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Abstract. During LBA-CLAIRE-98, we found atmospheric layers with aged biomass smoke at altitudes > 10 km over Suriname. CO, CO2, acetonitrile, methyl chloride, hydrocarbons, NO, 03, and aerosols were strongly enhanced in these layers. We estimate

Abstract. An intensive field measurement campaign was performed in July/August 2002 at the Global Atmospheric Watch station Izaña on Tenerife to study the interaction of mineral dust aerosol and tropospheric chemistry (MINATROC). A dense Saharan dust plume, with aerosol masses exceeding 500 µg m-3, persisted for three days. During this dust event strongly reduced mixing ratios of ROx (HO2, CH3O2 and higher organic peroxy radicals), H2O2, NOx (NO and NO2) and O3 were observed. A chemistry boxmodel, constrained by the measurements, has been used to study gas phase and heterogeneous chemistry. It appeared to be difficult to reproduce the observed HCHO mixing ratios with the model, possibly related to the representation of precursor gas concentrations or the absence of dry deposition. The model calculations indicate that the reduced H2O2 mixing ratios in the dust plume can be explained by including the heterogeneous removal reaction of HO2 with an uptake coefficient of 0.2, or by assuming heterogeneous removal of H2O2 with an accommodation coefficient of 5x10-4. However, these heterogeneous reactions cannot explain the low ROx mixing ratios observed during the dust event. Whereas a mean daytime net ozone production rate (NOP) of 1.06 ppbv/hr occurred throughout the campaign, the reduced ROx and NOx mixing ratios in the Saharan dust plume contributed to a reduced NOP of 0.14-0.33 ppbv/hr, which likely explains the relatively low ozone mixing ratios observed during this event.

Abstract. Formaldehyde (HCHO) is an important intermediate product in the photochemical degradation of methane and non-methane volatile organic compounds. In August 2001, airborne formaldehyde measurements based on the Hantzsch reaction technique were performed during the Mediterranean INtensive Oxidant Study, MINOS. The detection limit of the instrument was 42 pptv (1σ ) at a time resolution of 180 s (10-90%). The overall uncertainty of the HCHO measurements was 30% at a mixing ratio of 300 pptv. In the marine boundary layer over the eastern Mediterranean Sea average HCHO concentrations were of the order of 1500 pptv, in reasonable agreement with results from a three-dimensional global chemical transport model of the lower atmosphere including non-methane volatile organic compound (NMVOC) chemistry. Above the boundary layer HCHO mixing ratios decreased with increasing altitude to a minimum level of 250 pptv at about 7 km. At higher altitudes (above 7 km) HCHO levels showed a strong dependency on the airmass origin. In airmasses from the North Atlantic/North American area HCHO levels were of the order of 300 pptv, a factor of 6 higher than values predicted by the model. Even higher HCHO levels, increasing to values of the order of 600 pptv at 11 km altitude, were observed in easterlies transporting air affected by the Indian monsoon outflow towards the Mediterranean basin. Only a small part (∼30 pptv) of the large discrepancy between the model results and the measurements of HCHO in the free troposphere could be explained by a strong underestimation of the upper tropospheric acetone concentration by up to a factor of ten by the 3D-model. Therefore, the measurement-model difference in the upper troposphere remains unresolved, while the observed dependency of HCHO on airmass origin might indicate that unknown, relatively long-lived NMVOCs -or their reaction intermediCorrespondence to: H. Fischer (hofi@mpch-mainz.mpg.de) ates -associated with biomass burning are at least partially responsible for the observed discrepancies.

Abstract. During the Mediterranean Intensive OxidantStudy (MINOS) in August 2001 a total of 14 measurement flights were performed with the DLR Falcon jet aircraft from Heraklion, Crete. One objective of this campaign was to investigate the role of long-range transport of pollutants into the Mediterranean area. An analysis of 5-day back trajectories indicates that in the lower troposphere (0-4 km) air masses originated from eastern and western Europe, in the mid-troposphere (4-8 km) from the North Atlantic Ocean region and in the upper troposphere (8-14 km) from North Atlantic Ocean/North America (NANA) as well as South Asia. We allocated all back trajectories to clusters based on their ending height and source region. The mixing ratios of ozone, nitrogen oxide, total reactive oxidized nitrogen (NO y ), formaldehyde, methanol, acetonitrile, acetone, peroxyacetyl nitrate (PAN), carbon dioxide, carbon monoxide and methane measured along the flight tracks are examined in relation to the different cluster trajectories. In the lower troposphere the mean trace gas mixing ratios of the eastern Europe cluster trajectories were significantly higher than those from western Europe. In the upper troposphere air from the NANA region seems to be influenced by the stratosphere, in addition, air masses were transported from South Asia, being influenced by strong convection in the Indian monsoon.

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.

Abstract. An intensive measurement campaign was performed in June 2000 at the Mt. Cimone station (44 • 11' N-10 • 42' E, 2165 m asl, the highest mountain in the northern Italian Apennines) to study photochemical ozone production in the lower free troposphere. In general, average mixing ratios of important trace gases were not very high (121 ± 20 ppbv CO, 0.284 ± 0.220 ppbv NOx, 1.15 ± 0.8 ppbv NOy, 58 ± 9 ppbv O 3 ), which indicates a small contribution by local pollution. Those trace gas levels are representative of continental background air, which is further supported by the analysis of VOCs (e.g.: C 2 H 6 = (905 ± 200) pptv, C 3 H 8 = (268 ± 110) pptv, C 2 H 2 = (201 ± 102) pptv, C 5 H 8 = (111 ± 124) pptv, benzene = (65 ± 33) pptv). Furthermore, significant diurnal variations for a number of trace gases (O 3 , CO, NOx, NOy, HCHO) indicate the presence of free tropospheric airmasses at nighttime as a consequence of local catabatic winds. Average mid-day peroxy radical concentrations at Mt. Cimone are of the order of 30 pptv. At mean NO concentrations of the order of 40 pptv this gives rise to significant in situ net O 3 production of 0.1-0.3 ppbv/hr. The importance of O 3 production is supported by correlations between O 3 , CO, NOz, and HCHO, and between HCHO, CO and NOy.