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[1] This paper presents results from the first large-scale in situ intercomparison of oxygenated volatile organic compound (OVOC) measurements. The intercomparison was conducted blind at the large (270 m 3 ) simulation chamber, Simulation of Atmospheric Photochemistry in a Large Reaction Chamber (SAPHIR), in Jülich, Germany. Fifteen analytical instruments, representing a wide range of techniques, were challenged with measuring atmospherically relevant OVOC species and toluene (14 species, C 1 to C 7 ) in the approximate range of 0.5-10 ppbv under three different conditions: (1) OVOCs with no humidity or ozone, (2) OVOCs with humidity added (r.h. % 50%), and (3) OVOCs with ozone (%60 ppbv) and humidity (r.h. % 50%). The SAPHIR chamber proved to be an excellent facility for conducting this experiment. Measurements from individual instruments were compared to mixing ratios calculated from the chamber volume and the known amount of OVOC injected into the chamber. Benzaldehyde and 1-butanol, compounds with the lowest vapor pressure of those studied, presented the most overall difficulty because of a less than quantitative transfer through some of the participants' analytical systems. The performance of each individual instrument is evaluated with respect to reference values in terms of time series and correlation plots for each compound under the three measurement conditions. A few of the instruments performed very well, closely matching the reference values, and all techniques demonstrated the potential for quantitative OVOC measurements. However, this study showed that nonzero offsets are present for specific compounds in a number of instruments and overall improvements are necessary for the majority of the techniques evaluated here.Citation: Apel, E. C., et al. (2008), Intercomparison of oxygenated volatile organic compound measurements at the SAPHIR atmosphere simulation chamber,

Abstract. An analysis of the tropospheric ozone (O 3 ) columns (TOCs) derived from SCIAMACHY limb-nadirmatching (LNM) observations during the period 2003-2011, focusing on global variations in TOC, is described. The changes are derived using a multivariate linear regression model. TOC shows changes of −0.2±0.4, 0.3±0.4, 0.1±0.5 and 0.1 ± 0.2 % yr −1 , which are not statistically significant at the 2σ level in the latitude bands 30-50 • N, 20 • S-0, 0-20 • N and 50-30 • S, respectively. Tropospheric O 3 shows statistically significant increases over some regions of South Asia (1-3 % yr −1 ), the South American continent (up to 2 % yr −1 ), Alaska (up to 2 % yr −1 ) and around Congo in Africa (up to 2 % yr −1 ). Significant increase in TOC is determined off the continents including Australia (up to 2 % yr −1 ), Eurasia (1-3 % yr −1 ) and South America (up to 3 % yr −1 ). Significant decrease in TOC (up to −3 % yr −1 ) is observed over some regions of the continents of North America, Europe and South America. Over the oceanic regions including the Pacific, North Atlantic and Indian oceans, significant decreases in TOC (−1 to −3 % yr −1 ) were observed. In addition, the response of the El Niño-Southern Oscillation (ENSO) and quasi-biennial oscillation (QBO) to changes in TOC for the period 2003-2011 was investigated. The result shows extensive regions, mostly in the tropics and Northern Hemisphere extratropics, of significant ENSO responses to changes in TOC and a significant QBO response to TOC changes over some regions.

Abstract. The increasing amounts of reactive nitrogen in the stratosphere necessitate accurate global measurements of stratospheric nitrogen dioxide (NO 2 ). Over the past decade, the SCIAMACHY (SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY) instrument on ENVISAT (European Environmental Satellite) has been providing global coverage of stratospheric NO 2 every 6 days. In this study, the vertical distributions of NO 2 retrieved from SCIAMACHY limb measurements of the scattered solar light are validated by comparison with NO 2 products from three different satellite instruments (SAGE II, HALOE and ACE-FTS). The retrieval algorithm based on the information operator approach is discussed, and the sensitivity of the SCIAMACHY NO 2 limb retrievals is investigated. The photochemical corrections needed to make this validation feasible, and the chosen collocation criteria are described. For each instrument, a time period of two years is analyzed with several hundreds of collocation pairs for each year. As NO 2 is highly variable, the comparisons are performed for five latitudinal bins and four seasons. In the 20 to 40 km altitude range, mean relative differences between SCIAMACHY and other instruments are found to be typically within 20 to 30 %. The mean partial NO 2 columns in this altitude range agree typically within 15 % (both global monthly and zonal annual means). Larger differences are seen for SAGE II comparisons, which is consistent with the results presented by other authors. For SAGE II and ACE-FTS, the observed differences can be partially attributed to the diurnal effect error.

Abstract. Tropospheric ozone (O 3 ), has two main sources: transport from the stratosphere and photochemical production in the troposphere. It plays important roles in atmospheric chemistry and climate change. Its amount and destruction are being modified by anthropogenic activity. Global measurements are needed to test our understanding of its sources and sinks. In this paper, we describe the retrieval of tropospheric O 3 columns (TOCs) from the combined limb and nadir observations (hereinafter referred to as limb-nadir-matching (LNM)) of the SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY) instrument, which flew as part of the payload onboard the European Space Agency (ESA) satellite Envisat (2002Envisat ( -2012. The LNM technique used in this study is a residual approach that subtracts stratospheric O 3 columns (SOCs), retrieved from the limb observations, from the total O 3 columns (TOZs), derived from the nadir observations. The technique requires accurate knowledge of the SOCs, TOZs, tropopause height, and their associated errors. The SOCs were determined from the stratospheric O 3 profiles retrieved in the Hartley and Chappuis bands from SCIAMACHY limb scattering measurements. The TOZs were also derived from SCIAMACHY measurements, but in this case from the nadir viewing mode using the Weighting Function Differential Optical Absorption Spectroscopy (WFDOAS) technique in the Huggins band. Comparisons of the TOCs from SCIAMACHY and collocated measurements from ozonesondes in both hemispheres between January 2003 and December 2011 show agreement to within 2-5 DU (1 DU = 2.69 × 10 16 molecules cm −2 ). TOC values from SCIAMACHY have also been compared to the results from the Tropospheric Emission Spectrometer (TES) and from the LNM technique exploiting Ozone Monitoring Instrument (OMI) and Microwave Limb Sounder (MLS) data (hereinafter referred to as OMI/MLS). All compared data sets agree within the given data product error range and exhibit similar seasonal variations, which, however, differ in amplitude. The spatial distributions of tropospheric O 3 in the SCIAMACHY LNM TOC product show characteristic variations related to stratosphere-troposphere exchange (STE) processes, anthropogenic activities and biospheric emissions.