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 well-known cause of breathing problems. Hot weather can also bring on these symptoms.

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

And there is 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 outdoor air pollution have more asthma and asthmatic symptoms than children living further away from industrial areas. Similarly, people living close to mine dumps suffer more breathing problems than people living further away.

Despite this evidence, there are still relatively few air pollution epidemiology studies 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 respiratory disease hospital admissions in Secunda, South Africa – located about 130 km east of Johannesburg. This town is located in the infamous Highveld Air Pollution Priority Area, which is the heart of South Africa’s coal-fired power stations. Apart from the usual outdoor air pollution sources in Secunda, such as traffic, burning of household waste, outdoor household cooking and veld fires, there is also a large coal-to-fuels and chemical industrial plant.

Our study fills an important gap when it comes to understanding the Highveld Air Pollution Priority Area. There is data, for example on health and air pollution exposure as well as expensive reviews funded by South African taxpayers of the area’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 in the air. Two kinds of particulates are relevant: less than or equal to 10 micrometres in diameter (PM10) and less 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, daily PM10 and PM2.5 levels exceeded the daily World Health Organization air quality guidelines on 721 (34%) and 1,081 (51%) of the 2,131 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 is a better indicator of what the temperature feels like.

We defined warm days as days when Tapp was above 15°C (the middle value in 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 such as Tapp. PM10, PM2.5, nitrogen dioxide and sulphur dioxide had negative correlations with Tapp in Secunda – the air contained less of these air pollutants on warmer days.

In this study, increasing air pollutant levels on cold days did not significantly increase respiratory disease hospital admissions. But there were 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 women were particularly at risk to be admitted to hospital on warm days. Children of this age are likely to be physically active outdoors when it’s warm. They usually 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 are still growing and early exposure to environmental pollutants can easily alter lung development and function. The effects of air pollution on a child can have lifelong health implications.

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

What should be done

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

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

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

Bukola Olutola, , University of Pretoria and Janine Wichmann, Associate Professor, University of Pretoria

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Click here to learn more about how the University of Pretoria is working with NASA to satellite data to develop strategies to curb air pollution and associated human ill health. Watch a video about how Pretoria's air is more polluted than the World Health Organisation allows,  or use this infographic for fast facts on respiratory health. 

Researchers

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  Professor Janine Wichmann

  Professor Janine Wichmann is an associate professor at the School of Health Systems and Public Health (SHSPH), Faculty of Health Sciences, University of Pretoria. She is an environmental epidemiologist with a primary interest in air pollution exposure assessment and health effects. Since 2008, she has focused on climate change health effects, and mainly the short-term heat effects on and mortality and morbidity. She gained research and teaching experience in Europe from 2002 to 2012. Prof Wichmann has been a visiting researcher at the University of Gothenburg, Sweden, since 2013.
  
  She has lectured in various postgraduate (master's and PhD level) courses at the SHSPH for the past 18 years. She has also lectured in various postgraduate (master's and PhD level) courses at the University of Copenhagen during 2009-2012. She is the PhD coordinator at the SHSPH.
  
  She is committed to knowledge sharing and education which is evident in my postgraduate supervision track record at UP and other local as well as international universities.
  
  Prof Wichmann’s long-term research objective is to estimate the burden of non-communicable disease due to air pollution and climate change indicators whilst training postgraduate students in these skills. Her research addresses the evidence gaps in air quality management plans as required by the National Environmental Management Act: Air Quality Act (2005) in South Africa.
  
  In 2016, she received a prestigious Fulbright Research Visiting Scholarship. Since 2017, professor Wichmann has been the local principal investigator for short-term epidemiology studies of the Multi-Angle Imager for Aerosols (MAIA) project of the National Aeronautics and Space Administration (NASA). This is the first time NASA has entered into a partnership with epidemiologists and health organisations using space-based data to study human health and improve lives.
  
  

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  Dr Bukola Olutola

  Dr Bukola Olutola did her undergraduate studies at the University of Ibadan in Nigeria and has been doing research at the University of Pretoria (UP) for the past 10 years. She says UP provides the ideal atmosphere for researchers. “We have access to journal articles through the library, and there are many research workshops to help both upcoming and established researchers to improve their research.”
  
  Dr Olutola is a lecturer in public health at IIE MSA, formerly Monash South Africa, and an Extraordinary Lecturer at UP’s School of Health Systems and Public Health. Her research into air pollution contributes to the betterment of the world because, according to the World Health Organisation, pollution is the highest environmental cause of disease and premature death. Ambient (outdoor) and household air pollution causes seven million premature deaths annually, which amounts to 16% of global mortality. “Studies on pollution are relevant to find ways to prevent deaths arising from pollution,” says Dr Olutola.
  
  A recent highlight for her was the publication of her findings of the modifying effect of temperature on the association between air pollution and hospital admission for respiratory disease in one of South Africa’s air pollution priority areas.
  
  Her research matters, she says, because these findings are important in guiding policymakers to make appropriate decisions. Air pollution has always been a problem, especially in certain areas of South Africa. It affects the respiratory and cardiovascular systems of people who live in areas with high levels of air pollutants. Coupled with COVID-19, which also affects the respiratory system, this combination could place a great burden on already strained healthcare systems.
  
  Dr Olutola is part of a research group that is conducting epidemiology studies on the interaction effects of air pollution and climate change indicators on mortality and morbidity in South Africa. She is also involved with another research group that is working on the health effects of metals in women and in utero babies.
  
  From 2015 to 2017, the late Professor George Djolov of the Department of Geography, Geoinformatics and Meteorology in UP’s Faculty of Natural and Agricultural Sciences worked with Dr Olutola to use the Air Dispersion Potential (ADP) index for her PhD Studies. “Unfortunately, we could not continue because he passed away,” she says.
  
  Professor Djolov, who was born in Bulgaria, had an extraordinary academic career at various universities in southern Africa, among others. After his formal retirement, he joined UP as a meteorologist and Extraordinary Professor in 2007, and was highly active over the following decade. In his final three years, he managed the UP Laboratory for Atmospheric Studies.
  Dr Olutola says that Prof Halina Rollin of the School of Health Systems and Public Health inspired her research efforts. “She is never tired and is always full of ideas for research.” Dr Olutola has many academic role models, and particularly admires Prof Janine Wichmann’s work ethic. “Prof Wichmann is always there to support students, not necessarily only ‘her’ students. During my PhD studies, I could ask for her professional advice whenever I was stuck.”
  
  Dr Olutola’s dream is to be able to continue doing research, especially in the field of epidemiology. She encourages school learners and undergraduates interested in her field to continue to learn and to never give up.
  For recreation, she watches documentaries.
  

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  Children aged 0-14 years are likely to be physically active outdoors when it’s warm