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

Mukesh Rai,Siva Praveen Puppala,Arnico K Panday,Rijan Bhakta Kayastha,Chaman Gul,Parth Sarathi Mahapatra

doi:10.4209/aaqr.2018.09.0342

Abstract

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 Angstrom 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.

Highlights

Atmospheric aerosols are tiny particles suspended in the earth’s atmosphere
The present study estimated the aerosol radiative forcing near Yala Glacier region from October 2016 till May 2017 using in situ black carbon (BC) mass concentrations, satellite data sets, and model simulations
The mean BC mass concentration at the study site was observed to be 481.5 ± 273.7 ng m–3, with the highest concentration observed in the pre-monsoon season

Summary

Introduction

Atmospheric aerosols are tiny particles suspended in the earth’s atmosphere. Directly, aerosols absorb and scatter the incoming solar and the outgoing terrestrial radiation, thereby affecting the earth’s energy budget. The glacier melt in the Himalayas is accelerated due to surface darkening and atmospheric warming In this regard, a study by Xu et al (2016) indicates that at Tibetan Plateau altitudes, CO2 and BC concentrations exerted a warming of 1.7°C and 1.3°C respectively. Considering the above issues, to date, the BC mass concentration has been measured at only a few high-altitude locations in the Himalayan region These locations include Hanle (4520 masl) and Meerak (4300 masl) in India, the Nepal Climate Observatory-Pyramid (NCO-P; 5079 masl) in Nepal, and the Qomolangma Atmospheric and Environmental Observation Research Station (QOMS; 4,276 masl) in China (Marcq et al, 2010; Babu et al, 2011; Zhao et al, 2012; Cong et al, 2015; Wang et al, 2016).

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Conclusion