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

摘要

High levels of trace gas (O₃ and CO) and aerosol (BC, fine and coarseparticle volumes), as well as high scattering coefficient(σ_p) values, were recorded at the regional GAW-WMO station ofMt. Cimone (CMN, 2165 m a.s.l., Italy) during the period 26–30 August2007. Analysis of air-mass circulation, aerosol chemical characterizationand trace gas and aerosol enhancement ratios (ERs), showed that high O₃and aerosol levels were likely linked to (i) the transport of anthropogenicpollution from northern Italy, and (ii) the advection of air masses rich inmineral dust and biomass burning (BB) products from North Africa. Inparticular, during the advection of air masses from North Africa, the CO andaerosol levels (CO: 175 ppbv, BC: 1015 ng/m3, fine particle volume:3.00 μm3 cm−3, σ_p: 84.5 Mm−1) were evenhigher than during the pollution event (CO: 138 ppbv, BC: 733 ng/m3,fine particles volume: 1.58 μm3 cm−3, σ_p: 44.9 Mm3 concentration, the analysis of ERs showed that theBB event represented an efficient source of fine aerosol particles (e.g.BC), but also of the O₃ recorded at CMN. In particular, the calculatedO₃/CO ERs (0.10–0.17 ppbv/ppbv) were in the range of values found inliterature for relatively aged (2–4 days) BB plumes and suggestedsignificant photochemical O₃ production during the air-mass transport.For fine particles and σ_p, the calculated ERs was higher in theBB plumes than during the anthropogenic pollution events, stressing theimportance of the identified BB event as a source of atmospheric aerosolable to affect the atmospheric radiation budget. These results suggest thatepisodes of mineral dust mobilization and wildfire emissions over NorthAfrica could significantly influence radiative properties (as deduced fromσ_p observations at CMN) and air quality over the Mediterraneanbasin and northern Italy.