Work

Microphysical properties of refractory black carbon aerosols for different air masses at a central European background site

Year: 2025

Type: article

Abstract: . Uncertainties remain in estimating black carbon’s (BC) radiative forcing due to a limited understanding of its microphysical properties. This study investigated the physical properties of refractory black carbon (rBC) at the central European background site Melpitz during summer and winter, using a single particle soot photometer coupled with a thermodenuder. Different air masses associated with distinct rBC properties were identified in both seasons. In summer, rBC exhibited a similar mass concentration (~0.16 μg m-3) among different air masses, with the smallest mass median diameter (MMD) of rBC overserved in the long transportation from the northwest (140 nm), while in winter, the highest concentration (1.23 μg m-3) and largest MMD (216 nm) were both observed in the air mass influenced by the easterly winds. Thickly coated rBC fractions increased during the daytime in summer, indicating the photochemical processes significantly influence the rBC mixing state. In winter, a higher fraction (27 %) of rBC with thick coating in the cold air mass compared to the warm air mass (14 %) suggests the contribution of residential heating emissions to the mixing state. Most rBC retained a low-volatile coating in the thermodenuder samples (58 % mass fraction). In summer, photochemical processes also contribute to coating volatility, showing a higher fraction of rBC particles containing low-volatile coatings during the daytime. In winter, low-volatile coatings showed no significant diurnal variation and were more dependent on ambient temperature. Therefore, rBC coating volatility in winter is more influenced by emission sources, particularly residential heating, rather than atmospheric processes.

Source: Atmospheric chemistry and physics

DOI: 10.5194/acp-25-8637-2025