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; 10th Latin American Conference on Physical Organic Chemistry (CLAFQO); 2009

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 (CH3CH2SCH2CH3, DES) and ethyl methyl sulfide (CH3CH2SCH3, 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   à products (1) OH+ CH3CH2SCH3 à 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