Impact of palmitic acid coating on the water uptake and loss of ammonium sulfate particles

[摘要] While water insoluble organics are prevalent in the atmosphere, it is notclear how the presence of such species alters the chemical and physicalproperties of atmospheric aerosols. Here we use a combination of FTIRspectroscopy, Transmission Electron Microscopy (TEM) and Aerosol MassSpectrometry (AMS) to characterize ammonium sulfate particles coated withpalmitic acid. Coated aerosols were generated by atomizing pure ammoniumsulfate, mixing the particles with a heated flow of nitrogen with palmiticacid vapor, and then flowing the mixture through an in-line oven to createinternally mixed particles. The mixing state of the particles was probedusing the AMS data and images from the TEM. Both of these probes suggestthat the particles were internally mixed. Water uptake by the mixedparticles was then probed at 273 K. It was found that for ammonium sulfatecontaining ~20 wt% palmitic acid the deliquescence relativehumidity (DRH) was the same as for pure ammonium sulfate (80±3%RH). For particles with ~50 wt% palmitic acid however, the mixedparticles began to take up water at relative humidities as low at 69% andcontinued to slowly take up water to 85% RH without fully deliquescing.In addition to studies of water uptake, water loss was also investigated.Here coatings of up to 50 wt% had no impact on the efflorescence relativehumidity. These studies suggest that even if insoluble substances coat saltparticles in the atmosphere, there may be relatively little effect on theresulting water uptake and loss.

[学科分类] 大气科学