Molecular distribution and stable carbon isotopic composition of dicarboxylic acids, ketocarboxylic acids, and α-dicarbonyls in size-resolved atmospheric particles from Xi'an City, China

Laboratory study on the hygroscopic behavior of external and internal C2-C4 dicarboxylic acid-NaCl mixtures

Atmospheric aerosol is usually found to be a mixture of various inorganic and organic components in field measurements, whereas the effect of this mixing state on the hygroscopicity of aerosol particles has remained unknown. In this study, the hygroscopic behavior of mixtures of C2-C4 dicarboxylic acids and NaCl was investigated. For both externally and internally mixed malonic acid-NaCl and succinic acid-NaCl particles, correlation between water content and chemical composition was observed and the water content of these mixtures at relative humidity (RH) above 80% can be well predicted by the Zdanovskii-Stokes-Robinson (ZSR) method. In contrast, a nonlinear relation between the total water content of the mixtures and the water content of each chemical composition separately was found for oxalic acid-NaCl mixtures. Compared to the values predicted by the ZSR method, the dissolution of oxalic acid in external mixtures resulted in an increase in the total water content, whereas the formation of less hygroscopic disodium oxalate in internal mixtures led to a significant decrease in the total water content. Furthermore, we found that the hygroscopicity of the sodium dicarboxylate plays a critical role in determining the aqueous chemistry of dicarboxylic acid-NaCl mixtures during the humidifying and dehumidifying process. It was also found that the hydration of oxalic acid and the deliquescence of NaCl did not change in external oxalic acid-NaCl mixtures. The deliquescence relative humidity (DRHs) for both malonic acid and NaCl decreased in both external and internal mixtures. These results could help in understanding the conversion processes of dicarboxylic acids to dicarboxylate salts, as well as the substitution of Cl by oxalate in the atmosphere. It was demonstrated that the effect of coexisting components on the hygroscopic behavior of mixed aerosols should not be neglected.

Hygroscopic and chemical properties of aerosols collected near a copper smelter: implications for public and environmental health

Particulate matter emissions near active copper smelters and mine tailings in the southwestern United States pose a potential threat to nearby environments owing to toxic species that can be inhaled and deposited in various regions of the body depending on the composition and size of the particles, which are linked by particle hygroscopic properties. This study reports the first simultaneous measurements of size-resolved chemical and hygroscopic properties of particles next to an active copper smelter and mine tailings by the towns of Hayden and Winkelman in southern Arizona. Size-resolved particulate matter samples were examined with inductively coupled plasma mass spectrometry, ion chromatography, and a humidified tandem differential mobility analyzer. Aerosol particles collected at the measurement site are enriched in metals and metalloids (e.g., arsenic, lead, and cadmium) and water-uptake measurements of aqueous extracts of collected samples indicate that the particle diameter range of particles most enriched with these species (0.18-0.55 μm) overlaps with the most hygroscopic mode at a relative humidity of 90% (0.10-0.32 μm). These measurements have implications for public health, microphysical effects of aerosols, and regional impacts owing to the transport and deposition of contaminated aerosol particles.