Submicrometer Particles Are in the Liquid State during Heavy Haze Episodes in the Urban Atmosphere of Beijing, China

Liu, Yuechen; Wu, Zhijun; Wang, Yu; Xiao, Yao; Gu, Fangting; Zheng, Jie; Tan, Tianyi; Shang, Dongjie; Wu, Yusheng; Zeng, Limin; Hu, Min; Bateman, Adam P.; Martin, Scot T.

doi:10.1021/acs.estlett.7b00352

Cited by 161 publications

(176 citation statements)

References 39 publications

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“…In this study we assume that the bulk diffusivity within organic particles is independent of particle mixing state and morphology. Chamber experiments have demonstrated that evaporation of organic aerosol may be hindered if it is coated with organic aerosol from a different precursor (Loza et al, 2013;Boyd et al, 2017). Moreover, the phase separation has been observed in organic particles mixed with inorganic salts (You et al, 2014) and even without inorganic salts (Pöhlker et al, 2012;Riedel et al, 2016).…”

Section: Discussionmentioning

confidence: 99%

Timescales of secondary organic aerosols to reach equilibrium at various temperatures and relative humidities

Liu

Shiraiwa

2019

Atmos. Chem. Phys.

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Secondary organic aerosols (SOA) account for a substantial fraction of air particulate matter, and SOA formation is often modeled assuming rapid establishment of gas-particle equilibrium. Here, we estimate the characteristic timescale for SOA to achieve gas-particle equilibrium under a wide range of temperatures and relative humidities using a state-of-the-art kinetic flux model. Equilibration timescales were calculated by varying particle phase state, size, mass loadings, and volatility of organic compounds in open and closed systems. Model simulations suggest that the equilibration timescale for semi-volatile compounds is on the order of seconds or minutes for most conditions in the planetary boundary layer, but it can be longer than 1 h if particles adopt glassy or amorphous solid states with high glass transition temperatures at low relative humidity. In the free troposphere with lower temperatures, it can be longer than hours or days, even at moderate or relatively high relative humidities due to kinetic limitations of bulk diffusion in highly viscous particles. The timescale of partitioning of low-volatile compounds into highly viscous particles is shorter compared to semi-volatile compounds in the closed system, as it is largely determined by condensation sink due to very slow re-evaporation with relatively quick establishment of local equilibrium between the gas phase and the near-surface bulk. The dependence of equilibration timescales on both volatility and bulk diffusivity provides critical insights into thermodynamic or kinetic treatments of SOA partitioning for accurate predictions of gas-and particle-phase concentrations of semi-volatile compounds in regional and global chemical transport models.

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Section: Discussionmentioning

confidence: 99%

Timescales of secondary organic aerosols to reach equilibrium at various temperatures and relative humidities

Liu

Shiraiwa

2019

Atmos. Chem. Phys.

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“…Such variations are overall consistent with our previous results in winter of 2011-2012 . A recent study found a clear transition of particle phase state from solid/semisolid to liquid at RH = 40-60% (Liu et al, 2017), which might also facilitate the rapid increases in this RH range. In comparison, the variations of aerosol species are relatively small at high RH levels (60-80%), and the concentrations are consistently high in both winters.…”

Section: Chemically Resolved Pm Pollutionmentioning

confidence: 99%

Changes in Aerosol Chemistry From 2014 to 2016 in Winter in Beijing: Insights From High‐Resolution Aerosol Mass Spectrometry

et al. 2019

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Air quality has been continuously improved in recent years in Beijing, yet severe haze episodes still frequently occur in winter. Here we deployed an Aerodyne high‐resolution aerosol mass spectrometer in two winter seasons during the same period to investigate the changes in aerosol chemistry from 2014 to 2016 in Beijing. Compared to 2014, submicron aerosol (PM1) species showed ubiquitous increases in mass concentrations by 10–130% in winter 2016, of which nitrate showed the largest increase among all aerosol species leading to a much higher NO3/SO4 ratio in 2016 (1.36 ± 0.90) than 2014 (0.72 ± 0.59). This result highlights an increasing role of nitrate in particulate matter pollution in recent years in Beijing. Aerosol composition and size distributions also changed significantly. Secondary inorganic species showed elevated contributions by ~10% in winter 2016 associated with corresponding decreases in organic aerosol (OA). Positive matrix factorization of OA illustrated the significant changes in both primary emissions and secondary production. While cooking OA decreased substantially from 25% in 2014 to 15% in 2016, the contribution of biomass burning OA slightly increased instead. Although secondary OA contributed similarly to OA in the two winters (49% vs. 53%), we observed ubiquitous increases (~50%) in photochemically related oxygenated OA and oxidized primary OA, and oxygen‐to‐carbon ratios of OA, indicating the enhanced photochemical production in winter 2016. Aqueous‐phase production of secondary OA however was relatively similar in the two winters. Further analysis demonstrated that the changes in aerosol and OA composition varied differently across different pollution and relative humidity levels.

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“…Aerosol liquid water (ALW) is a ubiquitous component of ambient aerosol and exerts great influences on aerosol physical and chemical properties, especially in regions with high relative humidity (RH) (Cheng et al, , 2008Covert et al, 1972;Ervens et al, 2014;Nguyen et al, 2016;Pilinis et al, 1989;Wu et al, 2018;Zheng et al, 2015). From the perspective of aerosol physical processes, ALW influences particle lifetime, optical properties, radiative forcing, and the ability of particles to deposit in the humid human respiratory tract (Andreae and Rosenfeld, 2008;Cheng et al, 2008;Covert et al, 1972;Löndahl et al, 2008). ALW also promotes partitioning of some of the inorganic gases and water-soluble organic gases to the condensed phase, thus directly increasing aerosol mass loadings (Asa-Awuku et al, 2010;Parikh et al, 2011).…”

Section: Introductionmentioning

confidence: 99%

“…(1) aerosol mass loadings increase significantly, (2) particle phase changes from solid/semisolid to liquid phase (Liu et al, 2017), (3) both sulfur and nitrogen oxidation ratios increase Sun et al, 2013;Zheng et al, 2015), (4) water-soluble inorganics increase faster than organics Quan et al, 2015;Sun et al, 2013;Zheng et al, 2015). RH affects secondary species via heterogeneous uptake or aqueous processes.…”

Section: Introductionmentioning

confidence: 99%

“…Formation of SIA and SOA is thus suggested to be dominated by heterogeneous uptake or aqueous processes (Xu et al, 2017), which are largely dependent on ALW. Based on ALW measurements, previous studies have proposed positive feedback loops in which elevated RH increases particle concentration and particle inorganic fraction; increased particle concentration and inorganic fraction in turn increase the water uptake Liu et al, 2017;Wu et al, 2018). However, whether or how elevated ALW affects the evolution of SOA during haze episodes remains less understood than for SIA because of the complexity of SOA species.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Ac1

Li¹

2019

Preprint

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Aerosol liquid water (ALW) is ubiquitous in ambient aerosol and plays an important role in the formation of both aerosol organics and inorganics. To investigate the interactions between ALW and aerosol organics during haze formation and evolution, ALW was modelled based on longterm measurement of submicron aerosol composition in different seasons in Beijing. ALW contributed by aerosol inorganics (ALW inorg ) was modelled by ISORROPIA II, and ALW contributed by organics (ALW org ) was estimated with κ-Köhler theory, where the real-time hygroscopicity parameter of the organics (κ org ) was calculated from the real-time organic oxygen-to-carbon ratio (O/C). Overall particle hygroscopicity (κ total ) was computed by weighting component hygroscopicity parameters based on their volume fractions in the mixture. We found that ALW org , which is often neglected in traditional ALW modelling, contributes a significant fraction (18 %-32 %) to the total ALW in Beijing. The ALW org fraction is largest on the cleanest days when both the organic fraction and κ org are relatively high. The large variation in O/C, from 0.2 to 1.3, indicates the wide variety of organic components. This emphasizes the necessity of using real-time κ org , instead of fixed κ org , to calculate ALW org in Beijing. The significant variation in κ org (calculated from O/C), together with highly variable organic or inorganic volume fractions, leads to a wide range of κ total (between 0.20 and 0.45), which has a great impact on water uptake. The variation in organic O/C, or derived κ org , was found to be influenced by temperature (T ), ALW, and aerosol mass concentrations, among which T and ALW both have promoting effects on O/C. During high-ALW haze episodes, although the organic fraction decreases rapidly, O/C and derived κ org increase with the increase in ALW, suggesting the formation of more soluble organics via heterogeneous uptake or aqueous processes. A positive feedback loop is thus formed: during high-ALW episodes, increasing κ org , together with decreasing particle organic fraction (or increasing particle inorganic fraction), increases κ total , and thus further promotes the ability of particles to uptake water.Published by Copernicus Publications on behalf of the European Geosciences Union.

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Submicrometer Particles Are in the Liquid State during Heavy Haze Episodes in the Urban Atmosphere of Beijing, China

Cited by 161 publications

References 39 publications

Timescales of secondary organic aerosols to reach equilibrium at various temperatures and relative humidities

Timescales of secondary organic aerosols to reach equilibrium at various temperatures and relative humidities

Changes in Aerosol Chemistry From 2014 to 2016 in Winter in Beijing: Insights From High‐Resolution Aerosol Mass Spectrometry

Ac1

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