Summer and winter variations of BTEX concentrations in an oil refinery complex

Atmospheric conditions of the performed measurements

In our studies measurements of air temperature, relative humidity, and wind speed were performed along with the BTEX concentrations. In the summer season the mean value of air temperature was equal to 40.4 °C (standard deviation, SD 1.89 °C). In the winter season the mean air temperature was reported to be 15.3 °C (SD 1.64 °C). The mean value of the relative humidity in the summer season was equal to 45.1% with SD of 5.11%. In the winter season the mean value of the relative humidity was equal to 20.5% (SD 2.12%). The measurements of wind speed in summer season indicated the mean value equal to 1.88 m/s (SD 1.04 m/s). In the winter season the mean value of wind speed was reported to be 1.96 m/s, with the SD value of 0.89 m/s. To sum up, the measurements revealed that temperature and relative humidity at workplaces were much higher in summer than in winter seasons, while wind speed was higher in winter than in summer season.

Seasonal variations of BTEX concentrations

The concentrations of BTEX in the breathing zones of the employees in the various workstations in summer and winter seasons are presented in Fig. 1. It can be observed that analyzed BTEX concentrations were higher in the summer than in the winter season for all workstations and were particularly visible for toluene and ethylbenzene. It can be related with the fact that the mean temperature in the investigated production process was 40.4 °C in summer and 25.3 °C in winter affecting the higher vaporization of the BTEX compounds. Also, the relative humidity in summer season, which mean value was equal to 45.1%, while in winter season it was equal to 20.5% also might affected the increased BTEX emissions. The results of Friedman test revealed that exposure to xylene in supervisors and exposure to BTEX in safetymen, repairmen, and site men were significantly higher in summer season compered to winter seasons (P < 0.045) (Table 2). Moreover, it was revealed that the exposure in particular workstations was ordered decreasingly as follows: repairmen  site men  safety men  supervisors. In the particular groups of employees, the mean BTEX values in summer and winter seasons in the breathing zones were as follows (mean summer vs mean winter concentration, mg/m³): repairmen: benzene 7.193 vs 2.023, toluene 27.200 vs 10.070, ethylbenzene 18.326 vs 10.027, xylene 14.833 vs 10.615; site men: benzene 4.311 vs 3.369, toluene 26.791 vs 13.685, ethylbenzene 15.822 vs 12.135, xylene 14.242 vs 13.325; safetymen: benzene 0.522 vs 0.384, toluene 1.160 vs 0.782, ethylbenzene 1.333 vs 0.734, xylene 0.975 vs 0.735; supervisors: benzene 0.359 vs 0.267, toluene 1.129 vs 1.078, ethylbenzene 1.032 vs 1.002, xylene 0.755 vs 0.533. For all working groups the mean BTEX values in summer and winter seasons in the breathing zones were as follows (mean summer vs mean winter concentration, mg/m³): benzene 3.073 vs 1.534, toluene 14.070 vs 6.404, ethylbenzene 9.121 vs 5.982, and xylene 7.472 vs 6.531.

Concentration of BTEX (mg/m³) in the breathing zones of the various workstations in summer and winter seasons.

Investigations of Hawari et al.⁴⁰ performed in urban areas of Malaysia indicated positive correlations of BTEX concentrations with relative humidity, however negative correlations with wind speed, solar radiation, and air temperature. Study of Popitanu et al.⁴¹ in the ambient air of Arad city, Romania, revealed that the increase of the BTEX concentrations in winter season was related with the usage of fuels in the central heating season. Also, due to the higher reaction rates with OH radicals in the atmosphere BTEX were removed faster in summer than in winter⁴¹. The studies of Bodor et al.⁴ on seasonal differences in air pollution around Ploiesti oil refining complex in Romania also pointed that the highest.

BTEX values were measured in cold season, particularly in winter. Investigations of Seco et al.⁴² in the forest site in the Western Mediterranean Basin revealed that almost all analyzed VOCs had higher average mixing ratios during the summer than the winter season, except for VOCs that are linked to anthropogenic sources: for them lower (benzene) or similar (toluene) mixing ratios in summer than in winter were stated.

For all the workstations the decreasing order of BTEX was as follows: toluene  ethylbenzene  xylene  benzene. These finding stay in line with investigations of Rajabi et al.⁴³ indicating that among all VOCs emitted from crude oil, toluene, benzene, hexane, heptane, cyclohexane, and pentane were found to be highly detected and concentrated compounds. Investigations of Ercan et al.⁴⁴…