Significant Climate Impact of Highly Hygroscopic Atmospheric Aerosols in Delhi, India

Hygroscopicity of aerosol (κchem) is a key factor affecting its direct and indirect climate effects, however, long‐term observation in Delhi is absent. Here we demonstrate an approach to derive κchem from publicly available data sets and validate it (bias of 5%–30%) with long‐term observations in Beijing. Using this approach, we report the first estimation of κchem in Delhi and discuss its climate implications. The bulk‐averaged κchem of aerosols in Delhi is estimated to be 0.42 ± 0.07 during 2016–2018, implying a higher activation ability as cloud condensation nuclei in Delhi compared with Beijing and continental averages worldwide. To activate a 0.1‐μm particle, it averagely requires just a supersaturation of ~0.18% ± 0.015% in Delhi but ~0.3% (Beijing), 0.28%–0.31% (Asia, Africa, and South America) and ~0.22% (Europe and North America). Our results imply that representing κchem of Delhi using Asian/Beijing average may result in a significant underestimation of aerosol climate effects.