Rising thickness of Aerosol Optical Depth (AOD) in the national Capital’s atmosphere has created concern among the environment scientists as the escalated width increases the risk of Chronic Obstructive Pulmonary Diseases (COPD) due to blockage of required energy from the sun. A research by four universities and Council of Scientific and Industrial Research (CSIR) has revealed that in the coming years, those living in the national Capital will face visibility related problems.
To understand the variations in thickness of Delhi- AOD in a decade, environment scientists from School of Environmental Sciences, Jawaharlal Nehru Universrity (JNU); CSIR-National Physical laboratory, New Delhi; Centre for Environment Science, Central University Punjab; Department of Environment School, Tezpur University, Assam; and Indian Institute of Remote Sensing, Dehradun, Uttrakhand collected the pollutant load on aerosol through handheld microtops.
According to the environment scientists, the aerosol load in the atmospheric layer in Delhi has increased drastically during the last 10 years. In a collective research conducted by the environment scientists on AOD has revealed that Delhi’s AOD width has been oscillating between 0.7 to 1 whereas in the United States (US), it fluctuates between 0.1 and 0.15 (NASA observations). Physicists also said, there are variations in the thickness of AOD as a result of the climate and geographical locations of the city.
Dr Sachchidanand Singh, principal scientist, Radio and Atmospheric Sciences, National Physical laboratory (NPl) told The Pioneer that higher thickness is correlated to the amount of radiations, if thickness will be increasing gradually; there is the deduction of required ultraviolet radiations on earth surface.
“Besides the visibility factor, aerosol load creates obstruction for sunlight to reach plants. We all know that in photosynthesis process, plants require sunlight. Vegetation situation in Delhi and NCR will change and surface reflects — ability also changes. Capital is turning the Urban Heat Island (UHI). In near future, there are the possibilities of serious diseases due to less exposure to sunlight,” said the scientist.
Professor Krishna Kumar, School of Environmental Sciences, JNU, said atmospheric aerosols are known to affect the radiative balance: The relationship between the amount of energy reaching an object (or a portion of it) and the amount leaving it.
Explaining more on AOD load, professor Krishna said the microtops sun photometer measured AOD at discrete wavelengths between 340 and 1,020 nanometre with Full Width at Half Maximum (FWHM). “All calibrations were done by sending the instruments to Mauna loa, where it was calibrated using langley technique by the manufacturer, Solar light Company Inc., USA to the NIST (National Institute of Standards and Technology) traceable standards”
“To reach on conclusive observations, the AODs were measured over a long period of time (since December 2001 to May 2012), Among the 14, 651 point observations, AOD thickness was measured above the 0.6,” said Kumar. (AOD thickness at 500 nm is measured with respect to the levels/load of Suspended Particulate Matter (SPM)).
While explaining the reasons of AOD escalation width in past 10 years, professor Kumar further said land use in NCR region, loose soil and a rapid growth in urbanisation in the Capital has led to such outcome. “The variations in land cover observed through satellite data, use of land periodically with respect to time have direct relation with the thickness of AOD,” he said.
Reacting on the escalation of AOD, Ashwani Kumar, former Principal Secretary, Environment and Forest, Delhi Government, said the climatography and geography of Delhi is entirely different.
“To measure pollutant levels or aerosol loads in Delhi region, the norms or prescribed standards of World Health Organisation (WHO) cannot be considered in highly populated region like Delhi. For instance — WHO standards for PM 2.5 is 20-30, whereas Indian Metrological Standards are 60 which sounds considerable,” said Kumar, Civic agencies like PWD, DDA and Municipal Corporations can help more to reduce the load of aerosol particles by taking strict actions,” said the official.