Resolving the mechanisms of hygroscopic growth and cloud condensation nuclei activity for organic particulate matter

Abstract

Hygroscopic growth and cloud condensation nuclei activation are key processes for accurately modeling the climate impacts of organic particulate matter. Nevertheless, the microphysical mechanisms of these processes remain unresolved. Here we report complex thermodynamic behaviors, including humidity-dependent hygroscopicity, diameter-dependent cloud condensation nuclei activity, and liquid–liquid phase separation in the laboratory for biogenically derived secondary organic material representative of similar atmospheric organic particulate matter. These behaviors can be explained by the non-ideal mixing of water with hydrophobic and hydrophilic organic components. The non-ideality-driven liquid–liquid phase separation further enhances water uptake and induces lowered surface tension at high relative humidity, which result in a lower barrier to cloud condensation nuclei activation. By comparison, secondary organic material representing anthropogenic sources does not exhibit complex thermodynamic behavior. The combined results highlight the importance of detailed thermodynamic representations of the hygroscopicity and cloud condensation nuclei activity in models of the Earth’s climate system.

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

“…The parameter κ chem is widely used in laboratorial, field observational, and modelling studies, because it harmonizes the comparisons of hygroscopicity derived from different techniques and environments. The parameter κ chem can be derived from diameter growth factor measured by Hygroscopic Tandem Differential Mobility Analyser (HTDMA) or CCN activity following the κ‐Köhler theory (Liu et al, ; Liu et al, ; Petters & Kreidenweis, ; Wang et al, ; Wex et al, ) and can also be calculated with measurements of chemical components (Petters & Kreidenweis, ). A drawback of HTDMA method is missing the information of coarse particles (Titos et al, ), which could be highly hygroscopic (e.g., sea salt) and greatly contribute to hygroscopic growth (Chen, Wild, et al, ).…”

Liquid–liquid phase separation in organic particles consisting of α-pinene and β-caryophyllene ozonolysis products and mixtures with commercially-available organic compounds

“…The occurrence of LLPS in organic aerosol particles at high RH, as observed in the current studies, is important since LLPS at high RH can lower the barrier to CCN activation by decreasing the surface 225 tension of the particles Rastak et al, 2017;Liu et al, 2018). A decrease in surface tension and lowering of the barrier to CCN, can lead to an increase in cloud droplets numbers in the atmosphere, with implications for modelling the indirect effect of aerosols on climate Rastak et al, 2017).…”

“…. More recently, studies on LLPS in organic aerosol particles free of inorganic salts 55 have shown that LLPS occurs in SOA generated in environmental chambers when the average O:C of the organic material is smaller than roughly 0.5 across the RH range of ~95% to ~100% (Renbaum-Wolff et al, 2016;Rastak et al, 2017;Song et al, 2017;Ham et al, 2019) with implications for the CCN properties of the SOA (Petters et al, 2006;Hodas et al, 2016;Renbaum-Wolff et al, 2016;Ovadnevaite et al, 2017;Rastak et al, 2017;Liu et al, 2018;Ham et al, 2019). Consistent with these 60 laboratory studies, a recently introduced binary activity thermodynamic (BAT) model, with reduced complexity for atmospheric modelling, predicts that LLPS can occur when the O:C of the organic material is < 0.5 (Gorkowski et al, 2019), when considering different types of functional groups.…”

An investigation on hygroscopic properties of 15 black carbon (BC) from different carbon sources: Roles of organic and inorganic components

“…Additionally, the large specific surface area of BC creates a potential for heterogeneous reactions with trace gases (such as volatile halocarbons) in the atmosphere (Qiu et al, 2012), therefore heavily impacting atmospheric chemistry and air quality. Hygroscopicity is a key determinant of physical, chemical, and optical properties of BC by changing particle size, phase state, and quality and morphological development, which in turn affect aerosol radiation effect, formation of cloud and ice nuclei, and heterogeneous chemical reactions (Bond et al, 2013;Liu et al, 2018). Furthermore, the hygroscopicity of BC is an important factor contributing to the risk of human respiratory infections, cardiovascular diseases, and other infectious diseases (Haddrell et al, 2015).…”