Aircraft-based observation of meteoric material in lower-stratospheric aerosol particles between 15 and 68° N

Abstract

Abstract. We analyse aerosol particle composition measurements from five research missions between 2014 and 2018 to assess the meridional extent of particles containing meteoric material in the upper troposphere and lower stratosphere (UTLS). Measurements from the Jungfraujoch mountaintop site and a low-altitude aircraft mission show that meteoric material is also present within middle- and lower-tropospheric aerosol but within only a very small proportion of particles. For both the UTLS campaigns and the lower- and mid-troposphere observations, the measurements were conducted with single-particle laser ablation mass spectrometers with bipolar-ion detection, which enabled us to measure the chemical composition of particles in a diameter range of approximately 150 nm to 3 µm. The five UTLS aircraft missions cover a latitude range from 15 to 68∘ N, altitudes up to 21 km, and a potential temperature range from 280 to 480 K. In total, 338 363 single particles were analysed, of which 147 338 were measured in the stratosphere. Of these total particles, 50 688 were characterized by high abundances of magnesium and iron, together with sulfuric ions, the vast majority (48 610) in the stratosphere, and are interpreted as meteoric material immersed or dissolved within sulfuric acid. It must be noted that the relative abundance of such meteoric particles may be overestimated by about 10 % to 30 % due to the presence of pure sulfuric acid particles in the stratosphere which are not detected by the instruments used here. Below the tropopause, the observed fraction of the meteoric particle type decreased sharply with 0.2 %–1 % abundance at Jungfraujoch, and smaller abundances (0.025 %–0.05 %) were observed during the lower-altitude Canadian Arctic aircraft measurements. The size distribution of the meteoric sulfuric particles measured in the UTLS campaigns is consistent with earlier aircraft-based mass-spectrometric measurements, with only 5 %–10 % fractions in the smallest particles detected (200–300 nm diameter) but with substantial (> 40 %) abundance fractions for particles from 300–350 up to 900 nm in diameter, suggesting sedimentation is the primary loss mechanism. In the tropical lower stratosphere, only a small fraction (< 10 %) of the analysed particles contained meteoric material. In contrast, in the extratropics the observed fraction of meteoric particles reached 20 %–40 % directly above the tropopause. At potential temperature levels of more than 40 K above the thermal tropopause, particles containing meteoric material were observed in much higher relative abundances than near the tropopause, and, at these altitudes, they occurred at a similar abundance fraction across all latitudes and seasons measured. Above 440 K, the observed fraction of meteoric particles is above 60 % at latitudes between 20 and 42∘ N. Meteoric smoke particles are transported from the mesosphere into the stratosphere within the winter polar vortex and are subsequently distributed towards low latitudes by isentropic mixing, typically below a potential temperature of 440 K. By contrast, the findings from the UTLS measurements show that meteoric material is found in stratospheric aerosol particles at all latitudes and seasons, which suggests that either isentropic mixing is effective also above 440 K or that meteoric fragments may be the source of a substantial proportion of the observed meteoric material.

Radiative and chemical implications of the size and composition of aerosol particles in the existing or modified global stratosphere

“…None of these events were targeted during the flights. Such variations in the stratospheric aerosol layer are important for both heterogeneous chemistry (Solomon et al, 1996) and climate (Solomon et al, 2011).…”

“…Hofmann et al (2009) found an increasing trend after 2000, and Friberg et al (2014) found an increasing trend from 1999 to 2008. There has been recog-8916 D. M. Murphy et al: The size and composition of aerosol particles in the stratosphere nition that moderate volcanic eruptions frequently influence the stratospheric aerosol and true non-volcanic "background" concentrations are not necessarily present just because there has been no Pinatubo-scale eruption (Solomon et al, 1996. Different altitudes may exhibit different trends (Khaykin et al, 2017).…”

Polar Stratospheric Clouds: Satellite Observations, Processes, and Role in Ozone Depletion

“…Recent in situ instrumentation can distinguish various types of aerosol particles in the stratosphere and determine their relative abundance. In the background lower stratosphere, a large fraction of SSA droplets contains inclusions of meteoritic and/or organic material (Murphy et al, 2014;Schneider et al, 2021). The solid inclusions could have important implications for the ability of particles to act as freezing nuclei for PSCs.…”

“…This The scientific basis of PSC formation has been introduced in Section 3, with Figure 26 showing the different formation pathways of the individual PSC compositions: The nucleation of ice can occur homogeneously or heterogeneously on preexisting particles, whereas the nucleation of NAT must occur heterogeneously on solid nuclei. Recent studies have demonstrated the importance of heterogeneous nucleation on foreign nuclei, but not much is known about these nuclei other than they may consist of meteoritic or a variety of other materials (Ebert et al, 2016;Schneider et al, 2021;Schütze et al, 2017). Therefore, the simulation of heterogeneous PSC formation requires certain assumptions to be made.…”

Radiative forcing by volcanic eruptions since 1990, calculated with a chemistry-climate model and a new emission inventory based on vertically resolved satellite measurements

“…The meteoric material could act as sink for gaseous H 2 SO 4 . Detected meteoric dust in the UTLS (Schneider et al, 2021) also suggests that it has to be incorporated into the model to reproduce observations of higher aerosol concentrations in the upper stratosphere. Thus, the aerosol extinction for the upper stratosphere and mesosphere is underestimated in model simulations without implementation of meteoric material in the radiation calculations.…”