The aim of this work package is to develop novel methods for generating synthetic ambient aerosols (PM2.5) in the laboratory under well-controlled and reproducible conditions. These synthetic aerosol mixtures should (i) be stable over hours; (ii) simulate the main physical and chemical properties of real ambient aerosols such as chemical composition, particle size distribution, number and mass concentration (target uncertainty in mass concentration 15 %, number concentration <15 %, analysis of major chemical components <15 %); and (iii) be tunable in order to adjust aerosol properties at will (e.g. the source will be coupled to an OFR to mimic atmospheric photochemical ‘ageing’).

Commercial combustion generators produce only ‘fresh’ aerosols that consist of elemental carbon (EC) particles or a mixture of EC and, to some degree, primary organic matter (POM). These components are produced simultaneously during the combustion process. ‘Aged’ aerosol, on the other hand, as found in the atmosphere is a mixture of ‘fresh’ particles and secondary organic matter (SOM) produced after hours or days of atmospheric oxidation of relevant precursor substances of biogenic and anthropogenic origin. The result is a mixture of EC, POM and SOM.

To simulate ‘fresh’ and ‘aged’ particles, an innovative device, a novel portable prototype SCAA generator, which combines a combustion generator, a precursor dosing system and an OFR, will be developed and characterised in Task 1.1. In Task 1.2, a new mobile mixing chamber will be designed and validated based on numerical simulations, imaging and Laser Doppler Velocity (LDV) measurements. This chamber will allow mixing and homogenising of different aerosol components in order to generate synthetic ambient aerosols with the desired properties. In Task 1.3 a series of synthetic aerosols with well-defined physicochemical properties, will be defined and generated which will be used for in-vitro studies and imaging analysis in WP2 and WP3.

Task 1.1: Development of a novel portable prototype SCAA generator

The aim of this task is to develop a novel type of combustion generator that can produce both ‘fresh’ and ‘aged’ particles to better simulate real combustion aerosols found in the atmosphere. The novel prototype SCAA generator will also be portable. Currently, the generation of ‘aged’ particles can be only achieved by combining a combustion generator with an extra device, i.e. an OFR. However, the system is bulky and therefore not portable, whilst the experimental reproducibility in particle number and mass concentration (15 % – 20 %) is not adequate for metrological applications. Moreover, neither the oxidation flow reactor nor the precursor dosing system is automated and hence require manual input to adjust the operation points.

In this task, the OFR previously developed by FHNW, also known as a Micro Smog Chamber [12], will be miniaturised and integrated into the design of a suitable combustion generator to produce a single portable prototype SCAA generator. The precursor-dosing system for SOM production will be automated and standardised with the aim to attain a final reproducibility of better than 10 % in particle number and mass concentration. Finally, the physicochemical properties of the produced aerosols will be characterised and used to define optimal operations points in order to produce aerosols that best reproduce the properties of real ambient carbonaceous aerosols.

Task 1.2: Development of a mobile mixing chamber for the production of synthetic ambient aerosols at high concentrations

The aim of this task is to develop a small-scale (≤2 m3) mobile mixing chamber for the production of synthetic ambient aerosols at high concentrations (starting from the target limits set by the EU Directive 2008/50 and up to about 10 mg/m3). Even though small aerosol particles, such as combustion, metal and salt particles below 500 nm, can be efficiently mixed in tubes upon generation, additional mixing of large dust particles (1-2 μm size) can be only achieved within a suitable mixing chamber. The high particle number and mass concentrations are essential in this project in order to simulate ambient aerosol exposure of days/weeks within only a few hours in the laboratory.

Aerosol mixing and homogenisation will be achieved in the mixing chamber under controlled conditions by using a fan installed inside the chamber. The chamber will be further equipped with different aerosol outlets appropriate for i) real-time in-situ exposure of cell cultures at UBERN’s NACIVT chamber, ii) collection of particles on filters with high-volume samplers (and subsequent dispersion in liquid medium) and ii) live imaging of particle-cell interactions. The target reproducibility in aerosol number and mass concentration is better than 15 %.

Task 1.3: Generation and physicochemical characterisation of synthetic ambient aerosols ‘tailored’ for controlled in vitro studies

The aim of this task is to generate a series of synthetic aerosols with well-defined physicochemical properties, which will be used for in-vitro studies and imaging analysis in WP2 and WP3. The aerosol components will be selected in such a way so that clear trends between particle metrics (e.g. chemical composition, size, mass concentration) and cell/tissue response may be observed.

Task 1.1 generates carbonaceous aerosols. In Task 1.3 the project will go a step further and mix other components into the carbonaceous aerosols from A1.1.3. Therefore, both A1.1.3 and A1.3.1 generate aerosols but these will be of different compositions.

The synthetic aerosols will be then generated in the laboratory under well-controlled conditions using a variety of existing commercial nebulisers, combustion and fluidised-bed generators at METAS and custom-made aerosol generators, i.e. the novel portable prototype SCAA generator developed in Task 1.1, and the mobile mixing chamber constructed in Task 1.2. The physicochemical properties of the aerosol mixtures will be defined using online and offline analysis techniques.