Abstract. A large number of oxygenated organic chemicals (peroxyacyl nitrates, alkyl nitrates, acetone, formaldehyde, methanol, methylhydroperoxide, acetic acid and formic acid) were measured during the 1997 Subsonic Assessment (SASS) Ozone and Nitrogen Oxide Experiment (SONEX) airborne field campaign over the Atlantic. In this paper, we present a first picture of the distribution of these oxygenated organic chemicals (Ox-organic) in the troposphere and the lower stratosphere, and assess their source and sink relationships. In both the troposphere and the lower stratosphere, the total atmospheric abundance of these oxygenated species (ZOx-organic) nearly equals that of total nonmethane hydrocarbons (ZNMHC), which have been traditionally measured.
Large positive cluster ions with atomic mass numbers up to 2500 have for the first time been detected in the upper troposphere using an aircraft‐based large ion mass spectrometer (LIOMAS). Three ion families seem to be present (types 1, 2 and 3). Type 1 ions probably are H+BbWw (W is H2O and B is mostly acetone (CH3)2CO, and b ≤ 2). Type 2 ions are probably H+BbAaWw (A = H2SO4) formed by A‐attachment to type 1 ions. Type 3 ions are probably very small charged aerosols formed preferably by type 1 ion attachment to stable electrically neutral AxWy clusters. The latter are preferably formed by ion‐ion recombination. Hence our observations provide strong evidence for the ion‐mediated formation and growth of aerosol particles in the upper troposphere.
indicates that the ions observed in the plume were entrained ambient atmospheric ions. By contrast no indications for negative chemiions (with masses < 1100 amu) produced by the airbus engines were found in the plume. Furthermore our measurements indicate a modest decrease of the total concentration of entrained negative ions in the plume compared to the ambient atmosphere outside the plume. This decrease may be due to ion-removal by ion-attachment to aerosol-particles and/or ion-recombination with positive chemiions. We propose that the observed entrained ions can serve as probes for important plume components including gaseous sulfuric acid, aerosol particles and chemiions. Making use of this analytical potential we infer upper limits for the gaseous sulfuric acid concentration, total aerosol surface area density, and positive chemiion concentration. We conclude that initially formed gaseous sulfuric acid must have experienced rapid gas-to-particle conversion already in the very early plume at plume ages < 1.6 s.
Abstract. Acetone was measured in the free troposphere and lower stratosphere over the North Atlantic by aircraft-based CIMS (Chemical Ionization Mass Spectrometry) and GC (Gas Chromatography) instruments in fall 1997 within the framework of the POLINAT-2/SONEX campaigns. The measurements included 28 flights covering altitudes from 2.4 to 12.5 km, and geographic latitudes from 20 to 69 øN. The data are the most extensive measurements of acetone in the free troposphere and lower stratosphere published to date. A first comparison of the CIMS and the GC method is presented. The acetone data obtained by both instruments in the same air masses agree within 50% which is consistent with the uncertainty limits quoted. An inspection of all flights reveals upper tropospheric acetone to vary very substantially between 200 and 2200 pptv with a mean value of about 600 pptv. By contrast, in the lower stratosphere the acetone abundance is much less variable and is mostly around 100 to 200 pptv. Acetone rich air masses with volume mixing ratios exceeding 1000 pptv and reaching up to 2200 pptv were surprisingly frequently encountered in the upper troposphere. Probably these air masses had recent contact with the continental planetary boundary layer where they took up acetone and/or acetone precursor gases from ground-level sources.
Abstract.We have investigated the potential of upper tropospheric cloud condensation nuclei (CCN) formation from sulfur dioxide. This process involves three steps including SO2 conversion to gaseous sulfuric acid (GSA), homogeneous bimolecular nucleation of GSA and water vapor leading to new aerosol particles, and new aerosol particle growth via mutual coagulation and G SA-H20 condensation. Our investigation includes both measurements of SO2 and GSA as well as model calculations of SO2 conversion to new aerosol particles in the presence of preexisting aerosols which act as a competing sink for GSA. The model reproduces the measured abundance ratio GSA-SO2 reasonably well. Furthermore, the model predicts that efficient upper tropospheric CCN formation from SO2 may, in fact, occur under certain plausible conditions. These conditions are explored utilizing the factor Fcc•, defined as a ratio of the source and sink terms of gaseous sulfuric acid. In particular, a threshold FCCN value for efficient CCN formation is calculated with the model.
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