34 research outputs found
Production of highly oxygenated organic molecules (HOMs) from trace contaminants during isoprene oxidation
During nucleation studies from pure isoprene oxidation in the CLOUD chamber
at the European Organization for Nuclear Research (CERN) we observed
unexpected ion signals at m∕z  =  137.133
(C10H17+) and m∕z  =  81.070
(C6H9+) with the recently developed
proton-transfer-reaction time-of-flight (PTR3-TOF) mass spectrometer
instrument. The mass-to-charge ratios of these ion signals typically
correspond to protonated monoterpenes and their main fragment. We identified
two origins of these signals: first secondary association reactions of
protonated isoprene with isoprene within the PTR3-TOF reaction chamber and
secondly [4+2] cycloaddition (Diels–Alder) of isoprene inside the gas
bottle which presumably forms the favored monoterpenes limonene and
sylvestrene, as known from literature. Under our PTR3-TOF conditions used in
2016 an amount (relative to isoprene) of 2 % is formed within the
PTR3-TOF reaction chamber and 1 % is already present in the gas bottle.
The presence of unwanted cycloaddition products in the CLOUD chamber impacts
the nucleation studies by creating ozonolysis products as the corresponding
monoterpenes and is responsible for the majority of the observed highly
oxygenated organic molecules (HOMs), which in turn leads to a significant
overestimation of both the nucleation rate and the growth rate. In order to
study new particle formation (NPF) from pure isoprene oxidation under
relevant atmospheric conditions, it is important to improve and assure the
quality and purity of the precursor isoprene. This was successfully achieved
by cryogenically trapping lower-volatility compounds such as monoterpenes
before isoprene was introduced into the CLOUD chamber.</p
Rapid growth of new atmospheric particles by nitric acid and ammonia condensation
New-particle formation is a major contributor to urban smog, but how it occurs in cities is often puzzling. If the growth rates of urban particles are similar to those found in cleaner environments (1–10 nanometres per hour), then existing understanding suggests that new urban particles should be rapidly scavenged by the high concentration of pre-existing particles. Here we show, through experiments performed under atmospheric conditions in the CLOUD chamber at CERN, that below about +5 degrees Celsius, nitric acid and ammonia vapours can condense onto freshly nucleated particles as small as a few nanometres in diameter. Moreover, when it is cold enough (below −15 degrees Celsius), nitric acid and ammonia can nucleate directly through an acid–base stabilization mechanism to form ammonium nitrate particles. Given that these vapours are often one thousand times more abundant than sulfuric acid, the resulting particle growth rates can be extremely high, reaching well above 100 nanometres per hour. However, these high growth rates require the gas-particle ammonium nitrate system to be out of equilibrium in order to sustain gas-phase supersaturations. In view of the strong temperature dependence that we measure for the gas-phase supersaturations, we expect such transient conditions to occur in inhomogeneous urban settings, especially in wintertime, driven by vertical mixing and by strong local sources such as traffic. Even though rapid growth from nitric acid and ammonia condensation may last for only a few minutes, it is nonetheless fast enough to shepherd freshly nucleated particles through the smallest size range where they are most vulnerable to scavenging loss, thus greatly increasing their survival probability. We also expect nitric acid and ammonia nucleation and rapid growth to be important in the relatively clean and cold upper free troposphere, where ammonia can be convected from the continental boundary layer and nitric acid is abundant from electrical storms
Measurement of the collision rate coefficients between atmospheric ions and multiply charged aerosol particles in the CERN CLOUD chamber
Aerosol particles have an important role in Earth's
radiation balance and climate, both directly and indirectly through
aerosol–cloud interactions. Most aerosol particles in the atmosphere are
weakly charged, affecting both their collision rates with ions and neutral
molecules, as well as the rates by which they are scavenged by other aerosol
particles and cloud droplets. The rate coefficients between ions and aerosol
particles are important since they determine the growth rates and lifetimes
of ions and charged aerosol particles, and so they may influence cloud
microphysics, dynamics, and aerosol processing. However, despite their
importance, very few experimental measurements exist of charged aerosol
collision rates under atmospheric conditions, where galactic cosmic rays in
the lower troposphere give rise to ion pair concentrations of around 1000 cm−3. Here we present measurements in the CERN CLOUD chamber of the
rate coefficients between ions and small (<10 nm) aerosol particles
containing up to 9 elementary charges, e. We find the rate coefficient of a
singly charged ion with an oppositely charged particle increases from 2.0
(0.4–4.4) × 10−6 cm3 s−1 to 30.6 (24.9–45.1) × 10−6 cm3 s−1 for particles with charges of 1 to
9 e, respectively, where the parentheses indicate the ±1σ
uncertainty interval. Our measurements are compatible with theoretical
predictions and show excellent agreement with the model of
Gatti and Kortshagen (2008).</p
Mobile Tablet-basierte Datenerhebungen mit Feedbacksystem auf dem Weg in die Routineversorgung einer HNO-Klinik
TaBeL: gebrauchstaugliche Patient-Reported Outcomes für Patienten und Patientinnen mit Kopf-Hals-Tumoren
Sorption of 3,4-Dimethylpyrazole phosphate (DMPP) in Soils amended with different chabazite zeolitites
Interactive cognitive artifacts for enhancing situation awareness of incident commanders in mass casualty incidents
Effects of Different Chabazite Zeolite Amendments to Sorption of Nitrification Inhibitor 3,4-Dimethylpyrazole Phosphate (DMPP) in Soil
Application of natural zeolitites (ZTs, rock with > 50% of zeolites) as a soil amendment is recognized as a suitable method for increasing substrate quality. ZT is used at natural state or pre-enriched with specific cations (e.g., NH4+) to slow-release nutrients. ZT at natural state has been shown to mitigate gaseous N losses and favor crop yield, while NH4-enriched ZT has been reported to show quick NO3 12 production and relatively high gaseous N losses. The use of nitrification inhibitors (NIs) could alleviate these losses. In this work, the sorption behavior of a synthetic NI 3,4-dimethylpyrazole phosphate (DMPP) on different soil-ZT mixtures as well as on pure ZTs (natural and NH4-enriched) was tested. High sorption of NI can reduce its inhibitory effects and consequently the nitrogen use efficiency (NUE). Results show that natural ZTs had a deficient capacity for DMPP sorption and thus decreased the possibility to retain DMPP once applied to the soil. The sorption capacity strongly positively correlated to soil organic C content, supporting that sorption was mainly driven by soil organic matter. Any types of ZT added to the soil, notably that at natural state, have decreased the potential sorption of DMPP principally because of a dilution of the total organic C which reduced substrate hydrophobicity. A lower DMPP sorption in the substrate can mean higher availability of DMPP to soil microbial biomass and thus a higher potential in inhibiting nitrification. These beneficial effects may result in an advantageous strategy for increasing NUE