Emission characteristics of refractory black carbon aerosols from fresh biomass burning: a perspective from laboratory experiments
Xiaole Pan1, Yugo Kanaya2, Fumikazu Taketani2, Takuma Miyakawa2, Satoshi Inomata3, Yuichi Komazaki2, Hiroshi Tanimoto3, Zhe Wang1,4, Itsushi Uno4, and Zifa Wang11State Key Laboratory of Atmospheric Boundary Layer Physics and Atmospheric Chemistry, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, 100029, China 2Japan Agency for Marine-earth Science and Technology, Yokohama, 236-0001, Japan 3National Institute for Environmental Studies, Tsukuba, 305-8506, Japan 4Research Institute for Applied Mechanics, Kyushu University, Kasuga, 816-8580, Japan
Abstract. The emission characteristics of refractory black carbon (rBC) from biomass burning are essential information for numerical simulations of regional pollution and climate effects. We conducted combustion experiments in the laboratory to investigate the emission ratio and mixing state of rBC from the open burning of wheat straw and rape plants, which are the main crops cultivated in the Yangtze River Delta region of China. A single particle soot photometer (SP2) was adopted to measure rBC-containing particles at high temporal resolution and with high accuracy. The combustion state of each burning case was indicated by the modified combustion efficiency (MCE), which is calculated using the integrated enhancement of carbon dioxide and carbon monoxide concentrations relative to their background values. The mass size distribution of the rBC particles showed a perfect Gaussian shape with an average mass equivalent diameter (MED) of 189 nm (the measured MED values varied between 152 nm and 215 nm), assuming an rBC density of 1.8 g/cm3. rBC particles less than 80 nm in size (the lower detection limit of the SP2) accounted for only ~ 5 % of the total rBC mass, on average. The emission ratios, which are expressed as ∆rBC/∆CO (∆ indicates the difference between the observed and background values), displayed a significant positive correlation with the MCE values and varied between 1.8–34 ng/m3/ppbv. Multi-peak fitting analysis of the delay time (∆t, or the time of occurrence of the scattering peak minus that of the incandescence peak) distribution showed that rBC-containing particles with rBC MED = 200 ± 10 nm displayed two peaks at ∆t = 1.7 μs and ∆t = 3.2 μs, which could be attributed to the contributions from both flaming and smoldering combustion in each burning case. Both the ∆t values and the shell/core ratios of the rBC-containing particles clearly increased as the MCE decreased from 0.98 (smoldering-dominant combustion) to 0.86 (flaming-dominant combustion), implying the great importance of the rapid condensation of semi-volatile organics. This study highlights that open biomass burning produces the majority of coated rBC particles, which have considerable ability to affect cloud processes and influence regional climate.
Pan, X., Kanaya, Y., Taketani, F., Miyakawa, T., Inomata, S., Komazaki, Y., Tanimoto, H., Wang, Z., Uno, I., and Wang, Z.: Emission characteristics of refractory black carbon aerosols from fresh biomass burning: a perspective from laboratory experiments, Atmos. Chem. Phys. Discuss., doi:10.5194/acp-2017-326, in review, 2017.