The recently-publicized data from the National Aeronautics and Space Administration (NASA) reveals a dramatic drop in aerosol levels, hitting a 20-year low in Northern India at the start of April. The measurements, taken by NASA’s Moderate Resolution Imaging Spectroradiometer (MODIS), offer critical insights into global environmental conditions. Positioned on NASA’s satellites, MODIS provides data for informed policymaking regarding environmental protection.
Understanding Aerosols
Aerosols are a mix of liquid or solid particles suspended in either a gaseous or liquid milieu. In our atmosphere, these particles mostly inhabit the lower atmospheric layers, specifically less than 1.5 km from the earth’s surface, as aerosol sources are primarily terrestrial. However, certain types of aerosols, notably those associated with volcanic activities, can reach the stratosphere.
There are two primary origins of these atmospheric aerosols: natural and anthropogenic. Natural aerosols originate from sea salt production from wave actions, mineral dust carried by the wind from the earth’s surface, and volcanoes. On the other hand, human-induced (anthropogenic) aerosols comprise sulfates, nitrates, and carbonaceous aerosols, primarily derived from fossil fuel combustion.
The Effects of Aerosols
Aerosols have several significant impacts on the environment and human health. Firstly, they alter the chemical composition of the atmosphere. Secondly, they can impair visibility and significantly impact air quality. High aerosol levels can cause heart and lung diseases in humans. Lastly, they act as cores around which cloud droplets or ice crystals form, affecting weather patterns and climate.
Aerosol Optical Depth (AOD) Explained
The data shared by NASA includes Aerosol Optical Depth (AOD) readings for 2020, compared to the average figures from 2016-2019. AOD measures how airborne particles absorb or reflect light passing through the atmosphere. If aerosols are concentrated near the surface, an optical depth of 1 or more corresponds to extremely hazy conditions. Conversely, an optical depth of less than 0.1 across the atmospheric vertical column indicates cleaner air.
Impact of the COVID-19 Lockdown on Aerosol Levels
Human activities such as vehicle emissions, coal-fired power plants, and industrial processes contribute to a high concentration of anthropogenic aerosols. These lead to unhealthy air pollution levels in many Indian cities annually, particularly across the Indo-Gangetic Plains.
However, with the imposition of a nation-wide lockdown in India on March 25, 2020 to curb the pandemic’s spread, anthropogenic activity dramatically subsided. This included a significant decrease in factory operations and vehicular movement. The resultant drop in nitrate and sulphate production corresponded to the observed reduction in aerosol levels.
Notably, this finding corroborates the analysis by the government’s air monitoring service, System of Air Quality and Weather Forecasting and Research (SAFAR). They reported substantial decreases in PM10, PM2.5, and nitrogen oxide levels in several major cities post-lockdown.
Contrasting Aerosol Levels in Southern India
Interestingly, the same trend was not observed in southern India, with satellite data indicating comparatively stable aerosol levels. In some instances, these figures seemed marginally higher than the previous four-year average. The reasons for this discrepancy remain uncertain but could be attributed to varying weather patterns, agricultural fires, wind conditions, or other unidentified factors.
Last Modified: February 7, 2024