Pollution alerts have ‘limited impact’ on public health

Issuing air quality alerts on high pollution days “has a limited effect on public health” unless it is backed by ‘enforced public actions’ to reduce air pollution, a study published today (9 January) has claimed.

Many public authorities issue public alerts via text messaging, television bulletins or messaging on public transport systems to warn residents on days when high air pollution levels have been detected.

Services including AirText issue air quality warnings when air pollution is high

These might warn the public against strenuous physical activity as well as advising against activities which might worsen air pollution.

In London, for example, residents can sign up to the free airText service which offers air quality forecasts and alerts, while the Mayor of London has committed to using electronic signage across the capital’s transport network to publicise days when pollution is high.

Funded by Public Health Ontario – Canadian researchers, led by environmental scientist Hong Chen – have sought to establish the effectiveness of air quality alerts in helping to mitigate against the potential public health impacts

The study, focusing on Toronto, looked at health data from the city over a nine-year period between 2003 and 2012, comparing days when air quality alerts were issued with those falling just below the air quality alert threshold.

These were assessed using health impact data including mortality rates for cardiovascular and respiratory diseases and hospital admission numbers for conditions including heart problems, strokes and asthma – to assess whether any noticeable difference in impact could be measured on days when alerts had been issued.


Published in the public health journal the Lancet, the study suggested that there had been no evidence to indicate that air quality alerts had had an effect on cardiovascular or respiratory-related mortality.

The study also suggested that ‘no appreciable differences’ were noted in hospital admissions as a result of the air quality alert programme.

In London, alerts are displayed on the day before and during high air pollution episodes

However, the study did point to a reduction in admissions for asthma-related cases by around 2.05 in every 1,000,000 people per day. “A non-signifcant trend was noted towards decreased asthma-related and COPD [Chronic Obstructive Pulmonary Disease] related hospital admissions after the alerts,” the report stated.

“The findings of this large population-based cohort study show that the air quality alert programme in Toronto, Canada, yielded inadequate protection of the public from air pollution between 2003 and 2012. Air quality alerts resulted in some reductions in asthma-related emergency-department visits on high pollution days, and to a lesser degree COPD-related mortality. However, the programme did not prevent any mortality or cardiovascular morbidity.”

Summarising the report, researchers concluded: “Our results suggest that issuing air quality alerts to encourage avoidance behaviour alone has a limited effect on public health, and that implementing enforced public actions to reduce air pollution levels on high pollution days may be warranted.

“Together with accumulating evidence of substantial burden from long-term air pollution exposure, this study underscores the need for further strengthening global efforts that can lead to long-term improvement of overall air quality.”

Related Links
Effect of air quality alerts on human health: a regression discontinuity analysis in Toronto, Canada