Recently-developed novel trapping and manipulating techniques made it possible to measure single aerosol particles in air using advanced laser spectroscopy such as Raman spectroscopy, cavity ringdown spectroscopy (CRDS) or their combination. Early work on laser-induced fluorescence (LIF) of single aerosol particles provided insightful information on chemical and biological properties of the particles, but the spectroscopic specificity are limited to the level of LIF-clusters due to the chemical complexity and broad band fluorescence signature. Recent studies have demonstrated single-aerosol-particle Raman spectra that offer more selective information on chemical compositions based on individual Raman bands. Single particle Raman has the unique features of minimum to no interference from surroundings and high spatial and temporal resolution. But the issues of weak Raman scattering signals and possible strong fluorescence need to be taken care. CRDS measures the total extinction (sum of scattering and absorption) of the particles at one wavelength at a time. Theoretically, single particle CRDS can lead to determination of both real and imaginary parts of refractive index of a particle as well as its chemical compositions in near-real time. CRDS measurements of single polystyrene beams and water droplets have been reported; however measurements of single airborne
aerosol particles have not been much explored to date.
This talk gives a brief overview on advantages, status, and challenges of single-aerosol-particle trapping and its integration with Raman and CRDS techniques. We show our most recent results of Raman and CRDS measurements of single aerosol particles optically trapped in air. Future efforts are also discussed.