In this study we present gas-exchange measurements conducted in a large-scale wind–wave tank. Fourteen chemical species spanning a wide range of solubility (dimensionless solubility, α = 0.4 to 5470) ...and diffusivity (Schmidt number in water, Scw = 594 to 1194) were examined under various turbulent (u10 = 0.73 to 13.2 m s−1) conditions. Additional experiments were performed under different surfactant modulated (two different concentration levels of Triton X-100) surface states. This paper details the complete methodology, experimental procedure and instrumentation used to derive the total transfer velocity for all examined tracers. The results presented here demonstrate the efficacy of the proposed method, and the derived gas-exchange velocities are shown to be comparable to previous investigations. The gas transfer behaviour is exemplified by contrasting two species at the two solubility extremes, namely nitrous oxide (N2O) and methanol (CH3OH). Interestingly, a strong transfer velocity reduction (up to a factor of 3) was observed for the relatively insoluble N2O under a surfactant covered water surface. In contrast, the surfactant effect for CH3OH, the high solubility tracer, was significantly weaker.
Kinetics of HCI uptake on ice at 190 and 203 K Huthwelker, T.; Malmström, Maria E.; Helleis, F. ...
The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory,
07/2004, Letnik:
108, Številka:
30
Journal Article
Recenzirano
The uptake of HCl on vapor-deposited ice is investigated for HCl partial pressure p from 2 x 10(-8) to 10(-5) Torr at temperatures of 190 and 203 K in an especially designed Knudsen cell experiment. ...Two kinetic regimes can be distinguished experimentally: a long-lasting tailing which accounts for the major amount of the overall uptake and follows diffusion-like kinetics, gamma(t) proportional to t(-1/2) (gamma, uptake coefficient; t, time), and an initial period, where the uptake is higher than predicted by diffusion-like kinetics. The uptake kinetics are analyzed using analytical equations and also by full numerical simulation of simultaneous adsorption onto the surface and diffusion into the bulk. We derive the quantity H-d*D-1/2 (H-d*, effective Henry's law constant, D diffusion constant) and find H-d*D-1/2 proportional to p(-1/2), which implies that HCl dissociates upon uptake. The results for both analysis methods closely coincide. We suggest the use of a semiempirical parametrization for the total HCl uptake (molecules per geometric surface area) on vapor-deposited ice films as time dependent function n(t, p) = n(resid)(P) + C(T)(tp)(1/2), where C(T) is a constant which depends on temperature only. The compatibility of the residual, nondiffusive uptake, n(resid), with various adsorption isotherms is discussed. The analysis suggests that the experimentally observed diffusion-like kinetics dominates the overall trace gas uptake after a brief initial period. The diffusion-like kinetics must be considered when analyzing uptake experiments and when making applications to natural ice.
Size-resolved and vertical profile measurements of single particle chemical composition (sampling altitude range 50–3000 m) were conducted in July 2014 in the Canadian high Arctic during an ...aircraft-based measurement campaign (NETCARE 2014). We deployed the single particle laser ablation aerosol mass spectrometer ALABAMA (vacuum aerodynamic diameter range approximately 200–1000 nm) to identify different particle types and their mixing states. On the basis of the single particle analysis, we found that a significant fraction (23 %) of all analyzed particles (in total: 7412) contained trimethylamine (TMA). Two main pieces of evidence suggest that these TMA-containing particles originated from emissions within the Arctic boundary layer. First, the maximum fraction of particulate TMA occurred in the Arctic boundary layer. Second, compared to particles observed aloft, TMA particles were smaller and less oxidized. Further, air mass history analysis, associated wind data and comparison with measurements of methanesulfonic acid give evidence of a marine-biogenic influence on particulate TMA. Moreover, the external mixture of TMA-containing particles and sodium and chloride (Na ∕ Cl-) containing particles, together with low wind speeds, suggests particulate TMA results from secondary conversion of precursor gases released by the ocean. In contrast to TMA-containing particles originating from inner-Arctic sources, particles with biomass burning markers (such as levoglucosan and potassium) showed a higher fraction at higher altitudes, indicating long-range transport as their source. Our measurements highlight the importance of natural, marine inner-Arctic sources for composition and growth of summertime Arctic aerosol.
For efficient analysis and characterization of biological ice nuclei under immersion freezing conditions, we developed the Twin-plate Ice Nucleation Assay (TINA) for high-throughput droplet freezing ...experiments, in which the temperature profile and freezing of each droplet is tracked by an infrared detector. In the fully automated setup, a couple of independently cooled aluminum blocks carrying two 96-well plates and two 384-well plates, respectively, are available to study ice nucleation and freezing events simultaneously in hundreds of microliter-range droplets (0.1-40 µL). A cooling system with two refrigerant circulation loops is used for high-precision temperature control (uncertainty < 0.2 K), enabling measurements over a wide range of temperatures ( ⼠272-233 K) at variable cooling rates (up to 10 K min.sup.-1).
Volatile organic compounds (VOCs) are important for global air quality and oxidation processes in the troposphere. In addition to ground-based measurements, the chemical evolution of such species ...during transport can be studied by performing in situ airborne measurements. Generally, aircraft instrumentation needs to be sensitive, robust and sample at higher frequency than ground-based systems while their construction must comply with rigorous mechanical and electrical safety standards. Here, we present a new System for Organic Fast Identification Analysis (SOFIA), which is a custom-built fast gas chromatography–mass spectrometry (GC-MS) system with a time resolution of 2–3 min and the ability to quantify atmospheric mixing ratios of halocarbons (e.g. chloromethanes), hydrocarbons (e.g isoprene), oxygenated VOCs (acetone, propanal, butanone) and aromatics (e.g. benzene, toluene) from sub-ppt to ppb levels. The relatively high time resolution is the result of a novel cryogenic pre-concentration unit which rapidly cools (∼ 6 °C s−1) the sample enrichment traps to −140 °C, and a new chromatographic oven designed for rapid cooling rates (∼ 30 °C s−1) and subsequent thermal stabilization. SOFIA was installed in the High Altitude and Long Range Research Aircraft (HALO) for the Oxidation Mechanism Observations (OMO) campaign in August 2015, aimed at investigating the Asian monsoon pollution outflow in the tropical upper troposphere. In addition to a comprehensive instrument characterization we present an example monsoon plume crossing flight as a case study to demonstrate the instrument capability. Hydrocarbon, halocarbon and oxygenated VOC data from SOFIA are compared with mixing ratios of carbon monoxide (CO) and methane (CH4), used to define the pollution plume. By using excess (ExMR) and normalized excess mixing ratios (NEMRs) the pollution could be attributed to two air masses of distinctly different origin, identified by back-trajectory analysis. This work endorses the use of SOFIA for aircraft operation and demonstrates the value of relatively high-frequency, multicomponent measurements in atmospheric chemistry research.
We present a chemical ionization quadrupole mass
spectrometer (CI-QMS) with a radio-frequency (RF) discharge ion source through
N2∕CH3I as a source of primary ions. In addition to the expected
...detection of PAN, peracetic acid (PAA) and ClNO2 through well-established
ion–molecule reactions with I− and its water cluster, the instrument is
also sensitive to SO2, HCl and acetic acid (CH3C(O)OH) through
additional ion chemistry unique to our ion source. We present ionization
schemes for detection of SO2, HCl and acetic acid along with
illustrative datasets from three different field campaigns underlining the
potential of the CI-QMS with an RF discharge ion source as an alternative to
210Po. The additional sensitivity to SO2 and HCl makes the CI-QMS
suitable for investigating the role of sulfur and chlorine chemistry in the
polluted marine and coastal boundary layer.
In this paper, we present the design, development, and characteristics of the novel aerosol mass spectrometer ERICA (ERC Instrument
for Chemical composition of Aerosols; ERC – European Research ...Council) and
selected results from the first airborne field deployment. The instrument
combines two well-established methods of real-time in situ measurements of
fine particle chemical composition. The first method is the laser desorption and ionization technique, or laser ablation technique, for single-particle mass spectrometry (here with a frequency-quadrupled Nd:YAG laser at λ = 266 nm). The second method is a combination of thermal particle
desorption, also called flash vaporization, and electron impact ionization
(like the Aerodyne aerosol mass spectrometer). The same aerosol sample flow
is analyzed using both methods simultaneously, each using time-of-flight
mass spectrometry. By means of the laser ablation, single particles are
qualitatively analyzed (including the refractory components), while the flash vaporization and electron impact ionization technique provides quantitative information on the non-refractory components (i.e., particulate sulfate, nitrate, ammonia, organics, and chloride) of small particle ensembles. These
techniques are implemented in two consecutive instrument stages within a
common sample inlet and a common vacuum chamber. At its front end, the
sample air containing the aerosol particles is continuously injected via an
aerodynamic lens. All particles which are not ablated by the Nd:YAG laser in the first instrument stage continue their flight until they reach the second instrument stage and impact on the vaporizer surface (operated at 600 ∘C). The ERICA is capable of detecting single particles with
vacuum aerodynamic diameters (dva) between ∼ 180 and 3170 nm (d50 cutoff). The chemical characterization of single particles is achieved by recording cations and anions with a bipolar time-of-flight mass spectrometer. For the measurement of non-refractory components, the particle size range extends from approximately 120 to 3500 nm (d50 cutoff; dva), and the cations are detected with a time-of-flight mass
spectrometer. The compact dimensions of the instrument are such that the
ERICA can be deployed on aircraft, at ground stations, or in mobile laboratories.
To characterize the focused detection lasers, the ablation laser, and the
particle beam, comprehensive laboratory experiments were conducted. During
its first deployments the instrument was fully automated and operated during 11 research flights on the Russian high-altitude research aircraft M-55
Geophysica from ground pressure and temperature to 20 km altitude at 55 hPa and
ambient temperatures as low as −86 ∘C. In this paper, we show
that the ERICA is capable of measuring reliably under such conditions.
We describe the application of a three-laser tunable diode laser absorption spectrometer (TDLAS), called ‘tracer in-situ TDLAS for atmospheric research’ (TRISTAR), to measure nitrogen dioxide (NO
2), ...formaldehyde (HCHO) and hydrogen peroxide (H
2O
2), during an intensive measurement campaign on Mt. Cimone (44°11′N, 10°42′E, 2165 m asl), Northern Appenines, Italy in June 2000 as part of the EU-project ‘mineral dust and tropospheric chemistry’ (MINATROC). The TRISTAR instrument was a major component of an instrument package, provided by the Max-Planck-Insitut für Chemie, to investigate free tropospheric gas-phase chemistry over the Appenines. Here we discuss the optical, electronic, gas flow, and calibration setup of the TDLAS used during the campaign. We characterized extensively the instrument's performance during a preparatory phase in the laboratory and compared the laboratory results to the in-field results. Consistency checks with additional trace gas measurements obtained during the campaign create high confidence in the measured concentrations. Correlations between different trace gas species, along with other evaluation tools, allow a full chemical characterization of air masses to meet the goals of the campaign.
We present a novel and compact design of a constant-pressure inlet (CPI) developed for use in airborne aerosol mass spectrometry. In particular, the inlet system is optimized for aerodynamic lenses ...commonly used in aerosol mass spectrometers, in which efficient focusing of aerosol particles into a vacuum chamber requires a precisely controlled lens pressure, typically of a few hectopascals. The CPI device can also be used in condensation particle counters (CPCs), cloud condensation nucleus counters (CCNCs), and gas-phase sampling instruments across a wide range of altitudes and inlet pressures. The constant pressure is achieved by changing the inner diameter of a properly scaled O-ring that acts as a critical orifice. The CPI control keeps air pressure and thereby mass flow rate (≈0.1 L min−1) upstream of an aerodynamic lens constant, deviating at most by only ±2 % from a preset value. In our setup, a pressure sensor downstream of the O-ring maintains control of the pinch mechanism via a feedback loop and setpoint conditions are reached within seconds. The device was implemented in a few instruments, which were successfully operated on different research aircraft covering a wide range of ambient pressures, from sea level up to about 55 hPa. Details of operation and the quality of aerosol particle transmission were evaluated by laboratory experiments and in-flight data with a single-particle mass spectrometer.
The aim of this study is to show how a newly developed aerodynamic lens system (ALS), a delayed ion extraction (DIE), and better electric shielding improve the efficiency of the Aircraft-based Laser ...ABlation Aerosol MAss spectrometer (ALABAMA). These improvements are applicable to single-particle laser ablation mass spectrometers in general. To characterize the modifications, extensive size-resolved measurements with spherical polystyrene latex particles (PSL; 150–6000 nm) and cubic sodium chloride particles (NaCl; 400–1700 nm) were performed. Measurements at a fixed ALS position show an improved detectable particle size range of the new ALS compared to the previously used Liu-type ALS, especially for supermicron particles. At a lens pressure of 2.4 hPa, the new ALS achieves a PSL particle size range from 230 to 3240 nm with 50 % detection efficiency and between 350 and 2000 nm with 95 % detection efficiency. The particle beam divergence was determined by measuring the detection efficiency at variable ALS positions along the laser cross sections and found to be minimal for PSL at about 800 nm. Compared to measurements by single-particle mass spectrometry (SPMS) instruments using Liu-type ALSs, the minimum particle beam divergence is shifted towards larger particle sizes. However, there are no disadvantages compared to the Liu-type lenses for particle sizes down to 200 nm. Improvements achieved by using the DIE and an additional electric shielding could be evaluated by size-resolved measurements of the hit rate, which is the ratio of laser pulses yielding a detectable amount of ions to the total number of emitted laser pulses. In particular, the hit rate for multiply charged particles smaller than 500 nm is significantly improved by preventing an undesired deflection of these particles in the ion extraction field. Moreover, it was found that by using the DIE the ion yield of the ablation, ionization, and ion extraction process could be increased, resulting in up to 7 times higher signal intensities of the cation spectra. The enhanced ion yield results in a larger effective width of the ablation laser beam, which in turn leads to a hit rate of almost 100 % for PSL particles in the size range from 350 to 2000 nm. Regarding cubic NaCl particles the modifications of the ALABAMA result in an up to 2 times increased detection efficiency and an up to 5 times increased hit rate. The need for such instrument modifications arises in particular for measurements of particles that are present in low number concentrations such as ice-nucleating particles (INPs) in general, but also aerosol particles at high altitudes or in pristine environments. Especially for these low particle number concentrations, improved efficiencies help to overcome the statistical limitations of single-particle mass spectrometer measurements. As an example, laboratory INP measurements carried out in this study show that the application of the DIE alone increases the number of INP mass spectra per time unit by a factor of 2 to 3 for the sampled substances. Overall, the combination of instrument modifications presented here resulted in an increased measurement efficiency of the ALABAMA for different particle types and particles shape as well as for highly charged particles.
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