Characterization of Size-Resolved Hygroscopicity of Black Carbon-Containing Particle in Urban Environment

Abstract

The hygroscopic properties of BC-containing particles (BCc) are important to determine their wet scavenging, atmospheric lifetime, and interactions with clouds. Such information is still lacking in the real world because of the challenges in isolating BCc from other aerosols to be directly characterized. In this study, the size-resolved chemical components of BCc including the refractory BC core and associated coatings were measured by a soot particle–aerosol mass spectrometer in suburban Nanjing. The size-resolved hygroscopicity parameter of BCc (κBCc) was obtained based on this full chemical characterization of BCc. We found increased inorganic fraction and more oxidized organic coatings with thicker coatings, which modified κBCc besides the determinant of particle size. The bulk κBCc was observed to range from 0.11 to 0.34. The size-resolved κBCc consistently showed minima at coated diameter (D coated) of 100 nm, parametrized as κ­(x) = 0.28–0.35 × exp­(−0.004 × x), x = D coated. Under critical supersaturations (SS) of 0.1% and 0.2%, the D 50 values of BCc were 200 ± 20 and 135 ± 18 nm, respectively. On average 33 ± 16% and 59 ± 20% of BCc in number could be activated at SS = 0.1% and 0.2%, respectively. These results provide constraints on surface CCN sources for the light-absorbing BC-containing particles.

Characteristics of Black Carbon Particle-Bound Polycyclic Aromatic Hydrocarbons in Two Sites of Nanjing and Shanghai, China

“…Zhang et al [44] further provide standard procedures to evaluate PMF solutions and choose the optimal one. For NUIST dataset, five OA factors were resolved, as detailed in Wu et al [45]. Note in Wu et al [45], the PMF results were used to elucidate the relationship of OA with hygroscopicity of rBC-containing particles, while characteristics of rBC-bound PAHs were not discussed.…”

“…For NUIST dataset, five OA factors were resolved, as detailed in Wu et al [45]. Note in Wu et al [45], the PMF results were used to elucidate the relationship of OA with hygroscopicity of rBC-containing particles, while characteristics of rBC-bound PAHs were not discussed. For the SAES dataset, PMF analysis was conducted on the OA mass spectra including ions with m/zs of 12 to 120.…”

“…For the NUIST dataset, five factors were resolved, including the traffic-related hydrocarbon-like OA (HOA), industry-related OA (IOA), aged biomass burning OA (ABBOA), semi-volatile oxygenated OA (SV-OOA), and low-volatility oxygenated OA (LV-OOA). Their mass spectral profiles and time series are presented in Wu et al [45], therefore are not shown here. For SAES dataset, we separated six factors, including the enriched hydrocarbon-like OA (HOA-rich), rBC-enriched OA (rBC-rich), biomass burning OA (BBOA), nitrogen-enriched OA (NOA), less oxidized oxygenated OA (LO-OOA), and more oxidized oxygenated OA (MO-OOA).…”

Elemental analysis of Oxygenated Organic Coating on Black Carbon Particles using a Soot-Particle Aerosol Mass Spectrometer

“…Ambient BC particles are largely internally mixed with organic aerosols (OA). While BC and hydrophobic organic coating can be co-emitted from combustion processes, BC can be coated by oxygenated organic compounds formed via oxidation of organic vapors and heterogeneous processing (China et al, 2013;Lee et al, 2019;Wu et al, 2019). Organic coatings can alter the physio-chemical properties of BC particles, such as enhancements of light absorptivity (Liu et al, 2017;Peng et al, 2016), cloud 10 formation potential (Kuwata et al, 2009;Liu et al, 2013) and subsequently their atmospheric transport and lifetime (Bond et al, 2013;Laborde et al, 2013;McMeeking et al, 2011).…”

“…The soot-particle aerosol mass spectrometer (SP-AMS), which is a standard high-resolution time-of-flight aerosol 15 mass spectrometer (HR-ToF-AMS) equipped with an additional infrared (IR) laser vaporizer (Onasch et al, 2012), has been utilized to characterize refractory BC (rBC) and its coatings (Collier et al, 2018;Lee et al, 2017;Massoli et al, 2015;Willis et al, 2016;Wu et al, 2019). The laser vaporization scheme of SP-AMS can heat up rBC cores gradually (up to ~4000K) until they are completely vaporized, during which non-refractory coatings can be vaporized at a temperature lower than the operating temperature of thermal vaporizer (600 o C) typically used in HR-ToF-AMS 20 for flash vaporization (DeCarlo et al, 2006;Onasch et al, 2012) (Figure 1).…”