The data presented on this website come from the study “Premature mortality due to air pollution in European cities; an Urban Burden of Disease Assessment” (Khomenko et al., 2021), published in The Lancet Planetary Health in January 2021.
Where do data from cities come from?adttsran2020-12-29T12:36:17+01:00
Air pollution levels were estimated using three different mathematical and empirical models. Values given by the models were checked against actual air pollution measures extracted from the European air quality database AirBase. The data used in the study take 2015 as the reference year and were also compared to 2018 for temporary decreases in air pollution levels.
What is the air pollution ranking?adttsran2020-12-29T12:36:54+01:00
The air pollution ranking is based on a mortality burden score assigned to each city. Scores were calculated using an algorithm that takes into account the mortality rates, the percentage of preventable mortality and the years of life lost due to each air pollutant.
How many cities were included in the study?adttsran2020-12-29T12:37:44+01:00
Larger cities usually have a metropolitan area that includes other cities. Researchers considered metropolitan areas as part of the same urban area and decided to pool all the cities within them. The total number of cities resulting from this operation is 858. Cities included within a greater city do not appear in the ranking but can be found using the search box.
Fine particulate matter or PM2.5 is one of the main air pollutants. All PM particles are particulate matter containing a mixture of solid and liquid elements suspended in the air, including particles of dust, metals, cement and organic matter. They are classified by particle size, measured in micrometres (thousandths of a millimetre): the smaller the particles, the more easily they can penetrate our bodies. PM2.5 are fine particles with a diameter between 0.1 and 2.5 µm. They can penetrate the respiratory system as far as the pulmonary alveoli. One component of PM2.5 is black carbon, a product of incomplete combustion, especially of diesel fuel. The main sources of PM2.5 in cities include traffic, local fuel combustion from household heating, industrial combustion, and wood and coal burning.
NO2 or nitrogen dioxide is one of the main air pollutants: a toxic irritant gas that affects the respiratory system. NO2 can irritate the airways in the human respiratory system, aggravating respiratory diseases (such as asthma) and leading to increased hospital admissions and visits to emergency rooms. In the long term, NO2 exposure can lead to the development of asthma and increase susceptibility to respiratory infections. Its main source is motor vehicle emissions, particularly from diesel engines (the older they are, the more they pollute). NO2 levels are generally higher in cities due to their higher volume of traffic and are usually related to the way cities are designed.
How does air pollution affect health?adttsran2020-12-29T13:02:09+01:00
Due to its capacity to penetrate the bloodstream and cause inflammation, air pollution has the potential to damage almost every organ in the body. There is evidence that links air pollution to respiratory problems, heart disease, cancer, dementia, fertility problems and reduced cognitive function.
Air pollution peaks can exacerbate the symptoms of people with underlying conditions such as asthma or at risk of suffering heart attacks or strokes.
Chronic air pollution increases the risk of cardiovascular and respiratory diseases. Children exposed to higher levels of air pollution show slower cognitive development and more exposed adults show a higher risk of cognitive decline. Higher exposure to air pollution also increases the risk of preterm birth and low birth weight.
Avoidable deaths can be defined as the fraction of mortality that could be prevented each year if a particular risk factor was not present in the population. In this study, the avoidable deaths can be interpreted as the number of deaths that could be prevented each year if exposure to air pollution were reduced (in the case of the WHO recommendations) or almost eliminated (in the case of the lowest measured levels) as a risk factor for mortality.
How is the avoidable number of deaths calculated?adttsran2020-12-29T13:03:53+01:00
To calculate the number of avoidable deaths, the study uses city-specific natural-cause mortality data for 2015 from the Eurostat database and applies the most recent and robust scientific evidence on the relationship between air pollution levels and mortality. The study follows a comparative risk assessment approach by comparing current air pollution levels in cities to two theoretical air-pollution reduction scenarios (WHO recommendations and lowest measured levels). The number of preventable deaths is estimated as a function of these reductions and the scientific evidence on the relationship between air pollution and mortality.
What are the WHO guidelines?adttsran2021-01-04T15:39:58+01:00
Based on the existing scientific evidence, the World Health Organization (WHO) set recommended limits for concentration of air pollutants. According to these guidelines, outdoor concentrations of PM2.5 should not exceed an annual mean value of 10 µg/m3. The outdoor recommended limit for NO2 concentrations is 40 µg/m3.
Although these guidelines are considered the gold standard for the protection of human health, they are just recommendations and not mandatory.
The WHO guidelines on air pollution are currently under revision. The recommended values for air pollutants may change once the new guidelines have been published.
European legislation establishes the maximum air pollution levels allowed in the EU. In the case of PM2.5, annual mean concentrations should not exceed 25 µg/m3. The annual limit for NO2 concentrations is 40 µg/m3.
European standards are set by EU legislation and are mandatory for all member states. WHO guidelines are just recommendations. Though the recommended level is the same for NO2 (40 µg/m3), this is not the case for PM2.5, where the WHO guidelines (10 µg/m3) are more restrictive—and therefore provide better health protection—than the EU legislation (25 µg/m3).
The study considered the WHO guidelines because the maximum recommended level for PM2.5 concentrations is lower in the WHO guidelines than in the EU legislation and therefore provides more health protection.
Nevertheless, although the WHO guidelines are considered the gold standard for the protection of human health, there is a growing body of evidence that suggests that air pollution has a detrimental impact on human health even below the WHO thresholds. For this reason, the WHO guidelines are currently under review.
Is there any safety threshold for air pollution?adttsran2020-12-29T13:07:35+01:00
There is no scientific evidence suggesting that there is a particular threshold below which air pollution does not affect health. Recent studies have reported associations between air pollution and mortality at levels below the WHO thresholds. Greater reductions in air pollution levels are expected to offer larger health benefits.
The data presented in this study show that many more deaths could be prevented if air pollution levels were lowered below the current WHO thresholds.
Why does my city have preventable deaths if it meets the WHO guidelines?adttsran2020-12-29T13:08:07+01:00
The fact that the average air pollution levels of a city are below the guidelines doesn’t mean the whole city is below those levels. Certain areas of the city may have air pollution levels above the thresholds. In these cases, our study shows the deaths that could be prevented if those areas of the city also met the WHO recommendations.
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