T. Klüpfel

Free radicals and fast photochemistry during BERLIOZ

The free radicals OH, HO2, RO2, and NO3 are known to be the driving force for most chemical processes in the atmosphere. Since the low concentration of the above radicals makes measurements particularly difficult, only relatively few direct measurements of free radical concentrations have been reported to date. We present a comprehensive set of simultaneous radical measurements performed by Laser Induced Fluorescence (LIF), Matrix Isolation — Electron spin Resonance (MI-ESR), Peroxy Radical Chemical Amplification (PERCA), and Differential Optical Absorption Spectroscopy (DOAS) during the BERLIner OZonexperiment (BERLIOZ) during July and August of 1998 near Berlin, Germany. Most of the above radical species were measured by more than one technique and an intercomparison gave good agreement. This data set offered the possibility to study and quantify the role of each radical at a rural, semi-polluted site in the continental boundary layer and to investigate interconnections and dependencies among these free radicals. In general (box) modelled diurnal profiles of the different radicals reproduced the measurements quite well, however measured absolute levels are frequently lower than model predictions. These discrepancies point to disturbing deficiencies in our understanding of the chemical system in urban air masses. In addition considerable night-time peroxy radical production related to VOC reactions with NO3 and O3 could be quantified.

Airborne Measurements of Trace Organic Species in the Upper Troposphere Over Europe: the Impact of Deep Convection

Environmental Context. In the upper troposphere, sources of HOx such as acetone, peroxides, and aldehydes can play an important role in governing the production and destruction of ozone. Convection (over both land and sea) carries gases that can contribute to increased levels of HOx to the upper troposphere. The chemical impact of convection on the continental upper troposphere over Europe is studied by sampling the upper troposphere. Mass spectrometry techniques are used to analyze the collected samples. Such a study should aid in understanding the impact meteorological events have on atmospheric chemistry. Abstract. The volume mixing ratios of several organic trace gases and ozone (O3) were measured in the upper troposphere over Europe during the UTOPIHAN-ACT aircraft campaign in July 2003. The organic trace gases included alkanes, isoprene, aromatics, iodomethane, and trichloroethylene, oxygenates such as acetone, methanol, formaldehyde, carbon monoxide, and longer-lived tracer species such as chlorofluorocarbons and halochloroflurocarbons. The aim of the UTOPIHAN-ACT project was to study the chemical impact of deep convection on the continental upper troposphere. A Lear Jet aircraft, based in Germany, was flown at heights between 6 and 13 km in the region 59°N–42°N to 7°W–13°E during July 2003. Overall, the convectively influenced measurements presented here show a weaker variability lifetime dependence of trace gases than similar measurements collected over the Mediterranean region under more stable high-pressure conditions. Several cases of convective outflow are identified by the elevated mixing ratios of organic species relative to quiescent background conditions, with both biogenic and anthropogenic influences detectable in the upper troposphere. Enhancement at higher altitudes, notably of species with relatively short chemical lifetimes such as benzene, toluene, and even isoprene indicates deep convection over short timescales during summertime. The impact of deep convection on the local upper tropospheric formaldehyde and HOx budgets is assessed.

Ground‐based UV‐VIS spectroscopy: Diurnal OCIO‐profiles during January 1990 above Søndre Strømfjord, Greenland

Considerable amounts of chlorine dioxide, OClO, were observed from 5 January through 2 February, 1990 in the stratosphere above Soendre Stroemfjord showing a highly perturbed chlorine chemistry. Photolysis and simultaneous formation of the OClO leads to a typical concentration minimum at noon. Its changes in concentration indicate the release of the OClO precursors BrO and ClO from their respective reservoir substances in the morning. Two incidences of increased OClO production occur repeatedly at 92{degree} and 89{degree} solar zenith angle (SZA). Furthermore, in the beginning of January OClO morning values exceed those found at dusk for comparable SZA whereas towards the end of the month the morning values become depressed compared to the evening. The twilight vertical column densities of OClO often reach about 1.6 {times} 10{sup 13} molec/cm{sup 2} and a comparison shows an increase from 1988 to 1990.

Airborne measurements during the European Arctic Stratospheric Ozone Experiment: Observation of OClO

Within the European Arctic Stratospheric Ozone Experiment (EASOE) 1991/92, airborne UV-VIS spectral measurements of stratospheric OClO, NO2, and O3 were made by DOAS (Differential Optical Absorption Spectroscopy). The TRANSALL C160 was operated for the observation of the polar stratosphere from Kiruna (67°N), Sweden, during four campaigns from December 1991 to March 1992. Inside the vortex, the highest vertical column densities of OClO, up to 12 * 1012 molec cm−2 at a solar zenith angle of 90°, were observed during January and February 1992. The last OClO was detected on March 11 (4 * 1012 molec cm−2). Cross sections of the vortex showed the largest amounts of OClO within the core and lesser amounts in the vortex boundary. OClO was not detected outside the vortex within the detection limit which was 5*1012 molec cm−2 in December 1991 and about 2.5*1012 molec cm−2 in spring 1992.

Variation of atmospheric volatile organic compounds over the Southern Indian Ocean (30°S-49°S)

Environmental context. Oceans represent 70% of the blue planet, and surprisingly, ocean emission in term of volatile organic compounds is poorly understood. The potential climate impacts on a global scale of various trace organic gases have been established, and the terrestrial inputs are well studied, but little is known about which of these can be emitted from oceanic sources. In the present study, atmospheric samples were taken over the Southern Indian Ocean, while crossing some oceanic fronts and different phytoplankton species. Such a study should aid in understanding oceanic emission, especially from phytoplankton, and will help modellers to determine concentrations of organic traces in the remote marine troposphere. Abstract. Considering its size and potential importance, the ocean is poorly characterised in terms of volatile organic compounds (VOC) that play important roles in global atmospheric chemistry. In order to better understand their potential sources and sinks over the Southern Indian Austral Ocean, shipborne measurements of selected species were made during the MANCHOT campaign during December 2004, on board the research vessel Marion Dufresne. Along the transect La Reunion to Kerguelen Island, air measurements of selected VOC (including dimethylsulfide (DMS) isoprene, carbonyls and organohalogens), carbon monoxide and ozone were performed, crossing subtropical, temperate and sub-Antarctic waters as well as pronounced subtropical and sub-Antarctic oceanic fronts. The remote marine boundary layer was characterised at latitudes 45–50°S. Oceanic fronts were associated with enhanced chlorophyll and biological activity in the seawater and elevated DMS and organohalogens in the atmosphere. These were compared with a satellite-derived phytoplankton distribution (PHYSAT). Diurnal variation for isoprene, terpenes, acetone and acetaldehyde was observed, analogously to recent results observed in mesocosm experiments.

Cinema audiences reproducibly vary the chemical composition of air during films, by broadcasting scene specific emissions on breath.

Human beings continuously emit chemicals into the air by breath and through the skin. In order to determine whether these emissions vary predictably in response to audiovisual stimuli, we have continuously monitored carbon dioxide and over one hundred volatile organic compounds in a cinema. It was found that many airborne chemicals in cinema air varied distinctively and reproducibly with time for a particular film, even in different screenings to different audiences. Application of scene labels and advanced data mining methods revealed that specific film events, namely “suspense” or “comedy” caused audiences to change their emission of specific chemicals. These event-type synchronous, broadcasted human chemosignals open the possibility for objective and non-invasive assessment of a human group response to stimuli by continuous measurement of chemicals in air. Such methods can be applied to research fields such as psychology and biology, and be valuable to industries such as film making and advertising.

The measurement of active chlorine in the atmosphere by chemical amplification

Chemical amplification, CA, a method commonly used for the detection of peroxy radicals, HO2 and RO2, was found to be sensitive towards ClOx (Cl+ClO+OClO) as well. ClOx is reduced by NO to Cl atoms which react with carbon monoxide in the presence of O2. The reaction sequence thus initiated oxidizes CO to CO2 and NO to NO2, with a chain length of 300 ± 60. This allows the atmospheric ClOx content to be measured under ambient conditions with a detection limit of better than 1 ppt. In parallel peroxy radicals are indicated with a chain length of 160 ± 15. Chemical amplification is not specific and does not indicate which radical chain it is seeing. Identification relies solely on plausibility. During the ARCtic Tropospheric Ozone Chemistry (ARCTOC) campaign in spring 1995 and 1996 the CA technique was used at Ny-Ålesund. ClOx at mixing ratios of up to 2 ppt were found in the boundary layer under certain conditions. The low concentrations of ClOx indicate that the arctic boundary ozone depletion is mainly driven by bromine.

Groundbased measurements of stratospheric OClO, NO2, and O3 at Søndre Strømfjord in winter 1991/92

Experiment (EASOE) campaign Within the scope of the 1991/92 European Arctic Stratospheric Ozone stratospheric chlorine dioxide, OClO, nitrogen dioxide, NO2, bromine monoxide, BrO, and ozone, O3, were measured by groundbased UV-VIS remote sensing in Sondre Stromfjord, Greenland (50.4°W, 67.0°N). The measurement period was from the middle of November 1991 until the end of January 1992. The anticipated correlation between potential vorticity and OClO appeared less pronounced in the beginning and its abundance was similar inside and outside of the polar vortex. During November 1991 stratospheric temperatures throughout the polar region were still above threshold for polar stratospheric cloud (PSC) formation. During January when NO2 column densities were at their lowest, OClO inside of the vortex appeared to be highly variable. Average vertical column densities reached about 1013 molec cm−2, less than found in previous years. The chemistry as well as the observations may have been disturbed by the aerosol cloud from Mt. Pinatubo eruption.

Glyoxal measurement with a proton transfer reaction time of flight mass spectrometer (PTR-TOF-MS): characterization and calibration.

We examine the potential for PTR‐TOF‐MS systems to quantitatively measure glyoxal in ambient air by characterizing the response of the instrument to a dilute glyoxal sample, calibrating the system as a function of humidity. The concentration of glyoxal in a sample air‐stream was measured with an UV absorption spectrometer in parallel to a PTR‐TOF‐MS. This calibration demonstrated that the PTR‐TOF‐MS has a relatively low sensitivity to glyoxal particularly at high humidity. Extensive fragmentation of glyoxal to formaldehyde was observed. This behaviour not only desensitizes PTR‐MS system to glyoxal; it may also pose a problem to the quantification of formaldehyde.

Firework Emissions for Satellite Validation

Environmental Context. Satellite-based instruments for monitoring the Earth’s atmosphere observe the distribution of many gases and particles of interest. Many common sources of atmospheric gases and particles, such as fires, are geographically widespread and occur over a moderately long period. In contrast, fireworks pollute only a local area and for a brief period, and thus act as an ideal test of satellite instruments.