Particle number size distributions and new particle formation events over the northern Indian Ocean during continental outflow. (1st October 2020)

• Record Type: Journal Article
• Authors: Kompalli, Sobhan Kumar; Nair, Vijayakumar S.; Jayachandran, V.; Gogoi, Mukunda M.; Babu, S. Suresh
• Is Part Of: Atmospheric environment. Volume 238(2020)
• Publication Date: 2020-10-01
• Subjects: New particle formation -- Marine aerosols -- Indian Ocean aerosols -- ICARB -- Particle number size distributions -- South Asian outflow; Air -- Pollution -- Periodicals; Air -- Pollution -- Meteorological aspects -- Periodicals; 551.51
• DOI: 10.1016/j.atmosenv.2020.117719
• Languages: English
• ISSNs: 1352-2310

Abstract

Abstract: The particle number concentrations, size distributions, and new particle formation (NPF) events were investigated in the South Asian outflow over the southeastern Arabian Sea (SEAS), the northern (NIO) and equatorial Indian Ocean (EIO) during the winter of 2018 based on the extensive measurements of particle number size distributions in size range 10–414 nm in the marine atmospheric boundary layer (MABL) as part of the Integrated Campaign for Aerosols, gases, and Radiation Budget (ICARB - 2018) experiment. The total particle concentrations were higher (as high as 10 6 cm −3 ; mean ~8857 ± 13425 cm −3 ) over the SEAS in the proximity to the continental outflow, which gradually decreased to reach the lowest values over the remote EIO (~3206 ± 4406 cm −3 ). Several NPF events with conspicuous bimodal size distributions and 3–10 times enhancement in nucleation particle (<25 nm) concentrations were noticed. NPF occurred more frequently over the remote oceanic EIO, but more intensely over the regions in the continental proximity demonstrating the varying precursor vapor source strengths. The vertical winds and dew point temperatures revealed the entrainment of free tropospheric air masses to the MABL enabling the downward transport of the nucleation mode particles, possibly formed in the free tropospheric altitudes, to the MABL which advected southward along with the primary outflow aerosols due to north-easterly surface winds. Collocated submicron aerosol chemical composition measurements revealed that most of the events were associated with enhanced particulate organics mass concentrations. Further investigations suggested that volatile organic compounds were possibly involved in the NPF pathways whose sources were advected polluted plumes in the outflow regions and marine emissions over the remote ocean. The newly formed particles grew to larger sizes with a median growth rate of 12 nm h −1, which suggest that these NPF events can contribute considerably to the regional aerosol loading, and potentially affect regional climate. Highlights: Multimode PNSDs over the northern Indian Ocean. New particle formation (NPF) events in coastal and remote ocean. NPF events associated with subsidence of free-tropospheric air masses to the MABL. Enhanced organics mass concentrations during the NPF events.