Abstract:

Since decades it is known that aerosol particles are the most toxic component in polluted air. But despite decades of compelling epidemiological evidence, large uncertainty remains regarding the particle properties and sources that cause a wide range of adverse health outcomes. Oxidative potential (OP), referring to the catalytic production of reactive oxygen species (ROS) by particle components with subsequent depletion of anti-oxidants on the lung surface, is widely suggested as a measure of potential aerosol particle toxicity. The accurate quantification of OP and ROS in the ambient atmosphere is challenging due to the short lifetime of these components but a reliable quantification is urgently needed to assess if ROS or OP are potentially better aerosol toxicity proxies than total particle mass, which is the conventional metric in air pollution legislation.

We developed in recent years the first online field instruments to quantify OP and ROS with an unprecedented high time resolution of a few min. We established that OP and ROS, especially in organic aerosols, have a lifetime of only a few minutes and that after a few hours up to 99% of OP and ROS decays in aerosol particles. Thus, for a meaningful quantification of OP and ROS, online instruments are essential. We deployed the instruments in a series of laboratory experiments as well as field campaigns in cities in Europe and China. These measurements clearly point to photochemical processes as a dominant source for ROS formation.