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Aerosol Radiative Forcing Estimation over a Remote High-altitude Location (~4900 masl) near Yala Glacier, Nepal

Category: Optical/Radiative Properties and Remote Sensing

Volume: 19 | Issue: 8 | Pages: 1872-1891
DOI: 10.4209/aaqr.2018.09.0342
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Mukesh Rai1,2, Parth Sarathi Mahapatra2, Chaman Gul2,3,4, Rijan Bhakta Kayastha1, Arnico K. Panday2, Siva Praveen Puppala 2

  • 1 Department of Environmental Science and Engineering, Kathmandu University, Dhulikhel 42500, Nepal
  • 2 International Centre for Integrated Mountain Development (ICIMOD), Kathmandu 44700, Nepal
  • 3 State Key Laboratory of Cryosphere Science, Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences, Gansu 73000, China
  • 4 University of Chinese Academy of Sciences, Beijing 100049, China

Highlights

  • Pre-monsoon BC mass concentration maxima is attributed to long-range transport.
  • Aerosol optical properties indicate dominance of fine mode and scattering aerosols.
  • High ARF in the pre-monsoon was attributed to increased aerosol load and snow cover.
  • Heating rates were observed to be highest in the pre-monsoon season.

Abstract

In the present study, we estimated the aerosol radiative forcing and heating rates near Yala Glacier, Nepal (28.21°N, 85.61°E; 4900 masl), using in situ black carbon (BC) mass concentration measurements, satellite data sets, and model simulations. The real-time ambient BC mass concentration was continuously measured using an Aethalometer (AE-33) from October 2016 to May 2017. The Optical Properties of Aerosols and Clouds (OPAC) model was used to simulate the aerosol optical properties in conjunction with the in situ measurements and satellite data sets. Outputs from OPAC and the satellite data sets were used as inputs for the Santa Barbara Discrete Ordinate Radiative Transfer Atmospheric Radiative Transfer (SBDART) model to estimate the radiative forcing. The in situ measurements showed that the BC mass concentration peaked during the pre-monsoon season (707.9 ± 541.8 ng m–3), which was corroborated by the higher aerosol optical depth (AOD) values during this season (0.058 ± 0.002). The diurnal cycle of the BC mass concentration exhibited a night-time low and afternoon high, which were influenced by the boundary layer dynamics and valley wind flow pattern. The Concentration Weighted Trajectory (CWT) analysis indicated diverse source regions, including northern Asia, the Indo-Gangetic Plain (IGP), and parts of Nepal and Bangladesh. The Moderate Resolution Imaging Spectroradiometer (MODIS)-derived AOD and Ångström exponent (AE), and the OPAC-simulated single-scattering albedo (SSA) and asymmetry parameter (AP) over the study site were estimated to be 0.048 ± 0.009 and 1.32 ± 0.01, and 0.938 ± 0.019 and 0.710 ± 0.042, respectively, during the study period. The mean radiative forcing during the study period for the top of the atmosphere, surface and atmosphere were 3.4, –0.5 and 3.9 W m–2, respectively. Higher atmospheric forcing was observed in the pre-monsoon season, leading to changes in the heating rates.

Keywords

Black carbon Heating rates Himalayas OPAC SBDART


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