Traffic-related air pollution is associated with four million new cases of childhood asthma worldwide every year, according to the first global estimates of the problem.
A health impact assessment of children in 194 countries and 125 major cities globally led the study authors to suggest existing World Health Organisation (WHO) levels for Nitrogen Dioxide (NO2), the substance that creates smog, may need reviewed.
One in ten childhood asthma cases could be linked to poor air quality caused by traffic fumes. NO2 is a pollutant formed mainly from fossil fuel combustion, and traffic emissions can contribute up to 80 per cent of NO2 in cities.
NO2 is one component of air pollution, which is made up of many pollutants (including particulate matter, ozone, carbon monoxide), which are known to have adverse effects on health.
The UK ranked 24th worst out of 194 countries, with China 19th and the US 25th. South Korea had the highest proportion of traffic pollution-attributable childhood asthma incidence.
Lead author of the study, Ploy Achakulwisut of George Washington University, said: “Our study indicates policy initiatives to alleviate traffic-related air pollution can lead to improvements in children’s health and also reduce greenhouse gas emissions.
“Examples include Shenzhen’s electrification of its entire bus fleet and London’s Ultra-Low Emission Zone congestion charges.”
Globally, asthma is the most common non-communicable disease among children, and, according to the WHO, prevalence has increased dramatically since the 1950s. The reasons for this are multiple.
Traffic-related air pollution may result in asthma development as pollutants may cause damage to the airways, leading to inflammation that triggers asthma in genetically predisposed children.
Although it is not yet clear which specific pollutant within the traffic-related air pollution mixture is the source of asthma development, reviews by the US Environmental Protection Agency suggest a causal relationship is likely to exist between long-term nitrogen dioxide exposure and childhood asthma.
A Scottish Government spokesperson said: “Compared to the rest of the UK and other parts of Europe, Scotland enjoys a high level of air quality and we have set more stringent air quality targets.
“Low Emission Zones will help further improve the quality of the air by allowing access to only the cleanest vehicles.
“We provided over £10 million to support local authorities and bus operators with the costs of establishing LEZs, and we will continue to provide support to protect public health.”