And there is evidence that respiratory illnesses are increasing in South Africa. One study found that about 5% more children and teens had asthma in 2002 than in 1995. One cause 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 outdoor air pollution have more asthma and asthmatic symptoms than children living further away from industrial areas. Likewise, people living near mine dumps suffer more from respiratory problems than people living further away.
Despite this evidence, there are still relatively few epidemiological studies on air pollution in Africa. Our study is one of the few on the continent to study the synergy between temperature and outdoor air pollution and their impacts on human health.
We decided to investigate admissions to the respiratory illness hospital in Secunda, South Africa – located about 130 km east of Johannesburg. This city is located in the famous Highveld air pollution priority area, which is the heart of South African coal-fired power plants. Besides the usual sources of outdoor air pollution in Secunda, such as traffic, burning household garbage, outdoor cooking and veld fires, there is also a large industrial factory of fuel coal and products chemicals.
Our study fills an important gap in understanding the Highveld air pollution priority area. There are data, for example on health and exposure to air pollution, as well as costly reviews funded by South African taxpayers on the region’s air quality management plan. But peer-reviewed scientific journals are rare.
What we found
Secunda experiences high levels of sulfur dioxide, nitrogen dioxide and particulate matter in the air. Two types of particles are relevant: less than or equal to 10 micrometers in diameter (PM10) and less than or equal to 2.5 micrometers in diameter (PM2.5).
Our study included 14,568 hospitalizations for respiratory illnesses occurring between January 2011 and October 2016. During the study period, the daily levels of PM10 and PM2.5 exceeded the daily recommendations of the World Health Organization on air quality 721 (34%) and 1,081 (51%) of the 2,131 days, respectively. The apparent temperature (Tapp) varied from -1⁰C to 26⁰C and the average was 14.2⁰C. Tapp reflects the physiological experience of combined exposure to humidity and temperature – it is a better indicator of temperature.
We have defined hot days as days when Tapp was above 15 ° C (the average range value) and cold days as below 15 ° C, as has been done in other studies. The sources and chemical composition of air pollution can vary depending on meteorological indicators such as Tapp. PM10, PM2.5, nitrogen dioxide and sulfur dioxide had negative correlations with Tapp at Secunda – the air contained fewer of these air pollutants on warmer days.
In this study, increasing levels of air pollutants on cold days did not significantly increase hospital admissions for respiratory illnesses. But there has been a significant increase in admissions with increasing levels of air pollutants on hot days. Similar results have been reported for hospital admissions for respiratory diseases in Cape Town.
We found that children 0-14 years of age and women were particularly at risk of being admitted to hospital in hot weather. Children this age are likely to be physically active outside in hot weather. They generally spend more time outdoors than adults, performing more activities that increase breathing rates, which can lead to increased inhalation of outdoor air pollution.
Children’s lungs continue to grow and early exposure to environmental pollutants can easily affect lung development and function. The effects of air pollution on a child can have lifelong health consequences.
Other studies indicate that women are more vulnerable to the health effects of air pollution, although the results are not uniform. A Cape Town study also found that women are more vulnerable to PM10 than men. It is not yet known whether this difference in vulnerability is due to differences in the socially influenced activities of men and women or in their physiology, or to some interaction between them.
What should be done
Our study adds crucial epidemiological information on the health effects of air pollution, especially in cold and hot weather, in the town of Secunda, located in the famous priority air pollution area of Highveld.
It has been 13 years since Highveld’s priority air pollution zone was declared an air pollution hotspot. It is time for outdoor air pollution emissions in this area to be controlled and reduced.
Our results have implications for public health strategies which may include early warning systems specifically targeted for vulnerable population subgroups.