Long term (2011–2023) analysis of traffic and biomass burning contributions to black carbon in the third largest metropolitan area of Spain

Abstract

This work is focused on the temporal characterization of equivalent Black Carbon (eBC) mass concentrations and their sources in a suburban station notably impacted by traffic, located in the metropolitan area of Valencia, Spain (western Mediterranean Sea). The average ($\pm$ standard deviation) concentrations of fossil fuel (eBC_ff) and biomass burning (eBC_bb) contributions were 0.9 $\pm$ $0.5$ $\mu {\mathrm{gm}}^{-3}$ and 0.06 $\pm$ $0.05$ $\mu {\mathrm{gm}}^{-3}$, respectively. These values represent the anthropogenic character of local aerosols. Both contributions also show a very marked seasonality: higher values in winter and lower in summer, corresponding to the strong dependence of the atmospheric conditions. The eBC_ff concentrations exhibit a daily pattern consistent with the evolution of traffic: a morning peak (around 8 LT) and other in the evening (around 19 LT). The seasonal Mann–Kendall test was applied to identify long-term trends and the Sen slope estimation to quantify the annual variation. Decreasing trends were found for eBC_ff concentrations ($-0.023$ $\mu {\mathrm{gm}}^{-3}$/yr), showing the effectiveness of air quality regulations. Less noticeable trends were found for eBC_bb concentrations. This fact evidences the contribution of biomass burning is not only related to changes in anthropogenic emissions, but also to natural phenomena, making it more difficult to interpret long-term trends.