Abstract
While water uptake of aerosols exerts considerable impacts on climate, the effects of aerosol composition and potential interactions between species on hygroscopicity of atmospheric particles have not been fully characterized. The water uptake behaviors of potassium chloride and its internal mixtures with water soluble organic compounds (WSOCs) related to biomass burning aerosols including oxalic acid, levoglucosan and humic acid at different mass ratios were investigated using a hygroscopicity tandem differential mobility analyzer (HTDMA). Deliquescence points of KCl/organic mixtures were observed to occur at lower RH values and over a broader RH range eventually disappearing at high organic mass fractions. This leads to substantial under-prediction of water uptake at intermediate RH. Large discrepancies for water content between model predictions and measurements were observed for KCl aerosols with 75 wt% oxalic acid content, which is likely due to the formation of less hygroscopic potassium oxalate from interactions between KCl and oxalic acid without taken into account in the model methods. Our results also indicate strong influence of levoglucosan on hygroscopic behaviors of multicomponent mixed particles. These findings are important in further understanding the role of interactions between WSOCs and inorganic salt on hygroscopic behaviors and environmental effects of atmospheric particles.
Highlights
Mainly composed of black carbon, inorganic species, and organic material
The organic matter in the biomass burning particles contains a considerable amount of water soluble organic compounds (WSOCs), which are usually divided into three classes including mono/dicarboxylic acids, neutral compounds and polycarboxylic acids[18]
It was found that the effects of WSOCs on the deliquescence behavior of inorganic salt depended on the properties of organics[30]
Summary
The oxalic acid particles showed no obvious water uptake or deliquescence phase transition over the RH range studied, consistent with previous observations using electrodynamic balance (EDB) and other measurement methods[23,32]. Be seen that the predicted growth factors from AIOMFAC model for oxalic acid were in fair agreement with the fitting data in the literature at high RH but far too high at moderate RH while for levoglucosan the predictions underestimated the measurements at high RH. This discrepancy should be caused by the fact that solid oxalic acid is dissolved in the water absorbed by KCl after its full deliquescence contributing to water uptake of mixed particles It was confirmed by the ZSR predictions based on GFs for oxalic acid from.
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