Abstract. We report on the development of a cavityenhanced aerosol single-scattering albedometer based on incoherent broadband cavity-enhanced absorption spectroscopy (IBBCEAS) combined with an integrating sphere (IS) for simultaneous in situ measurements of aerosol scattering and extinction coefficients in an exact same sample volume. The cavity-enhanced albedometer employed a blue light-emitting-diode (LED)-based IBBCEAS approach for the measurement of wavelength-resolved aerosol optical extinction over the spectral range of 445-480 nm and an integrating sphere nephelometer coupled to the IBBCEAS setup for the measurement of aerosol scattering. The scattering signal was measured with a single-channel photomultiplier tube (PMT), providing an averaged value over a narrow bandwidth (full-width at half-maximum, FWHM, ∼ 9 nm) in the spectral region of 465-474 nm. A scattering coefficient at a wavelength of 470 nm was deduced as an averaged scattering value over the spectral region of 465-474 nm and used for data analysis and instrumental performance comparison. Performance evaluation of the albedometer was carried out using laboratory-generated particles and ambient aerosol. The scattering and extinction measurements of monodisperse polystyrene latex (PSL) spheres generated in the laboratory proved excellent correlation between two channels of the albedometer. The retrieved refractive index (RI) of the PSL particles from the measured scattering and extinction efficiencies agreed well with the values reported in previously published papers. Aerosol light scattering and extinction coefficients, single-scattering albedo (SSA) and NO 2 concentrations in an ambient sample were directly and simultaneously measured using the albedometer developed. The instrument developed was validated via an intercomparison of the measured aerosol scattering coefficients and NO 2 trace gas concentrations to a TSI 3563 integrating nephelometer and a chemiluminescence detector, respectively.

Despite the significant progress in the measurements of aerosol extinction and absorption using spectroscopy approaches such as cavity ring-down spectroscopy (CRDS) and photoacoustic spectroscopy (PAS), the widely used single-wavelength instruments may suffer from the interferences of gases absorption present in the real environment. A second instrument for simultaneous measurement of absorbing gases is required to characterize the effect of light extinction resulted from gases absorption. We present in this paper the development of a blue light-emitting diode (LED)-based incoherent broad-band cavity-enhanced spectroscopy (IBBCEAS) approach for broad-band measurements of wavelength-resolved aerosol extinction over the spectral range of 445-480 nm. This method also allows for simultaneous measurement of trace gases absorption present in the air sample using the same instrument. On the basis of the measured wavelength-dependent aerosol extinction cross section, the real part of the refractive index (RI) can be directly retrieved in a case where the RI does not vary strongly with the wavelength over the relevant spectral region. Laboratory-generated monodispersed aerosols, polystyrene latex spheres (PSL) and ammonium sulfate (AS), were employed for validation of the RI determination by IBBCEAS measurements. On the basis of a Mie scattering model, the real parts of the aerosol RI were retrieved from the measured wavelength-resolved extinction cross sections for both aerosol samples, which are in good agreement with the reported values. The developed IBBCEAS instrument was deployed for simultaneous measurements of aerosol extinction coefficient and NO(2) concentration in ambient air in a suburban site during two representative days.

Exploration of the low-lying structures of atomic or molecular clusters remains a fundamental problem in nanocluster science. Basin hopping is typically employed in conjunction with random motion, which is a perturbation of a local minimum structure. We have combined two different sampling technologies, "random sampling" and "compressed sampling", to explore the potential energy surface of molecular clusters. We used the method to study water, nitrate/water, and oxalate/water cluster systems at the MP2/aug-cc-pVDZ level of theory. An isomer of the NO3(-)(H2O)3 cluster molecule with a 3D structure was lower in energy than the planar structure, which had previously been reported by experimental study as the lowest-energy structure. The lowest-energy structures of the NO3(-)(H2O)5 and NO3(-)(H2O)7 clusters were found to have structures similar to pure (H2O)8 and (H2O)10 clusters, which contradicts previous experimental result by Wang et al.(J. Chem. Phys. 2002, 116, 561-570). The new minimum energy structures for C2O4(2-)(H2O)5 and C2O4(2-)(H2O)6 are found by our calculations.