Solid organic-coated ammonium sulfate particles at high relative humidity in the summertime Arctic atmosphere

Abstract

Significance Physical and chemical properties of individual atmospheric particles determine their climate impacts. Hygroscopic inorganic salt particles mixed with trace amounts of organic material are predicted to be liquid under typical tropospheric conditions in the summertime Arctic. Yet, we unexpectedly observed a significant concentration of solid particles composed of ammonium sulfate with an organic coating under conditions of high relative humidity and low temperature. These particle properties are consistent with marine biogenic-derived new particle formation and growth, with particle collision hypothesized to result in the solid phase. This particle source is predicted to have increasing relevance in the context of declining Arctic sea ice and increasing open water, with impacts on clouds, and therefore climate.

Kinetics and Products of Heterogeneous Hydroxyl Radical Oxidation of Isoprene Epoxydiol-Derived Secondary Organic Aerosol

“…The AFM-derived height images of IEPOX-SOA (Figure b) were used to calculate the spreading ratios of individual particles, which has been used in prior studies to distinguish changes in viscosity. − At least 98 particles at each • OH exposure level are selected to obtain the average ±2σ from Gaussian fit as shown in Figure c. The spreading ratio increased slightly from 1.7 ± 0.1 to 1.8 ± 0.3 during 0–14 aging days, suggesting that the aerosol viscosity change is not statistically significant.…”

Initial pH Governs Secondary Organic Aerosol Phase State and Morphology after Uptake of Isoprene Epoxydiols (IEPOX)

“…The phase state (liquid, semisolid, or solid) of atmospheric particles plays a critical role in determining their ability for further chemical reactions in the aerosol phase. ,− In the past decade, studies have shown that SOA particles can exist in an amorphous semisolid or solid state under different ambient conditions (e.g., relative humidity (RH) and temperature) , and the viscosity of SOA particles can have a wide range of viscosities from 3 × 10 1 Pa s (similar to honey) to 3.7 × 10 8 Pa s (similar to tar pitch). ,− Multiphase chemistry of IEPOX leads to the formation of organosulfates, − polyols, ,− and oligomers ,, in the condensed phase, whose increased molecular weights result in more viscous aerosol (i.e., 10 6 Pa s) . Previous studies have shown that increased viscosity leads to longer mixing timescales for molecules within particles, which decreases subsequent gaseous IEPOX uptake and SOA formation. ,− Due to decreased miscibility of organic components in high ionic strength aqueous phases, the viscous organic components of a particle salt out to form an outer layer (i.e., shell) at the edge of the inorganic components (i.e., core), commonly referred to as core–shell morphology. − For the resulting core–shell morphology, if the shell is highly viscous, it can kinetically inhibit further uptake of gaseous species, , reactivity, ,,, and ultimately SOA growth and evolution in the atmosphere .…”

Scratching the Surface of Individual Aerosol Particle Properties

“…For a nano-to-micrometer-sized aerosol particle, it is not uncommon to have ionic strengths >10 M, which leads to extreme activity coefficients and shifted acid–base equilibria compared to dilute solutions. Furthermore, fine aerosol particles frequently do not exist at thermodynamic equilibrium in the atmosphere but rather exist in metastable states where the particle would thermodynamically prefer to effloresce to a solid (i.e., crystallize), but it exists as a supersaturated solution until it can overcome the energy barrier to forming a new phase . This can lead to hysteresis effects of greater than 40% relative humidity between deliquescence (solid to liquid transition) and efflorescence (liquid to solid transition).…”