Cloud Condensation Nuclei properties of South Asian outflow over the northern Indian Ocean during winter

Abstract

<p><strong>Abstract.</strong> Extensive measurements of cloud condensation nuclei (CCN) and condensation nuclei (CN) concentrations in the South Asian outflow to the northern Indian Ocean were carried out on board an instrumented research vessel, as part of the Integrated Campaign for Aerosols, gases and Radiation Budget (ICARB) during winter season (January–February 2018). Measurements include a north-south transect across the South Asian plume over the northern Indian Ocean and east–west transect over the equatorial Indian Ocean (~ 2° S), which is far away from the continental sources. South Asian outflow over the northern Indian Ocean is characterized by the high values of CCN number concentration (~ 5000 cm<sup>−3</sup>), low CCN activation efficiency (~ 25 %) and steep increase in CCN concentration with an increase in supersaturation. In contrast, low CCN concentration (~ 1000 cm<sup>−3</sup>) with flat supersaturation spectra was found over the equatorial Indian Ocean. The CCN properties exhibited significant dependence on the geometric mean diameter (GMD) of the aerosol number size distribution and CCN activation efficiency decreased to low values (< 20 %) at the times of new particle formation events over near-coastal and remote oceanic regions. The analysis of the activation fractions for the <q>similar</q> aerosol size distributions over the northern Indian Ocean indicated the primary role of aerosol number size distribution, followed by the chemical composition on CCN activation efficiency. The dependence of CCN properties and activation fraction on size segregated aerosol number concentration, especially during the ultrafine particle events, is investigated in detail for the first time over the region.</p>

Variations in N<sub>cn</sub> and N<sub>ccn</sub> over China marginal seas related to marine traffic emissions, new particle formation and aerosol aging

“…×10 3 ) by Li et al (2015) in the continental atmosphere of Qingdao in May 2013, however, the increment of Nccn with the increase of SS was much weaker in our study, resulting in on average of 36% smaller in Nccn under SS of 0.4% to 1.0% compared to Li et al (2015). Consistently, the sensitivity differences of Nccn to SS between relatively clean (i.e., Ncn (8.1 ± 4.4×10 3 ) in this study) and polluted (with Ncn of 1.8 ± 1.4×10 4 cm -3 ) environment in Li et al (2015) is also reported by Nair et al (2019) In addition, Nccn at SS from 0.1% to 1.0% during the period with high NH4 + (17:00 LT on DOY 114 to 10:00 LT on DOY 120) is statistically significant higher (P<0.01) in comparison to the poor NH4 + period (11:00 LT on DOY 120 to 7:00LT on DOY 136; Fig. 3b).…”

Chemical Characteristics, Size Distributions, Molecular Composition, and Brown Carbon in South Asian Outflow to the Indian Ocean

“…The cruise track and sampling locations are shown in Figure 1. Detailed descriptions about the cruise track and prevention of possible contamination from the ship exhaust are available elsewhere (Nair et al., 2020). Calm and low winds (<5 ms −1 ) were noted during the sampling period.…”

“…During this season, north-easterly winds are persistent and convection over the continental source regions is concealed by largescale subsidence, thus restraining the vertical dispersion of pollutants. The studies as part of ICARB-2018 documented the CCN activity properties of SA outflow over the IO (Nair et al, 2020), bulk chemical composition , tropospheric carbon monoxide (CO) distribution (Girach et al, 2020), near-surface aerosol mass concentrations and its size…”

“…During this season, north‐easterly winds are persistent and convection over the continental source regions is concealed by large‐scale subsidence, thus restraining the vertical dispersion of pollutants. The studies as part of ICARB‐2018 documented the CCN activity properties of SA outflow over the IO (Nair et al., 2020), bulk chemical composition (Aswini et al., 2020), tropospheric carbon monoxide (CO) distribution (Girach et al., 2020), near‐surface aerosol mass concentrations and its size distributions along with BC mass concentration (Gogoi et al., 2018), and aerosol number size distribution focusing new particle formation events (Kompalli, Nair, et al., 2020). Nevertheless, there are no studies on size‐resolved chemical composition and molecular‐level analysis of OAs over the IO.…”

Observations of particle number size distributions and new particle formation in six Indian locations

“…In India, several intensive field campaigns such as the Indian Ocean Experiment (INDOEX; Ramanathan et al, 2001), Indian Space Research Organization (ISRO)-Geosphere-Biosphere Programme (GBP)-Land campaign II (Tripathi et al, 2006;Tare et al, 2006), and Integrated Campaign for Aerosols, gases, and Radiation Budget (ICARB; Moorthy et al, 2008;Nair et al, 2020;Kompalli et al, 2020) have measured sub-micron particle number size distributions (PNSDs). There are also short-and long-term field observations of sub-micron PNSDs in a variety of diverse locations in India (Hyvärinen et al, 2010;Kanawade et al, 2014a;Shika et al, 2020;Tripathi et al, 1988;Komppula et al, 2009;Singh et al, 2004;Moorthy et al, 2011;Babu et al, 2016;Kompalli et al, 2018).…”