Comment on egusphere-2022-1244

Abstract

Aerosol particle number concentration measurements are a crucial part of aerosol research. Vertical profile measurements and high-altitude/low pressure performance of the respective instruments become more and more important for remote sensing validation and as a key tool for the observation of climate variables. This study tests the new, commercially available, water condensation particle counter (MAGIC 210-LP) for the deployment at aircraft cruising pressure levels, that the European research infrastructure IAGOS (In-service Aircraft for a Global Observing System) is aiming for by operating measurement instrumentation on board of passenger aircraft. We conducted a series of laboratory experiments for conditions, which simulate passenger aircraft flight altitude operations. We demonstrate that this model water condensation particle counter shows excellent agreement with a butanol-based instrument used in parallel, and a Faraday cup aerosol electrometer serving as the reference instrument. Experiments were performed with test aerosols ammonium sulphate, fresh combustion soot as well as ambient aerosol, at pressure levels ranging from 700 hPa down to 200 hPa. For soluble particles like ammonium sulphate, the 50 % detection efficiency cut-off diameter (D50) was 5 nm and did not differ significantly for all performed experiments. For non-soluble fresh soot particles, the D50 cut-off diameter did not differ significantly for particle sizes around 10 nm, whereas the D90 cut-off diameter increased from 17 nm at 700 hPa to 34 nm at 200 hPa. The overall counting efficiency for particles larger 30 nm reaches 100 % for working pressures 200 hPa and higher. Though we observed a drop of the counting efficiency from 100 % to 90 % for particles smaller than 15 nm, as soon as we reached a pressure of 250 hPa. For pressure conditions down to 200 hPa, the counting efficiency for particles smaller than 15 nm dropped further and reached 80 %. This feature, however, has only minor impact on the overall excellent performance of the instrument at all tested pressure conditions.