Airborne measurements of the UTLS aerosol chemical composition over Germany using particle mass spectrometry
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Abstract
Aerosol particles affect the Earth’s radiation budget by interacting with solar
and terrestrial radiation but they can also act as cloud or ice nuclei both of which
depend on physical characteristics and chemical composition of the particles. In
addition to natural aerosols, commercial aircraft is a significant anthropogenic
source of aerosol particles in the extratropical upper troposphere and lower
stratosphere (UTLS). Yet, the knowledge of UTLS aerosol particles and the
contribution of aircraft exhaust on the formation e.g. of cirrus and contrails is
limited although these cloud types have a strong impact on radiative forcing.
This study focuses on the occurrence of individual particle types in UTLS
ambient air as well as cirrus and compares them with phases of aircraft exhaust
plumes and contrails. The hybrid mass spectrometer ERICA was deployed for
airborne measurements of aerosol chemical composition in a size range of 174 nm
and 3.2 μm. A standard aerosol inlet and counterflow virtual impactor were
used to sample interstitial particles (56058) and cloud residuals (3408) in the
wintertime UTLS region over Northern Germany. The particle analysis is based
on fuzzy c-means clustering and complementary measurements of trace gases
and cloud properties as well as synoptical analysis and simulations of air mass
history.
This study revealed that biomass burning (BB ) and carbon-containing particles
dominated the winter UTLS region over Northern Germany. Of the cloud
residuals, sea spray, mineral dust, and BB were the most abundant. Westerlies
largely influenced the particle occurrence: sea spray was attributed to Atlantic air
masses and BB particles were assigned to North American wild fires. Meteoric
material was detected above and inside the tropopause layer. In addition,
laboratory measurements of ammonium sulphate provided a potential source of
cation sulphur signals in ambient particle mass spectra. Further, the nitrate-rich
particle type detected during the ND-MAX campaign was not attributed to a
recombination process of nitrogen oxide precursors. Moreover, a comparison
unveiled that contrails can grow on the same particles as cirrus, suggesting
the formation of both via the liquid phase as confirmed by the ice water
content analysis. The composition of contrails was rather driven by the UTLS
aerosol background than by particles of aircraft fuel combustion. However,
the lower detection limit of ERICA inhibits the sampling of exhaust-related
particles below 174 nm, not allowing for the analysis of an impact on the aerosol
population and contribution to contrail formation.