THE RISK RELATED TO AIR POLLUTION IN AN URBAN
ENVIRONMENT
THE RISK RELATED TO AIR POLLUTION IN AN URBAN
ENVIRONMENT
The risk related to air pollution comes in second position in the list of perceived risks.
G. Thibaut, Head of the Air Pollution Department of the City of Paris here gives us an update on this question.
1 - AIR POLLUTION..
Définitions :
The Council of Europe, already in 1967, defined air pollution as follows:
"Air pollution exists when the presence of an extraneous substance or a significant variation in the proportion of its components is likely (based on existing scientific knowledge) to cause a noxious effect, and create a nuisance or discomfort".
The term "noxious effect" indicated that air pollution is a harmful phenomenon and is hence related to a health risk. The terms "extraneous substance" and "variation in the proportion of its components" define the notion of "POLLUTANT": a compound that is foreign to the normal composition of air or a component present in the air in abnormal quantities.
In this definition, no mention was made indicating that it referred only to outside air; it therefore implicitly contained the notion of internal pollution.
The French "Law on air and the rational use of energy" of 30 December 1996 now provides a legal definition of this point in its Article 2:
"Atmospheric pollution consists of the introduction by man, either directly or indirectly, into the atmosphere and closed spaces, of substances having prejudicial consequences likely to endanger human health, to harm biological resources and ecosystems, to influence climate change, to deteriorate physical property and to cause excessive olfactory nuisances."
This definition covers all the harmful effects on "human health", on "biological resources", on "ecosystems", and on "climate change". The term "closed spaces" shows that interior pollution is taken into account. With respect to the previous definition, the latter differs in that it does not take into account natural pollution, but that it does refer explicitly to pollution inside buildings and gives a more precise definition of the various harmful effects.
LThe parameters of air pollution: :
Air pollution cannot be reduced to the sole presence of "pollutants" in the air, but on the contrary this phenomenon is related to a chain of multiple parameters that go from human activities upstream right down to their downstream effects: "Energy > Activities > Energy consumption > Polluting emissions > Transformations, dilution > Levels in the environment > Exposure of targets > Effects".
Pollutants and indicators: :
1° Pollutants from fixed sources:
Pollutants that are characteristic of fixed sources are the chief compounds present in combustion gases:
- sulphurous anhydride or sulphur dioxide (SO2), because of the presence of sulphur (S) in fossil fuels;- the particles contained in the fumes rejected by heating or industrial units;
- nitrogen oxides (chiefly NO but also NO2) produced by the partial oxidation of nitrogen contained in the air (N2) in combustion processes:
- carbon oxides: dioxide (CO2), the chief compound of combustion, but also monoxide (CO), produced by incomplete combustion;
- hydrochloric acid (HCl) produced by incinerators.
A large number of pollutants can be emitted by industrial units, depending on their activities: organic compounds (solvents), fluorine (the aluminium industry), metallic particles, siliceous dusts, etc…
It is not possible to measure all of these pollutants in the environment, therefore one is limited to quantifying the pollution produced by fixed sources by measuring characteristic "test pollutants" called indicators: chiefly SO2 and particles.
2° Pollutants from mobile sources
The pollutants contained in the exhaust gases produced by the internal combustion engines of transport vehicles are also extremely numerous:
- carbon oxides (CO and CO2);- nitrogen oxides: chiefly nitrogen monoxide (NO), but also a little nitrogen dioxide (NO2), these two nitrogen oxides being termed together 'NOx";
- particles, chiefly Diesel, but also those emitted by petrol engines, among which lead that is still present in certain fuels;
- unburned hydrocarbons (called HC) and volatile organic compounds (called VOC), emitted with the exhaust or by evaporation of fuels.
The test-pollutants or indicators of these mobile sources are CO, NOx's, and even lead and HC's.
3° "Secondary" pollutants:
Meteorological conditions mean that emitted pollutants are blown by the wind, dissolved by rain and transformed into so-called "secondary" pollutants, in particular through the action of solar radiation.
These "photochemical" transformations are extremely complex. This phenomenon, called "photochemical fog", involves several hundred compounds. We can merely consider the following few simple ideas:
- it is triggered when primary automobile pollutants interfere with sunshine;- it can be very violent under intense sunshine, strong radiation and high temperatures;
- the intensity of the phenomenon depends on the initial levels of the primary pollutants (NO and HC) called "precursors";
- ozone (O3) and nitrogen dioxide (NO2) are the two secondary pollutant "indicators" of photochemical fog.
Conclusion :
We should retain therefore that the levels measured for this or that compound do not represent a quantification of the possible risk related to the specific toxicity of the said compound, but to the fact that they imply other non-measured pollutants included in the overall phenomenon quantified by the indicator.
As an example, a level of 200 µg/m3 of ozone measured in Paris during a pollution "peak" on a very hot day corresponds with a situation of intense photochemical fog in which hydrocarbons, aldehydes, nitrogen oxides and a large number of other pollutants are involved. This level therefore quantifies a much more serious health risk than a level of 400 µg/m3 of the same "natural" ozone compound, observed the same day… at the top of Mont Blanc!
This illustrates all the difference that exists between the notions of "pollutant" and "indicator", in order to have a correct perception of the real risk.
2 - THE EFFECTS OF POLLUTION ON HEALTH
Acute toxicity of the pollutants: :
At very high levels, for example in an indoor atmosphere, pollutants have the following well-known toxic effects:
- SO2 associated with dust: pulmonary effects, bronchitis;- Dusts: fixing on the respiratory apparatus: toxicity depending on their size and their chemical composition (asbestos, silica);
- NO: fixing on haemoglobin: mutagene effect; - O3 : irritation des muqueuses oculaires et pulmonaires ;
- NO2: reduction in respiratory functions and resistance to infection;
- O3: irritation of eye and lung mucous membranes;
- CO: fixing on haemoglobin instead of oxygen (death by suffocation: 15 casualties in Paris and its immediate suburbs in 1997 caused by carbon monoxide intoxication inside houses owing to massive discharges of CO in the household atmosphere, and 80 fatalities in 1982!!);
- Lead: nerve poison (saturnism);
- Hydrocarbons: variable toxicity according to compound (cancer-inducing for benzene and its polycyclic derivatives).
So we can clearly see the appearance of a major individual risk for very high levels - levels that are much higher than environmental levels - which can be obtained in closed spaces, houses or work places, for example.
Effects of air pollutants: :
Even at environmental levels, pollutants can have an effect on public health, when WHO recommendations are exceeded.
The ERPURS group (Evaluation des Risques de la Pollution atmosphérique URbaine pour la Santé - Evaluation of Urban Air Pollution Risks on Health) published a report showing that, in the Paris region and for the period 1987-1992, an increase in the principal pollution indicators was significantly associated with a short-term increase of certain health and medical-social parameters (calls to emergency doctors services, hospitalisations, absenteeism, number of asthmas and respiratory conditions, etc…). The relative risk associated with the principal pollution indicators appears to be low (a few percentage points). Though the methodology used does not make it possible to establish a relationship of causality, the relative risks are nevertheless higher among sensitive population groups (persons suffering from heart diseases, lung problems and allergies, old people or very young children). An updated study, bearing on the period 1991-1995, and published in 1998, confirmed the initial results and furthermore revealed the seasonality of the effects. Even though this and all similar studies do not take into account the real exposure of urban dwellers, they nevertheless put a figure on effects for levels lower than existing standards and recommendations. The cyndinics of pollution appear herefore to be more related to the mean levels of pollution than to the "peaks" which are most often accused.
Studies bearing on long-term effects are fewer, less conclusive and therefore more contested. They nevertheless lead to some strong presumptions as to possible long-term effects. Let us mention the so-called "six cities" study, which followed the age of the population of six average American cities. Statistically it appears from this study that there is a significant correlation between life expectancy and average levels of air pollution.
In conclusion, we may note that though the individual risk remains very low, nevertheless the continual increase in the number of persons exposed to air pollution in urban environments poses a very real problem for public health, which should neither be denied nor artificially dramatised.
3 - MONITORING AIR QUALITY INTHE PARIS REGION
In France, monitoring is carried out by local associations, approved by the Ministry for the Environment. In the Greater Paris region (Ile-de-France), it has been entrusted to AIRPARIF, and independent organisation that brings together the State, local authorities, industry and qualified individuals and representative voluntary associations. AIRPARIF currently has a budget of around 33 million francs, employs some 40 persons and manages around sixty fixed stations spread out over the whole of the Paris region, with over 200 permanent sensors.
These stations make up two main monitoring "networks", the aim of which is to monitor the exposure of the urban population to levels of pollution, in the context of a strategy for following the related health risk for the population. This strategy involves two networks that complement each other:
1 - "urban base stations": measurements are carried out far from the sources and from all local micro-meteorology. The indicators measured are characteristic of the general phenomena and the levels observed have a geographical representativeness for a given sector (of the order of one square kilometre, or even less in areas with a high density of exposed population). This allows the monitoring of average long-term exposure for the whole of the population.2. "proximity stations": measurements are carried out close to automobile sources, on the pavements where the pedestrian population is exposed. The indicators measured are those of primary pollution having an automobile origin. The stations have a topographical representativeness (street, main thoroughfare, "Boulevard Périphérique" (the main Paris ring road), suburban highways, large urban squares, etc…) The levels observed are characteristic of the short-term exposure for the general population or of the longer-term exposure for specific population categories (traffic police, road maintenance employees, messengers, taxis and… car drivers caught in the traffic!).
4 - THE LEVELS OF AIR POLLUTION
Evolution of the indicators: :
The evolution of the indicators for pollution deriving from fixed activities reveals there has been a significant drop now for several years.
Concerning automobile related pollutants, extremely varied evolutions have been observed. The CO indicator shows a favourable evolution and current levels are very low. The evolution of lead levels is even more favourable: 8 µg/m 3 in the middle of traffic in 1978 and 0.2 µg/m 3 in 1997! This pollutant has to all intents and purposes disappeared from the Paris air, as it has in other comparable cities.
Average levels of nitrogen oxides (NOx, NO and NO2) do not reveal any clear trend. We can note that NO2 levels measured in Paris, as in many other large conurbations, are higher than the guide-value (the public health objective to be aimed for) defined by the European Directive, namely 50 µg/m 3 . However, the "ceiling-value" has not been reached in any station that is characteristic of urban inhabitants' exposure. This indicator crystallises all the problematic issues related with the risk of automobile pollution in an urban environment: a public health objective is not being reached, yet the ceiling-values recognised as being directly "toxic" are far from being reached.
Average summer ozone levels in the Paris region reveal no clear trend, inasmuch as the key parameters are sunshine and temperature, which vary from one year to the next. It should be noted that the highest levels are observed in rural areas, far from the centre.
Overall air quality, the daily index :
A simple daily index, used in Paris since 1991, was validated in 1994 on the national level under the name "ATMO". It associates a value of 1 to 10, positioning all the levels measured with respect to recognised standards, with a qualifying adjective (from "excellent" to "very bad"). It is published daily by various regional and national media.
During 1998, the overall quality of air was qualified as being "very good" to "average" for 89% of the time. Conversely, a "mediocre" to "bad" air quality was observed 11% of the time. This index shows therefore that air quality is generally good but undergoes periods of degradation or pollution "peaks", which are not insignificant.
Intense pollution episodes and information and alert procedures :
One of the characteristics of urban pollution is therefore the appearance of pollution "peaks", caused by emissions and unfavourable weather conditions. These episodes are principally characterised by high levels of NO2 and O3 (in summer). The management of such "peaks" requires specific short-term actions. In the Paris region, these have been the subject of a decree, signed jointly by the three prefectoral authorities (Préfet de Police, Préfet de Région and Préfets of the suburban départements, i.e. the local representatives of central government) on 25 April 1994, which sets up a three-stage information and alert procedure:
- level 1 : AIRPARIF informs the technical and administrative services,- level 2 :AIRPARIF informs the authorities and the public via a press release addressed to all media,
- ALERT level: actions undertaken by the Préfet de Police to limit sources.
The hourly thresholds retained for the three indicators are as follows :
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Level 2 |
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ALERT LEVEL |
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Since 1994, level 2 (information of the public) has been triggered about 7 times a year. Since that same date, there have been three alerts: 10 October 1995, 8 November 1995 and 30 September 1997, each time based on the automobile pollution indicator (NO2).
The application decrees of the "Air Act" have provided for traffic limitations in case of an alert, which only authorise the use of vehicles bearing the so-called "green sticker" (granted to vehicles meeting strict emission criteria with catalytic converters). In the Paris region, the decree of 11 April 1997, already defined the provisions for "alternate traffic days" (vehicles are authorised to be on the road according to even or uneven number plates). This provision, first implemented on 1 st October 1997, has been well accepted by the public. Numerous dispensations are envisaged, as in cases of car-pooling. These restrictive provisions are complemented by speed restrictions on the major roads, by free residential parking measures from level 2 and free regional public transport at the alert level.
5 - THE MANAGEMENT OF URBAN AIR POLLUTION RISKS
Three major lines of action are taking shape for managing the risk as defined above:
- technological progress- urban management
- communication and awareness-raising.
Technological progress :
A whole technology of fixed source "depollution" is available today (dust separators, gas washers, solvent recuperators).
Numerous technologies make it possible to improve the individual quality of vehicle exhausts, among which the so-called "three-way" catalytic converter which has been compulsory for new lead-free petrol (gasoline) engined cars since 1 st January 1993, and the oxidation catalytic converter that has been compulsory for diesel-engined vehicles since 1 st January 1996.
Other technologies have been tried or are being implemented presently: recycling of exhaust gases, the "poor-mix" engine, particle filters for diesel engines, substitute fuels (diester, gas fuels such as LPG and natural gas, biogas, and desulphured diesel fuel, which has a very low sulphur content).
Progress in battery technology has made it possible to improve the performance of electric vehicles. A vast development programme was launched in July 1992, at a national level, by the Ministries concerned, in conjunction with industry (EDF (National Electricity Utility), PSA (Peugeot-Citroën), Renault) and local authorities. Today over 3000 electric vehicles are running in French cities. As a vehicle that is perfectly suited to travel in an urban environment, the electric vehicle should experience a rapid development and thus participate in the reduction of emissions, and therefore of the levels of vehicle-induced pollutants.
Urban management :
Numerous actions are under way to reduce the overall level of traffic in urban areas: creating pedestrian or limited traffic areas, limitation of parking in city centres, improvements in road conditions, development of public transport, actions encouraging non-polluting modes of transport.
A long study undertaken in 1993 in Paris showed that single or one-shot actions are not effective, and can even induce unavoidable pernicious effects. The actions undertaken need to be very comprehensive, and bearing on automobile pollution problems: management of urban planning, of travel facilities, of road design and maintenance and of parking facilities, the development of public transport, general improvements to vehicles, the improvement of fuels and exhaust gases, the development and promotion of less or non-polluting vehicles, etc…
Communication and awareness-raising actions:
In France, all the measurement networks are officially based on the same positioning scale of air quality with respect to existing standards, thus making it possible to provide the population with permanent information (the "ATMO" index). The 170 or so electronic municipal information boards of the city of Paris each day display the evaluation of the daily index and its probable evolution for the following day.
This simplified information published daily is completed by the French public teletext system (Minitel 3615-AIRPARIF or 3615-PARIS) and by provisions which are specific to each situation: as soon as the level 2 information procedure is launched, a telephone medical helpline (01 40 34 76 14) is available for persons whose health is more particularly at risk.
The communication programme aims to create awareness among the population and encourage the necessary changes in behaviour. Numerous courses, lectures and activities are carried out by SPAAS in the universities, schools and various training institutions. For the general public, two little booklets (on the "practical guide" model) have been published and widely circulated: "Drivers: 10 pieces of advice to help you pollute less" and "The air in Paris is everybody's business"..
6 - CONCLUSION
The management of the risk of urban pollution requires a comprehensive approach to the actions undertaken, something that requires multiple cooperation. In the Paris region, not only are the City of Paris services involved but also département and regional services (AIRPARIF, DRIRE, Météo-France, ADEME) as well as national services (ministries, public and private sector companies, etc…). All these actions are tending, whether directly or indirectly, towards a positive change in both individual and collective behaviours, encouraging civic responsibility on the part of each individual by offering alternatives to polluting modes of transport. This approach complements regulatory provisions as well as drastic bans. This complementarity appears fundamental if we wish to implement effective actions.
In conclusion, for the City of Paris, management of the pollution risk (which, let us remember, is low but nonetheless real) needs to be based on a few vital ideas which may be summarised by the following "key words": comprehensiveness of the actions in the framework of a consistent programme, a need for multiple collaboration and finally informing, training and creating awareness among the general public.
There is no doubt that, thanks to the media coverage of these issues, the awareness of all and sundry has progressed in the right direction and the fight against pollution is once and for all under way. Recently published legislative and regulatory texts as well as the application decrees which are to follow will be even defining the objectives and the means to be put to work. Yet so much remains to be done! It is essential that the actions already undertaken be pursued and successfully completed, inasmuch as they not only seek to be effective in terms of air quality but also to improve all environmental aspects, by reconciling both the improvement of the quality of life, the mastery of urban planning and travel, and economic activity.
Gérard Thibaut
Head of the Air Pollution Services
Air and Silence
Ville de Paris - France
Translation by Andrew WILES
© Institut Européen de Cindyniques -Lettre n° 26 - Février 1999