Mixing state of black carbon particles and its effect on light absorption in Shenzhen, China
Abstract
Black carbon (BC) has strong mass absorption efficiency (MAE) among atmospheric aerosol components, while the MAEs of BC from different sources and at different locations differ a lot. In addition, the mixing state of BC is an important factor affecting its light absorption. In this study, a differential mobility analyzer (DMA) and a single particle soot photometer (SP2) are coupled to measure BC aerosol and its mixing state, and analyze its optical properties, with the simultaneous observation using a three-wavelength photoacoustic soot spectrometer (PASS-3) in Shenzhen, a megacity in China, during the spring of 2013. The average mass concentration of BC is 3.0±2.5 μg/m3, accounted for 8.9% of the total PM2.5 mass. The MAEs of BC at 405, 532 and 781 nm are 11.0, 7.4 and 4.8, respectively, and presents an obvious diurnal pattern with high values in traffic rush hours and low values at noon. The diurnal pattern of the proportion of internally mixed BC in number is similar, implying chemical growth of particle coating at noon. The average percentage of internally mixed BC ranges from 0.94% to 24%, with an average value of 6.4%, and shows a decreasing trend with the increase of BC particle size. The ratio of coating thickness to BC core diameter also decreases with the increase of BC core diameter, and has a platform at 150-200 nm. Generally, the MAE increases with the proportion of the mixing state increasing, while it begins to decrease at a high level of the mixing state. The average enhancements of the BC mixing on MAE are similar at the three bands, i.e., 47%, 53% and 48%, respectively. During the high PM2.5 pollution period (>40 μg/m3), the enhancements of the BC mixing on MAE at the three wavelengths rise to 61%, 61% and 59%, respectively. Furthermore, the MAE of BC was found to increases with the thickness of coatings of the particles with BC core diameter less than 200 nm, but this relationship becomes vague for the particles with BC core diameter larger than 200 nm.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.A43L3263Z
- Keywords:
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- 0305 Aerosols and particles;
- ATMOSPHERIC COMPOSITION AND STRUCTUREDE: 0317 Chemical kinetic and photochemical properties;
- ATMOSPHERIC COMPOSITION AND STRUCTUREDE: 0345 Pollution: urban and regional;
- ATMOSPHERIC COMPOSITION AND STRUCTUREDE: 0365 Troposphere: composition and chemistry;
- ATMOSPHERIC COMPOSITION AND STRUCTURE