher.' Slower speeds, congested traffic, vehicle age and use of the heater raised concentrations. In-vehicle concentrations of non- vehicle source hydrocarbons were no higher than those outside. Meteorological conditions in winter raised concentrations of all pollutants inside and outside the vehicles. In a study of commuter traffic in Delft, Tonkelaar (1983) found that the mean levels of all in-vehicle vehicle-derived pollutants greatly exceeded those in local urban ambient air: CO by an average of 5 and a maximum of 8 times; benzene by an average of 8 times and a maximum of 18; and NO2 by an average of 1.8 and a maximum of 2.5. Average concentrations for different commuter routes at different times of day and night could range from 3.5-11.5 ppm (4.0 - 13.2 mg/m3) for CO, 24 - 140 5g/m3 for benzene, and 30-61 ppb (57 - 114 5g/m3) for NO2, levels lower than had been found in Frankfurt in 1977 and 1981 (Rudolf, 1980 and 1982, cited in Tonkelaar, 1983). Tonkelaar (1983) also found that mean concentrations of CO and benzene were higher when driving in urban traffic than on motorways (6.7 mg/m3: 3.5 mg/m3 and 66 5g/m3: 27 5g/m3 respectively), but that concentrations of NO and NO2 were lower (436 5g/m3: 524 5g/m3 and 77 5g/m3: 92 5g/m3 respectively). Maximum levels of all vehicle-derived pollutants were found when driving in dense traffic. These were 59 ppm (68 mg/m3) for CO, 2500 5g/m3 for benzene, 2670 5g/m3 for NO, 340 ppb (640 5g/m3) for NO2, and 9.7 5g/m3 for lead. The level of NO2 exceeded that recommended by the Dutch Health Council for outside air, and the levels of benzene exceeded those recommended by the German government. With the exception of interior NO2 levels, which depended on outside background levels and the availability of ozone, the major factors influencing interior concentration levels of the other gases were traffic density, vehicle speed, the outdoor temperature, and wind velocity. Consequently, with the exception of NO2, in which the pattern was reversed, concentrations were highest during the morning rush hour when traffic was heaviest. Type and level of ventilation appeared to have little effect. A study by Rudolf (1990), of motorway driving round Frankfurt in the summer of 1989 found that levels of in-vehicle pollution in passenger cars was 10% - 40% higher than that of trucks. The average levels of NO2 were 55 ppb for cars and 48 ppb for trucks; and for CO they were 5.5 ppm for cars and 4.2 ppm for trucks. The concentrations of nitrogen dioxide were highest, and those of CO lowest, when traffic was dense but fluent with a mix of vehicle types. This suggests that on motorways, where meteorological conditions have less impact, oxides of nitrogen are more significant in-vehicle pollutants than CO. In conclusion, Rudolf (1990) noted that pollutant concentrations inside vehicles were affected by the following main factors: truck to passenger car ratio; average speed; acceleration, deceleration, and 'stop-start' conditions; congestion; choice of lane (with the offside lane experiencing the most acute pollution); distance from preceding vehicles and from cars driving in adjacent lanes; meteorological conditions (wind direction and velocity; atmospheric stability; and temperature); and ventilation conditions inside the vehicle. He also noted that while pollution concentrations fell rapidly away from roads, car occupants drove in a 'tunnel' of high pollutant concentration. [] TL: THE EXPOSURE OF CAR DRIVERS AND PASSENGERS TO VEHICLE EMISSIONS: COMPARATIVE POLLUTANT LEVELS INSIDE AND OUTSIDE VEHICLES SO: Greenpeace UK (GP); Earth Resources Research DT: August 1992 Keywords: greenpeace reports cars air pollution smog safety transportation atmosphere / [part 3] 6. Conclusions These studies have shown that drivers and passengers can be exposed to significantly elevated levels of pollutants when driving and that they are, in effect, driving in a TtunnelU of pollutants (Rudolf, 1990). Studies from Britain, continental Europe and the United States agree that in-vehicle levels of the vehicle-derived pollutants benzene (and other hydrocarbons), carbon monoxide, and nitrogen dioxide are substantially elevated above the levels of these pollutants found in air at a distance of around 50-100 metres from the vehicle, whereas levels of non-vehicle derived pollutants are not. Levels of benzene have been found from 2 - 18 times higher than those in ambient air; for CO from 2 - 14 times higher; and for NO2 from 1.3 - 2.5 times higher. Recent data from the US, where the majority of vehicles now use catalytic converters, reveal absolute and relative levels of these pollutants comparable with those in Europe, suggesting that catalysts alone are not sufficient to solve the problem. The effects of such elevated levels of pollutants are difficult to predict at this stage and will also depend on the duration of exposure. Several of the studies indicate that drivers and passengers may be exposed to higher levels of these pollutants than pedestrians and cyclists. Not surprisingly, the factors exacerbating the interior levels of VOCs and CO seem to be dense, slow-moving traffic, stable air, vehicle age, and a faulty exhaust system. The in-vehicle levels of nitrogen oxides, on the other hand, seem to be worse during motorway driving, and levels of NO2 in particular seem to rise later in the day. Interestingly, in most studies the level of ventilation did not significantly alter interior concentrations, although conditions tended to be worse with the heater on and somewhat better with air conditioning in use. Drivers and passengers are therefore likely to be most exposed to the pollutants benzene and carbon monoxide during commuting in heavy traffic and nitrogen oxides during prolonged motorway journeys. These studies indicate, therefore, that vehicles offer little or no protection against the pollutants generated by vehicle traffic. Bibliography Borst J R, 1975, Koolmonoxyde Vergiftiging en Ischaemische Hartziekten, Uitgeversmaatschappij de Tidstroom bv, Bagijnestraat, Lochem, Nederland Chan C-C, zkaynak H, Spengler J D, Sheldon L, Nelson W and Wallace L, 1989, Commuters' Exposure to Volatile Organic Compounds, Ozone, Carbon Monoxide, and Nitrogen Dioxide, Air and Waste Management Association, Pittsburgh, Pennsylvania Chan C-C, Spengler J D, zkaynak H, & Lefkopoulou M, 1991a, TCommuter Exposures to VOCs in Boston, Massachusetts', Journal of the Air and Waste Management Association vol 41, pp. 1594-1600 Chan C-C, zkaynak H, Spengler J D, and Sheldon L, 1991b, TDriver Exposure to Volatile Organic Compounds, CO, Ozone, and NO2 under Different Driving Conditions', Environmental Science and Technology vol 25, pp. 964-72 Chaney L W, 1978, TCarbon Monoxide Automobile Emissions Measured from the Interior of a Travelling Automobile', Science vol 199, pp. 1203-4 Flachsbart P G, Howes J E, Mack G A, Rodes C E, 1987, TCarbon Monoxide Exposures of Washington Commuters', Journal of the Air Pollution Control Association vol 37, No 2, pp. 135-142 Hartwell T D, Clayton C A, Michie R M, Whitmore R W, Zelon H S and Whitehurst D A, 1984, Study of CO Exposures of Residents of Washington DC, paper 84-121.4, presented at the 77th Annual meeting of the Air Pollution Control Association, San Francisco, California Hickman A J, 1989, Personal Exposures to Carbon Monoxides and Oxides of Nitrogen, Research Report 206, Transport and Road Research Laboratory, Berkshire Hickman A J and Hughes M R, 1978, Exposure of Drivers to Carbon Monoxide, Laboratory Report LR 798, Transport and Road Research Laboratory, Berkshire Johnson T R, 1984, A Study of Personal Exposure to CO in Denver, Colorado, paper 84-121.3 presented at the 77th Annual Meeting of the Air Pollution Control Association, San Francisco, California Otterlin S, 1979, Exposition foer Bensen och Alkylbensener i Bil, Institutionen teborg, Sweden Petersen W B, Allen R, 1982, TCarbon Monoxide Exposures to Los Angeles Area Commuters', Journal of the Air Pollution Control Association vol 32, No 8, pp. 826-833 Petersson G, 1979, Bilavgaser i Fordon och Gatumiljoe. Expositionslaege och teborg, Sweden Rudolf W, 1990, TConcentrations of Air Pollutants inside and outside Cars Driving on Highways', The Science of the Total Environment, vol 93, pp. 263-276 Shikiya D, Liu C S, Kahn M I, Bargikowski W, and Juarros J, 1989, In-Vehicle Air Toxics Characterisation Study in the South Coast Air Basin of California, Air and Waste Management Association, Pittsburgh, Pennsylvania. Tonkelaar W den, 1983, Exposure of Car Passengers to CO, NO, NO2, Benzene, Toluene and Lead, TNO Research Institute for Environmental Hygiene, Delft, the Netherlands. Wallace L A, 1989, TMajor Sources of Benzene Exposure', Environmental Health Perspectives vol 82, pp. 165-169 Weisel C P, Lawryk N J, Lioy P J, 1992, `Exposure to Emissions from Gasoline within Automobile Cabins', Journal of Exposure Analysis and Environmental Epidemiology vol 2, pp. 79-96 APPENDIX I CONVERSION FACTORS oBenzene 1 ppm = 3.19 mg/m3 1 mg/m3 = 0.313 ppm oCarbon Monoxide 1 ppm =1.145 mg/m3 1 mg/m3=0.873 ppm oNitrogen Dioxide 1 ppm =1880 5g/m3 1 5g/m3=5.32 x10-4 ppm oFormaldehyde 1 ppm =1.2 mg/m3 1 mg/m3=0.833 ppm Note: for formaldehyde, ppm are calculated at 20-25!C [] TL: THE EXPOSURE OF CAR DRIVERS AND PASSENGERS TO VEHICLE EMISSIONS: COMPARATIVE POLLUTANT LEVELS INSIDE AND OUTSIDE VEHICLES SO: Greenpeace UK (GP); Earth Resources Research DT: August 1992 Keywords: greenpeace reports cars air pollution smog safety transportation atmosphere / [part 4] Appendix II [this goes on inside of front cover] Recent studies by Greenpeace, as well as the UK Government and other organisations, have highlighted the serious health effects of air pollution from road transport. Everyone exposed to air pollution exceeding guidelines, such as those set by the European Community and the World Health Organization to protect health, is potentially at risk from air pollution. Children, the elderly, pregnant women and people already suffering from respiratory or cardiovascular illness are particularly susceptible. The pollutants that are associated with these health effects are carbon monoxide and nitrogen dioxide. Furthermore, benzene is a known carcinogen, and this and other volatile organic compounds (VOCs) can cause a range of adverse effects. The health effects, and corresponding air quality limits, are set out in greater detail below. BENZENE: Benzene is one of a large number of aromatic hydrocarbons. It is present in the atmosphere primarily as a result of exhaust emissions from motor vehicles and evaporative losses from petrol. The latter occur while petrol is being stored, transported and sold at the pump, and from vehicle fuel systems themselves. Other sources of exposure to benzene are smoking, drinking water, household solvents and food (World Health Organization, 1987). Information on ambient benzene levels in the UK is scant, owing to lack of comprehensive monitoring. According to the World Health Organization, levels are typically higher in metropolitan areas. Very high levels have been recorded near petrol stations. In the United States mandatory vapour retrieval systems limit the public's exposure to benzene from these sources. In the UK however, such measures are not yet in wide use, and are not mandatory. Exposure limits: According to the World Health Organization, "no safe level for airborne benzene can be recommended as benzene is carcinogenic to humans and there is no known safe threshold level". Health Effects: Short term effects of exposure to benzene include irritation to the skin, eyes and upper respiratory tract. With further exposure, depression may occur as well as headaches, dizziness and nausea. Benzene is known to cause cancer; studies in the US have shown a greater than expected incidence of myelogenous leukaemia in exposed workers. The level of risk from ambient pollution is not established. CARBON MONOXIDE: Carbon monoxide is produced by the incomplete combustion of carbon, mainly from fossil fuels. Road vehicles account for 90% of emissions in the UK. The other sources are industry, heating and cooking facilities, and cigarette smoke. In urban areas, concentrations of carbon monoxide are highest near dense traffic; at intersections, in tunnels, in underpasses and in underground car parks. Carbon monoxide is responsible for the production of carboxyhaemoglobin (COHb) in the blood, which impairs delivery of oxygen to the heart, to the brain, and to other tissues. The concentrations of carboxyhaemoglobin experienced by individuals is related to the levels of carbon monoxide in the air, the duration of exposure, and the degree of physical activity undertaken. Foetuses are particularly susceptible. Exposure limits: World Health Organization recommended guidelines for carbon monoxide are: Maximum - 86 parts per million (ppm) for periods not exceeding 15 minutes. 50 parts per million for 30 minutes. These guidelines are established to prevent COHb levels of non- smokers exceeding 2.5 to 3%. Health effects: Sufferers of ischaemic heart disease are particularly vulnerable to the effects of carbon monoxide. In patients with narrowed coronary arteries, low concentrations of COHb increase the likelihood of chest pain on exertion. This can increase the tendency to develop abnormal electrical rhythms within heart muscles that can potentially result in sudden death. One study showed a greater than expected rate of death from ischaemic heart disease in New York bridge and tunnel workers, especially in those aged over 55 years. COHb levels of 3.5% are dangerous for sufferers from ischaemic heart disease, while in the general population, COHb levels of more than 5% cause impaired concentration, blurred vision, slowed reflexes and headache. NITROGEN DIOXIDE: Nitrogen dioxide is formed primarily as a result of oxidation of nitric oxide. Road transport is the main source of nitrogen oxides, accounting for 51% of total emissions. Power stations emit 29% of nitrogen oxides. Exposure limits: The EC has established a limit value for nitrogen dioxide to protect human health as well as guide values to improve protection of human health and to contribute to long term protection of the environment. Limit value: 104 parts per billion, 98 percentile of hourly values throughout the year. Guide values: 70 parts per billion, 98 percentile of hourly values throughout year 26 parts per billion, 50 percentile of hourly values throughout year. Health effects: nitrogen dioxide injures the smallest air passages of the lung and increases susceptibility to respiratory infections. Exposure to relatively low doses may trigger asthma attacks directly, or may render asthmatics more susceptible to other environmental factors which may trigger attacks. Children are especially vulnerable to the effects of nitrogen dioxide, which may increase incidence of symptoms such as cough, sore throat, fever, running nose and earache as well as lower respiratory tract illness. Children who have lower respiratory tract illness before the age of two are more at risk of suffering chronic lung problems in adult life. ============================================================== For further reading on air pollution and health: Air Pollution and Child Health, Cathy Read, Greenpeace, 1991, London. Populations at Risk from Ambient Air Pollution in England, a report for Greenpeace UK by Earth Resources Research, Greenpeace, 1992, London. Air Quality Guidelines for Europe, World Health Organization, Regional Office for Europe, 1987, Copenhagen. =============