Investigating the Chemical Composition of Organic Aerosols and their Contribution to the Oxidative Potential

Atmospheric aerosols play an important role not only due to the effect on climate but especially because of the adverse effects on human health, which studies consistently link to the exposure to particulate matter. Here, especially fine particles below a diameter of 2.5 μm can enter deep into the lungs, causing inflammation or translocate into the bloodstream and eventually lead to further disease.

To investigate and describe the potential toxicity of atmospheric particles, the oxidative potential (OP) can be measured. Since particles can be formed by many reaction paths and therefore be a mixture of many compounds, a deeper understanding of the composition is needed in order to understand the main chemical drivers for OP. It is known, that especially metals and secondary organic aerosols (SOA) lead to OP, but in order to attribute sources, a
further chemical characterization of SOA, linked to OP, is needed.

In this study, 42 samples from different locations in Frankfurt, Germany and Beijing, China have been measured by inductively coupled plasma - mass spectrometry (ICP-MS), in order to obtain the metal content and by high pressure liquid chromatography - high resolution mass spectrometry (HPLC-HRMS) to determine organic compounds and their composition groups via non target analysis. The OP then was determined by extracting the filters and either measuring directly or treating with Chelex^® 100 to remove the metals and carry out the measurement afterward. By employing this technique, the contribution of metals and organics can be investigated separately to gain a better understanding of the OP caused by SOA. In order to examine the contribution of different compound groups to OP, a hierarchical cluster analysis and several Pearson correlations have been carried out. By this approach, similarities between samples can be observed, which then might give an indication about relevant compounds. Moreover, correlations between the variability of the OP throughout the sample and the variability of compounds point to certain OP-effective compounds.

First results show that the metal containing extracts have a higher volume-normalized OP (OP_V ) compared to the non-metal ones, with 0.2 to 5 nmol DTT min^-1m^-3, which is mainly due to manganese and copper. After the Chelex^® 100 treatment, there is still a OP_V of 0.1 up to 4 nmol DTT min^-1m^-3, indicating the significance of organic matter, causing the oxidative potential. Comparing the different locations, the samples from Beijing show an OP up to four
times higher than samples from Frankfurt. Looking deeper into the chemical composition, especially chemical groups containing phosphor and nitrogen, such as CHOP and CHNO, correlate with high OP.