Emission factors of metals bound with PM2.5 and ashes from biomass burning simulated in an open-system combustion chamber for estimation of open burning emissions

Abstract Emission Factors (EFs) of metals bound with PM2.5 along with ashes from biomass burning were obtained using an open-system combustion chamber. The burning of agricultural residue (AR) (rice straw (RS) and maize residue (MR)) and forest leaf litter (FLL) collected from dry dipterocarp forests (DDF) and mixed deciduous forests (MDF) were performed. The EFs of PM2.5 of all biomass burning were 2.15–4.38 g kg−1. The order of the EFs of PM2.5-bound metals were K, Na, Mg, Cr and Zn. The EFs values were used to estimate the emissions of PM2.5 and the metals from open burning in Upper Northern Thailand (UNT) in 2019. About 66,990 km2 and 27,060 km2 of the UNT are covered by forests and agriculture areas, respectively. In 2019, 80% of the total burned area was identified in forest areas (8,344 km2) and only 16% (1,647 km2) was identified in agriculture areas. Emissions of PM2.5 recorded during the smoke haze episode of 2019 were from burnings of forests (11 kilotons) and agricultural fields (0.4 kilotons). The major metals present in ash samples were Ca, K, Mg, Al, Fe and Mn. About 0.86 kilotons of total metals were emitted into the atmosphere. Ash resulting from the burning of AR was rich in K, while that of FLL has high in Ca content. After the burning period, about 78 kilotons of metals remained on the ground and/or were found to have accumulated in the environment.