Most monitoring stations recorded increasing trend of aerosol optical depth
There has been “a phenomenal increase” in the levels of fine particles in the atmosphere over India, especially those generated by human activity, according to research published recently by a team of Indian scientists.
Such particles, known as aerosols, contribute to the growing levels of pollution in the country.
In addition, these particles scatter and absorb light. As their levels in the atmosphere increase, they can cut the amount sunlight that reaches the ground and also affect the extent to which heat from the planet escapes into space. Aerosols thereby have an influence on the climate.
Aerosols include naturally occurring particles like sea-salt and dust. But concern has growing over those produced by humans, such as soot from vehicle emissions and the burning of firewood and sulphate particles that spew out from thermal power stations and cement plants.
A team of scientists from the Indian Space Research Organisation’s Space Physics Laboratory in Thiruvananthapuram, along with colleagues at the Indian Institute of Science in Bangalore and several universities, analysed measurements of ‘aerosol optical depth’ (AOD), a index of aerosol levels, made over many years with ground-based instruments at ten stations situated in various parts of the country as well as one in the Maldives.
Many of those stations had aerosol data over only the past decade or so. However, the Thiruvananthapuram and Visakhapatnam stations possessed data that went back nearly 30 years.
Over most of the stations, AOD had shown an increasing trend. Particularly striking was the change registered at Thiruvananthapuram and Visakhapatnam, where the rate of increase in aerosol levels had jumped since 2000.
This indicated that the AOD “over the peninsula is not only increasing steadily, even the rate of increase has also increased, the situation being more alarming over the industrialised eastern coastal location (Visakhapatnam),” observed S. Suresh Babu and the other scientists in a paper published in the Journal of Geophysical Research .
Examination of the AOD levels at four different wavelengths of light made it possible to discern fine human-generated aerosols from the coarse ones that were naturally produced. The relative abundance of aerosols produced by humans had grown at both Thiruvananthapuram and Visakhapatnam, the rise being greater at the latter.
The team also utilised measurements made by the well-known Indian atmospheric scientist, Anna Mani, and others more than 40 years back.
When this data was taken into account, it too showed that the levels of human-produced aerosols had shot up alarmingly since then.
Climate models used by scientists to study what could happen in the coming decades were not taking into account this tremendous growth in aerosol levels, remarked S.K. Satheesh of the Indian Institute of Science, one of the authors of the paper.
If the current trend in India of increasing anthropogenic aerosol emissions were to continue unabated, the loading of such particles in the atmosphere could double by around 2050, he told this correspondent.
The aerosol-induced warming of the atmosphere might triple as a result, which could affect the monsoon and the regional climate, observed Dr. Satheesh, one of the lead authors for the latest assessment report published by the Intergovernmental Panel on Climate Change.