• S SURESH BABU

      Articles written in Journal of Earth System Science

    • Seasonal contrast in the vertical profiles of aerosol number concentrations and size distributions over India: Implications from RAWEX aircraft campaign

      MUKUNDA M GOGOI N B LAKSHMI VIJAYAKUMAR S NAIR SOBHAN KUMAR KOMPALLI K KRISHNA MOORTHY S SURESH BABU

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      Aircraft measurements of the vertical profiles of aerosol total number concentrations and size distributions (in the size range of 0.5–20 lm) were made over seven geographically diverse locations of theIndian mainland during two contrasting seasons, winter (December 2012) and spring (April–May 2013), as a part of the regional aerosol warming experiment (RAWEX). Our observations revealed an increase in the vertical extent of aerosol loading during spring having a significant enhancement in coarse mode aerosols in the lower free-troposphere (FT) over western and central parts of India and the Indo-Gangetic plains (IGP). The particulate depolarisation ratio (PDR) derived from the Cloud Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) over the same region showed the presence of dust (including polluted dust) at higher altitudes in spring. Concurrent and collocated measurements ofaerosol scattering and absorption properties aboard the aircraft revealed that the FT enhancement in coarse mode aerosol loading during spring is associated with a decrease in single scattering albedo and an increase in columnar absorption aerosol optical depth. This confirms that the elevated layers of coarse mode aerosols seen during spring are absorbing in nature, especially over the IGP. The presence of such coarse-mode absorbing aerosols plays a crucial role in governing the radiation balance over the IGP in spring through the diabatic heating of the upper atmosphere.

    • Ozone chemistry and dynamics at a tropical coastal site impacted by the COVID-19 lockdown

      IMRAN A GIRACH NARENDRA OJHA S SURESH BABU

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      The nationwide lockdown in India to curb the spread of Coronavirus disease 2019 (COVID-19) led to colossal reduction in anthropogenic emissions. Here, we investigated the impact of lockdown on surface ozone (O$_{3}$) and nitrogen dioxide (NO$_{2}$) over a tropical coastal station – Thumba, Thiruvananthapuram (8.5$^{\circ}$N, 76.9$^{\circ}$E). Daytime as well as night-time NO$_{2}$ showed reduction by 0.8 (40%) and 2.3 (35%) ppbv, respectively during the lockdown period of 25–30 March 2020 as compared with the same period of previous 3 years. Unlike many urban locations, daytime surface O$_{3}$ is found to be dramatically reduced by 15 ppbv (36%) with O$_{3}$ production rate being lower by a factor of 3 during the lockdown. Interestingly, a feature of O$_{3}$-hump during the onset of land breeze typically observed during 1997–1998 has reappeared with magnitude of 5–10 ppbv. A photochemical box model, capturing this feature, revealed that significant O$_{3}$ sustained till onset of land breeze over the land due to weaker titration with NO$_{x}$ during lockdown. It is suggested that the transport of this O$_{3}$ rich air with onset of land breeze led to the observed hump. Our measurements unravel a remarkable impact of the COVID-19 lockdown on the chemistry and dynamics of O3 over this tropical coastal environment.

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