Emission and outflow of polycyclic aromatic hydrocarbons from wildfires in China

On the basis of burned area, biomass density, burn efficiency and emission factor, annual emissions of polycyclic aromatic hydrocarbons (PAHs) from wildfires in China are estimated for the period from 1950 to 2005. During that period, 7.8 × 106 and 7.5 × 106 Mg of biomass are burned annually by forest and grassland fires, respectively. The average annual emission of 16 PAHs was estimated at 256 ± 185 Mg (average ± standard deviation). Among the 16 PAHs studied, NAP contributed 55% of the total emissions from wildfires. Emission rates varied erratically and the annual emissions declined significantly since 1988. Wildfire PAH emission in China has shown strong seasonality with peaks in spring and fall. The provinces of Inner Mongolia, Heilongjiang and Yunnan ranked as the most prolific PAH source areas with respect to both density and amount of PAH emission. Spatial variations seem to be primarily related to vegetation cover which has been used in a regression model to predict a county-resolved emission inventory in China. Forest fires in Heilongjiang and Russia led to visible haze over Japan during October 2004. In order to trace the potential influence of PAHs, numerical simulation of potential receptor influence function (PRIF) based on forward trajectory calculation was implemented to address the general outflow pattern.