Ground‐based measurement of fluorescent aerosol particles in Tokyo in the spring of 2013: Potential impacts of nonbiological materials on autofluorescence measurements of airborne particles

Abstract

AbstractWe present results from the observation of fluorescent (FL) aerosols in Tokyo in the spring of 2013. Ambient aerosol particles were analyzed using a single‐particle laser‐induced fluorescence instrument. The fluorescent emission from a single particle excited by a pulsed UV laser (excitation wavelength of 263 nm) was detected by three photomultiplier tubes with band‐pass filters (fluorescence wavelength of 335–379, 420–500, and 500–600 nm). Fluorescence patterns from single particles were analyzed for investigating fluorophores and their sources using backward trajectory analysis, factor analysis, and a comparison with other tracer observations. The backward trajectory analysis suggested possible influences of long‐range transport from northern China in some cases. Observed supermicron FL aerosols were classified into two types: combustion‐ and dust‐type particles. The detection of combustion‐type FL aerosols, which showed temporal variations similar to nitrogen oxides and elemental carbon, implied the presence of polyaromatic hydrocarbons (PAHs) and their derivatives. Dust‐type FL aerosols, which were well correlated with the lidar‐derived dust‐aerosol optical depth near the surface (<1 km) and with mineral ions, were dominant in the supermicron size range. The number concentrations of coarse FL aerosols (≥2 µm), with which nonnegligible levels of fluorescence were recorded in all three channels, increased during Asian dust events (relative to a local dust event). It is suggested that PAHs and/or biological materials mixed with dust particles were transported from the North China Plain to the outflow region in East Asia during the observation period. Moreover, the autofluorescence measurement of airborne particles can be substantially affected by nonbiological materials in this region.