Formation of Alkylammonium Salts in Particulate Matter
Eric Praskea, Su Anne Leeb, Xiaochen Tangd, Dr. David R. Cockerd, Dr. Phillip J. Silvae, Robert Brownf, Dr. Kathleen L. Purvis-Robertsc
a
Pitzer College, b Scripps College, c W.M. Keck Science Department of Claremont McKenna, Pitzer, and Scripps Colleges, d University of California Riverside, e United States Department of Agriculture, f Utah State University
Abstract
100%
90%
• The oxidation mechanism behind the salt formation in particulate matter is not fully
understood.
• Gaseous butylamine and diethylamine have been observed on dairy farms in Northern
California.1
• Ammonium salts in particles were observed in Logan, UT due to temperature
inversions between layers of hot and cold air, agriculture, and geographic
characteristics that are specific to the area.2
• Recent studies have also proven the presence of ammonium salts in places such as
Riverside and the Central Valley of California.3
• The amine starting materials are generally produced by livestock, during the
fermentation process of manure.4
• The nitrate radical has reportedly achieved a conversion rate of 65% from gas to
particle phase amines.5
• This study presents quantifiable data on methylamines, ethylamines, and butylamine.
Butylamine salt fraction (%)
Amines in the atmosphere originate from sources such as sewage treatment and
livestock feeding. The abundance of these amines in the atmosphere makes it important
to determine how amines react to form particles, specifically amine salts. Experiments
were conducted in an environmental chamber to determine the chemical mechanism of
salt formation. A Particle Into Liquid Sampler-Ion Chromatograph (PILS-IC), in
conjunction with other instrumentation, was used to identify and measure the
concentrations of salts formed during the experiments. Reactions of the amines with
oxidants, such as the nitrate and hydroxyl radicals, under varying levels of humidity
(0% – 40%) showed that diethylamine produced the highest concentration of amine
salts, followed by butylamine and trimethylamine. Our findings also indicate that
oxidization of the carbon side chain of the amine, as opposed to salt formation, seemed
to occur more readily in the reactions involving the hydroxyl radical compared to
nitrate radical reactions.
Background
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70%
~10% humidity
60%
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40%
~30% humidity
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10%
0%
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Reaction Time (min)
Figure 2. Example chromatogram, showing a standard separation of methylamines, ethylamines,
and butylamine. Peaks: 1) lithium 2) ammonium 3) methylammonium 4) ethylammoium
5) dimethylammonium 6) butylammonium 7) diethylammonium 8) trimethylammonium
9) N-hydroxy triethyl ammonium 10) triethylammoium.
Results
• Chromatogram observed for reactions with DEA + N2O5 (See Figure 3).
• Butylamine salt concentrations were higher in the experiments with N2O5, with the most salt
being produced in the dry experiment (See Figure 4).
• Data seems to be consistent with the concentrations of butylamine decreasing over time.
• Figure 5 shows the salt fraction for butylamine at varying levels of humidity with N2O5.
• Total aerosol volume concentration was generated via the SMPS while the APM-SMPS (Aerosol
Particle Mass Analyzer) provided real time density of bulk aerosol. Salt fraction was calculated
by dividing salt mass by total aerosol mass.
Figure 5. Salt fraction data for butylamine at varying levels of humidity with N2O5.
Table 1: Conclusion of salt formation of amines.
Amine
N2O5
H2O2
Trimethylamine
Does not form salt
Does not form salt
Diethylamine
Forms an amine salt
• 40-60% dry
• 80-100% wet
Does not form salt
Butylamine
Forms an amine salt
•80% dry
•20-30% low humidity
Does not form salt
Materials and Methods
• Experiments were conducted using the PILS-IC system (see Figure 1).5
• Annular denuders were used to remove reactive gasses such as nitric acid and ammonia.
• Experiments were carried out in a 12,500 L environmental chamber, connected directly
to our PILS, which allowed us to vary the humidity levels. About 100 ppb of amine and
oxidant were used in each experiment.
• A calibration curve was formed from standard dilutions of a primary solution with
methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine,
butylamine, and N-hydroxy triethylamine before online analysis was performed (See
Figure 2).
• For these chamber based experiments, reactions of trimethylamine, diethylamine and
butylamine with the oxidants N2O5, and H2O2 with black light were accomplished.
• Salt fraction data was later analyzed using a Scanning Mobility Particle Sizer (SMPS),
while an Aerosol Mass Spectrometer (AMS) was used to determine possible
fragmentation of the amines.
Discussion and Conclusion
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uS /cm
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Cond
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Figure 3. Sample chromatogram of one of the DEA + N2O5 experiments under dry
conditions. Peak: 1) lithium 2) ammonium 3) ethylamine 4) diethylamine.
• It was determined that only diethylamine and butylamine form salts when reacted
with N2O5.
• N2O5 seemed to form salts more readily with the amines compared to the hydroxyl
radical with more salt formation in the dry experiments than the wet experiments.
• The hydroxyl radical, when reacted with diethylamine or butylamine, resulted in the
carbon side-chain being oxidized instead.
• Amine-ketone/aldehyde reaction occurring with primary amines at higher RH.
Butylamine, for instance.
• Polymer formation mechanism proposed for TMA and nitrate.
• The data are being used to ascertain addition reaction pathways as well as to study
the kinetics of these reactions.
References
Concentration of Butylamine salt
70.00
1.
concentration (ug/m3)
60.00
2.
3.
50.00
BA + N2O5 dry
BA + N2O5 12% hum
BA + N2O5 30%hum
BA + OH 36% hum
BA + OH dry
40.00
30.00
20.00
0.00
4.
5.
6.
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Acknowledgements
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time (min)
Figure 1. Diagram of the Particle Into Liquid Sampler (PILS).5
Dry
Figure 4. Comparison of butylamine salt formation across various experiments.
We thank the National Science Foundation (AGS-0849243) and the Dreyfus Student
Research Fellowship for both summer stipends and laboratory supplies.