Published by Copernicus Publications on behalf of the European Geosciences Union. 458 A. J. M. Piters et al.: The CINDI campaign: design, execution and early resultsAbstract. From June to July 2009 more than thirty different in-situ and remote sensing instruments from all over the world participated in the Cabauw Intercomparison campaign for Nitrogen Dioxide measuring Instruments (CINDI). The campaign took place at KNMI's Cabauw Experimental Site for Atmospheric Research (CESAR) in the Netherlands. Its main objectives were to determine the accuracy of state-ofthe-art ground-based measurement techniques for the detection of atmospheric nitrogen dioxide (both in-situ and remote sensing), and to investigate their usability in satellite data validation. The expected outcomes are recommendations regarding the operation and calibration of such instruments, retrieval settings, and observation strategies for the use in ground-based networks for air quality monitoring and satellite data validation. Twenty-four optical spectrometers participated in the campaign, of which twenty-one had the capability to scan different elevation angles consecutively, the so-called Multi-axis DOAS systems, thereby collecting vertical profile information, in particular for nitrogen dioxide and aerosol. Various in-situ samplers and lidar instruments simultaneously characterized the variability of atmospheric trace gases and the physical properties of aerosol particles. A large data set of continuous measurements of these atmospheric constituents has been collected under various meteorological conditions and air pollution levels. Together with the permanent measurement capability at the CE-SAR site characterizing the meteorological state of the atmosphere, the CINDI campaign provided a comprehensive observational data set of atmospheric constituents in a highly polluted region of the world during summertime. First detailed comparisons performed with the CINDI data show that slant column measurements of NO 2 , O 4 and HCHO with MAX-DOAS agree within 5 to 15 %, vertical profiles of NO 2 derived from several independent instruments agree within 25 % of one another, and MAX-DOAS aerosol optical thickness agrees within 20-30 % with AERONET data. For the in-situ NO 2 instrument using a molybdenum converter, a bias was found as large as 5 ppbv during day time, when compared to the other in-situ instruments using photolytic converters.

Abstract. We present two Differential Optical Absorption Spectroscopy (DOAS) instruments built at RIVM: the RIVM DOAS and the miniDOAS. Both instruments provide virtually interference-free measurements of NH 3 concentrations in the atmosphere, since they measure over an open path, without suffering from inlet problems or interference problems by ammonium aerosols dissociating on tubes or filters. They measure concentrations up to at least 200 µg m −3 , have a fast response, low maintenance demands, and a high uptime. The RIVM DOAS has a high accuracy of typically 0.15 µg m −3 for ammonia for 5-min averages and over a total light path of 100 m. The miniDOAS has been developed for application in measurement networks such as the Dutch National Air Quality Monitoring Network (LML). Compared to the RIVM DOAS it has a similar accuracy, but is significantly reduced in size, costs, and handling complexity. The RIVM DOAS and miniDOAS results showed excellent agreement (R 2 = 0.996) during a field measurement campaign in Vredepeel, the Netherlands. This measurement site is located in an agricultural area and is characterized by highly variable, but on average high ammonia concentrations in the air. The RIVM-DOAS and miniDOAS results were compared to the results of the AMOR instrument, a continuous-flow wet denuder system, which is currently used in the LML. Averaged over longer time spans of typically a day, the (mini)DOAS and AMOR results agree reasonably well, although an offset of the AMOR values compared to the (mini)DOAS results exists. On short time scales, the (mini)DOAS shows a faster response and does not show the memory effects due to inlet tubing and transport of absorption fluids encountered by the AMOR. Due to its high accuracy, high uptime, low maintenance and its open path, the (mini)DOAS shows a good potential for flux measurements by using two (or more) systems in a gradient set-up and applying the aerodynamic gradient technique.

[1] Satellite instruments are efficient detectors of air pollutants such as NO 2 . However, the interpretation of satellite retrievals is not a trivial matter. We describe a novel instrument, the RIVM NO 2 mobile lidar, to measure tropospheric NO 2 profiles for the interpretation and validation of satellite data. During the DANDELIONS campaign in 2006 we obtained an extensive collection of lidar NO 2 profiles, coinciding with OMI and SCIAMACHY overpasses. On clear days and early mornings a comparison between lidar and in situ measurements showed excellent agreement. At other times the in situ monitors with molybdenum converters suffered from NO y interference. The lidar NO 2 profiles indicated a well-mixed boundary layer, with high NO 2 concentrations in the boundary layer and concentrations above not differing significantly from zero. The boundary layer concentrations spanned a wide range, which likely depends on the wind directions and on the intensity of local (rush hour) traffic which varies with the day of the week. Large diurnal differences were mainly driven by the height of the boundary layer, although direct photolysis or photochemical processes also contribute. Small-scale temporal and spatial variations in the NO 2 concentrations of the order of 20-50% were measured, probably indicative of small-scale eddies. A preliminary comparison between satellite and lidar data shows that the satellite data tend to overestimate the amount of NO 2 in the troposphere compared to the lidar data.

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[1] A detailed analysis of measurements and model calculations of clear-sky shortwave irradiances at the surface is presented for a set of 18 cases collected during 3 cloudless days in the Netherlands in 2000. The analysis is focused on the influence of the optical and physical properties of aerosols on simulations of direct and diffuse downward solar irradiance at the surface. The properties of aerosols in the boundary layer are derived from surface measurements, under the assumption that all aerosol is confined to a well-mixed atmospheric boundary layer. The simulations of the irradiances are performed with the radiative transfer model MODTRAN 4, version 1.1. The analysis reveals no discernable differences between model and measurement for the direct irradiance, but several significant differences for the diffuse irradiance. The model always overestimates the diffuse irradiance measurements by 7 to 44 Wm À2 (average: 25 Wm À2). On the basis of an estimated uncertainty in the differences of 18 Wm À2 , it appears that for 13 out of 18 cases the model significantly overestimates the measurements. This number decreases if instrumental errors (e.g., pyranometer zero-offset) and assumptions on the model input (e.g., wavelength-independent surface albedo) are considered. Nevertheless, the analysis presented here points to a persistent and significant positive model-measurement difference for the diffuse irradiance, which typically amounts to 1-4% of the top-ofatmosphere irradiance, and does not depend on the solar zenith angle. The reason for the discrepancy may be found in the presence of ultrafine absorbing aerosol particles that were not detected by the surface instrument for measuring aerosol absorption. It is also possible that these particles are not present near the surface, due to dry deposition, but do contribute to the total extinction if they are situated higher up in the boundary layer.

Abstract. Following a blind intercomparison of ozone profiling instruments in the

Abstract. An intercomparison of ozone-profiling instruments, two differential absorption lidars, a microwave radiometer, electrochemical concentration sendes, and the SAGE II satellite instrument is presented. The ground-based instruments were located at the Network for the Detection of Stratospheric Change (NDSC) primary station at Lauder, New Zealand. The campaign, which took place between April 15 and 29, 1995, strictly followed the NDSC guidelines for a blind intercomparison. Agreement between the measurements was within 15% for single profiles and within 10% for the campaign average, in the region from 20 to 40 km altitude. Outside of this region the differences were greater but can generally be ascribed to the limits of a particular instrument. IntroductionThe New Zealand National Institute of Water and Atmosphere (NIWA) atmospheric research station at Lauder (45.05øS, 169.68øE) has bccn designated as a primary site within the Network for the Detection of Stratosphcric Change (NDSC). To fulfil this role, a variety of instruments have been installed at Lauder in order to make regular measurements of a number of important atmospheric species in accordance with the NDSC goal to make observations through which changes in the physical and chemical state of the stratosphere and upper troposphere can bc determined and understood. In particular, the NDSC aims to make the carllest possible detection of changes in the ozone layer and to discern the cause of such changes. 1øIDEA Corporation, Beltsville, Maryland.•iNASA Goddard Space Flight Center, Laboratory for Atmospheres, Greenbelt, Maryland.•2Physics and Astronomy Department, University of Massachusetts, Amherst, and Millitech Corporation, South Deerfield, Massachusetts.•3Now at NASA Langley Research Center, Hampton, Virginia.•4Lockheed Engineering and Sciences Co., Hampton, Virginia.•SNow at GATS, Inc., Hampton, Virginia.•%cience and Technology Corporation, Hampton, Virginia.• ties in the intercomparisons due to spatial sampling, but it should be recognized that the instruments all did observe somewhat different air volumes. Similarly, attempts were made to coordinate measurements at the same time, nominally local midnight. The long integration times employed by the lidars and the microwave radiometer helped to smooth out differences due to spatial and temporal sampling, but this was not the case for the ozonesondes, which made essentially instantaneous measurements at each altitude during the balloon ascent. Since the lidars could not operate simultaneously because of interference caused by light backscattered by the different laser beams, the night was divided into four periods, two before midnight and two after, and the lidars were scheduled to run alternately during these periods. If the early lidar measurement appeared to be successful, determined primarily by the weather/cloud conditions, then an ozonesonde was launched as the next lidar measurement commenced.By mutual consent of the investigators it was decided that the results would be compared as ozone ...