The reaction between potassium chloride and carboxylic acid in internally mixed aerosols

In present work, the internally mixed carboxylic acid/potassium chloride aerosols are investigated by Raman spectra. The carboxylic acids include oxalic acid, malonic acid and maleic acid. When the mixed particles are performed dehydration-hydration process, chemical reactions take place and composition evolutions are observed. Furthermore, the efflorescence and deliquescence behaviors modify accordingly. The formed compounds are dependent upon acids and organic/inorganic ratios (OIRs).

For oxalic acid/potassium chloride particles, there are potassium hydrogen oxalate or potassium tetraoxalate crystals with the OIRs of 1:3 and 1:1 at 73% and 84% RH. When the OIR is 3:1, Potassium tetraoxalate crystals at 78% RH formed. The efflorescence relative humidities (ERH) of mixed oxalic acid/KCl droplets were higher than that of pure KCl, which was caused by higher ERH of potassium hydrogen oxalate and potassium tetraoxalate. For the hydration process, the DRH of mixed oxalic acid/KCl particles with an OIR of 1:3 was 84%. No deliquescence was observed within the RH range studied for the mixed particles with OIRs of 1:1 and 3:1.

When malonic acid was mixed with potassium chloride, the potassium hydrogen malonate formed during the dehydration process. At lowest RH, amorphous state in mixed malonic acid/potassium chloride particles was adopted. During the hydration process, the mixed particles continuously absorbed water but did not deliquesce obviously with increasing RH for 1:1 and 3:1 particles..

If the unsaturated acid-melaic acid was applied for mixing with KCl, the Raman spectra revealed the formation of potassium hydrogen maleate with .The formed potassium hydrogen maleate inhibited the efflorescence of mixed maleic acid/KCl droplets. The ERHs and DRHs for mixed maleic acid/KCl droplets were lower than that of pure KCl. At low RH, maleic acid interacts with potassium hydrogen maleate to produce the complex structures for the maleic acid-rich mixed particles (OIR = 3:1).

We thank for financial support from the National Natural Science Foundation of China (91644101, 91544223 and 21473009).