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The article presents a study which compares the efficiency of different techniques using various instruments in measuring interferences of commercial nitrogen dioxide (NO2) in the urban atmosphere and in a smog chamber. Chemiluminescence instruments with molybdenum or photolytic converters, Luminol based instrument and a proposed NO 2 Long Path Absorption Photometer (LOPAP) were compared with spectroscopic techniques. The methods and results of the study are discussed.

The article presents a study which compares the performances of different commercial nitrogen dioxide (NO2) instruments and a NO2-LOPAP in the urban atmosphere and in a smog chamber in Santiago de Chile. A field experiment was conducted wherein chemiluminescence instruments with molybdenum or photolytic converters were compared to NO2-LOPAP with spectroscopic techniques to detect interferences. Results show strong interferences and agreements in all instruments.

The article focuses on the development of a Long Path Absorption Photometer (LOPAP) instrument for the detection of NO2 in the atmosphere. The instrument is considered more sensitive than known instruments as it has an accuracy of 10 percent and a precision of 0.5 percent for three minutes time resolution. It is also deemed easier to apply than other methods. Its use is validated by intercomparison with chemiluminescence instrument with photolytic NO2 converter.

Abstract: A simple O3-LOPAP (Long Path Absorption Photometer) instrument for the selective detection of O3 in the atmosphere is presented, which is mainly intended to be used as an extension of a recently developed NO2-LOPAP. O3 is sampled in a stripping coil by a selective chemical reaction with the highly absorbing Indigo dye. The reduction of the optical absorption of the dye is detected in a liquid core waveguide. The instrument has a detection limit of 0.4 ppbv, an accuracy of 10%, a precision of 2% for 6 min time resolution and allows the absolute quantification of O3 according to Lambert–Beer''s law. Interferences towards nitrogen oxides (NO and NO2), N2O5, H2O2 and several VOCs were quantified in the laboratory and found to be negligible for atmospheric conditions. The new instrument was successfully validated against a commercial UV-absorption instrument during an urban field campaign and against the FTIR technique in a smog chamber under complex photosmog conditions. For the UV-absorption instrument significant positive interferences towards aromatic species were observed in the smog chamber. [Copyright &y& Elsevier]

Photochemical reactions in snow can have an important impact on the composition of the atmosphere over snow-covered areas as well as on the composition of the snow itself. One of the major photochemical processes is the photolysis of nitrate leading to the formation of volatile nitrogen compounds. We report nitrite concentrations determined together with nitrate and hydrogen peroxide in surface snow collected at the coastal site of Barrow, Alaska. The results demonstrate that nitrite likely plays a significant role as a precursor for reactive hydroxyl radicals as well as volatile nitrogen oxides in the snow. Pollution events leading to high concentrations of nitrous acid in the atmosphere contributed to an observed increase in nitrite in the surface snow layer during nighttime. Observed daytime nitrite concentrations are much higher than values predicted from steady-state concentrations based on photolysis of nitrate and nitrite indicating that we do not fully understand the production of nitrite and nitrous acid in snow. The discrepancy between observed and expected nitrite concentrations is probably due to a combination of factors, including an incomplete understanding of the reactive environment and chemical processes in snow, and a lack of consideration of the vertical structure of snow.

Biomass organization of Aspergillus niger biofilms and pellets stained with fluorescein isothiocyanate were analyzed by means of confocal laser scanning microscopy and detectable differences between both types of growth were found. Three-dimensional surface plot analysis of biofilm structure revealed interstitial voids and vertical growth compared with pellets. Growth was lower in biofilm and according to fluorescence profile obtained, biomass density increased at the surface (0-20 microm). However, a decrease in fluorescence intensity was observed through optical sections of pellets even though growth was significantly higher than biofilms. Cryo scanning electron microscopy also showed structural differences. While biofilms showed a spatially ordered mycelium and well structured hyphal channels, pellets were characterized by an entangled and notoriously compacted mycelium. These findings revealed common structural characteristics between A. niger biofilms and those found in other microbial biofilms. Thus, biofilm microstructure may represent a key determinant of biofilm growth and physiology of filamentous fungi., (Copyright (c) 2009 Elsevier Ltd. All rights reserved.)

Peroxides present in Santiago City dew waters readily decompose with first order kinetics. In order to minimize the loss of peroxides during the time elapsed between deposition and collection, the collectors were pre-treated with a mercury chloride solution. This reduces, but not completely eliminates, the decomposition. A correction is introduced by a comparison of the levels and decomposition kinetics of the samples collected in treated and untreated collectors. The average concentration estimated by this procedure was 8.1 microM. The mechanism of peroxide decomposition and its stabilization is discussed.