The sampled air mass was influenced by the vehicular emissions and biomass burning aerosols from local source or long-range transport. The closure ratio also varies with CN concentrations. It has been observed that CCN closure improved significantly (over-prediction reduced by 37.5% and 34.6% for Pantnagar and Gaya, respectively) with the assumption of internally mixed aerosols composed of ammonium sulfate and insoluble organics (Figure 2). Also, the effective
Figure 2: Change in closure ratio with assumption of internally mixed insoluble organic fraction for Gaya and Pantnagar sortie.
hygroscopicity parameter κ, calculated by simple mixing rule is also consistent with the assumption and suggests that CCN predicted concentration is highly sensitive for aerosols with high insoluble organic fraction (~80% for selected two sorties). CCN closure analysis on surface and airborne measurements over the Indian region is a step towards understanding the dependence of CCN efficiency on the size distribution and chemical composition of the aerosol, which is one of the key linkages between aerosols, clouds and ultimately climate. It also improves our understanding of hygroscopic properties of aerosols of Indian origin.
Acknowledgements
This work was supported through a grant from the Department of Science and Technology.
References
- Patidar, V., Tripathi, S. N., Bharti, P.K., and Gupta, T., First Surface Measurement of Cloud Condensation Nuclei over Kanpur, IGP: Role of Long Range Transport, Aerosol Science and Technology 46, 973-82, 2012.
- Srivastava, M., Tripathi, S.N., Dwivedi, A.K., Dalai, R., Bhattu, D., Bharti, P.K., Jaidevi., J., and Gupta T., CCN closure results from Indian Continental Tropical Convergence Zone (CTCZ) aircraft experiment, Atmospheric Research, 132-133.
Deepika Bhattu and S. N. Tripathi
IIT Kanpur
E-Mail: deepikab@iitk.ac.in
