Measurements of aerosol optical properties in central Tokyo during summertime using cavity ring-down spectroscopy: Comparison with conventional techniques

Abstract: A highly sensitive cavity ring-down spectrometer (CRDS) was used to monitor the aerosol extinction coefficient at 532nm. The performance of the spectrometer was evaluated using measurements of nearly monodisperse polystyrene particles with diameters between 150 and 500nm. By comparing the observed results with those determined using Mie theory, the accuracy of the CRDS instrument was determined to be >97%, while the upper limit for the precision of the instrument was estimated to be 0.6–3.5% (typically 2%), depending on the particle number concentration, which was in the range of 30–2300particlescm−3. Simultaneous measurements of the extinction (b ext), scattering (b sca) and absorption (b abs) coefficients of ambient aerosols were performed in central Tokyo from 14 August to 2 September 2007 using the CRDS instrument, two nephelometers and a particle/soot absorption photometer (PSAP), respectively. The value of b ext measured using the CRDS instrument was compared with the sum of the b sca and b abs values measured with a nephelometer and a PSAP, respectively. Good agreement between the b ext and b sca + b abs values was obtained except for data on days when high ozone mixing ratios (>130ppbv) were observed. During the high-O3 days, the values for b sca + b abs were ∼7% larger than the value for b ext, possibly because the value for b abs measured by the PSAP was overestimated due to interference from coexisting non-absorbing aerosols such as secondary organic aerosols. [Copyright &y& Elsevier]