Short-Term Effects of PM₁₀, NO₂, SO₂ and O₃ on Cardio-Respiratory Mortality in Cape Town, South Africa, 2006-2015

The health effect of air pollution is rarely quantified in Africa, and this is evident in global systematic reviews and multi-city studies which only includes South Africa.

A time-series analysis was conducted on daily mortality (cardiovascular (CVD) and respiratory diseases (RD)) and air pollution from 2006-2015 for the city of Cape Town. We fitted single- and multi-pollutant models to test the independent effects of particulate matter (PM₁₀), nitrogen dioxide (NO₂), sulphur dioxide (SO₂) and ozone (O₃) from co-pollutants.

daily average concentrations per interquartile range (IQR) increase of 16.4 µg/m³ PM₁₀, 10.7 µg/m³ NO₂, 6 µg/m³ SO₂ and 15.6 µg/m³ O₃ lag 0-1 were positively associated with CVD, with an increased risk of 2.4% (95% CI: 0.9-3.9%), 2.2 (95% CI: 0.4-4.1%), 1.4% (95% CI: 0-2.8%) and 2.5% (95% CI: 0.2-4.8%), respectively. For RD, only NO₂ showed a significant positive association with a 4.5% (95% CI: 1.4-7.6%) increase per IQR. In multi-pollutant models, associations of NO₂ with RD remained unchanged when adjusted for PM₁₀ and SO₂ but was weakened for O₃. In CVD, O₃ estimates were insensitive to other pollutants showing an increased risk. Interestingly, CVD and RD lag structures of PM₁₀, showed significant acute effect with evidence of mortality displacement.

The findings suggest that air pollution is associated with mortality, and exposure to PM₁₀ advances the death of frail population.