Dynamic Characteristics of Aerosol Optical Properties at Dibrugarh (Assam, India) AERONET Station during 2018-2020

Abstract:

The NASA AERONET station is operational on Dibrugarh University campus as of January 2018. The AERONET site is in the upper Brahmaputra basin, surrounded by Arunachal hills, dense forest and oil/gas producing wells. The pollution sources are biomass burning, oil refineries, tea industries, brick kilns, forest fires, anthropogenic emissions, and long-range transport of pollutants. Sometime the south-westerly winds bring the airmass from the southern parts of India and from the Bay of Bengal. We have carried out analysis of Dibrugarh AERONET (level 1.5) data for the periods January 2018- May 2020. The average temperature varies maximum in the July month and the lowest in January month and the monthly average humidity varies, 60 -90% during monsoon period. The aerosol optical depth (AOD) varies, 0.12 – 1.08, higher in the month of March and lower in the July month, the angstrom exponent is generally higher (0.89-1.5), higher values represent smoke due to anthropogenic activties, the lowest angstrom exponent is observed due to scavenging effect.

The effect of crop burning, and forest fires are observed during the pre-monsoon season. The AOD is higher in the morning and evening hours due to cooking and heating of the houses during winter season. In the pre-monsoon season, AOD is higher during noon time and in monsoon and post-monsoon seasons, higher during morning hours. The angstrom exponent is found to be higher in the morning and evening hours and lower during daytime in winter, monsoon, and post-monsoon seasons but in pre-monsoon season, it remains same that means no change in size of the particles. In general, the size of the particles is bio-model, the peak of finer particles is around 0.15 and coarse particles of maximum size 4.0 micrometre except the volume of the coarse particles enhance during pre-monsoon (March-May) season. During 2018 premonsoon season, long range transport of dust over the Indo-Gangetic Plains reach to the AERONET site. The water vapor column was higher during monsoon season 45-60 mm. The daily observations of the column water vapor clearly show the arrival of monsoon in the region and this also provide information about the strength of the monsoon. The dynamic aerosol properties observed in the eastern parts (Assam) of India will be discussed in detail and will be supported from the satellite data.