Abstract
Abstract. 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.
Highlights
Soot particles are solid, carbonaceous products resulting from incomplete combustion of materials such as coal, wood and other fossil fuels
It is crucial to mention for the rest of the discussion that the ice active fractions are normalized to the particles with a diameter larger than 50 nm in order to remove the contribution from nucleation mode particles that form in the photochemical process
Due to similar ice nucleation properties of the different vehicle types and wood burning phases, we decided for the rest of the discussion to average the values of both types of vehicles emission for the diesel experiments and to average the values for both phases of the wood burning experiments in order to facilitate the discussion on the photochemical effect at different temperatures
Summary
Carbonaceous products resulting from incomplete combustion of materials such as coal, wood and other fossil fuels. Both wood burning particles from house heating or cooking and diesel car emissions contribute to a large fraction of particulate matter (PM) in the atmosphere. These combustion particles consist of several types of volatile organic compounds (VOC) (McDonald et al, 2000; Schauer et al, 2001, 2002). This change in cloudiness due to the decrease in near-cloud relative humidity and the increase in static stability caused by absorbing aerosol is called the semi-direct aerosol effect
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