Measuring hygroscopicity of internally mixed NaNO3 and glutaric acid particles by vacuum FTIR

Feng-Min Wu; Xiao-Wei Wang; Shu-Feng Pang; Yun-Hong Zhang

doi:10.1016/j.saa.2019.04.034

Measuring hygroscopicity of internally mixed NaNO₃ and glutaric acid particles by vacuum FTIR

Spectrochim Acta A Mol Biomol Spectrosc. 2019 Aug 5:219:104-109. doi: 10.1016/j.saa.2019.04.034. Epub 2019 Apr 18.

Authors

Feng-Min Wu¹, Xiao-Wei Wang², Shu-Feng Pang³, Yun-Hong Zhang⁴

Affiliations

¹ School of Chemical Engineering and Pharmaceutics, Henan University of Science and Technology, Luoyang 471023, China; School of Chemistry and Chemical Physics Engineering, Beijing Institute of Technology, Beijing 100081, China. Electronic address: min49@126.com.
² School of Chemical Engineering and Pharmaceutics, Henan University of Science and Technology, Luoyang 471023, China; School of Chemistry and Chemical Physics Engineering, Beijing Institute of Technology, Beijing 100081, China.
³ School of Chemistry and Chemical Physics Engineering, Beijing Institute of Technology, Beijing 100081, China. Electronic address: sfpang@bit.edu.cn.
⁴ School of Chemistry and Chemical Physics Engineering, Beijing Institute of Technology, Beijing 100081, China. Electronic address: yhz@bit.edu.cn.

PMID: 31030037
DOI: 10.1016/j.saa.2019.04.034

Abstract

Sodium nitrate as an important inorganic component can be chemically formed from the reactions of nitrogen oxides and nitric acid (HNO₃) with sea salt in atmosphere. Organic acids contribute a significant fraction of photochemical formed secondary organics that can condense on the preexisting nitrate-containing particles. Atmospheric particles often include a complex mixture of nitrate and secondary organic materials accumulated within the same individual particles. Here we studied the hygroscopicity of aerosol particles composed of sodium nitrate and glutaric acid (GA) by using a pulsed RH controlling system and a rapid scan vacuum FTIR spectrometer (PRHCS-RSVFTIR). The water content in the particles and efflorescence ratios of both NaNO₃ and GA at ambient relative humidity (RH) as a function of time were obtained from the rapid-scan infrared spectra with a sub-second time resolution. Our study showed that both NaNO₃ and GA crystallized at 44.1% RH during two different RH control processes (stepwise and pulsed processes). It was found that the addition of GA could suppress the efflorescence of NaNO₃ during the dehumidifying process. In addition, the mixed NaNO₃/GA particles release HNO₃ during the dehumidifying and humidifying cycles. These findings are important in further understanding the role of interactions between water-soluble dicarboxylic acids and nitrates on hygroscopicity and environmental effects of atmospheric particles.

Keywords: Hygroscopicity; Organic-inorganic mixture; Vacuum FTIR.