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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
Author(s) -
Zhang Yuxuan,
Su Hang,
Ma Nan,
Li Guo,
Kecorius Simonas,
Wang Zhibin,
Hu Min,
Zhu Tong,
He Kebin,
Wiedensohler Alfred,
Zhang Qiang,
Cheng Yafang
Publication year - 2018
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
eISSN - 2169-8996
pISSN - 2169-897X
DOI - 10.1029/2018jd028810
Subject(s) - carbon black , soot , materials science , particle (ecology) , particle size , aerosol , mixing (physics) , carbon fibers , coating , photometer , analytical chemistry (journal) , optics , meteorology , natural rubber , chemistry , composite material , geology , physics , oceanography , organic chemistry , chromatography , quantum mechanics , composite number , combustion
Abstract We measured the mixing state of refractory black carbon (rBC) particles using a single‐particle soot photometer (SP2) on 11–27 July 2013 at a polluted regional site (~60 km to the south of Beijing) of the North China Plain. To improve retrieval of rBC mixing state, we validate and optimize the optical size ( D opt,p ) of ambient particles derived from SP2 and Mie calculation. By matching the retrieved D opt,p with the measured mobility diameter, we retrieve the densities (~0.3–0.6 g/cm 3 ) and refractive indices (from 1.21–0.21i to 1.42–0.42i) of rBC core for thinly coated BC particles at mobility size of 200–350 nm; the refractive index of non‐BC (or coating) materials is estimated as 1.42–0i. It is found that the leading‐edge‐only‐fit method of SP2 calculation can be used to retrieve D opt,p at least up to ~600 nm for ambient BC‐containing particles, and it can successfully provide D opt,p of ambient non‐BC particles only up to ~500 nm. During the measurement campaign, the aging rate from thinly coated (or bare) BC to thickly coated BC can reach up to ~21%/hr around noontime, indicating the fast coating of BC. The average coating thickness ( CT ) of BC‐containing particles (200–350 nm) is ~41–71 nm, with ~13–16 nm CT for thinly coated (or bare) BC particles and ~75–114 nm CT for thickly coated BC particles. The mixing state of rBC obtained in this study indicates fast aging process and strong light‐absorbing capacity of BC particles under the polluted conditions in the North China Plain.