Large Aerosols Play Unexpected Role in Ganges Valley

ARM study reveals surprising amount of light absorption by large aerosol particles.

Image courtesy of the Atmospheric Radiation Measurement (ARM) program via a Creative Commons license.
During a 10-month ARM experiment in India’s Ganges Valley, instruments including a Doppler lidar (shown here) collected measurements of various atmospheric dynamics, cloud properties, and radiative transfer. The data have revealed that large aerosols in this region absorb a greater amount of light than expected.

The Science

Aerosol particles in the atmosphere may absorb solar radiation, resulting in additional heating in the atmospheric column, which affects Earth’s radiative balance. Each aerosol type has distinctive light-absorbing characteristics related to its physical and chemical properties. Observations indicate that light absorption by these super-micron-sized particles is nearly 30% greater than that of the smaller particles.

The Impact

In this study, Department of Energy scientists used observations and radiative transfer calculations based on data from the Atmospheric Radiation Measurement (ARM) Mobile Facility deployment to the Ganges Valley. Their research indicates that large absorbing particles could be an important component of the regional-scale atmospheric energy balance in developing countries and thus should be considered in global and regional climate models.


Global climate models cannot resolve the details of individual aerosol particles, so they use broad assumptions about aerosol characteristics in their computations. Generally, climate models assume that absorbing aerosols are small (less than 1 micron). However, a recent field study in India’s Ganges Valley indicates a surprising amount of light absorption by larger aerosol particles (1 to 10 microns). Periods of increased absorption by the larger particles ranged from a week to a month. The exact origin of the large aerosol particles is unknown, but the research team analyzed air mass trajectories using meteorological data and determined that the particles were produced locally, rather than transported long distances from other regions. A potential source of the large particles is burning of trash in the populated valley below the observational site. Because similar economic and habitation conditions are common in much of the developing world, super-micron-sized particles could play a significant role in radiative transfer and cloud processes in such regions.


V. S. Manoharan
Argonne National Laboratory


This work was supported by the U.S. Department of Energy’s Office of Biological and Environmental Research under contract DE-AC02-06CH11357.


Manoharan, V. S., et al. “Increased absorption by coarse aerosol particles over the Gangetic-Himalayan region.” Atmos. Chem. Phys. 14, 1159–1165 (2014). [DOI: 10.5194/acp-14-1159-2014].

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