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

Abstract

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

Extreme levels of Canadian wildfire smoke in the stratosphere over central Europe on 21–22 August 2017

“…Such dense smoke layers disturb chemical processes, radiative fluxes, and even heterogeneous ice formation in the upper troposphere; this may continue over a period of weeks to several months. The black carbon aerosol partly enriches the natural soot particle reservoir between 20 and 30 km by upward motions (Renard et al, 2008).…”

“…Fromm et al (2000Fromm et al ( , 2003 and Rosenfeld et al (2007) showed that large amounts of fire smoke can be lifted up to the tropopause within a short time period (less than 1 h) and can partly reach the lower stratosphere via the formation of pyrocumulonimbus clouds that are associated with strong updrafts with vertical wind velocities of 10-30 m s −1 (Fromm et al, 2010;Peterson et al, 2017). Self-lifting effects (Boers et al, 2010;Siddaway and Petelina, 2011;de Laat et al, 2012) and gravito-photophoresis forces (Rohatschek, 1996;Pueschel et al, 2000;Cheremisin et al, 2005;Renard et al, 2008) lead to a further ascent of the soot-containing layers.…”

LOAC: a small aerosol optical counter/sizer for ground-based and balloon measurements of the size distribution and nature of atmospheric particles – Part 1: Principle of measurements and instrument evaluation

“…Aerosol particles counters are often used on the ground; some of them are used in the free atmosphere on-board aircraft or large balloons during dedicated campaigns, for example for the studies of desert dust events or volcanic aerosols (Bukowiecki et al, 2011;Jégou et al, 2013;Ryder et al, 2013) or for stratospheric studies (Rosen, 1964;Ovarlez and Ovarlez, 1995;Deshler et al, 2003;Renard et al, 2008, Renard et al, 2010b. We propose here a new optical particle counter concept called LOAC (Light Optical Aerosol Counter) that is light and compact enough to perform measurements on the ground and under all kinds of balloons in the troposphere and in the stratosphere, including meteorological balloons.…”

Optimal estimation retrieval of aerosol microphysical properties from SAGE~II satellite observations in the volcanically unperturbed lower stratosphere

“…Other minor constituents of stratospheric aerosol include upper tropospheric material such as nitrate, ammonia, organics, minerals and metals (e.g. Talbot et al, 1998;Murphy et al, 1998), or meteoric material (Murphy et al, 2007;Renard et al, 2008), aircraft and rocket exaust (Kjellstrom et al, 1999;Danilin et al, 2001;Jackman et al, 1996). A comprehensive review of the measurements, the importance, and the life cycle of local and global stratospheric aerosol can be found in Deshler (2008).…”