Measurement of Density and Shape for Single Black Carbon Aerosols in a Heavily Polluted Urban Area

Abstract

Black carbon (BC) aerosol imposes adverse effects on atmospheric visibility, climate, and health.The particle density and morphology are often needed to investigate the mixing state and aging process of BC particles. A method, combining an aerodynamic aerosol classifier (AAC), a differential mobility analyzer (DMA), a single-particle soot photometer (SP2) and a single particle aerosol mass spectrometer (SPAMS), was developed to determine the density and dynamic shape factor (𝜒𝜒 ) of ambient BC particles with three different aerodynamic diameters (𝐷𝐷 𝑎𝑎 , 200 nm, 350 nm, and 500 nm) in Shanghai, China, a typical urban area. The BC particles were either classified as "BC-dominated particle" which is mainly made of black carbon or "BC-mixed particle" which is a mixture of both BC and non-BC substances. The results show that BC-dominated particles whose BC core mass (~2.2 fg) was almost equal to particle mass (~2.3fg) were observed in particles with 200 nm 𝐷𝐷 𝑎𝑎 . The morphology of these BC-dominated particles was near-spherical (𝜒𝜒 ≈1.02), indicating that they had undergone rapid morphology modification from the initial highly irregular morphology to near-spherical shape. Most BC particles with 350 nm or 500 nm 𝐷𝐷 𝑎𝑎 were BCmixed particles. Combining the effective densities (1.62~1.77 g cm -3 ) and average single particle mass spectra of particle, the ammonium sulfate and ammonium nitrate were found to be the main secondary substances of these BC-mixed particles, indicating that condensation of inorganic species such as nitrates and sulfates could play a significant role in the aging process of fresh BC A C C E P T E D MA N U S C R I P T 2 in Shanghai. Generally, the morphology and density information of single BC particle is crucial to identify the mixing state and aging process of BC aerosols.

Efficient droplet activation of ambient black carbon particles in sub-urban environment

“…This means in the typical sub-urban environment, BC had been significantly associated with non-BC substance through condensation and coagulation process (Yu et al, 2022), and the bare BC without containing non-BC substance had taken a less proportion and most BCc had been enlarged during the aging process. This is consistent with previous studies that BC was associated with larger aerodynamic size than BCf (Pan et al, 2019;Wang et al, 2021). Previous studies also observed rapid aging of BC in a few hours in urban environment (Peng et al, 2016).…”

Measurement report: Inland ship emissions and their contribution to NOx and ultrafine particle concentrations at the Rhine

“…For all particle measurement devices, particulate matter concentration (PM 1 , PM 2.5 ) was derived from the PNC in the corresponding channels, assuming a constant density of 1.7 g cm −3 . This estimate is based on numerous literature studies on diesel exhaust and urban aerosols (Barone et al, 2011;Celik et al, 2020;Wang et al, 2021), also considering the relatively large BC fraction (∼ 2 g cm −3 ) measured in our study. Nevertheless, the number is subject to a substantial uncertainty as the exact particle composition is unknown and also changes over time.…”