Appendix E: Air Contaminants
This Appendix presents an overview of the key air contaminants arising from use of petrol and diesel in New Zealand. They are, the five key contaminants (CO, NO2, SO2, particulates and O3), plus a number of hazardous air pollutants (benzene, toluene, xylene, 1,3-butadiene, formaldehyde, acetaldehyde and benzo(a)pyrene). For each contaminant a discussion of its sources, health effects, ambient air levels and emission control strategies is presented.
Further information may be found in the VFECs reports, including Appendix A of the VFECS Final Report which contains a useful summary table of the ambient air quality, pollution levels and emission reduction targets for vehicles (MOT, 1998a).
The suite of technical reports commissioned by Ministry for the Environment for the review of the 1994 Ambient Air Quality Guidelines provide detailed information on the health effects of air pollutants, strategies for managing air quality and effects on ecosystems (MfE#12-16, 2000).
E.1 Carbon Monoxide
Carbon monoxide (CO) is a colourless, odourless and tasteless gas that is poisonous to humans in high concentrations. CO is a trace constituent in the atmosphere, produced by both natural processes (e.g. volcanoes) and human activities, (e.g. the incomplete combustion of carbon-containing fuels).
Petrol-fuelled motor transport is the major source of CO in urban airsheds. CO emitted from vehicles is solely the result of a lack of available oxygen within the combustion zone, caused by an over rich mixture or poor fuel volatilisation/mixing with air. Studies indicate that mobile sources make up approximately 90% of CO emissions in the Auckland region (MfE#14, 2000). Domestic fires also contribute a significant proportion of CO emissions in winter, possibly up to 50% in Christchurch (MfE#14, 2000).
Adverse Effects
CO affects human health by reducing the amount of oxygen that can be carried in the blood to the body tissues. When inhaled, CO combines with haemoglobin (Hb), the blood's oxygen-carrying protein molecule, to form carboxyhaemoglobin (COHb). In this state the Hb is unable to carry oxygen.
CO levels are of concern from a human health perspective if they exceed recommended air quality guidelines, which are generally based on a No Observed Adverse Effect Level (NOAEL) of 2.5% carboxyhaemoglobin in blood.
Ambient Air Quality Guidelines and Typical CO Concentrations
The Review of the Ambient Air Quality Guidelines has recommended that the ambient air quality guidelines for carbon monoxide remain unchanged, at 30 mg/m³, 1-hour average, and 10 mg/m³, 8-hour average. It is recommended that these guidelines be reviewed no later than 2002 in view of the emerging research on adverse health effects at lower than expected carboxyhaemoglobin levels in blood.
| New Zealand AAQ Guideline | 10 mg/m³, 8-hour average |
| Typical New Zealand Urban Actual | 5-10 mg/m³, 8-hour average |
| Typical New Zealand Rural Actual | <0.1 mg/m³, 8-hour average |
| Typical New Zealand Peak | 12 mg/m³, 8-hour average |
Most air quality monitoring to date has targeted CO, and there is now sufficient long term air quality monitoring data to clearly define the nature and extent of CO pollution. In New Zealand, CO levels can approach guideline levels (8-hour average) in "residential" urban areas ("alert" category), however, concentrations in specific traffic corridors have been found to exceed the guidelines.
VFECS developed the "traffic corridor" concept to isolate the effects of traffic pollution from other sources (MOT, 1997). Two particular sites have been confirmed as representative of the worst case traffic pollution environments: Khyber Pass Road in Auckland and Riccarton Road in Christchurch (MOT, 1997). In these cases, reductions in concentrations of CO of between 60-80% are required to meet the criteria of "acceptable" air quality, and reductions of greater than 80% are required to meet the "good" target.
Emission Control Strategies
Stage 1 of the VFECS focused on addressing CO emissions from vehicles. This stage included a detailed analysis of the potential costs and benefits of pursuing various control options (MOT, 1997).
In essence, to minimise CO emissions, vehicles must run at their optimal efficiency, and create CO2 instead of CO. Oxygenate content has a direct impact on CO emissions. Adding oxygenates induces a lean shift (i.e. introduces oxygen) which reduces CO emissions. Oxygenate levels (including MTBE) are currently specified by the Regulations and under review. Reducing the aromatic content of petrol could also reduce CO emissions, but tends to increase NOx emissions by a similar rate (MOT, 1997).
The VFECS reached the following conclusions (MOT, 1997):
- Of the technical control measures assessed, only two provide the necessary reductions in CO emissions, and over an extended timeframe:
- Introducing a progressive system of emissions standards for new vehicles. This is currently being formalised as a regulatory requirement through the LTSA Rules process, but it will be 15-20 years before the impacts are fully realised.
- Adopting a wholesale change to diesel fuelled light vehicles (diesel engines operate under excess air at all conditions). This would have an impact on particulate levels.
- Non-technical measures applied to traffic corridor management appear to provide the best means of preventing local air quality CO exceedances in the near term.
E.2 Nitrogen Dioxide
In the high temperature zones of combustion processes, nitrogen in air and in the fuel reacts with oxygen in air to form nitrogen oxides: nitric oxide (NO), nitrogen dioxide (NO2), and nitrous oxide (N2O). These are collectively referred to as NOx. For most combustion processes nitrogen oxides are emitted primarily in the form of NO, which slowly oxidises to NO2 in the atmosphere. Nitrogen dioxide is a pungent, acidic, reddish-brown gas, that is corrosive and strongly oxidising.
Sources of nitrogen oxides include "all types of road vehicles … domestic burning of wood, coal, natural gas and LPG and certain industrial processes. Depending on the presence of other local sources such as thermal power stations and industry using significant combustion processes, motor vehicles are estimated to contribute up to 80 to 95% of total emissions" of nitrogen oxides (MOT, 1998a). NOx emissions are a consequence of the thermodynamics of the combustion cycle, rather than fuel chemistry. The extent of NOx formation is determined by residence time at high temperatures in the presence of excess oxygen.
Adverse Effects
NO2 in the human respiratory system causes increases in both the susceptibility to and the severity of infections and asthma. Recent epidemiological studies have shown an association between ambient NO2 exposure and increases in daily mortality and hospital admissions for respiratory disease (MfE#12, 2000).
NO2 is a significant pollutant not only because of the health effects it directly causes, but also as a result of the role it can play in the generation of photochemical smog events and the production of secondary particles that cause visibility degradation. NO2 does have some synergistic effects, but the mechanisms are poorly understood.
Ambient Air Quality Guidelines and Typical NO2 Concentrations
The Review of the Ambient Air Quality Guidelines has recommended that the 1-hour average ambient air quality guideline for NO2 be reduced to 200 µg/m3 (from 300 µg/m³), and that the 24-hour average guideline remain unchanged at 100 µg/m³.
| New Zealand AAQ Guideline | 100 µg/m³, 24-hour average |
| Typical New Zealand Urban Actual | 5-30 µg/m³, 24-hour average |
| Typical New Zealand Rural Actual | <1 µg/m³, 24-hour average |
| Typical New Zealand Peak | 50 µg/m³, 24-hour average |
In New Zealand, NO2 levels within urban areas may be categorised as "good" (up to 30% of guideline value), for 24-hour periods. The maxima one-hour average recorded to date for traffic corridor locations have been up to 200 µg/m3 (equal to the guideline level "alert" category), and 60-90 µg/m³in urban areas ("acceptable" category).
Emission Control Strategies
Petrol
For petrol engines, tailpipe NOx emissions are predominantly controlled with the use of three-way catalysts, although exhaust gas recirculation (EGR) will also provide some benefit. Changes in fuel quality can influence the NOx emissions performance, but generally the magnitude is small. The main fuel parameters which can influence NOx emissions from gasoline cars are sulphur and aromatics, and to a lesser extent, olefins (CONCAWE, 1999).
Reducing sulphur levels in petrol (to 100 ppm or less) increases catalyst efficiency and may reduce NOx emissions by up to 10%. Currently, New Zealand's petrol contains very low sulphur levels (sometimes less than 50 ppm), although the Regulations permit higher levels.
Reducing the aromatic content of fuels also increases NOx emissions, as catalysts are thought to work more efficiently with relatively high aromatic fuels (CONCAWE, 1999).
Of the future technologies, lean-burn gasoline direct injection (G-DI) vehicles (favoured due to reduced fuel consumption and CO2 emissions) are expected to have higher NOx emissions than conventional petrol vehicles (CONCAWE, 1999). This will require new generation "lean de-NOx" catalysts to be developed, which are also expected to require low sulphur content fuels.
Diesel
For diesel engines, a number of fuel quality parameters have competing effects on NOx emissions. Changes in diesel engine technology which can reduce NOx emissions will generally increase particulate emissions and fuel consumption (CONCAWE, 1999). However, increasing cetane number has been found to reduce NOx emissions. The cetane number can be related to the aromatic content of the fuel; as the aromatic content decreases the cetane number increases. Therefore, decreasing the aromatic content of diesel may reduce NOx emissions. Currently, the aromatic content of diesel is unregulated.
Future after treatment systems are likely to require low sulphur content diesel, 50 ppm or lower, significantly lower than current New Zealand levels.
E.3 Sulphur Dioxide
Sulphur dioxide (SO2) is a colourless, soluble gas with a characteristic pungent smell. It reacts with water in air to form sulphuric acid aerosol (H2SO4).
SO2 is primarily produced through the combustion of fuels that contain sulphur, but can also be emitted from a number of specific industrial operations, such as sulphuric acid manufacturing, the roasting or smelting of mineral ores containing sulphur, and oil refining. Petrol can have a significant sulphur content, but this varies widely depending upon the source of the fuel. The sulphur content of petrol used in New Zealand is generally very low. The sulphur content of diesel fuels available in New Zealand is, however, comparatively high (see Section 8). The Auckland emissions inventory estimated that 27% of SO2 was from mobile sources (ARC, 1997).
Adverse Effects
The health effects of SO2 have been recognised for many years. SO2 is a potent respiratory irritant when inhaled and ambient levels of SO2 have been associated with increases in daily mortality, hospital admissions for respiratory and cardiovascular disease, increases in respiratory symptoms, and decreases in lung function. Due to the high correlation between ambient SO2 levels and other pollutants, especially particles, it is difficult to attribute the observed effects to SO2 alone.
Ambient Air Quality Guidelines and Typical SO2 Concentrations
The Review of the Ambient Air Quality Guidelines has recommended that the 1-hour and 24-hour average ambient air quality guidelines for SO2 remain essentially unchanged at, respectively, 350 µg/m³ and 120 µg/m³.
SO2 is monitored at two sites (in Auckland and Christchurch) as part of MfE's air quality management programme. Their 2000 report (MfE, 2001) shows that annual concentrations are less than 33% of the Ambient Air Quality Guideline and air quality in relation to SO2 levels is good.
Emission Control Strategies
While SO2 from vehicles is not considered to be of significant concern in New Zealand per se, SO2 is a significant pollutant because of the role it can play in the production of secondary particles. As such, any assessment of the benefits of reduction measures must also take into account the benefits that may be derived as a result of reduced levels of particles.
Ensuring that fuel is compatible with the future emissions control and fuel-efficient technologies (particularly catalytic converters) is a key issue. Sulphur reduces the efficiency of the catalysts used to remove a number of the other key air contaminants, namely NOx and hydrocarbons (i.e. sulphur "poisons" the catalyst). This is particularly relevant for diesel after treatment technologies, and will become increasingly important in the future for petrol engines.
In essence, to reduce sulphur emissions and to enable technologies to work optimally, sulphur levels in fuel must be reduced.
E.4 Particulates
Particles are emitted from motor vehicles (particularly diesel vehicles), domestic fuel burning, fossil fuel-based electricity generation, some industrial processes, and industrial and domestic incinerators. Secondary production of particles can be significant, with the most important being:
- Sulphates, which derive primarily from SO2 emissions.
- Nitrates, which derive primarily from NO emissions.
- Organic aerosols, which derive primarily from volatile organic compound emissions.
Natural sources of particles include dust (which can be exacerbated greatly by human activities), pollens and sea spray.
Airborne particles can occur in a range of different sizes. From a health perspective, particles smaller than 10 microns in diameter are of greatest concern as they are able to enter the lungs. Most air-quality monitoring is for particles less than 10 microns in diameter (PM10), although increasingly attention is turning to particles less than 2.5 microns in diameter (PM2.5).
The Auckland emissions inventory showed that, on a "typical winter day", domestic sources contribute approximately 48% of the annual total emissions, commercial sources contribute approximately 5%, major industry contributes 32% and mobile sources contribute the remaining 15% (ARC, 1997).
In Christchurch, where the extent of domestic fuel burning in winter is more significant than in Auckland, home heating contributes approximately 82% of the PM10 on a typical winter day, with motor vehicles contributing 10% and industry 8%. The "winter smoke" phenomenon is also experienced in some other South Island urban areas (MfE#14, 2000).
Adverse Effects
The major effects of concern with regard to airborne particles are increased mortality, aggravation of existing respiratory and cardiovascular disease, hospital admissions and lost work days.
Studies into the health effects of air pollution in Christchurch have focussed on particles (as PM10), NO2 and CO. A recent study into the effects of air pollution and weather on daily mortality showed that PM10 levels in Christchurch are associated with increases in daily mortality (MfE#14, 2000). The results of this study are consistent with international studies.
Ambient Air Quality Guidelines and Typical Particulate Concentrations
The Review of Ambient Air Quality Guidelines has recommended that the 24-hour average ambient air quality guideline for PM10 be reduced to 50 µg/m3 (from 120 µg/m³) and the annual average guideline be deleted. This proposed guideline has already been adopted by a number of regional councils.
Monitoring of PM2.5 is to be encouraged and the results compared with an ambient air quality guideline of 25 µg/m³, 24-hour average. In view of the emerging research on the relationship between PM2.5 and mortality, the PM2.5 guideline will be reviewed no later than 2004.
| Proposed New Zealand AAQ Guideline, PM10 | 50 µg/m³, 24-hour average |
| Typical New Zealand Urban Actual | 25-35 µg/m³, 24-hour average |
| Typical New Zealand Rural Actual | 2-10 µg/m³, 24-hour average |
| Typical New Zealand Peak | >500 µg/m³, 24-hour average |
In New Zealand, PM10 levels in urban areas are typically "acceptable", however, they can exceed the guidelines on occasions, particularly on winter days in urban areas where home heating fires and adverse meteorological conditions combine.
Emission Control Strategies
Emissions of particulate matter are generally associated with diesel vehicles.
The VFECS contains specific initiatives aimed at reducing the direct emission of particles from motor vehicles, which constitutes one of the most visible air pollution issues in New Zealand, even though the relative contribution of motor vehicles to direct PM10 emissions is minor. These include emission standards for new diesel vehicles, an education programme to improve tuning and maintenance of diesel fuel vehicles, and introduction of the "10-second rule" which is aimed at removing excessively smoky vehicles from the road (MOT, 1998a).
Changes in particulate pollution levels depend both on changes in emission of primary particulate and gaseous pollutants (NOx, SO2 and hydrocarbons), given the as yet unquantifiable contribution of other vehicle emission species to secondary particle formation. Specific (diesel) fuel parameters which affect PM emissions are density (reduced density will reduce PM emissions, but at the expense of fuel consumption) and sulphur (directly via SO2 emissions, and indirectly via the performance of after-treatment catalysts).
Visible Smoke
Distinction must be made between particulates and visible smoke: particulate matter is defined as anything that is collectable on a filter (particulates may be present in exhaust even though no visible smoke is apparent); the defining character of exhaust smoke is that it is comprised of solid or liquid aerosol particles that absorb or deflect light.
While visible smoke is a visible and important environmental issue, testing has shown that smoke puff emissions contribute no greater amounts of key air pollutants than many vehicles which appear to be well maintained (MOT, 1998a). The VFECS Final Report contains a thorough discussion of the causes of and control strategies for visible smoke (MOT, 1998a).
E.5 Ozone
Ozone (O3) is a secondary air pollutant formed by reactions of primary pollutants (nitrogen oxides and photochemically reactive organic compounds) in the presence of sunlight. O3 is the principal component of photochemical smog.
The primary pollutants that can lead to the generation of O3 arise from a range of sources. Nitrogen oxides come from motor vehicles, and commercial, industrial and domestic combustion activities. Sources of reactive organic compounds include industrial and domestic uses of solvents and coatings (for example, paints), and other combustion activities. Biogenic emissions or reactive organic compounds from vegetation can also be important.
Adverse Effects
Epidemiological evidence indicates that a wide variety of health outcomes are possible from exposure to O3: short-term effects on mortality, hospital admissions, respiratory symptoms and lung function. At an experimental level, evidence suggests that short-term effects present a greater risk than long-term effects.
Ambient Air Quality Guidelines and Typical O3 Concentrations
The Review of Ambient Air Quality Guidelines has recommended that the ambient air quality guidelines for ozone remain unchanged, at 150 µg/m³, 1-hour average, and 100 µg/m³, 8-hour average.
There is limited information available regarding O3 levels in New Zealand. However, studies have found that atmospheric conditions suitable for photochemical reactions occur around 10 days per year in Auckland, 15 days in Hamilton and 4 days in Christchurch. In 1977/78 in Auckland, breaches of the guideline values were found at sites 35-40km north and south of the city (MfE#14, 2000). Further O3 monitoring is required to gain a better understanding of its extent and significance.
Emission Control Strategies
The control of O3 requires management strategies that target reductions in nitrogen oxides and/or reactive organic compounds.
One component (either nitrogen oxides or reactive organic compounds) is likely to be the "limiting" pollutant, and it may be that targeting these emissions will provide the most effective mechanism to reduce O3 levels. In the absence of an understanding of which pollutant is `limiting', it may be appropriate to take a precautionary approach and instigate measures to reduce the range of precursor pollutants. This is likely to be achieved as a result of any programmes adopted to reduce emissions of the other key air pollutants.
E.6 Benzene
Based on the Auckland emissions inventory, the total 1993 VOC emissions in the Auckland region were estimated at 65,000 tonnes: 63% from motor vehicles; 13% from domestic solid fuel combustion; and 9% from surface coating operations (MfE#13, 2000). Emissions of benzene were estimated at about 7% of total VOCs, of which 80% originated from motor vehicles, and the remainder from domestic solid-fuel heating (MfE#13, 2000).
Motor vehicle exhaust emissions of benzene derive partly from evaporative emissions or unburnt benzene in the fuel (primarily from petrol engines), and partly from the dealkylation of other aromatic hydrocarbons in the petrol.
Adverse Effects
Adverse health effects arising from exposure to benzene are well documented. The most significant effects are haemotoxicity, genotoxicity and carcinogenicity. Benzene has been classified as a Group 1 (known human) carcinogen by the International Agency for Research and Cancer (IARC) and is assessed as a carcinogen by the World Health Organisation (WHO), which recommends jurisdictions establish their own guideline values by considering the unit risk factors and the level of risk deemed acceptable.
Acute exposures to very high levels of benzene can affect the nervous system, producing a range of symptoms such as headaches, dizziness, nausea, lack of co-ordination, and unconsciousness.
Ambient Air Quality Guidelines and Typical Benzene Concentrations
The Review of the Ambient Air Quality Guidelines has recommended benzene guidelines of 10 µg/m³, annual average, reducing to 3.6 µg/m³, annual average in year 2010. Compliance with the criteria would be assessed by monitoring at "residential" sites, with modelling or other assessment tools employed to characterise population exposure.
| Proposed New Zealand AAQ Guideline | 2000: 10 µg/m³, annual average
2010: 3.6 µg/m³, annual average |
| Typical New Zealand Urban Actual | 1.0-6.2 µg/m³, annual average |
| New Zealand Proximity to Heavy Traffic | 6.3-20.1 µg/m³, annual average |
Based on current monitoring data, most cities in New Zealand are in compliance with the year 2000 criterion (MfE#13, 2000). However, there are hot spots adjacent to major roads where levels have been measured close to double the criterion. Areas in Auckland, Christchurch and possibly other cities do not appear to meet the proposed 2010 criterion.
Population Exposure to Benzene
The annual average air concentration would be equivalent to the annual average exposure of an individual, if that individual spent all of their time for a year at the sample location. As people move around however, their exposure to benzene (or any contaminant), throughout a day/week/year, changes.
A study undertaken by the MOH over the period 1996-1999 was designed to establish current exposure levels to benzene and other toxic organic compounds in air for typical New Zealand populations (Stevenson and Narsey, 1999). The study involved monitoring of benzene and other aromatic compounds at 26 sites, covering both indoor and outdoor environments in a range of urban and suburban zones. It focused on typical situations in which most people are likely to be exposed, rather than specific (such as occupational) or unusual exposures.
The results indicated that (Stevenson and Narsey, 1999):
- Cigarettes are, by far, the largest source of benzene exposure for people smoking or non-smokers living in homes with smokers.
- Benzene concentrations in indoor air in non-smoking homes are essentially the same as outdoor air at the same location, except where the house has an in-built garage.
- The highest concentrations for any site (about 20 times typical ambient air levels) were from a home with an internal double garage, and almost certainly resulted from evaporative emissions from two petrol-fuelled carburetted cars, regularly used and parked in the garage.
- Benzene concentrations in vehicles while being driven are typically 10-50 times higher than ambient air (and sourced primarily from the traffic corridor rather than from the vehicle in question). For most non-smokers, vehicle travel for 2.5-10 hours per week contributes up to half of their overall benzene exposure.
Overall annual average benzene exposures were estimated for a range of scenarios by calculating the time- and scenario-weighted annual average concentrations, based on the annual average benzene concentrations found in the study. Estimated annual average benzene exposures for non-smokers in New Zealand cities and suburbs are in the range 1-40 µg/m³ (Stevenson and Narsey, 1999).
- The lower end of this range (<2 µg/m³) is representative of a person spending all of their time in the outer suburbs and less than 2.5 hours per week travelling in a motor vehicle.
- Exposure in the mid-range (2.5-10 µg/m³) is representative of a person living and working in a suburb of a major city, and spending 5-10 hours per week travelling in a motor vehicle in city and suburban traffic.
- The top end of this range (10-40 µg/m³) corresponds to exposures received by people living in houses significantly affected by evaporative emissions from petrol-fuelled cars in internal garages, and/or spending a high proportion of their time in vehicles in city and suburban areas e.g. couriers and taxi drivers.
The study indicated that, because benzene exposures in motor vehicles, where vehicle emissions are essentially the only benzene source, are a major exposure for most people, vehicle emissions make an even larger contribution to overall personal exposures than indicated by their estimated contributions to ambient air.
For a "typical" New Zealand population exposure to benzene of 3 µg/m³, the WHO cancer potency estimate for additional lifetime leukaemia risk suggests that up to 0.8 additional leukaemia deaths per year may occur in the total population (Stevenson and Narsey, 1999). This may be compared with the current annual total of about 250 deaths from all types of leukaemia in New Zealand (Stevenson and Narsey, 1999).
Emission Control Strategies
Both the benzene and the total aromatics content of petrol are important when addressing possible control measures. Reductions in benzene and total aromatic levels in petrol will have a direct effect on benzene emissions from motor vehicles. However, as discussed in Section 7.10, aromatics are an important source of octane number and must be replaced with either olefins or branched chain alkane content.
Fitting catalysts to cars is the most effective tail-pipe treatment to reduce benzene emissions. Maintaining low levels and/or reducing the sulphur content in petrol will also, indirectly, assist in minimising benzene emissions by ensuring that catalysts can work efficiently.
E.7 Toluene and Xylene
Based on the Auckland emissions inventory, toluene and xylene together accounted for just over 20% of the total 1993 VOC emissions (MfE#13, 2000). Emissions from motor vehicles accounted for 75% and 85% of toluene and xylene emissions respectively. Toluene and xylene are used as solvents, and the balance of their emissions come from surface-coating operations.
(Xylene exists as different isomers, however for the purposes of monitoring and assessing toxicology, mixtures and individual isomers are normally treated as equivalent).
Adverse Effects
A range of health effects have been associated with chronic and acute exposure to toluene, the most significant being those on the central nervous system. The range of health effects associated with chronic and acute exposure to xylene includes breathing difficulties, nose and throat irritation, and neurological effects (such as headaches, dizziness and fatigue).
Ambient air quality guidelines have been derived from the WHO LOAEL. Neither toluene nor xylene are considered carcinogenic.
Ambient Air Quality Guidelines and Typical Toluene and Xylene Concentrations
The Review of the Ambient Air Quality Guidelines has recommended toluene and xylene guidelines of 190 and 950 µg/m³, annual average, respectively. Compliance with the criteria would be assessed by monitoring at "residential" sites, with modelling or other assessment tools employed to characterise population exposure.
| Proposed New Zealand AAQ Guideline Toluene | 190 µg/m³, annual average |
| Typical New Zealand Urban Actual | 3.4-17.1 µg/m³, annual average |
| New Zealand Proximity to Heavy Traffic | 20.0-49.9 µg/m³, annual average |
| Proposed New Zealand AAQ Guideline Xylene | 950 µg/m³, annual average |
| Typical New Zealand Urban Actual | 2.3-14.3 µg/m³, annual average |
| New Zealand Proximity to Heavy Traffic | 17.0-52.9 µg/m³, annual average |
Based on current monitoring data, the proposed criteria are unlikely to be exceeded, and air quality may be categorised as "excellent". As with benzene, the data illustrate the influence of motor vehicles as well as regional and local meteorology on pollutant levels.
Both toluene and particularly xylene have a distinctive odour. The guideline documents contain recommendation for levels which may be protective of odour nuisance, however it is not proposed that these be adopted formally as guideline values.
Emission Control Strategies
For petrol handling and combustion, the aromatics content is the relevant fuel-quality parameter in managing emissions of toluene and xylene. Reductions in total aromatic levels in petrol will have a direct effect on toluene and xylene emissions from motor vehicles. However, as discussed in Section 7, aromatics are an important source of octane number and must be replaced with either olefins or branched chain alkane content.
E.8 1,3-Butadiene
1,3-Butadiene is a VOC, like benzene, toluene and xylene. The atmospheric half-life of 1,3-butadiene is quite short (several hours), compared with benzene (several days). There is little or no pre-formed 1,3-butadiene in petrol; its major source is combustion of petrol.
Emissions of 1,3-butadiene are believed to vary with the level of olefins in petrol, although one study has concluded that over 90% of 1,3-butadiene emissions originate from the common alkane and aromatic fractions of petrol (MfE#13, 2000).
There is little New Zealand data for quantifying 1,3-butadiene emissions. The most recent Australian inventory indicates that 76% of 1,3-butadiene emissions come from motor vehicles, 15% from industrial sources (including rubber and resin production), and the balance from domestic/commercial sources (MfE#13, 2000).
Adverse Effects
Adverse health effects arising from exposure to 1,3-butadiene are well documented. Chronic non-cancer effects include cardiovascular and blood diseases, and neurological effects (blurred vision, headaches). 1,3-Butadiene has been classified as a Group 2A carcinogen by IARC (probably carcinogenic to humans). New Zealand has therefore adopted a precautionary approach to setting ambient criteria.
Ambient Air Quality Guidelines and Typical 1,3-Butadiene Concentrations
The Review of the Ambient Air Quality Guidelines has recommended an annual average criterion of 2.4 µg/m³ (equivalent to a one-hour value of 15 µg/m³). Compliance with the criteria would be assessed by monitoring at "urban residential" sites.
There is little New Zealand monitoring data for 1,3-butadiene. Data indicates that ambient air concentrations of 1,3-butadiene in urban areas could be around 10-20% of benzene concentrations (Stevenson and Narsey, 1999). The maximum 24-hour value, equivalent to 1.1 µg/m³, recorded in Christchurch, is less than half the recommended annual average concentration (MfE#13, 2000). This suggests that cities within New Zealand appear to be well within the recommended criteria.
Population Exposure to 1,3-Butadiene
The annual average air concentration would be equivalent to the annual average exposure of an individual, if that individual spent all of their time for a year at the sample location. As people move around however, their exposure to contaminants changes, throughout a day/week/year.
The study undertaken by the MOH to establish current exposure levels to benzene and other toxic organic compounds in air also assessed 1,3-butadiene exposure (Stevenson and Narsey, 1999).
Estimated annual average 1,3-butadiene exposures for non-smokers in New Zealand cities and suburbs are in the range 0.2-2.6 µg/m³ (Stevenson and Narsey, 1999). Based on US EPA toxicity data, this is equivalent to an additional lifetime leukaemia risk of 7 x 10-7 to 1 x 10-5, approximately an order of magnitude less than that for benzene (Stevenson and Narsey, 1999).
Emission Control Strategies
Olefins, along with aromatic compounds, are an important source of octane number. Lowering olefin content while maintaining octane levels requires an increase in either the aromatic content or the branched chain alkane content of petrol. However, based on the findings of a recent New Zealand study, lowering olefin content may not reduce 1,3-butadiene emissions (MfE#13, 2000).
Catalytic converters are efficient at reducing 1,3-butadiene emissions.
E.9 Formaldehyde and Acetaldehyde
Formaldehyde and acetaldehyde are carbonyls. They are both emitted as primary air pollutants, formed during the combustion of petrol and diesel, and are also formed by secondary photochemical reactions in the atmosphere.
Sources include motor vehicles, domestic solid-fuel combustion, and various types of industry, such as the manufacture of particle board, which would be a significant source at a local level. Auckland inventory data indicates that the two compounds together form less than 2% of total VOC emissions, roughly equivalent to that emitted from domestic solid-fuel consumption (MfE#13, 2000).
Adverse Effects
Chronic non-cancer effects arising from exposure to formaldehyde include respiratory symptoms, eye, nose and throat irritation. Formaldehyde has been classified as a Group 2A carcinogen by IARC (probably carcinogenic to humans). WHO does not assess formaldehyde as a carcinogen, recommending a guideline value based on the NOAEL, an approach adopted by New Zealand.
Chronic non-cancer effects arising from exposure to acetaldehyde are similar to those for formaldehyde. Acetaldehyde has been classified as a Group 2B carcinogen by IARC (possibly carcinogenic to humans). WHO has assessed acetaldehyde as a carcinogen, recommending a guideline value based on the unit risk factor, an approach adopted by New Zealand.
Ambient Air Quality Guidelines and Typical Formaldehyde and Acetaldehyde Concentrations
The Review of the Ambient Air Quality Guidelines has recommended annual average criteria of 15 and 30 µg/m³ for formaldehyde and acetaldehyde respectively. Compliance with the criteria would be assessed by monitoring at "urban residential" sites.
Monitoring data for Khyber Pass Road (Auckland) indicate an annual average of 1-5 µg/m³ formaldehyde, which is well below the proposed criterion (MfE#13, 2000). There is no available acetaldehyde data for New Zealand, but similar levels to those of formaldehyde are expected, meaning that they also should be well below the proposed criterion (MfE#13, 2000).
Photochemical smog reactions can generate significant levels of formaldehyde in the atmosphere. Given the relatively low smog potential of most New Zealand cities, control of VOC concentrations is likely to ensure that carbonyl ambient air levels remain below the recommended criteria.
Emission Control Strategies
There are no specific control strategies for formaldehyde and acetaldehyde. Controlling VOC emissions should ensure ambient air levels remain below the recommended criteria, and this will be ascertained by further monitoring (MfE#13, 2000).
E.10 Benzo(a)pyrene
Benzo(a)pyrene is one of over 40 polyaromatic hydrocarbons (PAHs), but is considered the most hazardous and is commonly used as an indicator species for the group. PAHs arise from the incomplete combustion of solid and liquid fuels. They are semi-volatile compounds, and occur both in the gas phase or attached to fine particles.
The primary sources of PAHs in the New Zealand urban environment are domestic solid-fuel consumption and motor vehicles (primarily diesel), with industrial sources providing potentially significant local sources.
Adverse Effects
Chronic non-cancer effects arising from exposure to benzo(a)pyrene include dermatitis and eye irritation. Epidemiological studies have reported increases in lung cancer in humans exposed to coke oven and roof tar emissions, and cigarette smoke, all of which contain PAH mixtures (MfE#13, 2000). Benzo(a)pyrene has been classified as a Group 2A carcinogen by IARC (probably carcinogenic to humans). WHO has assessed benzo(a)pyrene as a carcinogen, recommending a guideline value based on the unit risk factor, an approach adopted by New Zealand.
Ambient Air Quality Guidelines and Typical Benzo(a)pyrene Concentrations
The Review of the Ambient Air Quality Guidelines has recommended an annual average criterion of 0.30 ng/m³ (0.0003 µg/m³) for benzo(a)pyrene.
Based on the limited data for New Zealand, and typical levels found elsewhere, there is a significant chance that existing (possibly background) levels exceed this recommendation (MfE#13, 2000).
Emission Control Strategies
Domestic solid-fuel consumption is the primary target for reducing (wider) benzo(a)pyrene emissions (MfE#13, 2000). PAH levels affect PM and PAH emissions, therefore reducing total PAH content and, to a lesser extent, aromatics, will reduce PAH emissions. Published data also indicate that exhaust treatment systems are highly effective at reducing PAH emissions (CONCAWE, 1999).
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