Unexpectedly high concentrations of ultrafine particles were observed over a wide range of latitudes in the upper troposphere and lower stratosphere. Particle number concentrations and size distributions simulated by a numerical model of ion-induced nucleation, constrained by measured thermodynamic data and observed atmospheric key species, were consistent with the observations. These findings indicate that, at typical upper troposphere and lower stratosphere conditions, particles are formed by this nucleation process and grow to measurable sizes with sufficient sun exposure and low preexisting aerosol surface area. Ion-induced nucleation is thus a globally important source of aerosol particles, potentially affecting cloud formation and radiative transfer.

Atmospheric lifetimes are evaluated for the fully fluorinated compounds CF4, C2F6, c‐C4F8, C6F14, and SF6 using a two‐dimensional transport and chemistry model which includes removal by electrons and ions in the mesosphere and lower thermosphere. Laboratory measurements of the pertinent reaction rates were carried out at thermal energy for free electrons and for the atmospheric ions O+, O2+, O−, O2−, NO+, H3O+, NO3−, and CO3−. Atmospheric removal by electrons reduces the lifetimes of c‐C4F8 and SF6 from about 3200 years to 1400 and 800 years, respectively, only if the respective product anions C4F8− and SF6− do not subsequently regenerate the parent neutral compounds. Atmospheric removal by ion reactions is minor or negligible, with the largest effect (∼5%) being removal of C6F14 by O2+. Removal of CF4 and C2F6 by O+ is probably the most important single destruction process in the atmosphere for these two compounds, but their lifetimes are governed by removal at the Earth's surface in high‐temperature combustors. While we show that the lifetimes of c‐C4F8 and SF6 may be significantly shorter than previously estimated, these compounds remain extremely long‐lived with significant global warming potentials.

No abstract

[1] On 28 February 2000, a volcanic cloud from Hekla volcano, Iceland, was serendipitously sampled by a DC-8 research aircraft during the SAGE III Ozone Loss and Validation Experiment (SOLVE I). It was encountered at night at 10.4 km above sea level (in the lower stratosphere) and 33-34 hours after emission. The cloud is readily identified by abundant SO 2 ( 1 ppmv), HCl ( 70 ppbv), HF ( 60 ppbv), and particles (which may have included fine silicate ash). We compare observed and modeled cloud compositions to understand its chemical evolution. Abundances of sulfur and halogen species indicate some oxidation of sulfur gases but limited scavenging and removal of halides. Chemical modeling suggests that cloud concentrations of water vapor and nitric acid promoted polar stratospheric cloud (PSC) formation at 201-203 K, yielding ice, nitric acid trihydrate (NAT), sulfuric acid tetrahydrate (SAT), and liquid ternary solution H 2 SO 4 /H 2 O/HNO 3 (STS) particles. We show that these volcanically induced PSCs, especially the ice and NAT particles, activated volcanogenic halogens in the cloud producing >2 ppbv ClO x . This would have destroyed ozone during an earlier period of daylight, consistent with the very low levels of ozone observed. This combination of volcanogenic PSCs and chlorine destroyed ozone at much faster rates than other PSCs that Arctic winter. Elevated levels of HNO 3 and NO y in the cloud can be explained by atmospheric nitrogen fixation in the eruption column due to high temperatures and/or volcanic lightning. However, observed elevated levels of HO x remain unexplained given that the cloud was sampled at night.

No abstract

A study has been made of the rate coefficients and product ion distributions for the reactions at 300 K of the ions N+, N2+, N3+, N4+, O+, O2+, and NO+ with CH3NH2, NH3, H2S, CH3OH, H2CO, COS, O2, H2O, CH4, CO2, CO, H2, and N2 molecules listed in increasing order of their ionization energies. These measurements are intended as a contribution to stratospheric chemistry. In the binary reactions of the ions of large recombination energy with molecules of low ionization energy, multiple ion products generally result and the rate coefficients are close to gas kinetic. Conversely, the low recombination energy ions NO+ and O2+ generally undergo ternary association reactions with the large ionization energy molecules. The reactions of N2+ and N4+ are very similar, the most common mechanism apparently being direct charge transfer usually followed by fragmentation, the nitrogen–nitrogen bonds in the reacting ions remaining intact. The N+ and N3+ reactions differ from the N2+ and N4+ reactions in that they show a greater propensity to form N–X bonds, X=O, C, S, H, etc. The O+ and O2+ reactions generally proceed via direct charge transfer where energetically possible.

Low-energy electron-molecule collisions are analyzed by kinetic modeling within the framework of statistical unimolecular rate theory. Nondissociative electron attachment to SF(6) is used to illustrate the approach. An internally consistent representation is provided for attachment cross sections and rate coefficients in relation to detachment lifetimes, and both thermal and specific rate coefficients for detachment. By inspecting experimental data, the contributions of intramolecular vibrational redistribution and vibrationally inelastic collisions can be characterized quantitatively. This allows for a prediction of attachment rate coefficients as a function of electron and gas temperature as well as gas pressure over wide ranges of conditions. The importance of carefully controlling all experimental parameters, including the carrier gas pressure, is illustrated. The kinetic modeling in Part II of this series is extended to dissociative electron attachment to SF(6).

An 80,000 km 2 stratospheric volcanic cloud formed from the 26 February 2000 eruption of Hekla (63.98° N, 19.70° W). POAM-III profiles showed the cloud was 9-12 km asl. During 3 days this cloud drifted north. Three remote sensing algo rithms (TOMS S0 2 , MODIS & TOVS 7.3 urn IR and MODIS 8.6 urn IR) estimat ed -0.2 Tg S0 2 . Sulfate aerosol in the cloud was 0.003-0.008 Tg, from MODIS IR data. MODIS and AVHRR show that cloud particles were ice. The ice mass peaked at -1 Tg -10 hours after eruption onset. A -0.1 Tg mass of ash was detected in the early plume. Repetitive TOVS data showed a decrease of S0 2 in the cloud from 0.2 Tg to below TOVS detection (i.e.O.Ol Tg) in -3.5 days. The stratospheric height of the cloud may result from a large release of magmatic water vapor early (1819 UT on 26 February) leading to the ice-rich volcanic cloud. The optical depth of the cloud peaked early on 27 February and faded with time, apparently as ice fell out. A research aircraft encounter with the top of the cloud at 0514 UT on 28 February, 35 hours after eruption onset, provided validation of algorithms. The aircraft's instruments measured -0.5-1 ppmv S0 2 and -35-70 ppb sulfate aerosol in the cloud, 10-30% lower than concentrations from retrievals a few hours later. Different S0 2 algorithms illuminate environmental variables which affect the qual ity of results. Overall this is the most robust data set ever analyzed from the first few days of stratospheric residence of a volcanic cloud.