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
