The critical role of light-absorbing aerosol black carbon (BC) in modifying the Earth's atmosphere and climate system warrants detailed characterization of its microphysical properties. The present study examines the BC microphysical properties (size distributions and mixing state) and their impact on the light-absorption characteristics over a semi-urban tropical coastal location in Southern Peninsular India. The measurements of refractory BC (rBC) properties, carried out using the single particle soot photometer during 2018–2021, covering four distinct air mass conditions (Marine, Continental, Mixed-1, and Mixed-2), were used for this purpose. These were supported by measurements of non-refractory submicron particulate matter (NR-PM₁) mass loadings and the core-shell Mie theory model for BC-containing particles. The results suggested that the BC particles exhibited varying sizes (mass median diameters from 0.181 ± 0.079 μm to 0.202 ± 0.064 μm) and relative coating thicknesses (RCT) (1.3–1.6) under distinct air mass conditions. These characteristics reflected varying source/sink strengths, aging processes of BC, and potential condensable coating material. The aerosol system during the Marine air mass period has lower BC (~ 0.67 ± 0.57 μg m⁻³) and NR-PM₁ (12.06 ± 10.81 μg m⁻³) mass concentrations, and the lowest RCT on BC (~ 1.34 ± 0.14). However, the other periods with continental influence depicted significant coatings on BC (mean RCT >1.5). The coatings on BC particles exhibited daytime enhancement, driven by photochemically produced condensable material, a contrasting diurnal pattern to that of other BC properties. Interestingly, the RCT on BC increased and/or remained invariant with increasing relative humidity (RH) until RH ≤82 %, and subsequently showed a decline. This is possibly due to deliquescence and subsequent detachment of the coating material (likely, inorganics) from the BC cores. Despite this, the BC particles retained coatings of ~30–50 % of their core sizes even under high RH (>85 %), indicating the potential role of secondary organics as coatings. The changes in the BC mixing state resulted in a significant alteration to its light-absorption properties. The mean light-absorption enhancement of BC (compared to uncoated BC) ranged from 1.36 ± 0.14 for the Marine air mass periods to 1.58 ± 0.15 for the Continental air mass periods, whereas the overall mass absorption cross-sections of BC varied between 7.91 ± 0.91 to 9.03 ± 0.84 m²/g at 550 nm. The key implication of this study is that changes to the BC mixing state, caused by multiple underlying processes unique to tropical atmospheric conditions, can lead to a significant enhancement in its light-absorption characteristics, which can lead to a notable increase in the positive radiative forcing of BC.