Recently, the Aryabhatta Research Institute of Observational Sciences (ARIES), based in Nainital, conducted a study, revealing that the radiative forcing of aerosols, or the effect of anthropogenic aerosols, is remarkably high over the high altitudes of the western trans-Himalayas. Operated under the Department of Science and Technology (DST), Ministry of Science and Technology, ARIES is an autonomous research institute. The trans-Himalayan Mountain Region, including the Karakoram, Ladakh, Zaskar, and Kailash ranges, which largely fall within Tibet, were the focus of this study.
Understanding Aerosol Radiative Forcing (ARF)
The research analyzed the variability of aerosol optical, physical, and radiative properties from January 2008 to December 2018, focusing on the role of fine and coarse particles in Aerosol Radiative Forcing (ARF) assessment. The ARF values at the top of the atmosphere were notably low over Hanle and Merak, both located in Ladakh and formed part of the Indian Astronomical Observatory (IAO). ARF refers to the impact of anthropogenic aerosols on the radiative fluxes at the top of the atmosphere, the surface, and the absorption of radiation within the atmosphere.
Illuminating Temperature Changes
Data shows that monthly-mean atmospheric radiative forcing of aerosols causes heating rates of 0.04 to 0.13 degrees Celsius per day. In addition, the temperature over the Ladakh region has been increasing by 0.3 to 0.4 degrees Celsius per decade over the last three decades.
Determining Aerosol Optical Depth (AOD)
The study’s observations demonstrated that the Aerosol Optical Depth (AOD) displayed a distinct seasonal variation, with higher values (0.07) in May and lower (0.03) during winter months. AOD measures how airborne particles absorb or reflect light as it travels through the atmosphere.
Examining Angstrom Exponent (AE)
In spring, lower values of the Angstrom Exponent (AE) pointed to a dominance of coarse-mode dust aerosols. The AE is a parameter that explains how the optical thickness of an aerosol usually relies on the wavelength of the light.
Investigating Air Composition
The study showed that both pure and polluted dust exhibited fractions between 16% and 23%, with a low frequency of less than 13% of absorbing aerosols, indicating a weak influence of anthropogenic aerosols and Black Carbon over the trans-Himalayan sites.
Importance of The Study
Atmospheric aerosols significantly influence the regional/global climate system by scattering and absorbing incoming solar radiation and modifying the cloud structure. Light-absorbing carbonaceous aerosols and dust’s transport from the polluted Indo-Gangetic Plain and desert areas over the Himalayas pose a major climatic issue due to their severe effects on atmospheric warming and glacier retreat.
Prior Background and Measurements
Measurements of aerosol optical and microphysical properties started during the last decade at Indian Astronomical Observatory (IAO) based in Hanle and Merak in the trans-Himalayas. In addition, few in-situ measurements of carbonaceous aerosols and ionic species have been performed at Himansh Observatory (Spiti Valley) in the western Himalayas.
Defining Aerosols
Aerosols, either solid or liquid particles suspended in a liquid or gaseous environment, are mainly located in the low atmospheric layers since aerosol sources are on the terrestrial surface. The origin of atmospheric aerosols can be either natural or a result of anthropogenic activities.
The Role and Impact of Aerosols
Aerosols reflect more energy from the sun back to space, affect the atmospheric chemical composition, and reduce visibility. These particles can have significant impacts on air quality and human health, causing damage to the heart and lungs, and serve as nuclei for cloud droplets or ice crystals in ice clouds.
Looking Ahead
Precise measurements of aerosol properties are required to reduce the uncertainties in the impact of different aerosols on radiative forcing, particularly over the oceans and high-altitude remote locations in the Himalayas.
