Hygroscopic behavior of sea spray aerosols in offshore waters and open sea areas investigated with aerosol optical tweezers

Sea spray aerosols (SSA) play a crucial role as a primary aerosol source on a global scale, exerting significant influence on the Earth's radiative balance. Variations in sea water composition and concentrations across different regions can introduce disparities in sea spray aerosol properties. This study focuses on investigating and comparing the hygroscopicity of artificial sea salt particles and nascent sea spray aerosols from offshore waters and open sea areas within the Pacific Ocean. An aerosol optical tweezer (AOT) system is developed to measure the diameter hygroscopic growth factor (GF) and the hygroscopicity parameter (kappa) of both artificial sea salt and natural sea spray aerosol particles. Our findings indicate that the hygroscopic properties of supermicron sea spray aerosols from offshore waters and open sea areas are remarkably similar and can be effectively represented by artificial sea salt particles. Furthermore, through the application of the theoretical Zdanovskii, Stokes, and Robinson (ZSR) mixing rule, the calculated kappa values reinforce the validity of our aerosol optical tweezer measurements. Hence, we propose that, for modeling supermicron sea spray aerosol particles produced in either offshore waters or open sea areas, the properties of artificial sea salt particles, rather than NaCl particles, serve as robust proxies for natural sea spray aerosols. To be specific, we recommend utilizing a kappa value of 1.20, for modeling sea spray aerosol properties at a relative humidity of 90% (RH = 90%). This empirically derived kappa value, rooted in our study, can enhance the accuracy of climate models and contribute to a more precise understanding of aerosol -climate interactions.