Processes affecting atmospheric aerosol and its effects on climate change are strongly dependent upon hygroscopic properties. The hygroscopic properties of atmospheric aerosol particles are vital for a proper description of their direct and indirect effect on the radiative budget of the Earth’s atmosphere. Once a particle is emitted or formed in the atmosphere, it can grow or shrink in size by water vapour uptake due to its hygroscopicity, therefore altering the scattering and absorption of solar radiation and consequently changing the Earth’s radiation balance. In addition, hygroscopic properties of aerosols play an important role in determining the impact of aerosols in cloud droplet formation, indicating that particles with a high hygroscopic growth factor (Gf) mode are predominantly scavenged into cloud droplets. Particle growth factor is also considered as a vital parameter in determining the deposition of aerosols in the human respiratory system as atmospheric aerosols at 200 nm can grow their size to more than double when exposed to a high relative humidity (>99.5%) in the human lung, enhancing their lung deposition efficiencies.
The response of aerosol particles to changes in relative humidity (RH) can be obtained by determining the growth factor of aerosol particles under enhanced RH conditions. The latter is possible by means of a hygroscopicity tandem differential mobility analyser (HTDMA). Hygroscopic properties of aerosols can be described by hygroscopic Gf measured by an HTDMA instrument. The Gf is defined as the ratio between the particle diameter measured at a high relative humidity (RH) condition (dw, RH~ 90%) and a dry particle diameter measured at a low RH condition (dp, RH < 10%).
These properties play a key role in the activation of cloud droplets, aerosol radiative impacts, visibility reduction, and eventually the formation of precipitation. Data from quantitative measurements of aerosol water uptake at known conditions are required to constrain models of ambient haze, cloud formation, wet deposition, and aerosol indirect effects. HTDMA techniques are used to characterise hygroscopic properties of atmospheric aerosols in different environments, including rural, marine, remote, urban background, and roadside areas.
The talk, summarized the state-of-the art in hygroscopic growth measurements and present future directions. We hoped you enjoyed our webinar “Hygroscopic growth and its effect on physical & chemical properties of aerosol” as much as we did! If you weren’t able to make it, catch our replay.