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The absorption cross-section of N2O5, ...(λ, T), which is known from laboratory measurements with the uncertainty of a factor of 2 (Table 4-2 in JPL-2011, Sander et al., 2011), was investigated by balloon-borne observations of the relevant trace gases in the tropical mid-stratosphere. The method relies on the observation of the diurnal variation of NO2 supported by detailed photochemical modelling of NOy (NOx(= NO + NO2) + NO3 + 2N2O5 + ClONO2 + HO2NO2 +BrONO2 + HNO3) photochemistry. Simulations are initialised with O3 measured by direct sun observations, the NOy partitioning from MIPAS-B (Michelson Interferometer for Passive Atmospheric Sounding-Balloon) observations in similar air masses at nighttime, and all other relevant species from simulations of the SLIMCAT chemical transport model (CTM). Best agreement between the simulated and observed diurnal increase of NO2 is found if the ...(λ, T) is scaled by a factor of 1.6 ± 0.8 in the UV-C (200-260 nm) and by a factor of 0.9 ± 0.26 in the UV-B/A (260-350 nm), compared to current recommendations. In consequence, at 30 km altitude, the N2O5 lifetime against photolysis becomes a factor of 0.77 shorter at solar zenith angle (SZA) of 30° than using the recommended ... (λ, T), and stays more or less constant at SZAs of 60°. Our scaled N2O5 photolysis frequency slightly reduces the lifetime (0.2-0.6%) of ozone in the tropical mid- and upper stratosphere, but not to an extent to be important for global ozone. [ABSTRACT FROM AUTHOR]

We report on time-dependent O3, NO2 and BrO profiles measured by limb observations of scattered skylight in the stratosphere over Kiruna (67.9° N, 22.1° E) on 7 and 8 September 2009 during the autumn circulation turn-over. The observations are complemented by simultaneous direct solar occultation measurements around sunset and sunrise performed aboard the same stratospheric balloon payload. Supporting radiative transfer and photochemical modelling indicate that the measurements can be used to constrain the ratio J(BrONO2)/kBrO+NO2, for which at T = 220±5K an overall 1.7(+0.4-0.2) larger ratio is found than recommended by the most recent Jet Propulsion Laboratory (JPL) compilation (Sander et al., 2011). Sensitivity studies reveal the major reasons are likely to be (1) a larger BrONO2 absorption cross-section σBrONO2, primarily for wavelengths larger than 300 nm, and (2) a smaller kBrO+NO2 at 220K than given by Sander et al. (2011). Other factors, e.g. the actinic flux and quantum yield for the dissociation of BrONO2, can be ruled out. The observations also have consequences for total inorganic stratospheric bromine (Bry) estimated from stratospheric BrO measurements at high NOx loadings, since the ratio J(BrONO2)/kBrO+NO2 largely determines the stratospheric BrO/Bry ratio during daylight. Using the revised J(BrONO2)/kBrO+NO2 ratio, total stratospheric Bry is likely to be 1.4 ppt smaller than previously estimated from BrO profile measurements at high NOx loadings. This would bring estimates of Bry inferred from organic source gas measurements (e.g. CH3Br, the halons, CH3Br3, CHBr3, etc.) into closer agreement with estimates based on BrO observations (inorganic method). The consequences for stratospheric ozone due to the revised J(BrONO2)/kBrO+NO2 ratio are small (maximum -0.8 %), since at high NOx (for which most Bry assessments are made) the enhanced ozone loss by overestimating Bry is compensated for by the suppressed ozone loss due to the underestimation of BrO/Bry with a smaller (BrONO2)/kBrO+NO2 ratio. [ABSTRACT FROM AUTHOR]

We report on time-dependent O3, NO2 and BrO profile measurements taken in the stratosphere by limb observations of scattered skylight at high-latitudes during autumn circulation turn-over. The observations are complemented by simultaneous direct solar occultation measurements around sunset and sunrise performed aboard the same stratospheric balloon payload. Supporting radiative transfer and photochemical modelling indicates that, the measurements can be used to constrain the ratio J(BrONO2)/kBrO+NO2 , for which overall a 1.69±0.04 larger ratio is found than indicated by the most recent JPL compilation (Sander et al., 2011). Sensitivity studies reveal the major reasons likely to be (1) a larger BrONO2 absorption cross-section σBrONO2, primarily for wavelengths larger than 300 nm, and (2) a smaller kBrO+NO2 at 220 K than given by Sander et al. (2011). Other factors, e.g. the actinic flux and quantum yield for the dissociation of BrONO2, can be ruled out. The observations also have consequences for total inorganic stratospheric bromine (Bry) estimated from stratospheric BrO measurements at high NOx loadings, since the J(BrONO2)/kBrO+NO2 ratio largely determines the stratospheric BrO/Bry ratio during daylight. Using the revised J(BrONO2)/kBrO+NO2 ratio, total stratospheric Bry is likely to be 1.4 ppt smaller than previously estimated from BrO profile measurements at high NOx loadings. This brings estimates of total stratospheric bromine inferred from organic source gas measurements (i.e. CH3Br, the halons, CH2Br2, CHBr3, ...) into closer agreement with estimates based on BrO observations (inorganic method). The consequences for stratospheric ozone due to the revised J(BrONO2)/kBrO+NO2 ratio are small (maximum -0.8%), since at high NOx (for which most Bry assessments are made) an overestimated Bry using the inorganic method would in return almost cancel out with the amount of reactive bromine calculated in the photochemical models. [ABSTRACT FROM AUTHOR]

The article presents a case study on the measurements of tropospheric trace gases using an airborne Differential Optical Absorption Spectroscopy (DOAS) spectrometer. The study performs spectral and profile retrievals of tropospheric trace gases, particularly on the distribution of halogen compounds. It also tackles several challenges arising from the radiative transfer model in an aerosol loaded atmosphere.

The article presents a case study that discusses a Bayesian minimization algorithm for retrieving diurnal variation of UV/vis absorbing radicals out of balloon-borne limb measurements. It states that the proposed method in the study assesses spectroscopic measurements and applies radiative transfer calculations to arrive into a mathematical inversion in a distinct height and time grid. It says that the method was used during deployments of mini-DOAS instruments in Brazil in June 2005.

The article presents a case study that discusses a Bayesian minimization algorithm for retrieving diurnal variation of UV/vis absorbing radicals out of balloon-borne limb measurements. It states that the proposed method in the study assesses spectroscopic measurements and applies radiative transfer calculations to arrive into a mathematical inversion in a distinct height and time grid. It says that the method was used during deployments of mini-DOAS instruments in Brazil in June 2005.

The article presents a study on NO2 and O3 where methods for the retrieval of time dependent trace gas profiles from balloon-borne UV/vis limb scattered skylight measurements are presented. The proposed methods involves the spectral retrieval, forward modelling for each measurement, and a suitable inversion algorithm that can handle both spatial and temporal domains. The retrieval exercises for O3 and NO2 were performed over tropical Brazil.