Abstract View
Online Shape and Density Measurement of Single Black Carbon Aerosol Particles
Shurong Wang, Kaili Zhou, JianMin Chen, Kimberly Prather, Xin Yang, XIAOFEI WANG, Fudan University
Abstract Number: 32
Working Group: Instrumentation and Methods
Abstract
Black carbon (BC) aerosols play crucial roles in affecting air quality, climate, and human health. Density and morphology reflect chemical composition, mixing state and aging pathway of BC particles. A novel method, which mainly consists of an aerodynamic aerosol classifier, a differential mobility analyzer and a single-particle soot photometer, was developed to calculate shape factor and density of single BC particle by measuring its aerodynamic diameter (D_a), electrical mobility diameters (D_m) and BC mass content (m_BC). Ambient BC aerosols with different D_a (200 nm, 350 nm, 500 nm) were studied by this method. BC-dominated particles were only observed in particles with 200nm D_a and 135nm D_m, which accounted for ~75.6% of particles with 200nm D_a in the winter sampling days. Surprisingly, morphology of BC-dominated particles was near-spherical, indicating just a few absorbed substances on BC particles could change their morphology from irregular to near-spherical. Aerosols of Mode(D_a=350nm, D_m=259.5nm) and of Mode(D_a=500nm, D_m=358.7nm) constituted up to ~73.6% and ~81.9% of ambient aerosols with 350nm D_a and 500nm D_a. Most BC particles in these two modes was internally mixed with secondary substances, and their morphology was likely to be spherical. Ammonium sulfate and ammonium nitrate were the main secondary substances of BC particles in these two modes, consistent with their measured densities (1.62 g/cm3 and 1.77g/cm3 respectively) and average single particle mass spectra. Generally, the new online system can investigate both morphology and density of each single BC particle, which can help identify the formation and aging pathway of BC aerosols.