Download THEORY AND PRACTICE OF AEROSOL SCIENCE

THE EFFECT OF METAL IONS ON CHEMICAL REACTION BETWEEN DICARBOXYLIC
ACID AND NITRATE WITHIN AEROSOLS DROPLETS
S. F. PANG, Y. H. ZHANG and S. XU
School of Chemistry and Chemical Engineering, Beijing Institute of Technology. Beijing 100081,
People’s Republic of China.
Keywords: reactivity, malonic acid, nitrate, IR spectroscopy.
INTRODUCTION
Aerosols processing within organic acid/inorganic salt mixtures has been shown to significant alter
aerosols properties such as hygroscopicity and volatility (Drozd et al, 2014). Previous studies reported the
reaction between dicarboxylic acid and nitrate, and thought that the reaction driven force is release of
volatile HNO3 and its partitioning between condensed and gas phases (Laskin et al, 2014). In order to
understand the reaction, various organic acids have been chosen to react with sodium nitrate. By
comparing the effect of acid dissociation constants and henry’s law constant, the release degree of gas
HNO3 was estimated. Herein, the reaction between malonic acid (MA) and various nitrate is investigated
by vacuum FTIR technology and the results show that the metal ions of nitrate also play the key role to the
reaction.
INTRODUCTION
The vacuum FTIR spectrometer (Bruker VERTEX 80v) is equipped with a SiC MIR/FIR source
(10000−20 cm−1), a high precision 21° Michelson interferometer (Ultra Scan), 16 selectable mirror
velocities (0.1−10 cms−1 opd) scanner, KBr on a gel beam splitter (range: 8000−350 cm−1) and liquid
nitrogen cooled mercury−cadmium−telluride (MCT) detector. In experiment, the ambient RH is provided
by pure water vapor and determined by the measurements of water vapor absorbance from IR spectra.
Therefore, water content within aerosols, feature of compounds and water vapor amount of the aerosol can
all be obtained from a same IR spectrum.
RESULTS
Figure 1 gives the FTIR spectra of mixture of MA/NaNO3, MA/Mg(NO3)2 and MA/Ca(NO3)2 when they
keep at 50% for 80 min. The band at 1723 cm-1 comes from ν-COOH of MA, and the 1595 cm-1 (1595
cm-1 or 1588 cm-1) peak is assigned to ν-COO- of malonate. For MA/NaNO3 droplets, the band at 1595 cm-1
appears and the band at 1723cm-1 becomes slightly weak, implying the monosodimun malonate formation.
In MA/Ca(NO3)2 aerosols, there are more monocalcium malonate formation and less MA left, because the
Figure 1 FTIR spectra of MA/NaNO3, MA/ Mg(NO3)2 and MA/Ca(NO3)2 droplets with 1:1 mole ratio when the
chemical reaction is over at 4%RH
intensity of MA feature decrease more than that in MA/NaNO3. Comparing them, there is least malonic
acid left for 80min in MA/Mg(NO3)2 droplets by almost disappearance of the peak at 1723cm-1. So it can
be concluded that most malonic acid is confused and magnesium malonate is formed. Hence, we can know
that the reaction between Mg(NO3)2 and MA is most easy and complete.
In addition, the integration area of composition IR features can estimate the reaction process. Figure 2
present the malonic acid, malonate and nitrate varying with the time at 50%RH. It implies that the
malonate increases with the reaction time, together with the decrease of MA and nitrate. After 80min, the
malonate is most in MA/Mg(NO3)2 mixture and MA and nitrate lest is least among these three mixtures.
So these quantitative feature area change assure that the reaction degree is dependent upon metal ions.
Figure 2 The ν-COOH、ν-COO- and ν1-NO3- band changes with the residence time in FTIR spectra of
MA/NaNO3, MA/ Mg(NO3)2 and MA/Ca(NO3)2 droplets (black open square: ν-COO-, orange open square: ν-COOH
and open pink circle: ν1-NO3-)
CONCLUSIONS
By FTIR technology, the capacity of nitrate and malonic acid has been studied. The feature bands
character the reaction process. At constant RH, the reaction in MA/Mg(NO3)2 is most complete and that in
MA/NaNO3 is least. So it shows that the reaction between malonic acid and nitrate is dependent upon the
metal ions.
ACKNOWLEDGEMENTS
This work was supported by the National Natural Science Foundation of China (91644101, 41175119,
21473009, and 21373026)
REFERENCES
Drozd, G., Woo, J., Häkkinen, S. A. K., Nenes, A., McNeil, V. F. (2014) Inorganic salts interact with
oxalic acid in submicron particles to form material with low hygroscopicity and volatility, Atoms. Chem.
Phys. 14, 5205.
Wang, B. and Lakin, A. (2014) Reactions between water-soluble organic acids and nitrates in atmospheric
aerosols: Recycling of nitric acid and formation of organic salts, J. Geophys. Res.:Atmos. 119, 3335.