Influence of water uptake on the aerosol particle light scattering coefficients of the Central European aerosol

Abstract

The influence of aerosol water uptake on the aerosol particle light scattering was examined at the regional continental research site Melpitz, Germany. The scattering enhancement factor f(RH), defined as the aerosol particle scattering coefficient at a certain relative humidity (RH) divided by its dry value, was measured using a humidified nephelometer. The chemical composition and other microphysical properties were measured in parallel. f(RH) showed a strong variation, e.g. with values between 1.2 and 3.6 at RH=85% and λ=550 nm. The chemical composition was found to be the main factor determining the magnitude of f(RH), since the magnitude of f(RH) clearly correlated with the inorganic mass fraction measured by an aerosol mass spectrometer (AMS). Hysteresis within the recorded humidograms was observed and explained by long-range transported sea salt. A closure study using Mie theory showed the consistency of the measured parameters.

• aerosol particle light scattering
• hygroscopic growth
• scattering enhancement
• aerosol mass spectrometer
• field measurements
• optical closure study

7. Acknowledgements

This work was financially supported by the EC projects European Supersites for Atmospheric Aerosol Research (EUSAAR, contract 026140) and Global Earth Observation and Monitoring (GEOMON, contract 026140), as well as by the European Space Agency's Climate Change Initiative (aerosol_cci). P. Zieger was supported by a PostDoc fellowship of the Swiss National Science Foundation (grant no. P300P2_147776). The aerosol measurements at Melpitz were supported by the European Integrated project on Aerosol Cloud Climate and Air Quality Interactions (EUCAARI), and the German Federal Environment Ministry (BMU) grant F&E 370343200 (German title: ‘Erfassung der Zahl feiner und ultrafeiner Partikel in der Aussenluft’). NILU is greatly acknowledged for providing the FLEXTRA trajectories. We thank Friederike Kinder, Nicole Niedermeier, and Andreas Massling (TROPOS) for their assistance with measuring and processing the H-TDMA data, as well as Thomas Tuch (TROPOS) for assistance with the measurement of the TDMPS data. We thank the anonymous reviewers for their helpful comments.