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Cross-Sectional View of Atmospheric Aerosols over an Urban Location in Central India
Subin Jose, Biswadip Gharai, Pamaraju Venkata Narasimha Rao
Atmospheric Chemistry & Processes Studies Division, Atmospheric and Climate Sciences Group, National Remote Sensing Center, Hyderabad, India
- Regional atmosphere is dominated by ﬁne mode aerosols.
- Surface BC shows winter maximum and minimum in pre-monsoon.
- Elevated dust aerosols are observed in pre-monsoon.
- A decline in SW flux at TOA is observed (0.66 Wm–2 yr–1).
Surface, column and vertically resolved variations of physical and optical properties of atmospheric aerosol over Hyderabad, a tropical urban location in central India are explored on the basis of ground based and satellite retrieved data. Annual mean aerosol optical depth (τ) observed with Microtops sun-photometer is 0.61 ± 0.07 and seasonally it varied from 0.71 ± 0.06 in pre-monsoon to 0.55 ± 0.05 in winter. Aerosol types are categorized based on Ångström exponent (α) and τ relations; revealed that the study region is dominated by mixed type (MT) aerosol followed by urban/industrial aerosols under high τ (HUI) category. A consistent diurnal variation of black carbon (BC) is observed irrespective of seasonal variation with annual BC mass concentration is found to be 9.7 ± 1.9 µg m–3. During Telangana Survey day, which was the least pollutant day showed a reduction of 75% BC concentration during day time in comparison to five years average values, indicating the influence of anthropogenic effect over Hyderabad. Vertical information’s on aerosol are analyzed using Cloud Aerosol Lidar Pathﬁnder Satellite Observations (CALIPSO) and ground based Lidar (LAMP) data. LAMP data analysis shows a signiﬁcant elevated aerosol layer up to 4 km during pre-monsoon while aerosols are conﬁned below 3 km during post-monsoon and winter. Long term CALIPSO observations revealed that during post-monsoon to winter, the study area is dominated (~60%) by ‘urban’ aerosol; while during pre-monsoon period ~75% of the aerosol type belongs to ‘dusty mix’ category. A decline in short wave ﬂux at the top of the atmosphere (0.66 Wm–2 yr–1) is observed, as revealed by long term Clouds and Earths Radiant Energy System (CERES) data analysis with higher decline rate observed in winter (1 Wm–2 yr–1) followed by pre-monsoon (0.8 Wm–2 yr–1).
Aerosol optical depth; Black carbon; Aerosol backscatter coefficient; SW ﬂux at TOA.