Emission characteristics of refractory black carbon aerosols from fresh biomass burning: a perspective from laboratory experiments

Abstract

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 burning of wheat straw and rapeseed plants, which are the main crops cultivated in the Yangtze River Delta region of China. A single particle soot photometer (SP2) was used 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 lognormal shape with a mode mass equivalent diameter (MED) of 189 nm (ranging from 152 to 215 nm), assuming an rBC density of 1.8 g cm −3 . rBC particles less than 80 nm in size (the lower detection limit of the SP2) accounted for ∼ 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 and 34 ng m −3 ppbv −1 . 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 laboratory study found that the mixing state of rBC particles from biomass burning strongly depends on its combustion processes, and overall MCE should be taken carefully into consideration while the climate effect of rBC particles from open biomass burning is simulated.

Optical Properties of Laboratory and Ambient Biomass Burning Aerosols: Elucidating Black, Brown, and Organic Carbon Components and Mixing Regimes

“…These results agree with Pan et al (2017) who observed significantly lower rBC emission ratios during the ignition of wet wheat straw (more smoldering; ER = 7.1 ng·m −3 ·ppbv −1 ) than the ignition of dry wheat straw (more flaming; ER = 25.3 ng·m −3 ·ppbv −1 ). Since MCE was >0.9 for all burns indicating either flaming-dominated or a mixed flaming-smoldering phase, we use ER (rBC/CO) to determine the combustion regime in our laboratory data.…”

Sizing of Ambient Particles From a Single‐Particle Soot Photometer Measurement to Retrieve Mixing State of Black Carbon at a Regional Site of the North China Plain

“…In terms of coated BC particles selected by DMA, the frequency distribution of CT exhibits three peaks, which characterize the coating materials of thinly coated BC (the first peak with the least CT ), thickly coated BC with single charge (the second peak with the medium CT ), and thickly coated BC with double/triple charges (the third peak with the most CT ), respectively. In this study, the thinly coated BC and thickly coated BC particles are distinguished based on the two‐mode distribution of lagtime (Figure S1), which is an indicator of BC mixing state (Moteki & Kondo, ; Pan et al, ). Larger lagtime can characterize more coating material on BC surface.…”

Reduction in black carbon light absorption due to multi-pollutant emission control during APEC China 2014

“…The validity of the LEO method for ambient BCcontaining particles observed in China has been evaluated by Y. . More details on the SP2 technique have been reported elsewhere (Gysel et al, 2011;Pan et al, 2017;Sedlacek et al, 2012;.…”

“…D c was calculated from m rBC and the density of the rBC core (ρ c ; here, a prescribed value of 1.8 g cm −3 ) (Cappa et al, 2012;Pan et al, 2017;Laborde et al, 2013). D p was determined via the Mie calculation and was related to D c , the C s of the BC-containing particle, and the refractive indices of NR-CM (RI NR−CM , 1.5-0i; Zhang et al, 2018) and rBC core (RI c , 2.26-1.26i; Taylor et al, 2015).…”

“…When fresh BC is emitted from incomplete combustion (e.g., traffic emissions) other than biomass burning (Q. Pan et al, 2017), they are most likely externally mixed with other aerosol components (e.g., primary organic aerosol). These fresh BC particles exist as almost bare particles with few other species condensed on their surfaces and are called externally mixed BC particles (Jacobson et al, 2001;Chung et al, 2005).…”