Air pollution, temperature and respiratory disease: a South African study

Global warming and air pollution have something in common: their effects on human health. Air pollution is a widely known reason for respiration problems. Hot weather may bring on these symptoms.

Pollution and global warming also affect health together. Studies have shown that air pollution can have an even bigger effect on health on very cold or very warm days. One country that ought to be concerned about that is South Africa, where it’s predicted that temperatures will rise by as much as 7°C inland over the following 80 years.

And there may be evidence that respiratory illness is increasing in South Africa. One study found that about 5% more children and adolescents suffered from asthma in 2002 than in 1995. One of the causes of this increase in respiratory symptoms is poor air quality.

In the South African city of Durban, children living in industrial areas with higher levels of out of doors air pollution have more asthma and asthmatic symptoms than children living further away from industrial areas. Similarly, people living near mine dumps suffer more respiration problems than people living further away.

Despite this evidence, there are still relatively few air pollution epidemiology studies in Africa. Our study is considered one of the few on the continent to check the synergy between temperature and outdoor air pollution and their impacts on human health.

We decided to investigate respiratory disease hospital admissions in Secunda, South Africa – positioned about 130 km east of Johannesburg. This town is positioned within the infamous Highveld Air Pollution Priority Area, which is the center of South Africa’s coal-fired power stations. Apart from the standard outdoor air pollution sources in Secunda, equivalent to traffic, burning of household waste, outdoor household cooking and veld fires, there may be also a big coal-to-fuels and chemical industrial plant.

Our study fills a crucial gap in terms of understanding the Highveld Air Pollution Priority Area. There is data, for instance on health and air pollution exposure in addition to expensive reviews funded by South African taxpayers of the world’s Air Quality Management Plan. But peer-reviewed scientific journal articles are rare.

What we found

Secunda experiences high levels of sulphur dioxide, nitrogen dioxide and particulate matter within the air. Two sorts of particulates are relevant: lower than or equal to 10 micrometres in diameter (PM10) and lower than or equal to 2.5 micrometres in diameter (PM2.5).

Our study included 14,568 respiratory disease hospital admissions that occurred between January 2011 and October 2016. During the study period, each day PM10 and PM2.5 levels exceeded the each day World Health Organization air quality guidelines on 721 (34%) and 1,081 (51%) of the two,131 days, respectively. The apparent temperature (Tapp) ranged from -1⁰C to 26⁰C and the mean was 14.2⁰C. Tapp reflects the physiological experience of combined exposure to humidity and temperature – it’s a greater indicator of what the temperature seems like.

We defined warm days as days when Tapp was above 15°C (the center value within the range) and cold days as below 15°C, as done in other studies. The sources and chemical composition of air pollution may vary with weather indicators equivalent to Tapp. PM10, PM2.5, nitrogen dioxide and sulphur dioxide had negative correlations with Tapp in Secunda – the air contained less of those air pollutants on warmer days.

In this study, increasing air pollutant levels on cold days didn’t significantly increase respiratory disease hospital admissions. But there have been significant increases in admissions with increasing air pollutant levels on warm days. Similar results were reported for respiratory disease hospital admissions in Cape Town.

We found that children aged 0-14 years and girls were particularly in danger to be admitted to hospital on warm days. Children of this age are prone to be physically energetic outdoors when it’s warm. They normally spend more time outdoors than adults, performing more activities that increase respiration rates, which might result in increased inhalation of out of doors air pollution.

Children’s lungs are still growing and early exposure to environmental pollutants can easily alter lung development and function. The effects of air pollution on a toddler can have lifelong health implications.

Other studies report that women are more vulnerable to air pollution health effects, although results usually are not uniform. A study from Cape Town also found that girls are more vulnerable to PM10 than men. It stays unclear whether this difference in vulnerability is attributable to differences within the socially influenced activities of men and girls or of their physiology, or attributable to some interplay of those.

What ought to be done

Our study adds crucial epidemiological information on air pollution health effects, especially on cold and warm days, within the town of Secunda, positioned within the infamous Highveld Air Pollution Priority Area.

It has been 13 years for the reason that Highveld Air Pollution Priority Area was declared an air pollution hot spot. It is time that outdoor air pollution emissions on this area are controlled and reduced.

Our results have implications for public health strategies that will include early warning systems especially targeted for vulnerable population subgroups.