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Abstract: In situ measurements of nitrogen dioxide (NO2) concentrations were conducted at an urban site in Tokyo (35°71′N, 139°76′E), Japan during the summers of 2007–2009. A chemiluminescence instrument equipped with a molybdenum oxide converter (Mo-CL) and a laser-induced fluorescence (LIF) instrument were used simultaneously for determining the ambient NO2 concentrations. A tight linear correlation between the NO2 concentrations determined by the LIF and Mo-CL techniques was evident except for high ozone concentration periods over 50 ppbv. During the high ozone episodes, correlation plots of the NO2 concentrations between Mo-CL and LIF techniques indicated an overestimation of Mo-CL NO2. To examine in detail the systematic differences between two techniques, a thermal dissociation laser-induced fluorescence (TD-LIF) instrument was employed in the summer of 2009 to measure total peroxy nitrates (ΣPNs) and total reactive nitrogen (NO z ). We found that the ΣPNs concentrations correlated well with the discrepancies in NO2 concentrations determined by the Mo-CL and LIF techniques. This result suggests that peroxy nitrate species significantly contribute to the observed interference in the Mo-CL measurements under high O3 concentrations in our observation at the urban site in Tokyo. [Copyright &y& Elsevier]

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]