Stephan Borrmann

A New Time-of-Flight Aerosol Mass Spectrometer (TOF-AMS)—Instrument Description and First Field Deployment

We report the development and first field deployment of a new version of the Aerosol Mass Spectrometer (AMS), which is capable of measuring non-refractory aerosol mass concentrations, chemically speciated mass distributions and single particle information. The instrument was constructed by interfacing the well-characterized Aerodyne AMS vacuum system, particle focusing, sizing, and evaporation/ionization components, with a compact TOFWERK orthogonal acceleration reflectron time-of-flight mass spectrometer. In this time-of-flight aerosol mass spectrometer (TOF-AMS) aerosol particles are focused by an aerodynamic lens assembly as a narrow beam into the vacuum chamber. Non-refractory particle components flash-vaporize after impaction onto the vaporizer and are ionized by electron impact. The ions are continuously guided into the source region of the time-of-flight mass spectrometer, where ions are extracted into the TOF section at a repetition rate of 83.3 kHz. Each extraction generates a complete mass spectrum, which is processed by a fast (sampling rate 1 Gs/s) data acquisition board and a PC. Particle size information is obtained by chopping the particle beam followed by time-resolved detection of the particle evaporation events. Due to the capability of the time-of-flight mass spectrometer of measuring complete mass spectra for every extraction, complete single particle mass spectra can be collected. This mode provides quantitative information on single particle composition. The TOF-AMS allows a direct measurement of internal and external mixture of non-refractory particle components as well as sensitive ensemble average particle composition and chemically resolved size distribution measurements. Here we describe for the first time the TOF-AMS and its operation as well as results from its first field deployment during the PM 2.5 Technology Assessment and Characterization Study—New York (PMTACS-NY) Winter Intensive in January 2004 in Queens, New York. These results show the capability of the TOF-AMS to measure quantitative aerosol composition and chemically resolved size distributions of the ambient aerosol. In addition it is shown that the single particle information collected with the instrument gives direct information about internal and external mixture of particle components.

Airborne observations of dust aerosol over the North Atlantic Ocean during ACE 2: Indications for heterogeneous ozone destruction

Aerosol size distribution measurements have been performed in the free troposphere during the Second Aerosol Characterization Experiment (ACE 2) near Tenerife, Canary Islands, in July 1997. During one measurement flight, on July 8, a uniform aerosol layer was encountered between 2.5 and 5.5 km altitude, characterized by a relatively low Aitken mode particle number concentration and high concentrations of accumulation and coarse mode particles, resulting in a relatively large aerosol surface area and mass, which is estimated to be about 400 μg m−3. Five-day backward trajectories indicate that the aerosol in this layer was mineral dust originating from arid regions on the North African continent. The dust layer was associated with reduced ozone mixing ratios. Model simulations have been performed with a photochemical box model including different heterogeneous removal reactions to study the interaction between gas phase chemistry and mineral aerosol. The best agreement between the observed and modeled ozone concentrations was obtained when heterogeneous removal of ozone and precursor gases on dust aerosol were taken into account. Heterogeneous O3 loss is estimated at 4 ppbv O3 per day. Although uncertainties concerning heterogeneous ozone removal remain, in particular related to the reactive uptake coefficient of O3, it is likely that the loss of O3 and precursor gases on mineral dust aerosol significantly reduces the O3 abundance in large-scale dust plumes.

The potential of cirrus clouds for heterogeneous chlorine activation

The ER-2 data from ascents and descents through layers of cirrus clouds are utilized to study the heterogeneous reactions of ClONO 2 with H 2 O, of HOCl and ClONO 2 with HCl, and their potential role for the activation of chlorine in the tropopause regions which could affect ozone there. Lacking measured data for the three chlorine containing molecules their abundances as a function of altitude have been calculated from a 2D model. The aerosol surface data measured by a Forward Scattering Spectrometer Probe (FSSP-300) on the ER-2 were corrected for the expected asphericity of cirrus cloud particles by means of a T-matrix method. The results indicate considerable potential of cirrus clouds for chlorine activation. If ClONO 2 and HCl are present in the tropopause region they are likely to be quickly converted to active chlorine by cirrus clouds.

Near‐field measurements on contrail properties from fuels with different sulfur content

Microphysical properties of jet exhaust aerosol and contrails were studied in the near field of the emitting aircraft for different fuel sulfur contents. Measurements were performed behind two different aircraft (ATTAS test aircraft of type VFW 614 and Airbus A310-300) using fuels with sulfur contents of 6 ppm and 2700 ppm, respectively. At closest approach (plume age ‹ 1 s), the total number concentrations exceeded the measuring range of the condensation particle counter, i.e., N › 10 5 cm -3 . The concentration of the dry accumulation mode aerosol, i.e., predominantly soot particles, was not affected by the fuel sulfur content. At a plume age of 10 s, an increase in total number concentration (D p › 0.01 µm) by a factor of 3.5 in the high sulfur case compared to the low sulfur case was observed. The ultrafine condensation nuclei fraction (0.007 µm ‹ D p ‹ 0.018 µm) contributed at maximum 70% to the total aerosol in the plume while this fraction was much less outside the plume. The high fuel sulfur content also caused an increase in the typical number concentrations of contrail particles by about one third with respect to low sulfur fuel, while the effective diameter of the size distribution was lowered at a fuel sulfur independent ice water content. The major differences in accumulation mode aerosol and microphysical contrail properties between the used aircraft were an increased number concentration of both the accumulation mode aerosol and the contrail particles in the Airbus A310-300 plume relative to the ATTAS plume. Part of the difference in contrail particles may be caused by different ambient conditions, but the major differences are assumed to be caused by different engine and wake properties.

The Kleiner Feldberg Cloud Experiment 1990. An overview

An overview is given of the Kleiner Feldberg cloud experiment performed from 27 October until 13 November 1990. The experiment was carried out by numerous European research groups as a joint effort within the EUROTRAC-GCE project in order to study the interaction of cloud droplets with atmospheric trace constituents. After a description of the observational site and the measurements which were performed, the general cloud formation mechanisms encountered during the experiment are discussed. Special attention is given here to the process of moist adiabatic lifting. Furthermore, an overview is given regarding the pollutant levels in the gas phase, the particulate and the liquid phase, and some major findings are presented with respect to the experimental objectives. Finally, a first comparison attempts to put the results obtained during this campaign into perspective with the previous GCE field campaign in the Po Valley.

ACRIDICON–CHUVA Campaign: Studying Tropical Deep Convective Clouds and Precipitation over Amazonia Using the New German Research Aircraft HALO

AbstractBetween 1 September and 4 October 2014, a combined airborne and ground-based measurement campaign was conducted to study tropical deep convective clouds over the Brazilian Amazon rain forest. The new German research aircraft, High Altitude and Long Range Research Aircraft (HALO), a modified Gulfstream G550, and extensive ground-based instrumentation were deployed in and near Manaus (State of Amazonas). The campaign was part of the German–Brazilian Aerosol, Cloud, Precipitation, and Radiation Interactions and Dynamics of Convective Cloud Systems–Cloud Processes of the Main Precipitation Systems in Brazil: A Contribution to Cloud Resolving Modeling and to the GPM (Global Precipitation Measurement) (ACRIDICON– CHUVA) venture to quantify aerosol–cloud–precipitation interactions and their thermodynamic, dynamic, and radiative effects by in situ and remote sensing measurements over Amazonia. The ACRIDICON–CHUVA field observations were carried out in cooperation with the second intensive operating period...

In situ measurements of background aerosol and subvisible cirrus in the tropical tropopause region

In situ aerosol measurements were performed in the Indian Ocean Intertropical Convergence Zone (ITCZ) region during the Airborne Polar Experiment-Third European Stratospheric Experiment on Ozone (APE-THESEO) field campaign based in Mahe, Seychelles between 24 February and 6 March 1999. These are measurements of particle size distributions with a laser optical particle counter of the Forward Scattering Spectrometer Probe (FSSP)-300 type operated on the Russian M-55 high-altitude research aircraft Geophysica in the tropical upper troposphere and lower stratosphere up to altitudes of 21 km. On 24 and 27 February 1999, ultrathin layers of cirrus clouds were penetrated by Geophysica directly beneath the tropical tropopause at 17 km pressure altitude and temperatures below 190 K. These layers also were concurrently observed by the Ozone Lidar Experiment (OLEX) lidar operating on the lower-flying German DLR Falcon research aircraft. The encountered ultrathin subvisual cloud layers can be characterized as (1) horizontally extending over several hundred kilometers, (2) persisting for at least 3 hours (but most likely much longer), and (3) having geometrical thicknesses of 100–400 m. These cloud layers belong to the geometrically and optically thinnest ever observed. In situ particle size distributions covering diameters between 0.4 and 23 μm obtained from these layers are juxtaposed with those obtained inside cloud veils around cumulonimbus (Cb) anvils and also with background aerosol measurements in the vicinity of the clouds. A significant number of particles with size diameters around 10 μm were detected inside these ultrathin subvisible cloud layers. The cloud particle size distribution closely resembles a background aerosol onto which a modal peak between 2 and 17 μm is superimposed. Measurements of particles with sizes above 23 μm could not be obtained since no suitable instrument was available on Geophysica. During the flight of 6 March 1999, upper tropospheric and lower stratospheric background aerosol was measured in the latitude band between 4°S and 19°S latitude. The resulting particle number densities along the 56th meridian exhibit very little latitudinal variation. The concentrations for particles with sizes above 0.5 μm encountered under these background conditions varied between 0.1 and 0.3 particles/cm3 of air in altitudes between 17 and 21 km.

ML-CIRRUS - The airborne experiment on natural cirrus and contrail cirrus with the high-altitude long-range research aircraft HALO

AbstractThe Midlatitude Cirrus experiment (ML-CIRRUS) deployed the High Altitude and Long Range Research Aircraft (HALO) to obtain new insights into nucleation, life cycle, and climate impact of natural cirrus and aircraft-induced contrail cirrus. Direct observations of cirrus properties and their variability are still incomplete, currently limiting our understanding of the clouds’ impact on climate. Also, dynamical effects on clouds and feedbacks are not adequately represented in today’s weather prediction models.Here, we present the rationale, objectives, and selected scientific highlights of ML-CIRRUS using the G-550 aircraft of the German atmospheric science community. The first combined in situ–remote sensing cloud mission with HALO united state-of-the-art cloud probes, a lidar and novel ice residual, aerosol, trace gas, and radiation instrumentation. The aircraft observations were accompanied by remote sensing from satellite and ground and by numerical simulations.In spring 2014, HALO performed 16 f...

Heterogeneous reactions on stratospheric background aerosols, volcanic sulfuric acid droplets, and type I polar stratospheric clouds: Effects of temperature fluctuations and differences in particle phase

Northern hemispheric ER-2 (NASA) data from stratospheric aerosol measurements during background conditions, periods disturbed by the influence of Mount Pinatubo, and polar stratospheric cloud (PSC) type I events are used to study the heterogeneous reactions of ClONO2 with H2O and of HOCl and ClONO2 with HCl in comparison to the gas phase reaction rate of OH with HCl. To calculate the reaction rates, the measured data of pressure, temperature, water vapor, and aerosol surface are utilized together with recent laboratory results for the heterogeneous reactive uptake coefficients. Because observations are limited, the mixing ratios of the gas phase species entering these rate calculations (i.e., ClONO2, HOCl, HCl, and N2O5) are taken from a two-dimensional model. It is found that in dense volcanic clouds at temperatures below 200 K the resulting heterogeneous reaction rates of chlorine activation can be of similar magnitude as the gas phase reaction rate. The heterogeneous rates in PSCs can exceed the gas phase rates by more than 2 orders of magnitude. For the ClONO2 and HOCl reactions the measured aerosol surfaces during the PSC events are treated both as liquid (e.g., ternary solution) droplets and as solid NAT to compare the effects of the different phases. The reaction rates on NAT are significantly lower than on liquid droplets. Indeed, this study shows that a transition from liquid ternary solutions to NAT is expected to reduce the rate of chlorine activation based on present chemical understanding and on observed aerosol surface areas. Additionally, the effect of temperature and surface area fluctuations on the heterogeneous reaction rates is discussed.

A Wind Tunnel Study on the Shape, Oscillation, and Internal Circulation of Large Raindrops with Sizes between 2.5 and 7.5 mm

Abstract Precipitation prediction using weather radars requires detailed knowledge of the shape parameters of raindrops falling at their terminal velocities in air. Because the raindrops undergo oscillation, the most important shape parameters from the radar prediction point of view are the equilibrium drop shape, the time-averaged axis ratio, and the oscillation frequency. These parameters for individual water drops with equivalent diameter from 2.5 to 7.5 mm were investigated in a vertical wind tunnel using high-speed video imaging. A very good agreement was found between the measured and the theoretically determined raindrop shape calculated by a force balance model. A new method was developed to determine the equivalent drop diameter with the help of the oscillation frequency. The drop size determination by means of the frequency method was found to be three times more precise than by volumetric methods. The time-averaged axis ratio was found to be equal to the equilibrium axis ratio in the investigat...