A proton-transfer reaction mass spectrometer based on time-of-flight mass spectrometry is described. This instrument couples a radioactive ion source and drift tube with a reflectron time-of-flight mass spectrometer. Volatile organic compounds in the gas phase with concentrations at the parts per billion by volume level can be detected in a matter of seconds, and crucially, the multichannel data acquisition in TOF-MS means that this detection sensitivity is available in all mass channels simultaneously. The typical mass resolution (m/Deltam) is in excess of 1000. The performance of the instrument is demonstrated using urban air measurements and a linear response/calibration test.

Abstract. A series of photooxidation experiments were conducted in an atmospheric simulation chamber in order to investigate the oxidation mechanism and secondary organic aerosol (SOA) formation potential of the model anthropogenic gas phase precursor, 1,3,5-trimethylbenzene. Alongside specific aerosol measurements, comprehensive gas phase measurements, primarily by Chemical Ionisation Reaction Time-of-Flight Mass Spectrometry (CIR-TOF-MS), were carried out to provide detailed insight into the composition and behaviour of the organic components of the gas phase matrix during SOA formation. An array of gas phase organic compounds was measured during the oxidation process, including several previously unmeasured primary bicyclic compounds possessing various functional groups. Analysis of results obtained during this study implies that these peroxide bicyclic species along with a series of ring opening products and organic acids contribute to SOA growth. The effect of varying the VOC/NOx ratio on SOA formation was explored, as was the effect of acid seeding. It was found that low NOx conditions favour more rapid aerosol formation and a higher aerosol yield, a result that implies a role for organic peroxides in the nucleation process and SOA growth.

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.

Both breakdown graphs and energy-dependent (ED) maps provide a means of visually representing the fragmentation processes resulting from collision-induced dissociation at different energies. The two presentation methods may be combined for a complete picture of the appearance, disappearance and maximum abundance collision potentials of each of the ions involved in the fragmentation process. A demonstration of this approach is presented using two very different classes of compound, an amino acid and a transition metal carbonyl cluster. Copyright # 2002 John Wiley & Sons, Ltd.Electrospray ionisation mass spectrometry (ESI-MS) is an enormously versatile analytical technique, allowing the collection of molecular weight data on a huge range of compounds hitherto inaccessible to mass spectrometry. 1Modern electrospray mass spectrometers also incorporate means of fragmenting ions produced in the ESI process, usually by collision-induced dissociation (CID) 2 either at the skimmer cone, in a collision cell or inside an ion trap or FTICR cell. 3 The extent of CID can be smoothly varied depending on the degree of fragmentation required, and the resulting ions provide useful structural information. A huge amount of data may be gathered in this way, and we have recently introduced the technique of energy-dependent electrospray ionisation mass spectrometry (EDESI-MS) as a convenient means of presenting this data. 4 It essentially involves a 2D projection (collision energy vs. m/z) of a 3D surface (the 3rd dimension, ion intensity, is on the axis perpendicular to the paper). The major advantages of this method are concise illustration of the data from up to 200 spectra and easy visualisation of the fragmentation sequence. EDESI-MS is a comprehensive solution to the problem of data presentation compared with the traditional approach of a stacked series of selected spectra. 5 We have recently extended the technique to laser-desorption/ionisation mass spectrometry (EDLDI-MS), 6 and, in the MS/MS mode, the`energy-dependent' method of data presentation is equally applicable to any ionisation technique. Breakdown graphs (a plot of percentage fragment ion abundance vs. collision energy or cone voltage) have been used by Harrison and others to obtain energy-resolved fragmentation data from CID experiments at the skimmer cone or in the collision cell of electrospray ionisation mass spectrometers.7 These breakdown graphs represent an alternative way of depicting the same data presented in an EDESI map, and may be incorporated into the EDESI-MS presentation in a logical way by including a breakdown graph on the right-hand side of the map. This approach results in a degree of redundancy, as the data illustrated on the map is projected both onto the mass axis (the summation spectrum at the top of the map) and to the cone (or collision) voltage axis (the breakdown graph at the side of the map). Nonetheless, it does provide an aid to interpretation in much the same way as the standard spectra that are typically projected onto two axes of a...

The recently developed technique of energy-dependent electrospray ionisation mass spectrometry (EDESI-MS) has been implemented on a triple quadrupole mass spectrometer such that fragmentation occurs in the collision cell rather than at the skimmer cone. This modification enables a superior two-dimensional map of the collision voltage versus mass-to-charge ratio to be generated, providing unambiguous peak assignments. This latest enhancement to the technique is referred to as energy-dependent electrospray ionisation tandem mass spectrometry (EDESI-MS/MS). In the present work the technique has been applied to investigate the sequential removal of ligands from the inorganic mixed-metal anionic cluster compound [Ru 5 EXPERIMENTALAll mass spectra were collected using a Micromass Quattro LC instrument, in negative-ion mode, with methanol as the mobile phase. The nebuliser tip was set at 3100 V and 90°C, and nitrogen was used as the bath gas. Samples were introduced directly into the source at 4 mLmin À1 via a syringe pump. Data collection was carried out in continuum mode. For the EDESI mass spectrum, the cone voltage was initially set at 0 V. A scan time of 7 s per spectrum and a low resolution setting (peak width at half-height $0.8 Da) were used to maximise the signal-to-noise ratio. The cone voltage was manually increased by increments of 1 V after every scan up to a maximum of 200 V. A full scan from 0±200 V therefore took approximately 25 min to collect. The EDESI-MS/MS spectrum was collected by selecting the m/z 1024.5

Abstract.A breadboard demonstrator of a novel UV/VIS grating spectrometer has been developed based upon a concentric arrangement of a spherical meniscus lens, concave spherical mirror and curved diffraction grating suitable for a range of atmospheric remote sensing applications from the ground or space. The spectrometer is compact and provides high optical efficiency and performance benefits over traditional instruments. The concentric design is capable of handling high relative apertures, owing to spherical aberration and comma being near zero at all surfaces. The design also provides correction for transverse chromatic aberration and distortion, in addition to correcting for the distortion called "smile", the curvature of the slit image formed at each wavelength. These properties render this design capable of superior spectral and spatial performance with size and weight budgets significantly lower than standard configurations. This form of spectrometer design offers the potential for exceptionally compact instrument for differential optical absorption spectroscopy (DOAS) applications from LEO, GEO, HAP or ground-based platforms. The breadboard demonstrator has been shown to offer high throughput and a stable Gaussian line shape with a spectral range from 300 to 450 nm at 0.5 nm resolution, suitable for a number of typical DOAS applications.

Abstract. A series of photooxidation experiments were conducted in an atmospheric simulation chamber in order to investigate the secondary organic aerosol (SOA) formed from the anthropogenic model gas phase precursor, 1,3,5-trimethylbenzene. Alongside specific aerosol measurements, comprehensive gas phase measurements, primarily by chemical ionisation reaction time-of-flight mass spectrometry (CIR-TOF-MS), were carried out to provide detailed insight into the composition and behaviour of the organic components of the gas phase matrix during SOA formation. An array of gas phase organic compounds was measured during the oxidation process, including several previously unmeasured primary bicyclic compounds possessing various functional groups. Analysis of results obtained during this study implies that these peroxide bicyclic species along with a series of furanones and organic acids contribute to SOA growth. The effect of varying the VOC/NOx ratio on SOA formation was explored, as was the effect of acid seeding. It was found that low NOx conditions favour more rapid aerosol formation and a higher aerosol yield, a finding that points towards a role for organic peroxides in the nucleation process and SOA growth.

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 in the Netherlands. Its main objectives were to determine the accuracy of state-of-the-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 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 Cabauw 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 NO₂, O₄ and HCHO with MAX-DOAS agree within 5 to 15%, vertical profiles of NO₂ derived from several independent instruments agree within 25%, and MAX-DOAS aerosol optical thickness agrees within 20–30% with AERONET data. For the in-situ NO₂ 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