Surface Partitioning in Organic-Inorganic Mixtures Contributes to the Size-Dependence of the Phase-State of Atmospheric Nanoparticles.
Atmospheric particulate matter is one of the main factors governing the Earth's radiative budget, but its exact effects on the global climate are still uncertain. Knowledge on the molecular-scale surface phenomena as well as interactions between atmospheric organic and inorganic compounds is necessary for understanding the role of airborne nanoparticles in the Earth system. In this work, surface composition of aqueous model systems containing succinic acid and sodium chloride or ammonium sulfate is determined using a novel approach combining X-ray photoelectron spectroscopy, surface tension measurements and thermodynamic modeling. It is shown that succinic acid molecules are accumulated in the surface, yielding a 10-fold surface concentration as compared with the bulk for saturated succinic acid solutions. Inorganic salts further enhance this enrichment due to competition for hydration in the bulk. The surface compositions for various mixtures are parametrized to yield generalizable results and used to explain changes in surface tension. The enhanced surface partitioning implies an increased maximum solubility of organic compounds in atmospheric nanoparticles. The results can explain observations of size-dependent phase-state of atmospheric nanoparticles, suggesting that these particles can display drastically different behavior than predicted by bulk properties only.
Department of Physics and Astronomy, Uppsala University , Box 516, SE-751 20 Uppsala, Sweden.|Department of Chemistry and Biotechnology, Swedish University of Agricultural Sciences , Box 7015, SE-750 07 Uppsala, Sweden.
Josephina
J
Werner
Department of Environmental Science and Analytical Chemistry (ACES) and Bolin Centre for Climate Research, Stockholm University , SE-106 91 Stockholm, Sweden.
Maryam
M
Dalirian
Department of Physics and Astronomy, Uppsala University , Box 516, SE-751 20 Uppsala, Sweden.
Marie-Madeleine
MM
Walz
Department of Physics and Astronomy, Uppsala University , Box 516, SE-751 20 Uppsala, Sweden.
Victor
V
Ekholm
Department of Environmental Science and Analytical Chemistry (ACES) and Bolin Centre for Climate Research, Stockholm University , SE-106 91 Stockholm, Sweden.
Ulla
U
Wideqvist
Department of Environmental Science and Analytical Chemistry (ACES) and Bolin Centre for Climate Research, Stockholm University , SE-106 91 Stockholm, Sweden.
Samuel J
SJ
Lowe
MAX IV Laboratory, Lund University , Box 118, SE-221 00 Lund, Sweden.
Gunnar
G
Öhrwall
Department of Chemistry and Biotechnology, Swedish University of Agricultural Sciences , Box 7015, SE-750 07 Uppsala, Sweden.
Ingmar
I
Persson
Department of Environmental Science and Analytical Chemistry (ACES) and Bolin Centre for Climate Research, Stockholm University , SE-106 91 Stockholm, Sweden.
Ilona
I
Riipinen
Department of Physics and Astronomy, Uppsala University , Box 516, SE-751 20 Uppsala, Sweden.
Olle
O
Björneholm
D000336:Aerosols / Q000737:chemistry; D000645:Ammonium Sulfate / Q000737:chemistry; D053758:Nanoparticles; D052638:Particulate Matter / Q000737:chemistry*; D012996:Solutions
D000336:Aerosols; D052638:Particulate Matter; D012996:Solutions; D000645:Ammonium Sulfate