Volatility of Atmospherically Relevant Alkylaminium Carboxylate Salts

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On the Volatility of Atmospherically Relevant Alkylaminium Carboxylate Salts Yinon Rudich J. Phys. Chem. A, Just Accepted Manuscript • DOI: 10.1021/jp507320v • Publication Date (Web): 30 Dec 2014 Downloaded from http://pubs.acs.org on January 6, 2015

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On the Volatility of Atmospherically Relevant Alkylaminium Carboxylate Salts

Journal:


Manuscript ID:

jp-2014-07320v.R2

Manuscript Type:

Special Issue Article

Date Submitted by the Author: Complete List of Authors:

25-Dec-2014 Lavi, Avi; Weizmann Institue, Earth and Planetary Sceinces Segre, Enrico; Weizmann Institute, Physics Services Gomez-Hernandez, Mario; Texas A&M University, Chemistry Zhang, Renyi; Texas A&M University, Atmospheric Sciences Rudich, Yinon; Weizmann Institute of Science, Earth and Planetary Sciences

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On The Volatility Of Atmospherically Relevant Alkylaminium Carboxylate Salts Avi Lavi1, Enrico Segre,2 Mario Gomez-Hernandez,3,4 Renyi Zhang,3,4 Yinon Rudich1,* AUTHOR ADDRESS 1. Department of Earth and Planetary Science, Weizmann Institute of Science, Rehovot, 76100 Israel 2. Physical Services, Weizmann Institute of Science, Rehovot, 76100 Israel 3. Department of Atmospheric Sciences, Texas A&M University, College Station, Texas 77843 4. Department of Chemistry, Texas A&M University, College Station, Texas 77843

* Corresponding author: [email protected]


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Abstract

Heterogeneous neutralization reactions of ammonia and alkylamines with sulfuric acid play an important role in aerosol formation and particle growth. However, little is known about the physical and chemical properties of alkylaminium salts of organic acids. In this work we studied the thermal stability and volatility of alkylaminium carboxylate salts of short aliphatic alkylamines with monocarboxylic and dicarboxylic acids. The enthalpy of vaporization and saturation vapor pressure at 298K were derived using the kinetic model of evaporation and the Clausius-Clapeyron relation.

The vapor pressure of alkylaminium dicarboxylate salts is ~10-6Pa and the vaporization enthalpy range from 73 to 134 kJ mol-1. Alkylaminium monocarboxylate salts show high thermal stability and their thermograms do not follow our evaporation model. Hence, we inferred their vapor pressure from their thermograms as comparable to ammonium sulfate (~10-9Pa). Further characterization showed that alkylaminium monocarboxylate are room temperature protic ionic liquids (RTPILs) which are more hygroscopic than ammonium sulfate (AS). We suggest that the irregular thermograms results from an incomplete neutralization reaction leading to a mixture of ionic and non-ionic compounds.

We conclude that these salts are expected to contribute to new particle formation, particle growth under ambient conditions and can significantly enhance the CCN activity of mixed particles in areas where SO2 emissions are regulated.


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KEYWORDS Amine ; atmosphere; new particle formation; volatility; thermal denuder; evaporation; partitioning

Introduction Short aliphatic alkylamines are atmospherically ubiquitous. These compounds are highly basic, reactive, hygroscopic and volatile compounds.1-2 Atmospheric amines have both anthropogenic and biogenic sources, and their atmospheric fate is governed by cloud processing, reactive uptake, wet and dry deposition, and new particle formation and particle growth by reactive uptake.3 Since alkylamines are highly volatile (p0298>200 kPa)4, their condensation from the gas to the particle phase under ambient conditions is unlikely.5 However, field studies have shown that organic nitrogen species substantially contribute to the particulate mass of ambient aerosols,6-13 and to the composition of rain and fog water.14-15 These observations suggest that species such as short aliphatic alkylamines may also contribute to secondary organic aerosol (SOA) formation. Particle-bound amine formation would require a prerequisite step that lowers the vapor pressure of the parent alkylamines. A possible pathway is oxidation by ozone, OH or NO3 radicals. If the oxidized products are sufficiently non-volatile they may condense or further react with acids. Murphy et al. showed that under dry conditions (RH99%), malic(C4,>99%), adipic(C6,>99%) and azelaic acids (C9,>99%). Nano pure water (18.2MΩ) was taken from an in-house system.

Synthesis of alkylaminium dicarboxylate salts Two equivalents of the required alkylamine were added drop-wise to a vigorously stirred aqueous solution of the required acid (succinic, malic, adipic or azelaic acid). For volatility measurements, this stock solution was further diluted with nanopure water to 0.1-1 mg L-1.

Synthesis of alkylaminium carboxylates One equivalent of the carboxylic acid was added slowly, while stirring, to the alkylamine contained in a round-bottomed flask over ice (following ref53). After the acid equivalent was added, the mixture was stirred for about 30 min until it reached room temperature. For volatility measurements the stock solution was further diluted with nanopure water. For bulk properties characterization, excess water was removed by drying under vacuum and the resulting salt was then stored under dry conditions. All the formed monocarboxylate salts are viscous liquids at room temperature. 1

H-NMR


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H-NMR spectroscopy (300MHz, Bruker) was used to confirm the structure of the formed salt

and the absence of water after evaporation Viscosity measurements The viscosity of the alkylaminium acetate and propionate was measured using a viscometer (Haake RV1) at 22ºC at rates from 20 to 1000 s-1.

The experimental setup for volatility measurements We used the Volatility Tandem Differential Mobility Analyzer (VTDMA)54 to quantify the volatility properties (i.e. the vapor pressure) of alkylaminium carboxylate species in a selected temperature range. The instrumental setup consists of four units: (i) aerosol generation section, (ii) initial size selection, (iii) a precisely controlled laminar flow oven and (iv) a final particle size measurement system. Polydispersed aerosol of the alkylaminium carboxylate species was generated from a solution by a constant output atomizer (TSI, 3076) and was subsequently dried by silica diffusion dryers. A nearly monodispersed aerosol was generated from the dried polydispersed population by a differential mobility analyzer (DMA, TSI 3081). The sheath flow of the DMA was kept at relative humidity

Volatility of Atmospherically Relevant Alkylaminium Carboxylate Salts

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