An assessment of BTEX concentrations from various fuel depots in parts of South Africa

Abstract

Volatile organic compounds (VOCs) are regarded major air pollutants as they have properties hazardous to the environment. They also play a vital role on the regional scale in the production of acid rain and photochemical ozone formation. The expansion of industries, growth in cities and wide use of vehicles has led to an increase in concerns about VOC being emitted into the atmosphere, particularly the BTEX (Benzene, toluene, ethyl-benzene and xylene) group as they are known to be potentially hazardous to both human and environmental health. The major sources of BTEX into the atmosphere are petroleum refineries, petrochemical facilities, automobiles, the use of solvents, combustion of fossil fuel and distribution of petroleum products.

The focus of this study was on assessing the BTEX concentrations from specific fuel depots in parts of South Africa. The seasonal variations and relationship between concentrations and the climatic conditions of the areas are also determined. Passive samplers were used to monitor the BTEX concentrations at depots that were located in industrial and mixed-use urban areas. The weather conditions for the areas were also acquired in order to understand the relationship between the BTEX concentrations and weather conditions. The monitoring was conducted quarterly from October 2015 up until January 2018.

The concentrations of BTEX compounds were determined and results obtained indicate that toluene was the most abundant compound at the monitored sites except at one site in the northern part of the country. A trend observed was that concentrations of benzene were lower in comparison to those of toluene while xylene concentrations were higher than those of ethylbenzene at all site during the various sampling periods. The T/B ratios calculated showed that majority of the sampling points were influenced by emission from traffic and mobile sources, industrial facilities or point sources and evaporative sources. Although the fuel depots monitored were the main sources of BTEX, the surrounding facilities and industries were also noted as potential sources in various sampling points particularly in sites located within industrial areas. The depots within the industrial areas had higher T/B ratios as compared to those in urban mixed-use areas, which could be caused by the use of gasoline and other solvents in industrial processes.

There were noted variations with regards to the weather conditions around the different sites, the influence of temperature on the recorded BTEX concentrations was significant throughout the sampling periods except in October 2017. The influence of other climatic conditions such as wind speed on BTEX concentration was less clear at most of the monitored sites. There were no distinct seasonal patterns established in the recorded BTEX concentrations throughout the different seasons.