Auflistung nach Autor:in "Stetzer, Olaf"

Gerade angezeigt 1 - 2 von 2

Effect of photochemical ageing on the ice nucleation properties of diesel and wood burning particles
(Copernicus, 2013) Chou, Cédric; Kanji, Zamin A.; Stetzer, Olaf; Tritscher, Torsten; Chirico, Roberto; Heringa, Maarten F.; Weingartner, Ernest; Prévôt, André; Baltensperger, Urs; Lohmann, Ulrike
A measurement campaign (IMBALANCE) conducted in 2009 was aimed at characterizing the physical and chemical properties of freshly emitted and photochemically aged combustion particles emitted from a log wood burner and diesel vehicles: a EURO3 Opel Astra with a diesel oxidation catalyst (DOC) but no particle filter and a EURO2 Volkswagen Transporter TDI Syncro without emission aftertreatment. Ice nucleation experiments in the deposition and condensation freezing modes were conducted with the Portable Ice Nucleation Chamber (PINC) at three nominal temperatures, −30 °C, −35 °C and −40 °C. Freshly emitted diesel particles showed ice formation only at −40 °C in the deposition mode at 137% relative humidity with respect to ice (RHi) and 92% relative humidity with respect to water (RHw), and photochemical ageing did not play a role in modifying their ice nucleation behaviour. Only one diesel experiment where α-pinene was added for the ageing process, showed an ice nucleation enhancement at −35 °C. Wood burning particles also act as ice nuclei (IN) at −40 °C in the deposition mode at the same conditions as for diesel particles and photochemical ageing also did not alter the ice formation properties of the wood burning particles. Unlike diesel particles, wood burning particles form ice via condensation freezing at −35 °C whereas no ice nucleation was observed at −30 °C. Photochemical ageing did not affect the ice nucleation ability of the diesel and wood burning particles at the three different temperatures investigated but a broader range of temperatures below −40 °C need to be investigated in order to draw an overall conclusion on the effect of photochemical ageing on deposition/condensation ice nucleation across the entire temperature range relevant to cold clouds.
01A - Beitrag in wissenschaftlicher Zeitschrift
Ice nuclei properties within a Saharan dust event at the Jungfraujoch in the Swiss Alps
(Copernicus, 04.10.2011) Chou, Cédric; Stetzer, Olaf; Weingartner, Ernest; Jurányi, Zsófia; Kanji, Zamin A.; Lohmann, Ulrike
The new portable ice nucleation chamber (PINC) developed by the Institute for Atmospheric and Climate Sciences of ETH Zurich was operated during two measurement campaigns at the high alpine research station Jungfraujoch situated at 3580 m a.s.l, in March and June 2009. During this time of the year, a high probability of Saharan dust events (SDE) at the Jungfraujoch has been observed. We used an impactor with a cutoff size of 1 μm aerodynamic diameter and operated the system at −31 °C and relative humidities of 127 % and 91 % with respect to ice and water, respectively. Investigation of the ambient number concentration of ice nuclei (IN) in the deposition nucleation mode and during a SDE in the free troposphere is reported. The results discussed in this paper are the first continuous IN measurements over a period of several days at the Jungfraujoch. The average IN concentration found during the campaign in March was 8 particles per liter whereas during the campaign in June, the average number concentration was higher up to 14 particles per liter. Two SDEs were detected on 15 and 16 June 2009. Our measurements show that the SDEs had IN number concentration up to several hundred per liter. We found the best correlation between the number concentration of the larger particle fraction measured by an optical particle counter and the IN number concentration during a Saharan dust event. This correlation factor is higher for particles larger than 0.5 μm meaning that a higher concentration of larger particles induced higher IN number concentration. No correlation could be found between the black carbon mass concentration and the variations in IN number concentration.
01A - Beitrag in wissenschaftlicher Zeitschrift