24 Mar 2021

24 Mar 2021

Review status: this preprint is currently under review for the journal ACP.

Physical and chemical constraints on transformation and mass-increase of fine aerosols in northeast Asia

Saehee Lim1, Meehye Lee1, Paolo Laj2,3, Sang-Woo Kim4, Kang-Ho Ahn5, Junsoo Gil1, Xiaona Shang1,6, Marco Zanatta7, and Kyeong-Sik Kang8 Saehee Lim et al.
  • 1Dept. of Earth and Environmental Sciences, Korea University, Seoul, 02841, South Korea
  • 2Univ. Grenoble-Alpes, CNRS, IRD, Grenoble INP, Institute for Geosciences and Environmental Research (IGE), Grenoble, 38000, France
  • 3Dept. of Physics, University of Helsinki, Helsinki, 00014, Finland
  • 4School of Earth and Environmental Sciences, Seoul National University, Seoul, 08826, South Korea
  • 5Dept. of Mechanical Engineering, Hanyang University, Ansan-si, Gyeonggi-do, 15588, South Korea
  • 6Shanghai Key Laboratory of Atmospheric Particle Pollution and Prevention (LAP3), Department of f Environmental Science & Engineering, Institute of Atmospheric Sciences, Fudan University, Shanghai, 200438, China
  • 7Alfred Wegener Institute (AWI), Helmholtz Center for Polar and Marine Research, Bremerhaven, Germany
  • 8Jeju Air Quality Research Center, National Institute of Environmental Research, Aewol, Jeju, 63040, South Korea

Abstract. Over the past few decades, northeast Asia has suffered from the extreme levels of PM2.5 (particulate matter with an aerodynamic diameter smaller than 2.5 μm). Despite extensive efforts and the scientific advances in understanding PM2.5 pollution, the fundamental mechanisms responsible for the occurrence of high PM2.5 concentrations have not been comprehensively understood. In this study, we investigated the physical and chemical drivers for the formation and transformation of atmospheric particles using a four-year dataset of nanoparticle number size distributions, PM2.5 chemical composition, gaseous precursors, and meteorological variables in northeast Asia outflows. The empirical orthogonal function (EOF) analyses of size-separated particle numbers extracted two modes representing a burst of nanoparticles (EOF1) and an increase in PM2.5 mass (EOF2) associated with persistent anticyclone and synoptic-scale stagnation, respectively. The vertical structure of the particles demonstrated that the synoptic conditions also affected the daily evolution of boundary layer, promoting either the formation of nanoparticles through deep mixing or conversion into accumulation-mode particles in shallow mixed layers. In the haze-development episode equivalent to EOF2 during the KORUS-AQ (KORea-US Air Quality) campaign, the PM2.5 mass reached 63 μg m−3 with the highest contribution from inorganic constituents, which was accompanied by a thick coating of refractory black carbon (rBC) that linearly increased with condensation-mode particles. This observational evidence suggests that the thick coating of rBC resulted from an active conversion of condensable gases into particle-phase on the BC surface, thereby increasing the mass of the accumulation-mode aerosol. Consequently, this result complies with the strategy to reduce black carbon as a way to effectively mitigate haze pollution as well as climate change in northeast Asia.

Saehee Lim et al.

Status: open (extended)

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  • RC1: 'Review of Lim et al.', Anonymous Referee #2, 29 Apr 2021 reply

Saehee Lim et al.


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Short summary
This study identifies the main drivers of the formation and transformation processes of submicron particles and highlights that the thick coating of rBC was a result of active conversion of hygroscopic inorganic salts leading to fine aerosol pollution. Consequently, we suggest BC particles as a key contributor to PM2.5 mass increase, which implies that BC reduction is an effective mitigation against haze pollution as well as climate change in Northeast Asia.