RESUMEN
Sulfuric acid is widely recognized as a very important substance driving atmospheric aerosol nucleation. Based on quantum chemical calculations it has been suggested that the quantitative detection of gas phase sulfuric acid (H2SO4) by use of Chemical Ionization Mass Spectrometry (CIMS) could be biased in the presence of gas phase amines such as dimethylamine (DMA). An experiment (CLOUD7 campaign) was set up at the CLOUD (Cosmics Leaving OUtdoor Droplets) chamber to investigate the quantitative detection of H2SO4 in the presence of dimethylamine by CIMS at atmospherically relevant concentrations. For the first time in the CLOUD experiment, the monomer sulfuric acid concentration was measured by a CIMS and by two CI-APi-TOF (Chemical Ionization-Atmospheric Pressure interface-Time Of Flight) mass spectrometers. In addition, neutral sulfuric acid clusters were measured with the CI-APi-TOFs. The CLOUD7 measurements show that in the presence of dimethylamine (<5 to 70 pptv) the sulfuric acid monomer measured by the CIMS represents only a fraction of the total H2SO4, contained in the monomer and the clusters that is available for particle growth. Although it was found that the addition of dimethylamine dramatically changes the H2SO4 cluster distribution compared to binary (H2SO4-H2O) conditions, the CIMS detection efficiency does not seem to depend substantially on whether an individual H2SO4 monomer is clustered with a DMA molecule. The experimental observations are supported by numerical simulations based on A Self-contained Atmospheric chemistry coDe coupled with a molecular process model (Sulfuric Acid Water NUCleation) operated in the kinetic limit.
RESUMEN
New particle formation (NPF) is the source of over half of the atmosphere's cloud condensation nuclei, thus influencing cloud properties and Earth's energy balance. Unlike in the planetary boundary layer, few observations of NPF in the free troposphere exist. We provide observational evidence that at high altitudes, NPF occurs mainly through condensation of highly oxygenated molecules (HOMs), in addition to taking place through sulfuric acid-ammonia nucleation. Neutral nucleation is more than 10 times faster than ion-induced nucleation, and growth rates are size-dependent. NPF is restricted to a time window of 1 to 2 days after contact of the air masses with the planetary boundary layer; this is related to the time needed for oxidation of organic compounds to form HOMs. These findings require improved NPF parameterization in atmospheric models.
RESUMEN
BACKGROUND: It is common practice to administer a premedication to patients about to undergo anesthesia. This study compared the effects of a small intravenous bolus of propofol versus midazolam administered as a premedication. METHODS: In this prospective, randomized, double-blind, placebo-controlled study, 60 healthy adult subjects scheduled for general anesthesia were given midazolam (0.04 mg/kg), propofol (0.4 mg/kg) or saline intravenously in the anesthesia waiting room. Before administration and three times at 2.5 min intervals subsequently, blood pressure, heart rate, oxygen saturation and scores for anxiety and dizziness were recorded. Recall of words and images shown to the patient 5 min after drug administration was tested 10-30 min after recovery from anesthesia. RESULTS: Both propofol and midazolam helped relieve anxiety and lowered blood pressure (P<0.001, compared to baseline), but both were associated with greater dizziness scores (P<0.001, compared to placebo). Compared to placebo and propofol, midazolam was associated with more frequent respiratory depression (P<0.05) and significant impairment of anterograde explicit memory (P<0.05). CONCLUSION: Propofol may be an economical and safe alternative to midazolam for i.v. premedication.
