Combustion Particles in the Atmosphere: Properties, Transformations, Fate & Impacts
Introduction
Airborne particulate matter has substantial impacts on air quality and climate. Combustion-derived particles make the largest of all anthropogenic contributions to the particulate burden and internal combustion, both traffic and non-traffic, contributes most in urban population centres. The Com-Part studies will quantify the physical and chemical transformations that modify combustion particulate emissions with a focus both on the primary soot and secondary organic fractions of the aerosol. Using a comprehensive series of chamber experiments, all relevant processes will be investigated using state-of-the-science online and offline instrumentation. Emissions under reasonable combustion conditions will be diluted into conditions representing the urban, and subsequently regional, background air. Single-particle and ensemble instruments will be used to follow the rearrangement of sooty agglomerates as organic aerosol components are photochemically processed in the oxidising atmosphere and partition between the condensed and vapour phases. Transformations will be physically and chemically characterised and the resulting particle properties quantified along with characteristic timescales for the processes under the prevailing conditions. This holistic approach will, for the first time, provide a physical basis for evaluation of the transformations and impacts of combustion aerosol on human health and climate.
Objectives
Primary combustion particles have been well studied and, more recently, the potential to form secondary aerosol in a diluting and oxidising exhaust plume has received quite widespread attention. Com-Part will systematically combine the two elements for the first time, to chemically and physically characterise the ambient transformations of primary and secondary particles emitted from internal combustion engines under reasonable atmospheric conditions. It will:
i) characterise transformations of particles formed by a light duty engine across a full range of load and speed conditions covering those encountered in all parts of the EU test cycle;
ii) similarly characterise the evolution of particles emitted from non-traffic combustion sources including 2-stroke appliance engines;
iii) directly measure particle optical properties and CCN behaviour transformations from both engine types
iv) evaluate transformation timescale in terms of the representative photochemical exposure time or "age", using chamber oxidant levels calculated from the decay rate of tracer molecules;
v) derive empirical relationships for the transformations for use in models where a complete description of the oxidative environment is unavailable.