Temporal variations of atmospheric black carbon and its relation to other pollutants and meteorological factors at an urban traffic site in Istanbul

This study aimed to investigate the variability of Black Carbon (BC) at one traffic site in Istanbul as a function of other pollutants, traffic density and meteorological parameters in order to identify the source and determinants of concentration. This was carried out through the statistical analyses of data measured in the period of May 2016–December 2018. The mean concentration of BC was observed as 6.5 ± 3.5 μg m⁻³. Daytime BC was observed to be higher than nighttime during the weekdays but slightly lower at the weekend, similar to oxides of nitrogen (NO_x). However, nighttime traffic during the weekend was found to be higher than the weekdays. The diurnal pattern showed two peaks of BC corresponding to the traffic rush hours in the morning and evening. Since the traffic density did not change during the day, the sharp decrease after the morning rush hour is attributed to enhanced atmospheric mixing, due to an increased wind speed and boundary layer depth. In addition, polar plots indicated that the only major source of BC is in the vicinity of the monitoring site, consistent with road traffic. Moreover, episodic north-easterly atmospheric transport events from the ship activity in the Bosphorus in summer can contribute to elevated BC concentrations. These results suggest that vehicular emissions heavily impact the environmental concentrations of BC and affect NO_x concentrations more than other pollutants. BC concentrations are highly correlated with NO_x, reflecting a common source in diesel vehicle emissions. Since the proportion of diesels in total vehicles in Istanbul is increasing every year, there may be future increases in BC and NO_x unless exhaust after-treatment works effectively on newer vehicles entering the fleet.