The COVID-19 lockdown: a unique perspective into heterogeneous impacts of transboundary pollution on snow and ice darkening across the Himalayas

Zhengyang Hou; Yang Li; Liqiang Zhang; Changqing Song; Jintai Lin; Chenghu Zhou; Yuebin Wang; Ying Qu; Xin Yao; Peichao Gao

doi:10.1093/pnasnexus/pgad172

The COVID-19 lockdown: a unique perspective into heterogeneous impacts of transboundary pollution on snow and ice darkening across the Himalayas

PNAS Nexus. 2023 Jun 27;2(6):pgad172. doi: 10.1093/pnasnexus/pgad172. eCollection 2023 Jun.

Authors

Affiliations

¹ Faculty of Geographical Science, Beijing Normal University, Beijing 100875, China.
² Laboratory for Climate and Ocean-Atmosphere Studies, Department of Atmospheric and Oceanic Sciences, School of Physics, Peking University, Beijing 100871, China.
³ State Key Laboratory of Resources and Environment Information System, Institute of Geographical Science and Natural Resources, Chinese Academy of Sciences, Beijing 100101, China.

Abstract

The Tibetan Plateau holds the largest mass of snow and ice outside of the polar regions. The deposition of light-absorbing particles (LAPs) including mineral dust, black carbon and organic carbon and the resulting positive radiative forcing on snow (RFS $_{LAPs}$ ) substantially contributes to glacier retreat. Yet how anthropogenic pollutant emissions affect Himalayan RFS $_{LAPs}$ through transboundary transport is currently not well known. The COVID-19 lockdown, resulting in a dramatic decline in human activities, offers a unique test to understand the transboundary mechanisms of RFS $_{LAPs}$ . This study employs multiple satellite data from the moderate resolution imaging spectroradiometer and ozone monitoring instrument, as well as a coupled atmosphere-chemistry-snow model, to reveal the high spatial heterogeneities in anthropogenic emissions-induced RFS $_{LAPs}$ across the Himalaya during the Indian lockdown in 2020. Our results show that the reduced anthropogenic pollutant emissions during the Indian lockdown were responsible for 71.6% of the reduction in RFS $_{LAPs}$ on the Himalaya in April 2020 compared to the same period in 2019. The contributions of the Indian lockdown-induced human emission reduction to the RFS $_{LAPs}$ decrease in the western, central, and eastern Himalayas were 46.8%, 81.1%, and 110.5%, respectively. The reduced RFS $_{LAPs}$ might have led to 27 Mt reduction in ice and snow melt over the Himalaya in April 2020. Our findings allude to the potential for mitigating rapid glacial threats by reducing anthropogenic pollutant emissions from economic activities.

Keywords: COVID-19 lockdown; Himalayas; heterogeneous impacts; snow and ice darkening; transboundary pollution.