Significant variations of trace gas composition and aerosol properties at Mt. Cimone during air mass transport from North Africa – contributions from wildfire emissions and mineral dust

Abstract. High levels of trace gas (O₃ and CO) and aerosol (BC, fine and coarse particle volumes), as well as high scattering coefficient (σ_p) values, were recorded at the regional GAW-WMO station of Mt. Cimone (CMN, 2165 m a.s.l., Italy) during the period 26–30 August 2007. Analysis of air-mass circulation, aerosol chemical characterization and trace gas and aerosol enhancement ratios (ERs), showed that high O₃ and aerosol levels were likely linked to (i) the transport of anthropogenic pollution from northern Italy, and (ii) the advection of air masses rich in mineral dust and biomass burning (BB) products from North Africa. In particular, during the advection of air masses from North Africa, the CO and aerosol levels (CO: 175 ppbv, BC: 1015 ng/m³, fine particle volume: 3.00 μm³ cm⁻³, σ_p: 84.5 Mm⁻¹) were even higher than during the pollution event (CO: 138 ppbv, BC: 733 ng/m³, fine particles volume: 1.58 μm³ cm⁻³, σ_p: 44.9 Mm). Moreover, despite the presence of mineral dust able to affect significantly the O₃ concentration, the analysis of ERs showed that the BB event represented an efficient source of fine aerosol particles (e.g. BC), but also of the O₃ recorded at CMN. In particular, the calculated O₃/CO ERs (0.10–0.17 ppbv/ppbv) were in the range of values found in literature for relatively aged (2–4 days) BB plumes and suggested significant photochemical O₃ production during the air-mass transport. For fine particles and σ_p, the calculated ERs was higher in the BB plumes than during the anthropogenic pollution events, stressing the importance of the identified BB event as a source of atmospheric aerosol able to affect the atmospheric radiation budget. These results suggest that episodes of mineral dust mobilization and wildfire emissions over North Africa could significantly influence radiative properties (as deduced from σ_p observations at CMN) and air quality over the Mediterranean basin and northern Italy.