10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
Interactions between Aerosol Compositions and Liquid Water Content during Beijing’s Haze Episodes at Different Seasons
XIAOXIAO LI, Wei Zhou, Jiming Hao, Jingkun Jiang, Tsinghua University
Abstract Number: 231 Working Group: Aerosol Chemistry
Abstract Aerosol liquid water (ALW) is an abundant composition in atmospheric aerosol. It is believed to play an important role in both secondary organic and inorganic formation through elevating gas-particle transformation, heterogeneous and aqueous reactions, especially in region with high RH. To explore the interactions between ALW and aerosol compositions during haze formation and evolution in Beijing. ALW were modeled based on long term measurement of non-refractory submicron aerosol compositions in different seasons in Beijing. The water content contributed by inorganics was modelled by ISORROPIA version 2.0 using both thermodynamic and metastable mode. The water content contributed by organics was estimated using the Zdanovskii-Stokes-Robinson(ZSR) mixing rule with κ-Köhler theory. In which κ is a real-time variation value related to the real time O: C ratio of organics instead of using a fixed value of 0.1 often used in previous calculations. Organic water in Beijing accounts for 7-33% of total water, the highest proportion happens in the cleanest days when the proportion and oxidation state of organics are both higher. During haze evolution, although the fraction of organics decreases with an increase in aerosol mass loading, the proportion of water content contributed by organics to the total aerosol mass is still increasing. The influence of water to aerosol compositions was explored by looking at the variation of acid/base, SO42-/NO3- and O/C during haze episodes which behave totally different with high and low ALW. In low-ALW episodes acid/base, SO42-/NO3- and O/C do not change much with haze evolution and O/C even decreases at high volatile species partitioning. While during high-ALW episode, acid/base, SO42-/NO3- and O/C increase with haze evolution. The increasing O/C ratio indicates the formation of more soluble organics, such as carboxylic acid which will increase the hygroscopicity and thus further increase water uptake. Most of the 23 classified haze episodes are high-ALW episodes. A few previous studies proposed a positive feedback loop that an increase in RH leads to an increasing aerosol inorganic fraction and subsequently increase the rate of water uptake. This study indicates that this loop also exists for aerosol organic species in Beijing.