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Over the last 3 decades, satellite data have been used to monitor long-term global changes in stratospheric ozone. The TOMS series (1978-present) and GOME (1995-present) are two very important instruments in this context. In this paper, TOMS total ozone and three approaches to derive total ozone from GOME measurements are validated with ground-based Dobson network data. Beyond the operational products of both instruments, e.g. TOMS version 7 and GOME Data Processor version 2.7, total ozone is calculated by integrating FURM ozone profiles and by applying the TOMS algorithm to the GOME spectra. All algorithms show in general good agreement with ground-based measurements. The operational GOME total ozone shows seasonal variations, most likely introduced by difficulties in the derivation of airmass factors, which convert measured slant columns into vertical columns. The TOMS algorithm estimates on average 2% higher total ozone in the southern hemisphere than in the northern for both instruments as compared to the ground-based data, indicating that the source of the observed hemispheric differences is in the TOMS algorithm. Both instruments show aging effects in 2000, leading to enhanced variability in the ozone column differences with respect to Dobson data. In addition, the integrated GOME ozone profiles and the TOMS algorithm applied to GOME data show larger mean deviations in 2000.
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During the SATURN experiment, which took place from 27 May to 14 June 2002, new particle formation in the continental boundary layer was investigated. Simultaneous ground-based and tethered-balloon-borne measurements were performed, including meteorological parameters, particle number concentrations and size distributions, gaseous precursor concentrations and SODAR and LIDAR observations.<br> <br> Newly formed particles were observed inside the residual layer, before the break-up process of the nocturnal inversion, and inside the mixing layer throughout the break-up of the nocturnal inversion and during the evolution of the planetary boundary layer.</p>
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This study gives an overview of interannual variations of total ozone and 50 hPa temperature. It is based on newer and longer records from the 1979 to 2001 Total Ozone Monitoring Spectrometer (TOMS) and Solar Backscatter Ultraviolet (SBUV) instruments, and on US National Center for Environmental Prediction (NCEP) reanalyses. Multiple linear least squares regression is used to attribute variations to various natural and anthropogenic explanatory variables. Usually, maps of total ozone and 50 hPa temperature variations look very similar, reflecting a very close coupling between the two. As a rule of thumb, a 10 Dobson Unit (DU) change in total ozone corresponds to a 1 K change of 50 hPa temperature. Large variations come from the linear trend term, up to -30 DU or -1.5 K/decade, from terms related to polar vortex strength, up to 50 DU or 5 K (typical, minimum to maximum), from tropospheric meteorology, up to 30 DU or 3 K, or from the Quasi-Biennial Oscillation (QBO), up to 25 DU or 2.5 K. The 11-year solar cycle, up to 25 DU or 2.5 K, or El Niño/Southern Oscillation (<i>ENSO</i>), up to 10 DU or 1 K, are contributing smaller variations. Stratospheric aerosol after the 1991 Pinatubo eruption lead to warming up to 3 K at low latitudes and to ozone depletion up to 40 DU at high latitudes. Variations attributed to QBO, polar vortex strength, and to a lesser degree to <i>ENSO</i>, exhibit an inverse correlation between low latitudes and higher latitudes. Variations related to the solar cycle or 400 hPa temperature, however, have the same sign over most of the globe. Variations are usually zonally symmetric at low and mid-latitudes, but asymmetric at high latitudes. There, position and strength of the stratospheric anti-cyclones over the Aleutians and south of Australia appear to vary with the phases of solar cycle, QBO or <i>ENSO</i>.
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We investigate theoretical, laboratory, and atmospheric evidence for a recently proposed hypothesis: homogeneous ice nucleation initiates at the surface, not in the volume, of supercooled water drops. Using existing thermodynamic arguments, laboratory experiments, and atmospheric data, we conclude that ice embryo formation at the surface cannot be confirmed or disregarded. Ice nucleation rates measured as a function of drop size in an air ambient could help distinguish between volume and surface nucleation rates.
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During the Mediterranean Intensive Oxidant Study (MINOS) campaign in August 2001 gas-phase organic compounds were measured using comprehensive two-dimensional gas chromatography (GCxGC) at the Finokalia ground station, Crete. In this paper, C<sub>7</sub>-C<sub>11</sub> aromatic and n-alkane measurements are presented and interpreted. The mean mixing ratios of the hydrocarbons varied from 1±1 pptv (i-propylbenzene) to 43±36 pptv (toluene). The observed mixing ratios showed strong day-to-day variations and generally higher levels during the first half of the campaign. Mean diel profiles showed maxima at local midnight and late morning, and minima in the early morning and evening. Results from analysis using a simplified box model suggest that both the chemical sink (i.e. reaction with OH) and the variability of source strengths were the causes of the observed variations in hydrocarbon mixing ratios. The logarithms of hydrocarbon concentrations were negatively correlated with the OH concentrations integral over a day prior to the hydrocarbon measurements. Slopes of the regression lines derived from these correlations for different compounds are compared with literature rate constants for their reactions with OH. The slopes for most compounds agree reasonably well with the literature rate constants. A sequential reaction model has been applied to the interpretation of the relationship between ethylbenzene and two of its potential products, i.e. acetophenone and benzeneacetaldehyde. The model can explain the good correlation observed between [acetophenone]/[ethylbenzene] and [benzeneacetaldehyde]/[ethylbenzene]. The model results and field measurements suggest that the reactivity of benzeneacetaldehyde may lie between those of acetophenone and ethylbenzene and that the ratio between yields of acetophenone and benzeneacetaldehyde may be up to 28:1. Photochemical ages of trace gases sampled at Finokalia during the campaign are estimated using the sequential reaction model and related data. They lie in the range of about 0.5-2.5 days.
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On occasion of the project YOGAM (year of gas phase and aerosol measurements), the spatial and temporal variation of selected aerosol and gas phase parameters was assessed for the Zürich (Switzerland) area with a new mobile pollutant measurement laboratory. This assessment based on on-road measurements along a specified route on selected days during different seasons in 2001/2002, covering urban, suburban and rural regions. Special focus was put on the investigation and characterization of particles in the fine (particle diameter D<2.5 <font face="Symbol">m</font>m) and ultrafine (D<100 nm) size ranges. Analysis of Variance (ANOVA) showed that the variance of all considered fine and ultrafine aerosol parameters (i.e. particle background and total number concentration for particles larger than 3 nm, number concentrations in the size ranges 7-30 nm and 80-140 nm, as well as the active surface area concentration) was significantly larger for day-to-day than for spatial variation. However, Principal Component Analysis (PCA) found a similar regional pollution pattern within every single measuring day. Lowest particle background levels (D>3 nm) were found in rural areas at higher elevation (15 000 cm<sup>-3</sup>), while corresponding mean background values for urban and freeway-influenced areas were typically 35 000 cm<sup>-3</sup> and >80 000 cm<sup>-3</sup>, respectively. Meteorology, i.e. prevailing weather conditions not only governed the day-to-day concentration variations in the selected area, but also influenced the formation of primary (directly traffic-related) and in few cases secondary (biogenic or anthropogenic) ultrafine particles. Overall, low temperatures regularly enhanced primary ultrafine particle formation in urban areas. There was a possible indication for relatively low number concentrations of secondary ultrafine particles during a few warm and sunny spring days. Mobile measurements as they were performed in this study have been shown to be suitable for pollutant assessments to obtain good information on spatial and day-to-day variability. For experimental studies concerning spatial resolution on a relatively short time scale (<1 day), a mobile measurement design may even be more appropriate than a network of stationary measuring sites.
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Space-borne thermal infrared instruments working in the nadir geometry are providing spectroscopic measurements of species that impact on the chemical composition of the atmosphere and on the climate forcing: H<sub>2</sub>O, CO<sub>2</sub>, N<sub>2</sub>O, CH<sub>4</sub>, CFCs, O<sub>3</sub>, and CO. The atmospheric abundances obtained from the analysis of IMG/ADEOS measurements are discussed in order to demonstrate the potential scientific return to be expected from future missions using advanced infrared nadir sounders. Some strengths and limitations of passive infrared remote sensing from space are illustrated.
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The European-funded MOZAIC programme (Measurements of ozone and water vapour by Airbus in-service aircraft) has been operational since 1994 aboard 5 commercial Airbus A340. It has gathered ozone and water vapour data between the ground and an altitude of 12 km from more than 20 000 long-range flights. A new infrared carbon monoxide analyser has been developed for installation on the MOZAIC equipped aircraft. Improvements in the basic characteristics of a commercial CO analysers have achieved performance suitable for routine aircraft measurements : ±5 ppbv, ±5% precision for a 30 s response time. The first year of operation on board 4 aircraft with more than 900 flights has proven the reliability and the usefulness of this CO analyser. The first scientific results are presented here, including UTLS exchange events and pollution within the boundary layer.
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Only a few previous observations of very low O<sub>3</sub> mixing ratios in the upper troposphere are available. The aim of this study was to examine the rich MOZAIC data set for more. Flights with at least 25 4 s averaged mixing ratios less than 8 ppbv at pressures lower than 500 hPa measured using commercial aircraft within the MOZAIC project have been analysed. There are eleven flights that fulfil these conditions (excluding artefacts as discussed below), representing about 0.001% of all measurements during the analysed period August 1994-December 1997. The low O<sub>3</sub> events occurred over Southeast Asia, Africa, Brazil and the sea area 200 km east of Florida (US) and were all likely to be associated with transport of air masses from tropical sea areas. These low mixing ratio events occur in the upper troposphere during periods with generally low mixing ratios. They are not only found over sea, but also over land at pressure levels as low as 179 hPa. It could well be that some of the low O<sub>3</sub> mixing ratio events measured during two or more flights belong to the same bigger low O<sub>3</sub> mixing ratio area.
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Measurements of OH, total peroxy radicals, non-methane hydrocarbons (NMHCs) and various other trace gases were made at the Meteorological Observatory Hohenpeissenberg in June 2000. The data from an intensive measurement period characterised by high solar insolation (18-21 June) are analysed. The maximum midday OH concentration ranged between 4.5x10<sup>6</sup> molecules cm<sup>-3</sup> and 7.4x10<sup>6</sup> molecules cm<sup>-3.</sup> The maximum total RO<sub>x </sub>(RO<sub>x</sub> =OH+RO+HO<sub>2</sub>+RO<sub>2</sub>) mixing ratio increased from about 55 pptv on 18 June to nearly 70 pptv on 20 and 21 June. A total of 64 NMHCs, including isoprene and monoterpenes, were measured every 1 to 6 hours. The oxidation rate of the NMHCs by OH was calculated and reached a total of over 14x10<sup>6</sup> molecules cm<sup>-3 </sup>s<sup>-1</sup> on two days. A simple photostationary state balance model was used to simulate the ambient OH and peroxy radical concentrations with the measured data as input. This approach was able to reproduce the main features of the diurnal profiles of both OH and peroxy radicals. The balance equations were used to test the effect of the assumptions made in this model. The results proved to be most sensitive to assumptions about the impact of unmeasured volatile organic compounds (VOC), e.g. formaldehyde (HCHO), and about the partitioning between HO<sub>2</sub> and RO<sub>2</sub>. The measured OH concentration and peroxy radical mixing ratios were reproduced well by assuming the presence of 3 ppbv HCHO as a proxy for oxygenated hydrocarbons, and a HO<sub>2</sub>/ RO<sub>2</sub> ratio between 1:1 and 1:2. The most important source of OH, and conversely the greatest sink for peroxy radicals, was the recycling of HO<sub>2</sub> radicals to OH. This reaction was responsible for the recycling of more than 45x10<sup>6</sup> molecules cm<sup>-3 </sup>s<sup>-1</sup> on two days. The most important sink for OH, and the largest source of peroxy radicals, was the oxidation of NMHCs, in particular, of isoprene and the monoterpenes.
