Exhaust fumes contain many hazardous chemicals
Helsinki air quality is most adversely affected by emissions from transport, because these emissions are released low near the breathing height. Exhaust fume concentrations are also at their highest in busy areas during peak hours, so large numbers of people are exposed.
Exhaust fumes contain gaseous and particulate impurities. The gaseous impurities include nitrogen dioxide (NO2), nitrogen monoxide (NO), carbon monoxide (CO) and diverse volatile organic compounds (VOCs) including benzene.
Fine particles in exhaust fumes (PM2.5) mainly consist of back coal and other organic compounds such as polycyclic aromatic hydrocarbons (PAH). The particles also contain some metallic compounds. The main source of particulate matter in transport is diesel vehicles.
Developments in automotive technology have reduced emissions in recent years
Catalytic converters and particulate filters have reduced exhaust-fuel based emissions over the years. Nevertheless, exhaust fumes still markedly weaken air quality in the vicinity of busy streets and main routes.
When air quality is poor, it can adversely affect vulnerable individuals, including elderly people suffering from pulmonary and coronary disorders, asthma patients and children.
Nitrogen limits exceeded in busy street canyons
Because of transport, nitrogen dioxide levels can exceed the annual limit in some busy Helsinki street canyons. Helsinki was granted permission to exceed the annual limit until 2015.
National limits defined for nitrogen dioxide and particulate matter and the World Health Organization’s limits for fine particles are exceeded in larger areas – in the vicinity of many streets and main routes in the Helsinki Metropolitan Area. Exhaust fumes cause limits to be exceeded especially during calm weather, when winds do not disperse and dilute pollution.