Aerosols are fine dust like particles which can suspend in the atmosphere for weeks to months until their deposition on the Earth through rainfall and dry deposition.
Aerosols can be natural or anthropogenic. Industry and anthropogenic activities are expanding due to increasing population and present luxuries in the human life style, resulting in increased levels of aerosols with varying size, shape and composition.
Aerosol are changing temperature profiles of earth surface and atmosphere. They are cooling earth surface by reflecting sunlight and warming the atmosphere by absorbing light. Relationship between aerosols and climate system is quite complex, but they are expected to influence the climate adversely.
Greenhouse gases (carbon dioxide and methane) have uniform distribution around the globe while the spatial and temporal distributions of aerosols are heterogeneous. So, the impact of aerosols on the climate is more complex than greenhouse gases.
Cooling of Earth surface and warming of atmosphere slows down the hydrologic cycle by reducing both the evaporation from the surface and cloud formation in the atmosphere. Effects of aerosols on the cloud droplet size around the globe are shown the picture below.
Due to increase in concentration of aerosols, rain and snow falling may shift from polluted populated areas to clean oceanic regions. It may change the availability of fresh water in populated areas. So, population may need to shift from populated areas to cleaner areas.
Anthropogenic aerosols cool the Earth surface by reflecting the sunlight while greenhouse gases warm the Earth surface by reducing the thermal emissions from it to the space. Net effect is increase of the Earth temperature due to shift in the radiation balance of the Earth.
In the last century, rise in the earth temperature is more than a half of a degree centigrade. It is an impactful increase to alter the climate of the Earth.
Aerosol are regional in nature due to shorter lifetime in comparison with greenhouse gases. Local sources and activities contribute to the aerosols in the atmosphere. Aerosols also have vertical distribution in the atmosphere.
Aerosols in the upper atmosphere are driven by strong winds and can be transported from one continent to others. Aerosol change their compositions and forms during long transportation owing chemical reactions in the atmosphere.
Understanding atmospheric aerosols and their long range transport involve several subjects including environment, climate system, chemistry, physics and geology. It is cross-disciplinary research area which is interesting and essential for long term safety of the human society.
It may be noted that aerosols in the atmosphere are being observed/monitored by satellites and network of experiments on the earth. Below is a simple visualization of atmospheric aerosols by NASA
Lesson: Dangers of aerosols are strongly linked to urban and industrial pollution which is increasing quite quickly around the globe, especially, in dense populated areas. Big and quickly growing economies along with big metropolitan cities should mend their ways and listen to environment and climate experts.
Acknowledgements: Discussions with my colleague and student Dr. Nawab Ali are gratefully acknowledged.
Declaration: Pictures and information are adopted from several in-print and digital sources and presented here in a coherent manner.