Spatial variability of dust concentration and deposition around an industrial port in South Africa emphasises the complexity of sources and transport

Abstract

The port and industrial zone of Saldanha Bay in South Africa accommodates activities related to the transport, processing, and production of commodities such as iron ore, manganese ore, and steel. The visible emission of dust from this area raised concerns for public health and to address this, the municipality has monitored the fine particulate matter (PM_2.5) concentration and dust deposition since 2015. Here, this monitoring data served to assess spatial and temporal changes and to evaluate the potential contribution of industrial and meteorological processes to these changes. We observed high temporal variability in both PM_2.5 concentration and dust deposition, and high spatial variation in dust depositions. Dust originated from local sources such as industry and traffic, but industrial activities could not explain the observed spatial variability, and concentration and deposition fluxes did not significantly increase over the years despite the extension of industrial activities. Meteorological factors such as rain, wind speed, wind direction, as well as topography exerted an important influence, but could also only partially explain the observed variability in both dust concentration and deposition. Furthermore, the PM_2.5 concentration and dust deposition are not significantly correlated, which highlights the challenges in appropriate dust monitoring. It follows that such monitoring efforts, though meeting national standards, require improvement to assess risks accurately. Our study illustrates that in areas with such high complexity of industrial activities, the high variability of dust load and deposition must be considered to evaluate implications for public and environmental health, adherence to guidelines, and mitigation strategies.