New particle formation observed from a rain shadow region of the Western Ghats, India

Abstract

This study reports on new particle formation (NPF) and characteristic features observed from a rural site falling in the rainshadow of the Western Ghats in peninsular India. A total of 35 NPF events observed during August 2018 - January 2019 are classified and analyzed here. The apparent formation rates ranged from 0.2 to 10.0 cm^–3 s^–1, while the growth rates of nucleation mode particles ranged from 1.2 to 13.8 nm h^–1. The frequency of occurrence was least during August (core monsoon) and highest during post-monsoon. The local winds were calm and southeasterly to easterly (from the urban centre) supplying the essential precursor gases during October and November, leading to a frequent occurrence of nucleation events. Observations suggest that an increased condensation sink could limit the NPF while promoting Aitken mode growth. The newly formed particles accounted for about 10–80% of the total aerosol concentration. These newly formed particles were able to act as cloud condensation nuclei after growing to approximately 50 nm with an average activation fraction of 0.4.

Keywords:

• New particle formation
• particle growth characteristics
• apparent formation rate
• southwest India

Acknowledgments

The authors thank the N. B. N. Sinhgad College of Engineering, Solapur, for facilitating the ground monitoring station. CAIPEEX data are property of MoES, India, and are available on request from website http://www.tropmet.res.in/∼caipeex/. The authors gratefully acknowledge the NOAA Air Resources Laboratory (ARL) for the provision of the HYSPLIT transport (https://www.ready.noaa.gov) used in this publication. The authors acknowledge the use of data and imagery from LANCE FIRMS operated by NASA's Earth Science Data and Information System (ESDIS) with funding provided by NASA Headquarters (MODIS fire count data). The authors are grateful to the entire CAIPEEX team for their efforts in making the measurements, especially Imran Sayyed, Dhananjay Kadge, and Dinesh Gurnule. Author MV thanks Deepa Jayaprakash Sudha for the valuable discussions.

Disclosure statement

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this article.

Additional information

Funding

The Indian Institute of Tropical Meteorology (IITM) and the CAIPEEX program is fully funded by the Ministry of Earth Sciences (MoES), Government of India, New Delhi.