1 Explanation of the work carried per work package (WP)
(1) My current host group previously developed the first portable online ROS instrument (OPROSI) based on the HRP/DCFH assay (Atmos. Meas. Tech., 9, 4891–4900, 2016). After started my Marie-curie Fellowship at University of Cambridge, I firstly improved the detection limit of the OPROSI about a factor of 5 compared to the previous version through redesign of some hardware components, adding some new hardware components as well as modification of the software. This makes it sensitive enough to detect ROS levels even at moderate pollution conditions in European cities, which was not possible before.
(2) We then successfully conducted field campaigns during different seasons in two contrasting urban locations, in London, UK and in Padua in Po Valley, Italy. The campaign in London was conducted at a national air quality monitor station in central London during August 2019, which represents urban traffic emission. While in the Po Valley (Italy) in the winter, wood combustion from home heating significantly contributes to atmospheric aerosols. The two field campaigns established for the first time a comprehensive data set of atmospheric particle-bound ROS concentrations and temporal variability, measured with high time resolution, and explored how different sources and atmospheric conditions govern particulate ROS formation.
(3) We further comprehensively studied the evolution and yields of ROS during SOA formation from individual volatile organic compounds (VOCs) under a wide range of atmospherically relevant oxidation conditions by using an atmospheric simulation chamber and oxidation flow reactor. This study allowed us to get a deeper insight into atmospheric transformation processes of anthropogenic and biogenic emissions contributing to aerosol particle toxicity.
(4) In addition to the online ROS measurements, we further established standard protocol to systematically evaluate and compare offline ROS production in aerosol particles from the two European cites (London, UK, and Padua, Italy) and two Asian cities (Guangzhou, China and Kolkata, India), and from laboratory-generated SOA by using four ROS detection techniques. The detailed chemical composition of these samples has also been analyzed to allow us to correlate ROS concentrations with aerosol components.
(5) We have further extended the study to build correlations between ROS concentration in particles and the biological responses (e.g. cytotoxicity, cellular ROS production, gene expression) after exposing human lung cells in particle extracts. The detailed analyses of all these chemical and biological parameters are ongoing.
2 Main results achieved so far
(1) From the campaign in London, we observed clearly that atmospheric photochemical aging of traffic emissions significantly promoted ROS formation in particles. While, the results from the Po Valley’s campaign highlighted that biomass burning particles contain a substantial amount of ROS, which was significantly enhanced during fog episodes, indicating possibly an aqueous phase formation route of ROS during periods with low photochemical activity.
(2) The overall results from atmospheric simulation chamber and oxidation flow reactor experiments indicate that the ROS production in SOA is highly dependent on SOA precursors and formation conditions (e.g. oxidants, NOx and relative humidity).
(3) The results from offline ROS measurement clearly showed that the sources and chemical composition of atmospheric aerosols as well as atmospheric conditions affect aerosol oxidative potential significantly.
