Species-Separated Absorption Coefficient and Atmospheric Heating Rate for Black Carbon and Mineral Dust in the Western Mediterranean

Mineral dust significantly impacts the Earth's climate, representing 75% of global aerosol mass and 25% of aerosol optical depth (Kinne et al., 2006). Black Carbon (BC) is the most influential short-lived climate-warming forcer, while Mineral Dust (MD) contributes to atmospheric heating and cooling through absorption and scattering (IPCC, 2021). The effects of BC and MD on atmospheric heating depend, among other factors, on their mixing state, which is not well-known presently.

             We present in situ surface measurements of dust and BC during dusty and non-dusty days. Measurements were conducted between February 12 to September 20, 2019, at three measuring stations, part of the EGAR monitoring and ACTRIS networks: Barcelona (BCN), Montseny (MSY), and Montsec (MSA), and from May 27 to August 27 at the MSA site. We will compare fine and coarse particles (BC and MD) at the three stations to understand the background environment and how dust particles affect aerosol light absorption in urban, remote, and continental sites.

             We used a pair of Aethalometers AE33 (Drinovec et al., 2015) with PM1 and a virtual impactor (VI) inlets to determine the absorption coefficient for fine (PM1) and coarse fractions (Drinovec et al., 2020). We have quantified the absorption of dust and BC at different wavelengths using AAE values of 1.1 for BC and 2.88 for MD for the multi-wavelength apportionment model  (Massabo et al., 2015), and calculated the Heating Rate(HR) for MD and BC (Ferrero et al., 2021). Similarly, the Mass Absorption Cross-section (MAC) of MD was calculated using the method proposed by Drinovec et al.(2020), which assumes calcium constitutes about 12% of the total mineral dust mass.

           Our results show that during dusty days in summer, dust absorption is higher in the MSA site at 370 nm (2.29 ± 2.85 Mm^-1), with increases of 1.7 and 6 times compared to MSY (1.28 ± 1.22 Mm^-1) and BCN (0.33 ± 0.48 Mm^-1), respectively. The MAC values progressively increase from lower to higher altitudes, with values of MAC during dusty days in summer: BCN (77 m a.s.l) 0.11 ± 0.19 m²g^-1, to MSY (720 m a.s.l) 0.39 ± 0.82 m²g^-1, and at MSA (1600 m a.s.l) 1.05 ± 1.9 m²g^-1. These results show an increasing trend in dust MAC with altitude within our study area, where anthropogenic influence decreases at higher elevations. Finally, we will also present our results for the HR during dusty events, which show mean values of 0.13 ± 0.27 K day⁻¹ in the MSA and 0.066 ± 0.052 K day⁻¹ in the MSY for MD, and 0.29 ± 0.31 K day⁻¹ in the MSA and 0.53 ± 0.39 K day⁻¹ in the MSY for BC.