Physical and chemical properties of black carbon and organic matter from different combustion and photochemical sources using aerodynamic aerosol classification

Abstract

Abstract. The physical and chemical properties of black carbon (BC) and organic aerosols are important for predicting their radiative forcing in the atmosphere. During the Soot Aerodynamic Size Selection for Optical properties (SASSO) project and a EUROCHAMP-2020 transnational access project, different types of light-absorbing carbon were studied, including BC from catalytically stripped diesel exhaust, an inverted flame burner, a colloidal graphite standard (Aquadag) and controlled flaming wood combustion. Brown carbon (BrC) was also investigated in the form of organic aerosol emissions from wood burning (pyrolysis and smouldering) and from the nitration of secondary organic aerosol (SOA) proxies produced in a photochemical reaction chamber. Here we present insights into the physical and chemical properties of the aerosols, with optical properties presented in subsequent publications. The dynamic shape factor (χ) of BC particles and material density (ρm) of organic aerosols was investigated by coupling a charging-free Aerodynamic Aerosol Classifier (AAC) with a Centrifugal Particle Mass Analyzer (CPMA) and a Scanning Mobility Particle Sizer (SMPS). The morphology of BC particles was captured by transmission electron microscopy (TEM). For BC particles from the diesel engine and flame burner emissions, the primary spherule sizes were similar, around 20 nm. With increasing particle size, BC particles adopted more collapsed/compacted morphologies for the former source but tended to show more aggregated morphologies for the latter source. For particles emitted from the combustion of dry wood samples, the χ of BC particles and the ρm of organic aerosols were observed in the ranges 1.8–2.17 and 1.22–1.32 g cm−3, respectively. Similarly, for wet wood samples, the χ and ρm ranges were 1.2–1.85 and 1.44–1.60 g cm−3, respectively. Aerosol mass spectrometry measurements show no clear difference in mass spectra of the organic aerosols in individual burn phases (pyrolysis or smouldering phase) with the moisture content of the wood samples. This suggests that the effect moisture has on the organic chemical profile of wood burning emissions is through changing the durations of the different phases of the burn cycle, not through the chemical modification of the individual phases. In this study, the incandescence signal of a Single Particle Soot Photometer (SP2) was calibrated with three different types of BC particles and compared with that from an Aquadag standard that is commonly used to calibrate SP2 incandescence to a BC mass. A correction factor is defined as the ratio of the incandescence signal from an alternative BC source to that from the Aquadag standard and took values of 0.821 ± 0.002 (or 0.794 ± 0.005), 0.879 ± 0.003 and 0.843 ± 0.028 to 0.913 ± 0.009 for the BC particles emitted from the diesel engine running under hot (or cold idle) conditions, the flame burner and wood combustion, respectively. These correction factors account for differences in instrument response to BC from different sources compared to the standardised Aquadag calibration and are more appropriate than the common value of 0.75 recommended by Laborde et al. (2012b) when deriving the mass concentration of BC emitted from diesel engines. Quantifying the correction factor for many types of BC particles found commonly in the atmosphere may enable better constraints to be placed on this factor depending on the BC source being sampled and thus improve the accuracy of future SP2 measurements of BC mass concentrations.

Refractive Index of Engine‐Emitted Black Carbon and the Influence of Organic Coatings on Optical Properties

“…We note that the CPMA‐measured mass distributions were not used in optical closure calculations because the CPMA scanning time takes several minutes, and the particle concentration may change during this time and therefore determined size distributions based on an assumed density were not regarded as accurate. Nonetheless, the CPMA was used to calibrate the SP2 for black carbon mass (Hu et al., 2021a) and therefore inclusion of CPMA measurements in our set‐up remained highly beneficial.…”

“…This work provides fundamental underpinning information needed to improve the prediction of the radiative forcing of BC and BrC in the atmosphere. The work presented here builds on the results reported in our previous publication (Hu et al., 2021a), which described our experimental apparatus, aerosol generation, and conditioning methods, and the chemical and morphological characterization of the particles, but did not investigate the optical properties.…”

Analysis of satellite-derived data for the study of fouling in aircraft engines

“…The aerosol model named dust comprises the characteristics of African and Asian desert dust (Sahara, Gobi, and Arabian Deserts). The polluted continental refers to the contaminant generated in urban-industrial areas, and it is commonly recognized as representative of black [12] 2650 [13] 1800 [14] 1000 [15] 2173 [16] 1695 [16] ATI Annual Congress (ATI 2022) Journal of Physics: Conference Series 2385 (2022) 012134 carbon emission. The polluted dust aerosol model accounts for episodes of dust mixed with biomass burning smoke typical of African and Asian regions.…”

Characterization of soot produced by the mini inverted soot generator with an atmospheric simulation chamber

“…In this context, soot generators are employed as stable sources of soot particles. So far, soot generators have been employed for studies on optical properties (Zhang et al, 2008;Cross et al, 2010;Mamakos et al, 2013;Utry et al, 2014b;Bescond et al, 2016), instrument calibration (Onasch et al, 2012;Durdina et al, 2016), and several other purposes, such as studies on the atmospheric processing of soot particles and the characterization of uncoated/coated and fresh/denuded of soot particles (Pagels et al, 2009;Henning et al, 2012;Hu et al, 2021). The inverted-flame burner (Stipe et al, 2005) is often considered as an ideal soot source (Moallemi et al, 2019 and references therein), due to its capacity to generate almost pure EC particles and the stability of the flame and of its exhaust (Stipe et al, 2005).…”

“…ASC experiments are the best compromise between laboratory and field experiments, since they simulate quasi-real situations but without the uncertainties and variability typical of field measurements. Recent examples of ASC applications concern the investigation of the optical properties of mineral dust (Caponi et al, 2017) and wood-burning exhausts (Kumar et al, 2018;Hu et al, 2021).…”