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The thermal-optical analysis (TOA) of black carbon in particulate matter (PM) collected on filters has been recommended and used for the calibration of mass-concentration instruments. However, filter-based TOA calibrations have substantial practical limitations, requiring high sample flow rates (>10 litres per minute), long sampling times (up to 3 h), and subsequently manual filter processing with long analysis times (>15 min per filter). These limitations are avoided by in situ calibration techniques such as the centrifugal particle mass analyzer (CPMA)–electrometer reference mass system (CERMS). The CERMS is capable of producing and monitoring in situ reference mass concentrations below 1 µg m⁻³ and in real-time (∼1 Hz). Additional advantages of the CERMS are its improved repeatability (1.1%) over TOA (9–11%), and its measurement of a well-defined quantity: total post-CPMA suspended PM mass. In the present work, we demonstrate closure between these two techniques in terms of PM mass concentration for three different soot generators (viz., the Argonaut miniature inverted soot generator, Jing miniCAST, and National Research Council inverted-flame burner) under carefully controlled conditions. We also demonstrate the sensitivity of the CERMS by characterizing the limits of detection of a commercial laser-induced incandescence instrument and a photoacoustic instrument. Our data support the use of the CERMS with well-characterized PM sources to provide reference mass concentrations for the calibration of instruments measuring PM or black-carbon mass concentration.

International audience; The specific surface area of ultrafine particles is an important parameter affecting their physical and chemical properties. For example, the specific surface area of combustion-generated black carbon (BC) particles has been linked to their toxicity and identified to be a more relevant metric to assess their biological response than particle size or mass (Schmid and Stoeger, 2016). Several methods have been developed to measure or determine the specific surface area of aerosol particles, such as the Brunauer-Emmett-Teller (BET) method based on nitrogen adsorption, the diffusion charging (DC) method, scanning Mobility Particle Sizing (SMPS), and the laser-induced incandescence (LII). BET is used as a reference method; however, it is an off-line method and requires a large quantity of sample (several hundreds of milligrams). DC, SMPS, and LII are on-line and faster methods, however, they are indirect methods and rely on various assumptions. Although DC and LII hold a good potential for online determination of the specific surface area of irregular particles, they require further development and evaluation. Recently, it has been demonstrated that the specific surface area of combustion generated black carbon particles can also be determined based on transmission electron microscope (TEM) image analysis; fairly good agreement between the results of BET and TEM was shown in several recent studies (Bau et al., 2010; Bourrous et al., 2018; Ouf et al., 2019). The fairly good agreement between the specific surface areas determined by BET and TEM image analysis of various BC and carbon black (CB) aerosols is an indication that there are negligible internal voids in BC and CB particles. Although TEM image analysis is an off-line method, its main advantage is that it requires only a small amount of sample to be collected on the grid for TEM analysis. Combustion generated BC particles appear as fractal aggregates formed by primary particles that display certain degrees of polydispersity, overlapping, and necking, which in general vary with fuel and flame conditions. Although the specific surface area of BC particles is mainly related to the mean primary particle diameter, other parameters, such as the aggregate size, fractal parameters (pre-factor and fractal dimension), the distribution of primary particles, and the degrees of primary particle overlapping and necking are also relevant. It is important to point out that whereas primary particle overlap reduces both the particle surface area and volume, primary particle necking reduces the particle surface area but increases the particle volume. Figure 1 shows two typical TEM images of flame generated soot particles. Figure 1. Two typical TEM images of flame generated soot particles showing primary particle overlapping, a, and primary particle necking, b (Yon et al., 2015). The effect of primary particle overlapping on the specific surface area of BC particles inferred from TEM image analysis has been investigated recently by Bourrous et al. (2018) and Ouf et al. (2019). However, the potential importance of primary particle necking to BC particle specific surface area determined by TEM image analysis has not been previously investigated. In this study, the TEM images of BC particles produced in laboratory soot generators and from literature were analysed to obtain the primary particle size distribution, primary particle overlapping, and necking. Based on these parameters, the particle specific surface area was inferred, and the results are compared with those obtained from BET or reported previously in the literature. Bau, S., Witschger, O., Gensdarmes, F., Rastoix, O., and Thomas, D. (2010) Powder Technol. 200, 190-201.Bourrous, S., Ribeyre, Q., Lintis, L., Yon, Y., Bau, S., Thomas, D., Vallières, C., and Ouf, F.-X. (2018) J. Aerosol Sci. 126, 122-132. Ouf, F.-X., Bourrous, S., Vallières, C., Yon, J., and Lintis, L. (2019) J. Aerosol Sci. 137, 105436.Schmid, O., and Stoeger, T. (2016) J. Aerosol Sci. 99, 133-143.Yon, J., Bescond, A., Liu, F. (2015) J. Quantitative Spectroscopy & Radiative Transfer 162, 197-206.

In-use exhaust stream CH₄ emissions from two dual fuel marine engines were characterized and strategies for CH₄ reduction were identified and evaluated. For this, a low-cost, portable, wavelength modulation spectroscopy (WMS) system was developed. The performance of the developed WMS sensor was assessed using gas standards and demonstrated on a heavy-duty, diesel pilot ignited, direct-injection natural gas research engine through comparison to a flame ionization detector. The WMS sensor was subsequently used to measure the exhaust-stream CH₄ concentration from two diesel pilot-ignited, port-injected natural gas engines on a coastal vessel while under normal operation. Using cylinder deactivation to reduce the excess air ratio, λ, and vessel operation changes to minimize operation at lower loads, the total CH₄ emission were reduced by up to 33%. The measured, load specific CH₄ emissions were subsequently used to identify an improved vessel operation strategy, with an estimated 56–60% reduction in CH₄ emissions. These results demonstrate the importance of considering the real-world engine operation profile for accurate estimates of the global warming potential, as well as the utility of a WMS sensor for characterizing and mitigating in-use CH₄ emissions.

The evolution of Particulate Matter (PM) emissions from a CFM56-7B aircraft engine in a controlled test cell was investigated in terms of their physical, chemical, and optical properties. Measurements were performed at the engine exit plane (P1), in front of the silencer (P2), and at the stack exit (P3) of the test cell at SR Technics, Zurich, Switzerland. Black carbon (BC) mass was measured using Micro Soot Sensor (MSS), Laser Induced Incandescence (LII), and Photoacoustic Extinctiometer (PAX). Elemental carbon (EC) and organic carbon (OC) analyses were performed using the Sunset Labs EC-OC analyser. Effective density was measured using a Centrifugal Particle Mass Analyzer (CPMA). Particle size distributions were measured with a Scanning Mobility Particle Sizer (SMPS). A nucleation mode was observed at low thrust for measurements at P2 and P3, which was not present at P1. The single scattering albedo (SSA) was determined at P1 and P2 with two PAX monitors (λ = 870 nm), and two Cavity Attenuated Phase Shift SSA monitors (CAPS PMSSA, λ = 660 and 532 nm), both operated at P2. A significant increase in the SSA was observed between P1 and P2 for thrust levels below 30%. The increase in SSA is most likely related to an increase in the light scattering due to condensed volatile material at P2.

The largest contributors to the uncertainty in assessing the anthropogenic contribution in radiative forcing are the direct and indirect effects of aerosol particles on the Earth's radiative budget. Soot particles are of special interest since their properties can change significantly due to aging processes once they are emitted into the atmosphere. Probably the largest obstacle for the investigation of these processes in the laboratory is the long atmospheric lifetime of 1 week, requiring tailored experiments that cover this time span. This work presents results on the ability of two types of soot, obtained using a miniCAST soot generator, to act as cloud condensation nuclei (CCN) after exposure to atmospherically relevant levels of ozone (O3) and humidity. Aging times of up to 12 h were achieved by successful application of the continuous-flow stirred tank reactor (CSTR) concept while allowing for size selection of particles prior to the aging step. Particles of 100 nm diameter and rich in organic carbon (OC) that were initially CCN inactive showed significant CCN activity at supersaturations (SS) down to 0.3 % after 10 h of exposure to 200 ppb of O3. While this process was not affected by different levels of relative humidity in the range of 5 %–75 %, a high sensitivity towards the ambient/reaction temperature was observed. Soot particles with a lower OC content required an approximately 4-fold longer aging duration to show CCN activity at the same SS. Prior to the slow change in the CCN activity, a rapid increase in the particle diameter was detected which occurred within several minutes. This study highlights the applicability of the CSTR approach for the simulation of atmospheric aging processes, as aging durations beyond 12 h can be achieved in comparably small aerosol chamber volumes (, Atmospheric Chemistry and Physics, 19 (24), ISSN:1680-7375, ISSN:1680-7367

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