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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

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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 estimate 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 Cloud (OPAC) model was used to simulate the aerosol optical properties in conjunction with in situ measurements and satellite data sets. Outputs from OPAC and satellite data sets were used as inputs for the Santa Barbara DISORT (Discrete Ordinate Radiative Transfer) Atmospheric Radiative Transfer (SBDART) model to estimate radiative forcing. The BC mass concentration measurements depicted a pre-monsoon high (707.9 ± 541.8 ng m-3) during the study period, which was also supported by a higher aerosol optical depth (AOD) during the season (0.058 ± 0.002). The diurnal cycle of BC mass concentration depicts night time low and afternoon high which were influenced by the boundary layer dynamics and valley wind flow pattern. The CWT analysis indicates a diversity of source regions including Northern part of Asia, Indo-Gangetic Plains, parts of Nepal and Bangladesh. The MODIS (or Moderate Resolution Imaging Spectroradiometer) derived AOD and AE and the OPAC-simulated SSA and AP over the study site were estimated to be 0.048 ± 0.009, 1.32 ± 0.01, 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 atmosphere, surface and atmosphere were found to be 3.4, -0.5 and 3.9 Wm-2 respectively. Higher atmospheric forcing was observed in the pre-monsoon season, leading to subsequent changes in heating rates.

Keywords

Black carbon Heating rates Himalayas OPAC SBDART


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