Air sampling

Air samples for optimisation purposes were collected in Singapore at a roof-top balcony of a university building (N1.346247, E103.679467). As the study focuses on improving the time resolution of the analysis, a high-flow rate, filter-based air sampler (SASS3100, Research International, USA) was used to collect total suspended particles (TSP) with no size cut-off. The filter medium was SASS Bioaerosol electret filter (6 cm diameter, expected 50% efficiency for 0.5 µm particle size, Research International, USA). For sample collection, air samplers were attached upright on a tripod 1.5 m above the concrete floor of the balcony.

In addition to Singapore, samples from different climatic settings were collected in a consistent manner from sites in Germany, Russia and Israel to test the robustness of the proposed pipeline. These international locations showed contrasting settings for temperature (T) and relative humidity (RH).

After sampling, the filters were returned to their original filter pouches and transported to the laboratory for direct processing or storage at −20 °C. Information on exact sampling time, flow rate, duration and the environmental parameter measurements of all sampling activities used in this study can be found in Table ​Table11.

Details of sampling activities.