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.