We must distinguish between acute health effects (immediate few hours of breathing the polluted air) and long-term or chronic.
Acute effects include increasing the probability of death or enter the emergency due to respiratory and cardiovascular causes for each increase in the level of particles (about 2.8% per 10 micrograms/m3, according to the most recent Barcelona by Perez et al 2009). This would mean that for a city like Barcelona with 50 deaths per day, would be an increase in a person death due to an increase of 10 micrograms/m3 particles (average particle Barcelona is around 50). While these data cannot be underestimated at the whole population, individual risk is very small and should not cause alarm.
For none of the acute effects of air pollution (cardiovascular death, myocardial infarction, exacerbation of COPD, reduced lung function, effect on cardiac function) has been able to detect a level of no effect. In all cases at any level of exposure is an increased risk proportional to the dose-response curve. This means that for every increase in pollution levels is a greater response, whatever the level of pollution.
Current legislation marks a level of warning and alert when they are high to those who need to take urgent action. Health-wise the recommendations of international agencies (for example, http://www.airfobep.org/docs/avisCSHPF1.pdf) in situations of notice or warning to prepare especially sought services compared to the potential increase of cases, but in general the plans do not recommend containment measures and changes in attitude of the population. These levels have not reached these days according to data from air quality networks of competent authorities.
Although it may seem surprising, the health effects of isolated episodes are only a small part of the cumulative effects over the years, most of which are chronic or long-term rate have shown a reduction of hope of life in the most exposed populations.
For CREAL the most important lesson is the health gain that would occur if pollution were reduced (Report). A reduction of 10 particle micrograms/m3 recently led to an increase in half year of life expectancy (in US areas did it). These points the importance of taking measures to reduce urban pollution every day of the year and not just during the am frightened of air stagnation.
* This is an official communication of CREAL. The center's researchers made no further statements about it to allow more conclusions of scientific studies.