PhARRAO · Photo- And Radical induced Reactivity of Atmospheric Oxidants

Photo- And Radical induced Reactivity of Atmospheric Oxidants

Climate change and environmental sustainability are at the forefront of public interest as issues related to the emission of pollutants in the atmosphere. Although natural sources of pollutants (have always contributed to emission of chemical species in the atmosphere, air pollution has become a the second most complex manmade issue. The chemical processes which take place in the atmosphere are complex in nature and involve a wide range of chemical species in a composite environment, including reactions in the gas phase, aerosols, gas-liquid and gas-solid interfaces. Reactions between atmospheric molecular of anthropogenic and natural origin, can produce a rich variety of compounds. The outcomes of such reactions will heavily depend on the atmospheric conditions – e.g. pressure, temperature, humidity and presence of electromagnetic radiation (light). As such, direct investigation of atmospheric processes is challenging. On the contrary, laboratory studies are typically aimed at studying chemical reactions under more controlled and less complex conditions. Such studies aim at understanding the reaction mechanisms at a fundamental level and are therefore pivotal to help unravel the rich chemistry in the complex environments and aid in the predictions of the ways in which changes in conditions could affect the outcome of such processes. In this context, the project mainly focussed on the UV-Visible properties and photochemistry of carbonyl oxides, known as Criegee Intermediates (CIs) through laboratory studies. CIs are atmospheric species formed in the troposphere via reaction of unsaturated hydrocarbons (alkenes) with ozone, via a process known as ozonolysis. CIs are important as they are involved in the breakdown of many air pollutants and are a significant source of hydroxyl radicals (atmospheric detergents). The laboratory studies undertaken throughout the funding period were aimed at studying the interaction of CIs with electromagnetic radiation in the UV/Visible spectral region to determine efficient ways of detecting CIs and investigating their mechanisms of reaction with other atmospherically abundant species. The studies provided insights on the light-induced chemistry and physics which can also occur in the atmosphere due to absorption of sun light. The research included a pioneering synthesis which allowed for the first generation of ‘large’ CIs (MVK-oxide and MACR-oxide) in the laboratory and for the first time allowed recording their UV-Vis absorption spectrum across atmospherically relevant spectral range (300-500 nm). The outcomes of the laboratory studies are expected to guide field investigations of chemical reactions of CIs in the atmospheric environment.

Data: CORDIS, © European Union