Seven years of measurements of equivalent black carbon at the Capo Granitola WMO-GAW station: influence of local vegetation fires

Abstract

This study investigates the influence of local vegetation fires on equivalent black carbon (eBC) concentrations using seven years of satellite and ground-based observations combined with HYSPLIT back-trajectory analysis. Measurements were collected at the ‘Rita Atria’ Climate Observatory at Capo Granitola (CGR), a WMO-GAW background-coastal regional station located on the south-west coast of Sicily in the central Mediterranean Basin. Between 2015 and 2021, the Sicilian region experienced approximately 6330 vegetation fires, with 74% occurring during the summer season. The total burned area amounted to 135 thousand hectares (ha), with roughly 30% being forested land, averaging about 6.1 kha per year, and 67% affecting other types of vegetation. The average eBC concentration was 0.49 ± 0.69 µg m⁻³, with significant interannual variability. 10% of the days were characterized by eBC concentrations exceeding the climatological average, referred to as acute days. Using back-trajectory analysis, vegetation fire influence on acute eBC days was evaluated using satellite-based MODIS/VIIRS active-fire pixels and ground-based burned areas from the Sicilian Forest Information System (SIF). We found matches for 46% and 18% of acute days, respectively, consistent with the different nature and coverage of the two products. A statistically significant increasing trend of eBC concentration during the acute days was observed (0.04 µg m⁻³ per year), consistent with an increase in the frequency of vegetation fires, highlighting the intensifying impact of these events on air quality in the central Mediterranean.