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Number concentrations of total and non-volatile aerosol particles with sizediameters >0.01 μm as well as particle size distributions (0.4–23 μmdiameter) were measured in situ in the Arctic lower stratosphere (10–20.5 kmaltitude). The measurements were obtained during the campaigns EuropeanPolar Stratospheric Cloud and Lee Wave Experiment (EUPLEX) andEnvisat-Arctic-Validation (EAV). The campaigns were based in Kiruna, Sweden,and took place from January to March 2003. Measurements were conductedonboard the Russian high-altitude research aircraft Geophysica using thelow-pressure Condensation Nucleus Counter COPAS (COndensationPArticle Counter System) and a modified FSSP 300(Forward Scattering Spectrometer Probe). Around 18–20 km altitude typicaltotal particle number concentrations nt range at 10–20 cm−3 (ambientconditions). Correlations with the trace gases nitrous oxide (N2O) andtrichlorofluoromethane (CFC-11) are discussed. Inside the polar vortex thetotal number of particles >0.01 μm increases with potentialtemperature while N2O is decreasing which indicates a source ofparticles in the above polar stratosphere or mesosphere. A separate channelof the COPAS instrument measures the fraction of aerosol particlesnon-volatile at 250°C. Inside the polar vortex a much higher fraction ofparticles contained non-volatile residues than outside the vortex (~67%inside vortex, ~24% outside vortex). This is most likelydue to a strongly increased fraction of meteoric material in the particleswhich is transported downward from the mesosphere inside the polar vortex.The high fraction of non-volatile residual particles gives thereforeexperimental evidence for downward transport of mesospheric air inside thepolar vortex. It is also shown that the fraction of non-volatile residualparticles serves directly as a suitable experimental vortex tracer.Nanometer-sized meteoric smoke particles may also serve as nuclei for thecondensation of gaseous sulfuric acid and water in the polar vortex andthese additional particles may be responsible for the increase in theobserved particle concentration at low N2O. The number concentrationsof particles >0.4 μm measured with the FSSP decrease markedly insidethe polar vortex with increasing potential temperature, also a consequenceof subsidence of air from higher altitudes inside the vortex. Another focusof the analysis was put on the particle measurements in the lowermoststratosphere. For the total particle density relatively high numberconcentrations of several hundred particles per cm3 at altitudes below~14 km were observed in several flights. To investigate the origin ofthese high number concentrations we conducted air mass trajectorycalculations and compared the particle measurements with other trace gasobservations. The high number concentrations of total particles in thelowermost stratosphere are probably caused by transport of originallytropospheric air from lower latitudes and are potentially influenced byrecent particle nucleation

atmospheric chemistry and physics

Observations of meteoric material and implications for aerosol nucleation in the winter Arctic lower stratosphere derived from in situ particle measurements