Considering the relative importance of energy consumers on such pollution provides an idea of potential evolutions. Examination of contamination modes unlocks possible action, at the level of public authorities or individuals, to limit - if not eliminate - risks to health, particularly in large urban agglomerations.
As pollution policies are still mainly national, this brief study will focus on one example, France. The current conditions in European and North-American countries are quite similar. But many cities in Asia, with the exception of Japan, are suffering from dramatic pollution: sulfur and nitrogen oxides (from coal) directly threaten the health of urban dwellers. Whereas in Paris in 2014 or 2015, only one episode exceeds the alert threshold (80μg/m3), routine days reach 180μg/m3 in Mexico City, Jakarta or Beijing, with peaks exceeding 300μg/m3.
The dry air we breathe contains 78% nitrogen, 21% oxygen, 0.95% argon and 400 ppm of carbon dioxide (CO2). The rest consists of contaminants of natural or artificial origin. In France, those still questioning for health are solid particles and nitrogen oxides, plus domestic and professional exposures, pollen and, in the countryside, contaminants related to livestock and agricultural spraying.
As a greenhouse gas involved in global warming, it is not a pollutant strictly speaking because it is not harmful at normal levels. In a closed room, the human body detects any increase of the CO2 it produces by breathing (12 liters of CO2 over 600 respired liters per hour) and adapts breathing pace by a reflex reaction. CO2 is considered toxic above 0.5% for eight hours. In the Paris Metro, CO2 can vary from 400 to 1000 ppm: it is measured by RATP to evaluate the effectiveness of ventilation. Outdoors, the concentration of CO2 remains stable. It has to be differentiated from carbon monoxide (CO), very toxic but which mostly concerns confined places with improperly adjusted burners as well as ... smokers.
Called PM10 and PM2,5 (less than 10 and 2.5 microns), they come from heating, industrial emissions, agricultural spraying, breeding dust and old diesel vehicles. Or from natural phenomena: The Eyjafjallajökull volcano in Iceland in 2010, seasonal pollens, and Saharan dust. In cities, the highest concentrations are found along the roads, with the exhaust gas, tires and car brake dusts, moved upward by the traffic. But also in the subway and RER trains, where dusts concentrates due in particular to train brakes and the sliding of power brushes. PM10 are multiplied by seven and PM2.5 by four in the monitored Paris Metro stations, as compared with surface air. Industrial dusts were reduced in the last thirty years by improved processes and numerous site shut down.
Nitrogen oxydes produced by combustions are combining with agricultural spraying of nitrate fertilizers to generate NOx aerosols which contribute to the formation of surface ozone (O3), a lung irritant (whereas ozone in the upper atmosphere is useful to filter ultraviolet). Indoor, ozone also comes from old dust collectors, copying machines and laser printers.
Other pollutants were reduced to minimum values in France: sulfur (SO2), which came from coal plants, arsenic and heavy metals. And among the organic pollutants, aromatic hydrocarbons from all combustions of wood, coal and oil. Lead in gasoline, banned in the US since 1975, it is so in Europe since 2000. Today at very low levels, lead traces in the air primarily come from garbage incinerators.
According to Paracelsus’ principle, it is the dose that makes the poison ... the paradox is that in France all contaminants in the air decreased significantly over the last thirty years as bronchiolitis in infants, cardiovascular disease and cancer are increasing. What are the facts? Too many announcements are made without medical foundations and required statistics and easily mix problems of developing countries with the situation in Europe. So let’s consider actual medical studies.
Inhaling diesel combustion products at high concentration does trigger cancer, as demonstrated by IARC’s study on occupational exposures and tests on rodents. With the low levels observed in developed country cities, it is very different. A study by the University of Utrecht (The Lancet, 2013), often quoted in the media, attributed to PM10 particles an increase by 7% of cancer in Europe each year, over the last thirteen years, close to urban roads. However, the Lancet’s commentator warned about the weaknesses of this (still serious) study involving 360,000 people over 13 years: it gives a result of + 14% for men and -1% for women, hence the average of 7%. This unexplained result, which by the way detects nothing on cardiovascular diseases, suggests statistical biases in its analysis, probably because of strong interfering factors (See tobacco below).
The effect of solid particles and nitrogen oxides on respiratory discomfort of sensitive people with asthma is demonstrated, but mortality from cardiovascular diseases at low European doses is so low that it is difficult to quantify. For example, urban housing near the main roads also accumulate noise, stress and more difficult living conditions.
For bronchiolitis in infants, a vast Californian epidemiological study demonstrated the lack of correlation with PM10 and PM2.5. Due to its viral origin, other causes are to be considered (such as type of nursery care in cities?).
Smoking affects more than a quarter of the French people and is the first contamination of the respiratory tract, in spite of the laws passed (Veil in 1976 and Evin in 1991). Smokers absorb carbon monoxide, nitrogen oxides, hydrogen cyanide, acetone, phenols, ammonia, tar and heavy metals. Life expectancy of smokers 30 to 69 years is reduced by about 20 years on average, with 85 to 90% of lung cancers directly caused by tobacco, and 80% of myocardial infarction among victims less than 45 year old. For the health of smokers, the pollution of European cities is negligible as compared to their intoxication.
It is interesting to observe the main sources of emissions of pollution, to provide means of action, by behavioral incentives or by decision of the public authorities.
In France, 14% of PM10, 18% of PM2.5 and 54% of emitted NOx originate with vehicles exhaust, and their effect on local contamination also depends on other sources, as well on the weather: in March 2015, similar PM10 peaks were found in Paris and on some beaches in Normandy ...
PM10 pollution peaks in March 2014 and March 2015 allowed to test in Paris the - limited - interest of alternating traffic: traffic decreased each time by only 18%. Indeed, traffic in Paris tends to be regulated by saturation: many Paris commuters who anticipated fluid traffic and crowded public transports, decided to use their car that day ... PM10 concentrations were then reduced by 2%, and NOx on Paris ring-road by 10%. In European cities where such measure is permanent, people adapt, for example with two cars per household. Other cities have established an entry fee, such as Bergen, Oslo, London and Stockholm. Paris is moving towards narrower road lanes for cars: wider corridors for buses and bicycles, roads on banks closed to reduce the saturation flow, and consequently the traffic.
Public transport is energy efficient, with low polluting emissions, but we observed that the subway air is highly contaminated by particles, in addition to microbial promiscuity. RATP is transparent on the high measured rates, and works are underway, but it takes time: the media’s attention was more drawn to the replacement of former diesel bus in 2016 ... even if the effects of such measures is quite limited.
Diesel engines consume 15 to 20% less fuel than gasoline engines of same performance, but older models produce too much particles and nitrogen oxides. The effect of Euro 5 and 6 standards will slowly ramp up given the old vehicles fleet. The arrival of new, “cleaner” models just led Japan, where diesel cars are traditionally forbidden, to authorize their use as of 2015.
Regulatory frameworks are numerous: WHO’s recommendations – few are complying – the Gothenburg protocol (1999) in France the LAURE law (1996), the particles Plan (2010) the PUQA (2013), and for industrialists the adapted IED directive in 2013.
The French electricity (2014) is by only 5% of fossil origin, compared to still 55% in Germany, which vast plan of renewable energy was compensated by its gradual withdrawal from nuclear power.
Investments by resident owners in energy efficient heaters, solar production for warm water and heat insulation are limited by the relatively low cost of energy: pay back often takes more than ten years. And how to encourage a non-resident owner to invest in new heating measures, when it is his tenant who will save money?
For transport, better distribution of living and working places could reduce daily transhumance. The French outside Paris and its suburbs use mainly a car, as do those who want to go from a Paris suburbs to another. Conversely, intramural Parisians do enjoy public transportation, walking, even cycling. We may imagine the further development of electric bicycles and electric car such as the AutoLib, and for workers in the tertiary sector, partial teleworking.
For sure, we now better breathe in our cities than we used to twenty years ago, but 17 European countries out of 28, including France, occasionally exceed European standards.
The best atmospheric air cleaner is the rain. Aeration of houses and apartments after rain is a sanitation measure. The wearing of masks is very common in Chinese cities to filter dust, as well as in Japan, to avoid the spread of infectious diseases in public transport, but this practice is not consistent with our culture ... Reducing heating fuel particles and NOx emissions : a 18°C thermostat (with a sweater!) and, for owners, house insulation. You can also adjust your washing machine cycles at 40°C instead of 60°C, limit the use of the dryer, and adopt a more quiet driving behavior...
Before the 60s, in Europe and North America, industrial sites were located in cities, as in China today. The development of vehicles allowed to install our industrial sites away from residential areas, with advancements but also the side effects that we know. And in the countryside, we have a more productive agriculture but with the spraying of fertilizers and pesticides, and livestock dust.
What can be done? The demanding European standards are not yet fully effective, particularly in transport. In our industries, too restrictive regulations compared with benefits would lead to relocation to lenient countries, with negative ecological and social consequences. And energy efficient investments will hardly develop among the 46% of inhabitants who are tenants without a strong public incitement of their non-resident owners.
Science and medical data are impartial: we must read them without corporatist or activist filters. The stakes for our health, our lifestyle and our wealth should leave nothing to emotion or to chance.
And after all, clinical aspects are not everything, as a clean air and agreeable smell also play a major role in our well-being, and also deserve to be taken into account.
Note. The data sources can be consulted in the long version of this article, which will be published on the ParisTech site. We thank Citepa, Insee, The Lancet, Airparif, RATP etc., for the quality of the information they make available to the public. The content of this article is independent and does not commit them in any way.