A 150-year record of black carbon (soot and char) and polycyclic aromatic compounds deposition in Lake Phayao, north Thailand

Abstract An improved understanding of the historical variation in the emissions and sources (biomass burning, BB vs. fossil fuel combustion) of soot and char, the two components of black carbon (BC), and polycyclic aromatic compounds (PACs) may help in assessing environmental effects of the Atmospheric Brown Cloud (ABC) in SE Asia. We therefore determined historical variations of the fluxes of soot, char, and PACs, (24 polycyclic aromatic hydrocarbons (PAHs), 12 oxygenated-PAHs (OPAHs), and 4 azaarenes) in a dated sediment core of Phayao Lake (covering the past ∼150 years) in Thailand. The soot fluxes have been increasing in recent times, but at a far lower rate than previously reported based on BC emission inventories. This may be associated with a decreasing BB contribution as indicated by the decreasing char fluxes from old to young sediments. The fluxes of high- and low-molecular-weight (HMW and LMW) PAHs, OPAHs, and azaarenes all sharply increased after ∼1980, while the ΣLMW-/ΣHMW-PAHs ratios decreased, further supporting the reduction in BB contribution at the expense of increasing fossil fuel combustion emissions. We also suggest that the separate record of char and soot, which has up to now not been done in aerosol studies, is useful to assess the environmental effects of ABC because of the different light-absorbing properties of these two BC components. Our results suggest that besides the establishment of improved fossil fuel combustion technology, biomass burning must be further reduced in the SE Asian region in order to weaken the ABC haze.