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In this study, an electrodynamic balance (EDB) and a single particle Raman spectroscopic system were used to investigate the heterogeneous reactions of linoleic acid and linolenic acid with ozone under ambient temperatures (22−24 °C) and dry conditions (RH < 5%). Raman characterizations provide evidence that ozone-induced autoxidation, in addition to direct ozonolysis, is a plausible pathway in the reactions between ozone and linoleic acid and linolenic acid particles. Furthermore, the significance of this specific oxidation pathway depends on the ozone concentrations used in the experiment. A low ozone concentration (∼200−250 ppb) with a longer exposure period (20 h) favors autoxidation but an extremely high ozone concentration (∼10 ppm) favors ozonolysis and forces most unsaturated fatty acids to react with ozone in a relatively short period of time. In the low ozone concentration experiments, the mass of the ozone-processed linoleic acid and linolenic acid particles increased by about 2−3% and 10−13%, respectively. In addition, the mass ratios (particle mass at RH 85% to particle mass at RH < 5%) of the ozone-processed linoleic acid and linolenic acid particles increased by about 2−3% and 3−4%, respectively. The morphology of the pure and ozone-processed linoleic acid and linolenic acid particles are compared, based on imagining and their light scattering patterns. [ABSTRACT FROM AUTHOR]

The effects of the polymorphism of glutaric acid (GA) particles on their deliquescence properties at room temperature were studied. The polymorphic states of GA, including the metastable α-form and the thermodynamically stable β-form, were characterized by Raman spectral measurements. The deliquescence of GA particles was also studied by Raman and optical observations. It was found that the α-form deliquesced at 85−86% relative humidity (RH), whereas some α-form transformed to the β-form rather than completing full deliquescence. The β-form absorbed water slowly at 87−89% RH, which was higher than the deliquescence relative humidity (DRH) of the α-form. The water-uptake process was not completed in 5 h, but the particles deliquesced quickly (<15 min) when the RH was increased to about 90%, indicating that mass transfer was delayed in the β-form and that a higher RH of 90% was needed to cross the kinetic barrier. We showed that polymorphic transformation alters the deliquescence properties of GA particles, which might explain the discrepancies in DRH values of GA particles (83−90%) reported in the literature. This transformation should be taken into account in future laboratory experiments and aerosol thermodynamic models. [ABSTRACT FROM AUTHOR]

Particle size distributions are of profound interest in the study of ambient aerosols. Electrostatic classification using the Scan-ning Mobility Particle Sizer (SMPS) and more recently the Fast-Mobility Particle Sizer (FMPS) is the most commonly employed approach to establish particle size distributions for submicron par-ticles in field and laboratory applications. The FMPS enables fast size distribution measurements on a timescale of seconds but has been speculated to underestimate particle size. Aerosol mass spec-trometry has emerged as another well-accepted method for size-resolved compositional aerosol analysis with particle sizing being accomplished by flight time separation over a specified flight path under vacuum conditions. In this work, we characterized the parti-cle sizing performance of an FMPS against simultaneous measure-ments with an Aerodyne Aerosol Mass Spectrometer (AMS) and an SMPS by sampling ambient particles, as well as polydisperse and monodisperse particles from aqueous inorganic salt solutions in the size range from 50 nm to 450 nm. The particle size mea-surements by AMS and SMPS produced similar results, while the FMPS significantly underestimated particle size by 40-50%. The discrepancy was observed in all studied ambient and laboratory-generated aerosols and appeared to be largely independent of the sampled species. The observations suggest that it is crucial to eval-uate the sizing performance of the FMPS against other instruments to ensure an adequate accuracy of the particle size measurements. In this study, a simple postcorrection method for the FMPS mea-surements was applied, which was able to successfully reduce the initial underestimation. [ABSTRACT FROM AUTHOR]

Grown nucleated particles > 50 nm in diameter are an important source of cloud condensation nuclei (CCN) and when the size is > 100 nm, they can also have direct influence on the climate. In this study, the nucleation and growth of new particles in the atmosphere in Hong Kong were investigated during dry season (monthly averaged RH < 75%). The maximum size of grown nucleated particles was generally less than 40 nm during new particle burst and growth events. The exception, accounting for ∼ 20% of all burst and growth events, was those induced by strong photochemical reactions, in which subsequent particle shrinkage occurred. Temporal particle and gas concentration variability and meteorological conditions support the occurrence of particle shrinkage. The shrinkage rate calculated (∼ 8 nm h-1) was close to the growth rate. The observation of particle shrinkage sheds new light on particle transformation dynamics and it would add to the understanding of particle behavior in the atmosphere. [ABSTRACT FROM AUTHOR]