The fluorescence properties of aerosol larger than 0.8 µm in an urban and a PBA-dominated location

Abstract

Dual-wavelength Ultraviolet light-induced fluorescence (UV-LIF) measurements were performed on ambient environmental aerosol in Manchester, UK (urban city centre, winter) and Borneo, Malaysia (remote, tropical), which are taken to represent environments with negligible and significant primary biological aerosol (PBA) influences, re- spectively. Single-particle fluorescence intensity and optical equivalent diameter were measured with a Wide Issue Bioaerosol Sensor, version 3 (WIBS3) in the diameter range 0.8 µm≤DP≤20 µm for 2–3weeks and filters were analysed using energy dis- persive X-ray (EDX) spectroscopy, which revealed mostly non-PBA dominated particle sizes larger than 1 µm in Manchester. The WIBS3 features three fluorescence channels: Fluorescence excited at 280nm is recorded at 310–400nm and 400–600nm and fluorescence excited at 370nm is detected at 400–600 nm. In Manchester the primary size mode of fluorescent and non-fluorescent material was at 1.2 µm. In Borneo non-fluorescent material peaked at 1.2 µm and fluorescent at 3–4 µm. The fluorescence intensity at 400–600nm generally increased with DP at both sites, as did the 310–400nm intensity in Borneo. In Manch- ester the 310–400m fluorescence decreased at DP>4 µm, suggesting this channel offers additional discrimination between fluorescent particle types. Finally, the ratio of fluorescence intensity in two pairs of channels was investigated as a function of particle diameter and this varied significantly between the two environments, demonstrating that the fluorescent aerosol in each can in principle be distinguished using a combina- tion of fluorescence and elastic scattering measurements.