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The laser ablation aerosol particles time-of-flight mass spectrometer (LAAPTOF, Aeromegt GmbH) is able to identify the chemical composition and mixing state of individual aerosol particles, and thus is a tool for elucidating their impacts on human health, visibility, ecosystem and climate. The overall detection efficiency (ODE) of the instrument we use was determined to range from ~(0.01 ± 0.01)% to ~(6.57 ± 2.38)% for polystyrene latex (PSL), ammonium nitrate (NH4NO3), and sodium chloride (NaCl) particles in the size rage of 200 to 2000nm. Reference mass spectra of 32 different particle types relevant for atmospheric aerosol (e.g. pure compounds NH4NO4, K2SO4, NaCl, oxalic acid, pinic acid, and pinonic acid; internal mixtures of e.g. salts, secondary organic aerosol, and metallic core-organic shell particles; more complex particles such as soot and dust particles) were determined. Our results show that internally mixed aerosol particles can result in spectra with new clusters of ions, rather than simply a combination of the spectra from the single components. An exemplary one-day ambient data set was analysed by classical Fuzzy-clustering leading to six different particle classes. Correlating these particle classes with the reference spectra as well as direct comparison of the ambient data with the reference spectra has proven how useful they are for the interpretation of field measurements, for e.g. grouping data, and identifying special particle types and potential sources. [ABSTRACT FROM AUTHOR]

Recent studies have shown that heterogeneous reactions of hydrogen peroxide (H2O2) on aerosol surfaces may play an important role in tropospheric chemistry. The data concerning the kinetics and mechanisms of these reactions, however, are quite scarce so far. Here, we investigated, for the first time, the heterogeneous reactions of gaseous H2O2 on SiO2 and (α-Al2O3 particles, two major components of mineral dust aerosol, using transmission-Fourier Transform Infrared (T-FTIR) spectroscopy, and high-performance liquid chromatography (HPLC). It is found that H2O2 molecularly adsorbs on SiO2, and a small amount of molecularly adsorbed H2O2 decomposes due to its thermal instability. For α-A12O2, catalytic decomposition of H2O2 evidently occurs, but there is also a small amount of H2O2 molecularly adsorbed on the particle surface. The BET uptake coefficients of H2O2 on both particles appear to be independent of gaseous H2O2 concentration (1.27-13-8 ppmv) and particle sample mass (2.8-6.5 mg for SiO2 and 8.6-18.9 mg for α-Al2O3), but are strongly dependent on relative humidity with the values ranging from (1.55±0.14) x 10-8 and (l.21 ± 0.04) x 10-7at 2% RH to (0.61 ± 0.06) x 10-8 and (0.76 ± 0.09) x 10-7 at 76% RH for SiO2 and α-Al2O3, respectively. On the basis of the experimental results and literature data, the potential mechanisms for heterogeneous decomposition of H2O2 were proposed, and the atmospheric implications of these reactions were discussed. It is found that heterogeneous reaction of H2O2 on both mineral oxides plays a significant role in processing mineral aerosols, although its role as a sink for ambient H2O2 is probably limited. [ABSTRACT FROM AUTHOR]