Size distribution of water-soluble ions in particles emitted from domestic firewood burning

Six kinds of domestic firewood were burned in a laboratory. The emitted particles in fourteen sizes were collected using a dilution sampling system and an electrical low-pressure impactor. The emission characteristic and size-resolved emission factors (EFs) of eight types of water-soluble ions were identified. Results showed that the EFs of Ca2+ exhibited a bimodal size distribution, with peaks of 0.14 and 0.16mg/kg for particles within 0.25~0.38 and 2.5~3.6µm, respectively. The EFs of other ions were characterized by a unimodal size distribution. The EFs of NH4+, NO3- and SO42- peaked at 0.25~0.38µm, with peaks of 0.41, 0.58 and 0.84mg/kg, respectively. The EFs of K+ and Cl- exhibited highest values at 0.15~0.25µm of 0.89 and 0.99mg/kg, respectively. The mass median diameters of total water-soluble ions from firewood burning were (0.30±0.07)µm, and those of individual ions ranged in 0.24~0.44µm. The EFs of water-soluble ions in PM0.094, PM0.94, PM2.5 and PM10 were 1.04~9.33, 5.00~48.87, 5.46~52.00 and 6.14~53.68mg/kg, respectively. The ratios of K+/Cl-, K+/NO3-, K+/SO42- and SO42-/NO3- in particles emitted from firewood burning varied with particle size. Their primary emission values should be emphasized when they were used in source apportionment and smoke aging researches. The anion/cation equivalent ratios of PM10 from firewood burning were 0.80±0.11. The acidity of PM0.94 and PM2.5 were higher than those of PM0.094 and PM2.5~10. This study is significant to establish emission inventory of size-resolved water-soluble ions, update and improve the parameter settings of corresponding climate and air quality models, and identify the evolution mechanisms of smokes during transport and aging. © 2021, Editorial Board of China Environmental Science. All right reserved.