Characterization of equivalent Black Carbon (eBC) in different environments in the western Mediterranean

This work is focused on the characterization of equivalent Black Carbon (eBC) mass concentrations at two sites (suburban and rural background) in Valencia, Spain. The suburban station is in the metropolitan area of Valencia (the third largest in Spain), so the analysis of eBC is crucial to determine its impact on urban pollution. The mean ($\pm$standard deviation) concentration from April 2011 to March 2023 was 1.0 $\pm$ 0.5 $\mu$gm⁻³, ranging from 0.7 $\mu$gm⁻³ in summer to 1.4 $\mu$gm⁻³ in winter. The seasonality is related to the intraannual variability of the Boundary Layer Height (BLH) and the daily variation is closely related to the daily traffic pattern, especially to rush hours. Applying the Mann–Kendall test, eBC levels exhibited decreasing trends for all seasons, showing slopes between −15%/yr and −5%/yr. In addition, the Absorption Å ngström Exponent shows a significant upward trend for all periods analyzed.

The rural station is in a remote site at 1280 m.a.s.l., 80 km from the suburban station. The overall mean from 2017 to 2023 ($\pm$ standard deviation) was 0.17 $\pm$ 0.14 $\mu$gm⁻³, ranging from 0.08 $\mu$gm⁻³ in winter to 0.20 $\mu$gm⁻³ in summer. This seasonality is due to a combined effect of local dynamics of the BLH and the station altitude. The daily variability is smoother, without marked changes. The maximum daily concentration is reached in the late afternoon. According to the Conditional Bivariate Probability Function (CBPF) diagrams, the transport from the city of Valencia (SE direction) is the most relevant contribution at the measurement location.