COMPASS – COMparative Particle formation in the Atmosphere using portable Simulation chamber Study techniques

[摘要] In this study we report the set-up of a novel twin chamber technique thatuses the comparative method and establishes an appropriate connection ofatmospheric and laboratory methods to broaden the tools for investigations.It is designed to study the impact of certain parameters and gases on ambientprocesses, such as particle formation online, and can be applied in a largevariety of conditions. The characterisation of both chambers proved that bothchambers operate identically, with a residence time x_T(COMPASS1) = 26.5 ± 0.3 min and x_T (COMPASS2) = 26.6 ±0.4 min, at a typical flow rate of 15 L min⁻¹ and a gas leak rate of (1.6 ±0.8) × 10⁻⁵ s⁻¹. Particle loss rates were found to belarger (due to the particles' stickiness to the chamber walls), with an extrapolated maximum of1.8 × 10⁻³ s⁻¹ at 1 nm, i.e. a hundredfold of the gas leakrate. This latter value is associated with sticky non-volatile gaseouscompounds, too. Comparison measurement showed no significant differences.Therefore operation under atmospheric conditions is trustworthy. To indicatethe applicability and the benefit of the system, a set of experiments wasconducted under different conditions, i.e. urban and remote, enhanced ozone andterpenes as well as reduced sunlight. In order to do so, an ozone lamp wasapplied to enhance ozone in one of two chambers; the measurement chamber wasprotected from radiation by a first-aid cover and volatileorganic compounds (VOCs) were added using asmall additional flow and a temperature-controlled oven. During the elevatedozone period, ambient particle number and volume increased substantially aturban and remote conditions, but by a different intensity. Protection of solarradiation displayed a clear negative effect on particle number, while terpeneaddition did cause a distinct daily pattern. E.g. adding β pineneparticle number concentration rose by 13% maximum at noontime, while nosignificant effect was observable during darkness. Therefore, the system is auseful tool for investigating local precursors and the details of ambient particleformation at surface locations as well as potential future feedbackprocesses.

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