Large Aerosol Particles Play Unexpected Role in Ganges Valley
Aerosol particles in the atmosphere may absorb solar radiation, resulting in additional heating in the atmospheric column that affects Earth’s radiative balance. Each aerosol type has distinctive light absorbing characteristics related to its physical and chemical properties. Global climate models cannot resolve the details of each individual aerosol particle, so they use broad assumptions about aerosol characteristics in their computations. Generally, climate models assume that absorbing aerosols are small (less than 1 micron). Recent observations and radiative transfer calculations by U.S. Department of Energy scientists using data from the Atmospheric Radiation Measurement (ARM) Mobile Facility (AMF) deployment to India’s Ganges Valley indicate a surprising amount of light absorption by larger aerosol particles (1-10 microns). The observations indicate that light absorption by the super-micron-sized particles was nearly 30% greater than that by smaller particles. 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 team analyzed the 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 trash burning in the populated valley below the observational site. The study indicates that large absorbing particles could be an important component of the regional-scale atmospheric energy balance in developing countries and need to be considered in global and regional climate models.
Manoharan, V. S., R. Kotamarthi, Y. Feng, and M. P. Cadeddu. 2014. “Increased Absorption by Coarse Aerosol Particles over the Gangetic-Himalayan Region,” Atmospheric Chemistry and Physics 14, 1159-65. DOI: 10.5194/acp-14-1159-2014.