Indian Institute of Tropical Meteorology, Pune, Ministry of Earth Sciences, India; Savitribai Phule Pune University, Pune, India.
Indian Institute of Tropical Meteorology, Pune, Ministry of Earth Sciences, India.
Sci Total Environ. 2023 Apr 15;869:161753. doi: 10.1016/j.scitotenv.2023.161753. Epub 2023 Jan 21.
Hygroscopicity of atmospheric aerosol primarily depends on the size and chemical composition of the particle and is important for estimating anthropogenic aerosol radiative forcing. There is limited information exists over the Indian region on size segregated aerosol hygroscopicity (κ) in different seasons. This study presents 'κ' as derived from a Humidified Tandem Differential Mobility Analyzer (HTDMA) over a High Altitude Cloud Physics Laboratory (HACPL) in the Western Ghats, India for more than a year (from May 2019 to May 2020). The average hygroscopicity values of aerosol particles of diameters 32, 50, 75, 110, 150, 210 and 260 nm at 90 % RH condition are 0.19, 0.18, 0.16, 0.17, 0.18, 0.20, 0.21 respectively during the entire observation period. κ was observed to decrease with an increase in size in the Aitken mode regime (32-75 nm) and an increase in the accumulation mode (110-260 nm). Seasonal variation of hygroscopicity for a wide range of particle diameters is reported which is highly demanding as there is a change in the air mass flow pattern in each of the seasons. The diurnal cycle of hygroscopicity showed a prominent peak during the midnight to early morning hours followed by a decrease in the forenoon hours and a secondary peak in the afternoon hours. κ is found to be higher in pre-monsoon compared to winter season as Chl is approximately 3 % higher in pre-monsoon and NHCl is highly hygroscopic among the assumed chemical composition. Hygroscopicity derived through chemical speciation observations assuming internal and external mixing of aerosols i.e. κ and κ are overestimating as compared to κ. However, the bias between k and k is relatively lower as external mixing type of aerosol is evident through the growth factor data sets measured by HTDMA. Utilizing the hygroscopicity measurements available for discrete diameters by HTDMA, a parameterization of hygroscopicity with the dry diameter of sub-micron particles is developed.
大气气溶胶的吸湿性主要取决于粒子的大小和化学成分，对估算人为气溶胶辐射强迫很重要。在印度地区，关于不同季节大小分离气溶胶吸湿性（κ）的信息有限。本研究提供了在印度西高止山脉的一个高空云物理实验室（HACPL）使用加湿串联差分迁移率分析仪（HTDMA）在一年多的时间内（从 2019 年 5 月到 2020 年 5 月）得出的κ值。在整个观测期间，在 90%相对湿度条件下，直径为 32、50、75、110、150、210 和 260nm 的气溶胶粒子的平均吸湿性值分别为 0.19、0.18、0.16、0.17、0.18、0.20 和 0.21。κ值随着爱根模态区（32-75nm）中尺寸的增加而减小，并且在积聚模态（110-260nm）中增加。报道了大范围粒径的吸湿性季节性变化，这是非常需要的，因为在每个季节中空气流量模式都会发生变化。吸湿性的日变化在午夜到清晨时段表现出明显的峰值，然后在上午时段下降，并在下午时段出现二次峰值。与冬季相比，前季风季的κ值更高，因为前季风季的 Chl 约高 3%，而 NHCl 在假设的化学成分中具有很强的吸湿性。通过假设气溶胶的内部和外部混合，即κ和κ，对吸湿性进行化学分类观测得出的κ值偏高。然而，由于通过 HTDMA 测量的生长因子数据集明显表明气溶胶为外部混合类型，因此 k 和 k 之间的偏差相对较低。利用 HTDMA 提供的离散直径吸湿性测量值，开发了亚微米粒子干直径与吸湿性的参数化。
