New evidence has found that exceeding the World Health Organisation (WHO) ozone limit, is linked to substantial increases in hospitalisation for cardiac events such as stroke.
They also found that ozone levels below the WHO maximum were linked with worsened health.
Study author, Professor Shaowei Wu, explains why this increased is caused by exceeding the ozone limit: “During this three-year study, ozone was responsible for an increasing proportion of admissions for cardiovascular disease as time progressed.
“It is believed that climate change, by creating atmospheric conditions favouring ozone formation, will continue to raise concentrations in many parts of the world. Our results indicate that older people are particularly vulnerable to the adverse cardiovascular effects of ozone, meaning that worsening ozone pollution with climate change and the rapid ageing of the global population may produce even greater risks of cardiovascular disease in the future.”
It is important to know that ozone pollution is different to the ozone layer, which absorbs most of the sun’s ultraviolet radiation.
Ozone pollution is formed when other pollutants react in the presence of sunlight. These other pollutants are volatile organic compounds and nitrogen oxides which are emitted by the likes of cars and power plants.
Previous studies suggest that ozone pollution causes harm to the heart and blood vessels, however, there is limited and inconclusive evidence about its influence on the risk of cardiovascular disease.
This study focused on the link between ambient ozone pollution and hospital admissions for cardiovascular disease. Data on daily hospital admissions for cardiovascular disease during 2015 to 2017 in 70 cities in China were collected from the two main national health insurance systems.
During the study period, the two databases covered approximately 258 million people across the 70 cities, which is equivalent to more than 18 per cent of China’s population.
The types of cardiovascular disease included stroke, as well as coronary heart disease and heart failure.
Daily eight-hour maximum average concentrations of ozone, fine particulate matter (PM2.5), inhalable particles (PM10), sulphur dioxide, nitrogen dioxide and carbon monoxide were obtained for each cart from the China National Urban Air Quality Real-time Polishing Platform.
During the study period there were 6,444,441 hospital admissions for cardiovascular disease in the 70 cities and the average daily eight-hour maximum ozone concentration was 79.2 μg/m3.
Researchers found that exposure to ambient ozone was linked to increased hospital admissions for all cardiovascular diseases studied except haemorrhagic stroke, independent of other air pollutants.
For example, each 10 μg/m3 rise in the two-day average eight-hour maximum ozone concentration was associated with a 0.40% increase in hospital admissions for stroke and 0.75% for acute myocardial infarction.
Professor Wu, says: “Although these increments look modest, it should be noted that ozone levels may surge to higher than 200 μg/m3 in summer, and these increases in hospitalisations would be amplified by more than 20 times to over 8% for stroke and 15% for acute myocardial infarction.”
The researchers also estimated the excessive admission risk for cardiovascular disease associated with ozone concentrations at or above the WHO air quality guideline (100 µg/m3) compared to levels below 70 μg/m3. Ozone levels below 70 μg/m3 are mostly naturally occurring and not due to human activity.
Compared to two-day average eight-hour maximum concentrations below 70 μg/m3, levels of 100 µg/m3 or higher were associated with substantial increases in hospital admissions for cardiovascular disease, ranging from 3.38% for stroke to 6.52% for acute myocardial infarction.
Nevertheless, lower concentrations of 70 to 99 µg/m3 (vs. below 70 μg/m3) were also linked with increases in hospital admissions, ranging from 2.26% for heart failure to 3.21% for coronary heart disease.
During 2015 to 2017, 3.42%, 3.74% and 3.02% of hospitalisations for coronary heart disease, heart failure and stroke, respectively, were attributable to ozone pollution. When each year was analysed separately, the proportions rose with time. For coronary heart disease, ozone was responsible for 109,400 of 3,194,577 admissions over three years.
Professor Wu, says: “This suggests that 109,400 coronary heart disease admissions could have been avoided if ozone concentrations were 0 µg/m3. This may be impossible to achieve given the presence of ozone from natural sources. However, we can conclude that considerable numbers of hospital admissions for cardiovascular disease could be avoided if levels were below 100 μg/m3, with further reductions at lower concentrations.”
Study co-author, Professor Thomas Münzel, highlights what health effects ozone pollution will have in Europe: “Projections for Europe suggest that ozone will play a more dominant role as a health risk factor in the future due to climate change with rising temperature and, accordingly, increasing photochemical formation of ozone. The strong link between climate change and air quality means that reducing emissions in the long term to tackle global warming will play a key role in alleviating ozone pollution and improving the air that we breathe.”
