AEROSOL IMPACTS

Subject : Environment

Context : Scientists have found that aerosols like black carbon and dust, which makes the Indo-Gangetic Plain one of the most polluted regions of the world, have led to increased incidents of high rainfall events in the foothills of the Himalayan Region.

Concept :

• The Indo-Gangetic Plain is located South and upwind of the Himalayan foothills is associated with high aerosol loading, much of which is black carbon and dust,
• It thus provides an opportunity for studying how aerosol  affects extreme rainfall events, particularly when air mass is forced from a low elevation to a higher elevation as it moves over rising terrain technically called orographic forcing.
• The study showed us that particulate emissions can alter the physical and dynamical properties of cloud systems and, in turn, amplify rainfall events over orographic regions downwind of highly polluted urban areas.
• The study used 17 years (2001–2017) of rainfall rate, aerosol measurements called aerosol optical depth (AOD), meteorological reanalysis fields such as pressure, temperature, and moisture content at different altitudes are used to compute the thermodynamic variable “moist static energy” and outgoing long-wave radiation from Indian region to investigate high precipitation events on the foothills of the Himalayas.
• The team found clear associations between high precipitation events, high aerosol loading, and high moist static energy (MSE) values (Moist static energy of an air mass includes the potential energy due to its height above the ground and the latent heat due to its moisture content).
• The findings also highlight the crucial role of the radiative effect of aerosol on high precipitation events over the Himalayan region.

Aerosols

• Aerosols are defined as a combination of liquid or solid particles suspended in a gaseous or liquid environment.
• In the atmosphere, these particles are mainly situated in the low layers of the atmosphere (< 1.5 km) since aerosol sources are located on the terrestrial surface.
• However, certain aerosols can still be found in the stratosphere, especially volcanic aerosols ejected into the high altitude layers.