Size-resolved measurement of the mixing state of soot in the megacity Beijing, China: diurnal cycle, aging and parameterization

Cheng, Yafang; Su, Hang; Rose, D.; Gunthe, Sachin S.; Berghof, M.; Wehner, B.; Achtert, Peggy; Nowak, Andreas; Takegawa, N.; Kondo, Yutaka; Shiraiwa, Manabu; Gong, Yongquan; Shao, Min; Hu, Min; Zhu, Tong; Zhang, Y. H.; Carmichael, G. R.; Wiedensohler, Alfred; Andreae, Meinrat O.; Pöschl, Ulrich

doi:10.5194/acp-12-4477-2012

Cited by 79 publications

(67 citation statements)

References 65 publications

(94 reference statements)

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“…Smaller values of the k E ab / k PM 1 ratio indicated that the change of calculated E ab was not sensitive to variations in PM 1 concentrations. The growth rate of E ab (for BC samples with k E ab > 0: 0.1-7.3 % h −1 ) observed at our study was consistent with the BC aging rate (0.2-7.8 % h −1 ) in previous studies Shiraiwa et al, 2007;Cheng et al, 2012).…”

Section: Light Absorption Of Bc-containing Particles During the Campasupporting

confidence: 92%

Amplification of light absorption of black carbon associated with air pollution

Zhang

Cheng

et al. 2018

Atmos. Chem. Phys.

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Abstract. The impacts of black carbon (BC) aerosols on air quality, boundary layer dynamics and climate depend not only on the BC mass concentration but also on the light absorption capability of BC. It is well known that the light absorption capability of BC depends on the amount of coating materials (namely other species that condense and coagulate on BC). However, the difference of light absorption capability of ambient BC-containing particles under different air pollution conditions (e.g., clean and polluted conditions) remains unclear due to the complex aging process of BC in the atmosphere. In this work, we investigated the evolution of light absorption capability for BC-containing particles with changing pollution levels in urban Beijing, China. During the campaign period (17 to 30 November 2014), with an increase in PM 1 concentration from ∼ 10 to ∼ 230 µg m −3 , we found that the mass-weighted averages of the aging degree and theoretical light absorption capability of BC-containing particles increased by ∼ 33 % and ∼ 18 %, respectively, indicating stronger light absorption capability of BC-containing particles under more polluted conditions due to more coating materials on the BC surface. By using an effective emission intensity (EEI) model, we further found that aging during regional transport plays an important role in the difference in the light absorption capability of BC-containing particles under different air pollution levels. During the pollution episode, ∼ 63 % of the BC over Beijing originated from regional sources outside of Beijing. These regionally sourced BC-containing particles were characterized by more coating materials on BC surfaces due to more coating precursors within more polluted air, which contributed ∼ 75 % of the increase in theoretical light absorption capability of BC observed in Beijing during the polluted period (PM 1 of ∼ 230 µg m −3 ) compared to that in the clean period (PM 1 of ∼ 10 µg m −3 ). Due to the increase in theoretical light absorption capability of BC associated with air pollution, the direct radiative forcing of BC was estimated to be increased by ∼ 18 % based on a simple radiation transfer model. Our work identified an amplification of theoretical light absorption and direct radiative forcing under a more polluted air environment due to more coating materials on BC. The air pollution control measures may, however, break the amplification effect by reducing emissions of both BC and the coating precursors and achieve co-benefits of both air quality and climate.

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Section: Light Absorption Of Bc-containing Particles During the Campasupporting

confidence: 92%

Amplification of light absorption of black carbon associated with air pollution

Zhang

Cheng

et al. 2018

Atmos. Chem. Phys.

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“…At night, aging by condensation is slow, so coagulation is the dominant aging mechanism. This diurnal variation in aging rates is consistent with observations (Rose et al, 2011;Cheng et al, 2012). We define particles that "age" over a specific time period as those that transition from CCN-inactive to CCN-active, that is, the particles that move from below a supersaturation line (CCN-inactive) at time t to above supersaturation line (CCN-active) at t + t.…”

Section: κ-Köhler Model For Computing Ccn Activitysupporting

confidence: 64%

Explaining variance in black carbon's aging timescale

2015

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Abstract. The size and composition of particles containing black carbon (BC) are modified soon after emission by condensation of semivolatile substances and coagulation with other particles, known collectively as "aging" processes. Although this change in particle properties is widely recognized, the timescale for transformation is not well constrained. In this work, we simulated aerosol aging with the particle-resolved model PartMC-MOSAIC (Particle Monte Carlo -Model for Simulating Aerosol Interactions and Chemistry) and extracted aging timescales based on changes in particle cloud condensation nuclei (CCN). We simulated nearly 300 scenarios and, through a regression analysis, identified the key parameters driving the value of the aging timescale. We show that BC's aging timescale spans from hours to weeks, depending on the local environmental conditions and the characteristics of the fresh BCcontaining particles. Although the simulations presented in this study included many processes and particle interactions, we show that 80 % of the variance in the aging timescale is explained by only a few key parameters. The condensation aging timescale decreased with the flux of condensing aerosol and was shortest for the largest fresh particles, while the coagulation aging timescale decreased with the total number concentration of large (D > 100 nm), CCN-active particles and was shortest for the smallest fresh particles. Therefore, both condensation and coagulation play important roles in aging, and their relative impact depends on the particle size range.

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“…BC particles also become increasingly hydrophilic after emission, through condensation of sulfate, nitrate and secondary organic aerosol (SOA) onto the particle surfaces, referred to as particle "ageing" (e.g. Shiraiwa et al, 2007;Moffet and Prather, 2009;Wang et al, 2010;Cheng et al, 2012). The degree of mixing, or "mixing state", of atmospheric BC particles with these hydrophilic aerosol components not only influences their CCN activity (e.g.…”

Section: Introductionmentioning

confidence: 99%

The mass and number size distributions of black carbon aerosol over Europe

et al. 2013

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Abstract. Black carbon-containing aerosol particles play an important role in the direct and indirect radiative forcing of climate. However, the magnitude and sign of the net radiative effect is strongly dependent on the physical properties of the black carbon (BC) component of the particles, such as mass concentration, number size distribution and mixing state. Here we use a global aerosol model combined with aircraft measurements of BC particle number and size from the Single Particle Soot Photometer (SP2) to assess the realism with which these physical properties are predicted by global models. The comparison reveals a substantial mismatch between the measured and modelled BC size distribution over the size range of the SP2 instrument (90–400 nm BC diameter). The model predicts BC particle number concentrations a factor ~3.5–5.7 higher than measured and a mode diameter that is ~40–65 nm smaller than observed. More than ~90% of the model particles with dry diameters &gtrsim;260 nm contain BC, while the observations suggest only 14% on average. These model–observation biases in the BC properties are considerably greater than for the overall particle distribution, suggesting that the discrepancy is associated with model assumptions about the size and mixing state of the emitted carbonaceous particles. We expect the discrepancy in BC size distribution to be common among most global aerosol models, with implications for model estimates of absorption optical depth and direct radiative forcing.

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Size-resolved measurement of the mixing state of soot in the megacity Beijing, China: diurnal cycle, aging and parameterization

Cited by 79 publications

References 65 publications

Amplification of light absorption of black carbon associated with air pollution

Amplification of light absorption of black carbon associated with air pollution

Explaining variance in black carbon's aging timescale

The mass and number size distributions of black carbon aerosol over Europe

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