Tropospheric photooxidation of (CH3CH2)2S and CH3CH2SCH3 initiated by OH radicals : An FTIR product study

GABRIELA OKSDATH-MANSILLA; ALICIA B. PEÑÉÑORY; MIHAELA ALBU; IAN BARNES; PETER WIESEN; MARIANO A. TERUEL

Florianópolis, Brazil

Congreso; 10a Conferencia Latinoamericana de Físico-Química Orgánica; 2009

Tropospheric photooxidation of (CH₃CH₂)₂S and CH₃CH₂SCH₃ initiated by OH radicals : An FTIR product study

 

Gabriela Oksdath-Mansilla^a, Alicia Peñéñory^a, Mihaela Albu^b, Ian Barnes^b, Peter Wiesen^b and Mariano A. Teruel^*a

 

^aInstituto de Investigaciones en Fisicoquímica de Córdoba (INFIQC),  Dpto. de Fisicoquímica, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba. Ciudad Universitaria, 5000 Córdoba, Argentina. E-mail: mteruel@fcq.unc.edu.ar

 

^bPhysikalische Chemie/FBC, Bergishe Universitaet Wuppertal, Wuppertal, Germany.

 

Sulfur plays an important role in both the tropospheric and stratospheric budgets of atmospheric gases and investigation of the chemistry of atmospheric sulfur has been a subject of intense scientific interest for many years. Dimethyl sulfide (CH₃SCH₃: DMS), is considered to be the dominant natural source of sulfur released to the atmosphere.¹ Although, there have been many studies of the photo-degradation reactions of DMS, only limited information is available for other longer chain alkyl sulfides like diethyl sulfide (CH₃CH₂SCH₂CH_3, DES) and ethyl methyl sulfide (CH₃CH₂SCH_3, EMS) ² which have been observed in coastal areas.³ The homogeneous atmospheric degradation of DMS and other organic sulfur compounds is controlled mainly by chemical reaction with OH radicals during the day and by NO₃ radicals at night.  These processes lead to the formation of sulfur-containing species, both inorganic and organic in nature, which may significantly contribute to the acidity of the atmosphere. It has been postulated that emissions of DMS from the oceans may have a significant influence on the Earth?s radiation budget and possibly in climate regulation due to the formation of CCN (Cloud Condensation Nuclei) from the oxidation of SO₂ formed in the photooxidation of DMS.⁴

The aim of this work was to investigate the product distribution of the reactions of OH-initiated oxidation of two alkyl sulfides, DES and EMS, at 298 K and at atmospheric pressure of air:

                                    

                                     OH +  (CH₃CH₂)₂S  → products                                                         (1)

                                     OH+ CH₃CH₂SCH₃ → products                                                                   (2)

                                    

The experiments were conducted using a 1080 liters quartz-glass reaction chamber at (298 ± 2) K in one atmosphere of synthetic air using in situ FTIR spectroscopy to monitor the compounds.

Product identification and quantification under atmospheric conditions was performed for the first time for these reactions.

SO₂, HC(O)H and HC(O)OH were found as primary products of the studied reactions with yields of 50-60%, 10-14% and 2-4%, respectively. An atmospheric chemical mechanism is postulated and the atmospheric implications of the title reactions assessed.

This work is a part of an ongoing plan in our laboratory to study the atmospheric degradation of sulfur containing compounds in the troposphere using different environmental chambers.⁵

 

References

1. B.J. Finlayson-Pitts and J.N. Pitts Jr.; Chemistry of the Upper and Lower Atmosphere, Academic

    Press, California, 2000.

2. http://kinetics.nist.gov/kinetics/index.jsp

3. G. Mouvier, P. Carlier, Physico Chemical Behavoiur of Atmospheric Pollutants, 3^rd

    European Symposium, Varese, Italy, 10-12 April. 1984.

4. R.J. Charlston, J.E. Lovelock, M.O. Andreae, S.G. Warren, Nature 326 (1987), 655.

5. G. Oksdath-Mansilla, A.Peñéñory, M. Albu, I. Barnes, P. Wiesen and M. A. Teruel. Chem.

    Phys.Lett. (2009) in press.