Improved air quality in India during the 2020 lockdown caused an uptick in surface greenness and photosynthetic activity in plants as compared to pre-lockdown levels, a new study has revealed. Conducted by scientists at the Centre for Ocean, River, Atmosphere and Land Sciences at the Indian Institute of Technology, Kharagpur, the study compares air quality levels during the COVID-19 necessitated lockdown in 2020 against similar pre-lockdown data (March-September, 2017-19) and notes reduced levels of aerosols and particulate matter (PM 2.5). The improved air quality during the lockdown in turn increased photosynthetic activity in plants, the study says.
What are the findings of the study?
The study notes a substantial improvement in air quality during the 2020 lockdown in India. As a result of cleaner air, increased photosynthetic activity was seen in vegetation. The increase in greenness was noted more in croplands instead of forests, supported by the prolonged growing season.
Changes in air quality modify the solar radiation that reaches the earth, thus affecting the photosynthetic activity and surface greenness (density of green vegetation). Air pollutants act as mechanical barriers that hinder light penetration in plants and block stomatal openings. This causes a decline in photosynthetic rates, which subsequently reduces chlorophyll content in vegetation. Air pollution can also affect the species richness of plant communities in an ecosystem, resulting in lower agricultural yields.
As far as aerosols are concerned, they affect both solar radiation as well as surface greenness. Higher concentration of sulphur dioxide, a greenhouse gas, promotes stomatal opening in plants, leading to excessive loss of water and a decline in plant growth.
What parameters were considered during the course of the study?
The study analyses enhanced vegetation index (EVI) and solar-induced fluorescence (SiF) to measure changes in surface greenness and photosynthetic activity respectively in response to improved air quality in India during the 2020 lockdown.
EVI is used to quantify vegetation greenness and accounts for sensitivity to factors like biomass, atmospheric background, and soil condition. According to the U.S. National Aeronautics and Space Administration, SiF is a measure that serves as a proxy of photosynthetic activity in plants. “When photosynthesis occurs, some unused energy absorbed from the sun is emitted as heat and a red glow, or SiF,” notes NASA.
Results
The study notes a sharp rise in both EVI and Sif – 11.54% and 16.24% – during the 2020 lockdown compared to the pre-lockdown levels (2001-19). The increase in both EVI and SiF is higher in croplands than in forests.
Enhanced Vegetation Index (EVI) and Solar Induced Fluorescence (SiF) for vegetated land, croplands, and forests averaged over March–September in 2000–2021. | Photo Credit: Science Direct
The study also uses changes in aerosol optical depth (AOD – a parameter to measure air pollution), PM 2.5, and sulphur dioxide levels to study the impact of air quality on surface greenness and photosynthetic activity. There was a noticeable reduction in AOD, PM 2.5, and sulphur dioxide levels in India during the lockdown as compared to pre- and post-lockdown.
Percentage change in aerosol optical depth, PM 2.5, and sulphur dioxide over India for the three time periods: lockdown (2020) – pre-lockdown (2017–2019); post-lockdown (2021) – pre-lockdown (2017–2019); and lockdown (2020) – post-lockdown (2021). | Photo Credit: Science Direct
Scientists involved with the study claim that reducing the intensity of human activity can cause rapid response in the environment, as was seen during the lockdown.
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