Significant Contribution of Coarse Black Carbon Particles to Light Absorption in North China Plain

Black carbon (BC) has adverse impacts on human health and significantly influences the global climate as one of the major atmospheric heating contributors. These effects strongly depend on the microphysical properties of BC. BC particles and their distributions are mostly monitored and studied by online refractory BC instruments, which account for particles with aerodynamic diameters 1 mu m. During a field campaign conducted in the beginning of the heating season in Beijing, coarse BC particles (aerodynamic diameter 1 mu m) were found to take up a high mass proportion (similar to 50%) of all BC particles, and they consisted of two types. One type was coarse-BC-containing particles with massive coating from secondary processes. Super-aggregated BC (fractal BC structure) with a diameter of 2.6 mu m was also noticed using transmission electron microscopy. Such two types of coarse BC particles unnoticed by typical online refractory BC instruments contribute to 17-43% of BC light absorption, indicating a possible underestimation of BC warming effects. Thus the emission and physical and chemical properties of such coarse BC should be further investigated to better constrain aerosol radiative effects.