Björn Nillius

Resurgence in Ice Nuclei Measurement Research

Understanding cloud and precipitation responses to variations in atmospheric aerosols remains an important research topic for improving the prediction of climate. Knowledge is most uncertain, and the potential impact on climate is largest with regard to how aerosols impact ice formation in clouds. In this paper, we show that research on atmospheric ice nucleation, including the development of new measurement systems, is occurring at a renewed and historically unparalleled level. A historical perspective is provided on the methods and challenges of measuring ice nuclei, and the various factors that led to a lull in research efforts during a nearly 20-yr period centered about 30 yr ago. Workshops played a major role in defining critical needs for improving measurements at that time and helped to guide renewed efforts. Workshops were recently revived for evaluating present research progress. We argue that encouraging progress has been made in the consistency of measurements using the present generation of ic...

ACRIDICON–CHUVA Campaign: Studying Tropical Deep Convective Clouds and Precipitation over Amazonia Using the New German Research Aircraft HALO

AbstractBetween 1 September and 4 October 2014, a combined airborne and ground-based measurement campaign was conducted to study tropical deep convective clouds over the Brazilian Amazon rain forest. The new German research aircraft, High Altitude and Long Range Research Aircraft (HALO), a modified Gulfstream G550, and extensive ground-based instrumentation were deployed in and near Manaus (State of Amazonas). The campaign was part of the German–Brazilian Aerosol, Cloud, Precipitation, and Radiation Interactions and Dynamics of Convective Cloud Systems–Cloud Processes of the Main Precipitation Systems in Brazil: A Contribution to Cloud Resolving Modeling and to the GPM (Global Precipitation Measurement) (ACRIDICON– CHUVA) venture to quantify aerosol–cloud–precipitation interactions and their thermodynamic, dynamic, and radiative effects by in situ and remote sensing measurements over Amazonia. The ACRIDICON–CHUVA field observations were carried out in cooperation with the second intensive operating period...

Characterization of an Automated, Water-Based Expansion Condensation Nucleus Counter for Ultrafine Particles

The design and experimental characterization of a condensation nucleus counter (CNC) is presented. The counter produces supersaturation by means of fast volume-controlled adiabatic expansion. The aerosol number concentration is derived from observing scattered laser light in the forward direction under a solid angle between 1.1° and 4.4° over the full annular sector. The number concentration is derived by application of Mie theory from the characteristic pattern in the temporal evolution of the detected signal during the droplet growth process. The equation for calculation of the aerosol number density by this method is presented. Theoretical considerations for the smallest aerosol particles that can be activated indicate a lower size cut-off between 2.5 and 3.0 nm. Model calculations of the expected Mie scatter signal during expansion agree very well with the experimental observations. The Expansion-CNC can be operated fully automated under computer (PC) control in 10-second sample cycles. For characterization it is compared with a TSI 3025A Ultrafine-CPC (TSI UCPC) for measurements of monodisperse sodium chloride and sulfuric acid aerosol particles, indicating good agreement between the two counters down to particle sizes as low as 3.5 nm under laboratory conditions. In addition, ambient aerosol measurements in urban air show excellent agreement with simultaneous TSI UCPC measurements for particle number concentrations ranging from roughly 50 cm− 3 to 130000 cm− 3.