Air is indispensable to life. Clean and unpolluted air should be a prerequisite. Over the past decades, the air quality has substantially improved in Europe. The visible and noticeable air pollution (smoke, dust, smog) has disappeared from many cities due to local, national and European initiatives and stricter regulations, e.g., increased thresholds on particle matters such as PM2.5 and PM10 challenging local municipalities. Occasionally air quality poses an immediate threat, such as during industrial incidents or pollution episodes. Fortunately these are rare. Nevertheless the current air quality still affects people’s health. In many European cities, air quality is a concern and it is therefore monitored around the clock. In most cities, industrial air pollution is, or tends to be, replaced by traffic-related air pollution. Air quality is therefore a common problem to almost all major cities (cited from http://www.airqualitynow.eu).

Occasionally air quality poses an immediate threat, such as during industrial incidents or pollution episodes. Fortunately these are rare. Nevertheless the current air quality still affects people’s health. In many European cities, air quality is a concern and it is therefore monitored around the clock. In most cities, industrial air pollution is, or tends to be, replaced by traffic-related air pollution. Air quality is therefore a common problem to almost all major cities (cited from http://www.airqualitynow.eu).