Measurements of Aerosols and Charged Particles On the BEXUS18 Stratospheric Balloon

This paper describes the aerosol measurement setup and results obtained during the BEXUS18 (Balloon-borne Experiments for University Students) stratospheric balloon within the A5-Unibo (Advanced Atmospheric Aerosol Acquisition and Analysis) experiment performed on 10 October 2014 in northern Sweden (Kiruna). The experimental setup was designed and developed by the University of Bologna with the aim of collecting and analyzing vertical profiles of atmospheric ions and particles together with atmospheric parameters (temperature, relative humidity, and pressure) all along the stratospheric ascent of the BEXUS18 stratospheric balloon. Particle size distributions were measured with the MeteoModem Light Optical Aerosol Counter (LOAC) and air ion density was measured with a set of two commercial and portable ion counters. Though the experimental setup was based upon relatively low-cost and light-weight sensors, vertical profiles of all the parameters up to an altitude of about 27\u2009km were successfully collected. The results obtained are useful for elucidating the relationships between aerosols and charged particles between ground level and the stratosphere, with great potential in collecting and adding useful information in this field, also in the stratosphere where such measurements are rare. In particular, the equipment detected coherent vertical profiles for particles and ions, with a particularly strong correlation between negative ions and fine particles, possibly resulting from proposed associations between cosmic rays and ions as previously suggested. In addition, the detection of charged aerosols in the stratosphere is in agreement with the results obtained by a previous flight and with simulations conducted with a stratospheric ion\u2013aerosol model. However, further measurements under stratospheric balloon flights equipped with a similar setup are needed to reach general conclusions about such important issues

Impact of volcanic eruptions on decadal variability of stratospheric age of air

A major uncertainty in current climate model simulations concerns the evolution of the stratospheric Brewer-Dobson circulation. Models show decreasing mean age, indicating an accelerating circulation, while observations show opposite decadal age variations in the Northern hemisphere. Here, we quantify the effect of the stratospheric volcanic aerosol on mean age variability, using mean age from reanalysis-driven TRACZILLA and CLaMS simulations for the 1989-2010 period, showing decadal variations consistent with observations. Our method is based on a multilinear regression technique using satellite observations of aerosol optical depth including Pinatubo and smaller volcanoes after 2002. We find that the decadal age variations can be primarily attributed to the volcanic signals. In particular the smaller volcanic eruptions after 2002, which are not included in most climate model simulations, cause most of the positive mean age decadal change in the Northern hemisphere after 2002. Consequently, the discrepancy between climate models and observations regarding decadal mean age changes (2002-2010) is likely related to the representation of volcanic stratospheric aerosol in the models

Significant contributions of volcanic aerosols to decadal changes in the stratospheric circulation

The stratospheric circulation is an important element of climate as it determines the amount of stratospheric water vapour and aerosol above the tropopause. It also impacts surface climate through downward coupling. Climate models predict that increasing greenhouse gas levels speed up the stratospheric circulation. However, these results have been challenged by observational estimates of the circulation strength, constituting an uncertainty in current climate simulations. Recent model simulations driven by observed meteorology suggest that the pattern of stratospheric circulation change is more complicated than a uniform speed up. Here, we quantify the effect of volcanic aerosol on the stratospheric circulation focussing on the Mt. Pinatubo eruption and discussing further the minor extratropical volcanic eruptions after 2008. We show that the observed pattern of decadal circulation change over the past few decades is substantially driven by volcanic aerosol injections. Thus, climate model simulations need to realistically take into account the effect of volcanic eruptions, including the minor eruptions after 2008, for a reliable reproduction of observed stratospheric circulation changes

Vertical distribution of the different types of aerosols in the stratosphere: Detection of solid particles and analysis of their spatial variability

Stratospheric aerosols play a significant role in stratospheric chemistry. In the past, it was assumed that only liquid droplets are present in the stratosphere. Nevertheless, a few lidar measurements have shown that sudden enhancement of aerosol content in the middle stratosphere could be due to meteoritic debris. Aircraft measurements have shown that solid particles can be found in the lower stratosphere; these particles are mainly soot, but also include some interplanetary material. In order to better document the various characteristics of aerosols in the unperturbed stratosphere (i.e., free of volcanic aerosols), we have performed observations using different balloon-borne instruments (Stratospheric and Tropospheric Aerosol Counter (STAC), Spectroscopie d'Absorption Lunaire pour l'Observation des Minoritaires Ozone et NOx (SALOMON), and Micro Radiometre Ballon (MicroRADIBAL)) and also some satellite data (Global ozone monitoring by occultation of stars Envisat (GOMOS-Envisat)). These instruments allow us to obtain the number of particles in different size classes, the wavelength dependence of aerosol extinction, and the radiance of the light scattered by aerosols. Combining all the data together, it appears that significant amounts of particles are ubiquitous in the middle stratosphere, above the canonical sulfate aerosol layer. "Background'' interplanetary dusts in low concentration are likely present in the stratosphere. Above 30 km, interplanetary dust and largest grains from meteoroid disintegration dominate. Although the disintegration of meteoroids occurs in the upper stratosphere or in the mesosphere at all latitudes, these solid aerosols can be transported to the polar regions by the general circulation and can descend into the middle and lower stratosphere during winter mesospheric descents. Between about 22 km and 30 km, soot particles contribute to the population of aerosols at all latitudes. These soot, likely originating from biomass burning at all latitudes, could be injected into the lower stratosphere by the pyroconvective effect and can then reach the middle stratosphere perhaps owing to the gravitophotophoresis effect as was theoretically proposed. In the lower unperturbed stratosphere, liquid sulfate aerosols dominate, although soot particles are still present. Local horizontal and vertical enhancements of solid aerosols have sometimes been detected, although their origin is not yet determined. The presence of these solid particles can strongly bias the interpretation of in situ and remote sensing measurements when only the presence of liquid aerosols is assumed. Therefore, a new strategy of measurement will be necessary in the future to better characterize the stratospheric aerosol content free of volcanic particles

In situ measurement of the Icelandic Holuhraun/ Bárðarbunga volcanicplume in an early “young state” using a LOAC

International audienceVolcanic eruptions have huge societal and economic consequences. In Iceland, one of the best known examples isthe Laki eruption (1783-84 CE) (Thordarson and Self, 2003) which caused the death of > 20% of the Icelandicpopulations and likely increased European levels of mortality through air pollution (Witham and Oppenheimer,2004). The recent fissure eruption at Holuhraun (31 August 2014 – 27 February 2015) was a major source ofsulfur gases and aerosols and caused also both local and European-wide deteriorations to air quality (Gislason etal. 2015; Schmidt et al. 2015).The capability of atmospheric models to predict volcanic plume impacts is limited by uncertainties in thenear-source plume state. Most in-situ measurements of the elevated plume involve interception of aged plumesthat have already chemically or physically evolved. Small portable sensors airborne drone or balloon platformsoffer a new possibility to characterize volcano plumes near to source.We present the results of a balloon flight through the plume emitted by Baugur the main vent during the nightof the January 22th 2015. The balloon carrying a LOAC (Renard et al. 2015) has intercepted the plume at 8kmdistance downwind from the crater which represents a plume age of approximately 15 minutes. The plume waslocated in altitude between 2 and 3.1km above the sea level. Two layers were observed, a non-condensed lowerlayer and a condensed upper layer. The lower layer of 400m thick was characterized by a mode of fine particlescentered on 0.2m in diameter and a second mode centered on 2.3m in diameter and a total particle concentrationaround 100 particles per cubic centimeter. The upper layer of 800m thick was a cloud-like signature with dropletscentered on 20 m in diameter and a fine mode, the total particles concentrations was 10 times higher than thefirst layer. The plume top height was determined between 2.7 and 3.1 km, the plume height is in good agreementwith an estimate made by analysis of IASI satellite remote sensing data, thus demonstrating in-situ validation ofthis recent satellite algorithm (Carboni et al. 2015).This experimentation shows that under such difficult field campaign conditions (strong wind, low temperatures,only car batteries for power supply, night time and active volcano close to the launch site) it is possible to launchmeteorological balloons with novel payloads to directly sample in-situ the near-source plume, determine theplume altitude, identify dynamical phases of the plume and document the size distribution of particles inside aplume which is only a quarter of an hour old