Formation of Alkylammonium Salts in Particulate Matter

1. 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 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. Figure 5. Salt fraction data for butylamine at varying levels of humidity with N2O5. Background 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. Table 1: Conclusion of salt formation of amines. • 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. 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. Materials and Methods Discussion and Conclusion • 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. • 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. Figure 3. Sample chromatogram of one of the DEA + N2O5 experiments under dry conditions. Peak: 1) lithium 2) ammonium 3) ethylamine 4) diethylamine. References Rabaud, N. E.; Ebeler, S. E.; Ashbaugh, L. L.; and Flocchini, R. G. Atmospheric Environment. 2003. 37, 933-940. Price, D. J. Thesis for Utah State University. 2010. J.N. Smith, K.C. Barsanti, H.R. Friedli, M. Ehn, M. Kulmala, D.R. Collins, J.H. Scheckman, B.J. Williams, P.H. McMurry, Proc. Natl. Acad. Sci. USA 107 (2010) 6634. D.N. Miller and Varel, V.H. Journal of Animal Science. 2002. 80, 2214-2222. P.J. Silva, M.E. Erupe, D. Price, J. Elias, Q.G.J Malloy, Q. Li, B. Warren, D.R. Cocker, Environmental Science & Technology. 2008. 42, 4689. Orsini, D. A.; Ma, H.; Sullivan, A.; Sierau, B.; Baumann, K.; Weber, R. J. Atmospheric Environment. 2003. 37, 1243-1259. Acknowledgements We thank the National Science Foundation (AGS-0849243) and the Dreyfus Student Research Fellowship for both summer stipends and laboratory supplies. Figure 1. Diagram of the Particle Into Liquid Sampler (PILS).5 Figure 4. Comparison of butylamine salt formation across various experiments.