The study addresses the challenge of accurately assessing the light absorption of black carbon (BC) after it is mixed with non-BC components, which significantly impacts its climate warming effect. Through comprehensive in situ measurements of BC single-particle microphysics, including size, coating amounts, density, and shape, the researchers found that observed particle-to-particle heterogeneities in size and coating, and the non-spherical shape of BC, explain only a portion of the lower observed BC absorption. The remaining gap is attributed to the off-center position of the BC core in fully aged spherical BC-containing particles. The global climate model assessment indicates that fully accounting for these observed BC complexities reduces the global BC direct radiative forcing by up to 23%.The study addresses the challenge of accurately assessing the light absorption of black carbon (BC) after it is mixed with non-BC components, which significantly impacts its climate warming effect. Through comprehensive in situ measurements of BC single-particle microphysics, including size, coating amounts, density, and shape, the researchers found that observed particle-to-particle heterogeneities in size and coating, and the non-spherical shape of BC, explain only a portion of the lower observed BC absorption. The remaining gap is attributed to the off-center position of the BC core in fully aged spherical BC-containing particles. The global climate model assessment indicates that fully accounting for these observed BC complexities reduces the global BC direct radiative forcing by up to 23%.