Trends in aerosol optical depth over Indian region: Potential causes and impact indicators

Abstract

[1] The first regional synthesis of long-term (back to~25 years at some stations) primary data (from direct measurement) on aerosol optical depth from the ARFINET (network of aerosol observatories established under the Aerosol Radiative Forcing over India (ARFI) project of Indian Space Research Organization over Indian subcontinent) have revealed a statistically significant increasing trend with a significant seasonal variability. Examining the current values of turbidity coefficients with those reported~50 years ago reveals the phenomenal nature of the increase in aerosol loading. Seasonally, the rate of increase is consistently high during the dry months (December to March) over the entire region whereas the trends are rather inconsistent and weak during the premonsoon (April to May) and summer monsoon period (June to September). The trends in the spectral variation of aerosol optical depth (AOD) reveal the significance of anthropogenic activities on the increasing trend in AOD. Examining these with climate variables such as seasonal and regional rainfall, it is seen that the dry season depicts a decreasing trend in the total number of rainy days over the Indian region. The insignificant trend in AOD observed over the Indo-Gangetic Plain, a regional hot spot of aerosols, during the premonsoon and summer monsoon season is mainly attributed to the competing effects of dust transport and wet removal of aerosols by the monsoon rain. Contributions of different aerosol chemical species to the total dust, simulated using Goddard Chemistry Aerosol Radiation and Transport model over the ARFINET stations, showed an increasing trend for all the anthropogenic components and a decreasing trend for dust, consistent with the inference deduced from trend in Angstrom exponent.

Spring-Time Enhancement in Aerosol Burden over a High-Altitude Location in Western Trans-Himalaya:Results from Long-Term Observations

“…Recently, Babu et al have discussed long-term regional AOD trends over the Indian region using the database from the network of observatories equipped with MWR instruments. More details about this system, its data deduction methodology, error budgeting, and comparison of its performance with other instruments are extensively available in the literature 23,24,32 .…”

“…This observatory is also a part of the network of observatories under Aerosol Radiative Forcing over India (ARFI) project of ISRO-GBP, which is now known as ARFINET 23,24 . Some of the findings from this observatory have been published earlier [25][26][27][28][29][30][31] .…”

Simulation of Aerosol Fields over South Asia Using CHIMERE - Part-II:Performance Evaluation

“…These stations are part of the ARFINET chain 28 . For BC, the continuous measurements have been carried out using inter-compared Aethalometers (Magee Scientific Ins, USA) following a common measurement protocol at the chosen location.…”

“…These stations formed the components of the ARFINET chain 28 . At these stations, BC mass concentrations have been measured using inter-compared Aethalometers, following a common measurement protocol.…”

Satellite-based study of physico-optical properties of aerosols over a westernmost location of Brahmaputra valley

“…There is an increasing trend of aerosols over the Indo-Gangetic Plain (IGP) region during pre-monsoon and summer monsoon seasons which is mainly attributed to the combined effects of dust transport and wet deposition of aerosol [4] . Many studies [5][6][7][8] have revealed the aerosol environment over Dibrugarh, a remote continental location in North-East India on the basis of ground based observations.…”