摘要
Understanding the interactions between water and atmospheric aerosols is critical for estimating their impact on the radiation budget and cloud formation. The hygroscopic behavior of ultrafine （〈100nm） ammonium sulfate particles internally mixed with either succinic acid （slightly soluble） or levoglucosan （soluble） in different mixing structures （core-shell vs. well-mixed} were measured using a hygroscopicity tandem differential mobility analyzer （HTDMA）. During the hydration process （6-92% relative humidity （RH））, the size of core-shell particles （ammonium sulfate and succinic acid） remained unchanged until a slow increase in particle size occurred at 79Y~ RH; however, an abrupt increase in size （i.e., a clear deliquescence） was observed at ~72% RH for well-mixed particles with a similar volume fraction to the core-shell particles （80：20 by volume）. This increase might occur because the shell hindered the complete dissolution of the core-shell particles below 92% RH. The onset RH value was lower for the ammonium sulfate/levoglucosan core-shell particles than the ammonium sulfate/succinic acid core-shell particles due to levoglucosan＇s higher solubility relative to succinic acid. The growth factor （GF） of the core-shell particles was lower than that of the well-mixed particles, while the GF of the ammonium sulfate/levoglucosan particles was higher than that of ammonium sulfate/succinic acid particles with the same volume fractions. As the volume fraction of the organic species increased, the GF decreased. The data suggest that the mixing structure is also important when determining hygroscopic behavior of the mixed particles.
Understanding the interactions between water and atmospheric aerosols is critical for estimating their impact on the radiation budget and cloud formation. The hygroscopic behavior of ultrafine （〈100nm） ammonium sulfate particles internally mixed with either succinic acid （slightly soluble） or levoglucosan （soluble） in different mixing structures （core-shell vs. well-mixed} were measured using a hygroscopicity tandem differential mobility analyzer （HTDMA）. During the hydration process （6-92% relative humidity （RH））, the size of core-shell particles （ammonium sulfate and succinic acid） remained unchanged until a slow increase in particle size occurred at 79Y~ RH; however, an abrupt increase in size （i.e., a clear deliquescence） was observed at ~72% RH for well-mixed particles with a similar volume fraction to the core-shell particles （80：20 by volume）. This increase might occur because the shell hindered the complete dissolution of the core-shell particles below 92% RH. The onset RH value was lower for the ammonium sulfate/levoglucosan core-shell particles than the ammonium sulfate/succinic acid core-shell particles due to levoglucosan＇s higher solubility relative to succinic acid. The growth factor （GF） of the core-shell particles was lower than that of the well-mixed particles, while the GF of the ammonium sulfate/levoglucosan particles was higher than that of ammonium sulfate/succinic acid particles with the same volume fractions. As the volume fraction of the organic species increased, the GF decreased. The data suggest that the mixing structure is also important when determining hygroscopic behavior of the mixed particles.
基金
supported by the National Leading Research Laboratory Program funded from the National Research Foundation of Korea (NRF) (No. 2011-0015548)
an NRF grant (NRF-C1ABA001-2012-0005668)
