[1] Meteorological and chemical measurements, including peroxy radicals, made during the Berlin Ozone Experiment (BERLIOZ) in summer 1998 at Pabstthum, a rural site about 50 km NW of the city, are described. The analytical techniques and data quality are discussed, including the comparison of different methods deployed side by side at Pabstthum. The highest concentrations of NO x (>20 ppb) and other precursors were observed on days when relatively young air was advected to Pabstthum from the greater Berlin area. NO x often increased during the night due to emissions from the surrounding soils under stagnant conditions with a shallow boundary layer as is evident in the strong negative correlation between nocturnal NO mixing ratios and product of ozone and wind speed. The ozone production rate (PO 3 ) calculated from the photostationary state (PSS) of NO x and O 3 increased with NO and reached values of up to 90 ppb h À1 . PO 3 calculated from NO and the measured peroxy radical concentrations was much lower, around or below 10 ppb h À1 . The lower production rates obtained from the peroxy radical measurements are consistent with the ozone budget in the city plume of Berlin. The new JPL recommendation for the rate coefficient of the reaction of NO with O 3 slightly improves the disagreement between PSS and measured peroxy radicals. However, another enhancement of 10-20% in the rate coefficient would be required in order to match the results within the uncertainty of the measurements in the high NO x regime. Even then, PSS remains to overpredict PO 3 by a factor of 2 at low NO x concentrations. Hence, a yet unidentified process must exist in the atmosphere that converts NO to NO 2 without leading to a net production of ozone. The PSS results from other studies are similar as at Pabstthum, suggesting that the overestimation of peroxy radicals and PO 3 by the PSS approach is not a particular feature of the conditions at the site.

[1] The Photochemistry Experiment in BERLIOZ (PHOEBE) was conducted in July/August 1998 at a rural site located near the small village Pabstthum, about 50 km NW of downtown Berlin. More than 60 nonmethane hydrocarbons (NMHC) in the range of C 2 -C 10 were measured using two in situ gas chromatography (GC) systems. The first (GC1) was capable of measuring C 2 -C 10 hydrocarbons with a relatively high separation efficiency but low time resolution (80-90 min), while GC2 provided quasi-continuous measurements of C 5 -C 10 hydrocarbons with a time resolution of 20 min but with a poorer separation efficiency than GC1. The advantages of both systems were joined by interpolation between two data points of GC1 with the pattern given by GC2. For compounds that could not be reliably measured with GC2, patterns of compounds with similar reactivity were used. Air masses with the lowest photochemical age as estimated from the toluene/benzene ratio and the highest hydrocarbon mixing ratios were observed on 20 and 21 July when air was advected from the direction of Berlin. Alkanes were the most abundant hydrocarbons ($60%) on a molecular basis, followed by alkenes and aromatics. The reactivity of the hydrocarbons toward OH was dominated by the alkenes (>60%), with isoprene and a-pinene constituting the major part. The hydrocarbon data were used together with the other trace gases measured at Pabstthum to simulate OH, HO 2 , and RO 2 concentrations with the condensed chemical box model RACM. Relatively good agreement of the simulated radical concentrations with the spectroscopic measurements made at Pabstthum is observed for NO x mixing ratios >5 ppb, whereas the model overestimates OH and HO 2 by 100% and 40%, respectively, at low NO x . The discrepancy between measured and modeled OH does not correlate with the concentration of particles. The RO 2 concentrations are in good agreement with the measurements over the entire range of NO x . Sensitivity studies show that peroxyacetyl nitrate (PAN) is an important radical source and that missing volatile organic compound (VOC) reactivity is an unlikely explanation for the overestimation of HO x : By doubling of the VOC reactivity, OH and HO 2 can be brought into agreement. However, the model then overestimates the organic RO 2 concentrations by almost a factor of 2. Another important finding is that RACM overestimates the measured NO/NO 2 ratio by 25%. This and the overestimation of HO 2 lead to an overprediction of the local ozone formation rate by about 40% at low NO x mixing ratios.

Abstract.A small system for the unattended measurement of total odd nitrogen (NO y , i.e., the sum of NO and its atmospheric oxidation products) aboard civil in-service aircraft in the framework of MOZAIC is described. The instrument employs the detection of NO by its chemiluminescence with O 3 in combination with catalytic conversion of the other NO y compounds to NO at 300 • C on a gold surface in the presence of H 2 . The instrument has a sensitivity of 0.4-0.7 cps/ppt and is designed for unattended operation during 1-2 service cycles of the aircraft (400-800 flight hours). The total weight is 50 kg, including calibration system, compressed gases, mounting, and safety measures. The layout and inlet configuration are governed by requirements due to the certification for passenger aircraft. Laboratory tests are described regarding the conversion efficiency for NO 2 and HNO 3 (both >98%). Interference by non-NO y species is <1% for CH 3 CN and NH 3 , <5×10 −5 % for N 2 O (corresponding to <0.2 ppt fake NO y from ambient N 2 O) and 100% for HCN. The time response of the instrument is <1 s (90% change) for NO 2 . The response for HNO 3 is nonlinear: 20 s for 67%, 60 s for 80%, and 150 s for 90% response, respectively.

A B S T R A C T This work presents the characterisation of the Aerosol Package for the European Research Infrastructure IAGOS (In-service Aircraft for a Global Observing System). Condensation particle counter (CPC) are used to measure the aerosol number concentration of the total and the non-volatile particles. The size distribution is measured by means of an optical particle counter (OPC) in the diameter range of 0.25Á3 mm. In particular the OPC is characterised for (1) leakage, (2) flow and calibration stability over the expected IAGOS pressure range of 170 hPa to 1013 hPa, (3) OPC accuracy test by comparing extinction measurements with calculated values from Mie theory using the OPC size distribution and (4) the inter-instrumental precision. The CPC is characterised in the same pressure range for (1) the lower cut-off diameter, (2) the instrument accuracy by comparing with a reference instrument (Faraday Cup Electrometer, FCE) and (3) the instrument precision. We conclude that the IAGOS Aerosol Package is a fully automated, robust, low-maintenance instrument providing high precision measurements with good accuracy.

, a fully automatic NO y instrument was installed on one of the five Airbus A340 aircraft used in the MOZAIC project (Measurement of Ozone and Water Vapour by Airbus in-service Aircraft) for measurements of O 3 and H 2 O since 1994. This long-range aircraft was operated by Lufthansa, mainly out of Frankfurt and Munich. After an initial testing period, regular data collection started in May 2001. Until May 2005, 1533 flights have been recorded, corresponding to 8500 flight hours of NO y measurements. Concurrent data of NO y and O 3 are available from 1433 flights and concurrent data for CO, O 3 and NO y exist from 1125 flights since 2002. The paper describes the data availability in terms of geographical, vertical and seasonal distribution and discusses the quality and limitations of the data, including interference by HCN. The vast majority of vertical profiles were measured over Frankfurt, followed by Munich and North American airports. While most of the data were collected in the upper troposphere and lower stratosphere over the North Atlantic, significant data sets exist also from flights to Far and Middle East, whereas data from the tropics and the Southern Hemisphere are relatively sparse.