Optimising solvent composition to reduce ground-level ozone
In the upper levels of the Earth's atmosphere, ozone blocks harmful incoming ultraviolet radiation from the Sun. Yet near the surface ozone negatively impacts human health as the main component of photochemical smog. Ozone is not directly emitted by any source, but is formed from precursors such as Volatile Organic Compounds (VOCs). Industrial solvents are an important source of VOCs. An EESD project entitled MOST was commissioned to study the potential reduction in ozone formation that could result from proposed changes in the chemical composition of these solvents. The main tool employed by the 11 universities and research institutes participating in MOST was the atmospheric chemistry/transport model TM3. The model was thoroughly renovated for the purposes of MOST. First, the solvents currently in use as well as the proposed solvents, mainly oxygenated solvents, had to be incorporated into the model. Altogether, TM3 was expanded to include 133 different species involved in 281 different reactions generated with CHEMATA (CHEmical Mechanism Adaptation to Tropospheric Applications). Next, a team of specialists at the University of Crete integrated aerosol chemistry into TM3, ensuring that key physical phenomena, such as wet and dry deposition, are properly accounted for. Finally, critical emissions inventory data and VOC speciation information were gathered from EMEP/CORINAIR and EDGAR for the solvents currently in use. Since emissions data for the new solvents does not exist, the model was used to perform a sensitivity analysis of the different oxygenated compounds. The ability of a given species to generate ozone was gauged by the maximum ozone concentration after five model days and the total amount of ozone created per unit VOC. Ultimately, TM3 was run both with and without the VOC emissions from solvents in order to determine the overall contribution to ozone levels from this significant source of precursors. The results of these experiments highlight which solvents should be used in order to optimise air quality.
