10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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On-road Measurements of Secondary Aerosol and Size Dependent Number Emission Factors for Motorway Traffic Emissions across Europe Using a Mobile Laboratory Setup
MIIKKA DAL MASO, Joni Heikkilä, Miska Olin, Pauli Simonen, Antti Rostedt, Erkka Saukko, Heino Kuuluvainen, Joni Kalliokoski, Outi Potila, Anssi Järvinen, Mikko Poikkimäki, Topi Rönkkö, Jorma Keskinen, Tampere University of Technology, Tampere, Finland
Abstract Number: 1352 Working Group: Combustion-Generated Aerosols: the Desirable and Undesirable
Abstract Motorways make up a minor fraction of roads in Europe but carry a disproportionately large amount of traffic. Vehicle emission measurements have shown that highway driving at high engine loads may cause above average emissions of both primary and secondary particulate matter. These factors together make highways a significant source of air pollutants. Presently, comprehensive data of simultaneous primary and potential secondary aerosol mass measurements on motorways does not yet exist. We present data from three trans-European measurement expeditions that were carried out on highways reaching from Southern Finland to the Mediterranean, covering in total close to 8'000 km of highways. This dataset elucidates the relative fractions of primary and secondary emissions for highway driving, as well as gives new insights on the particle number emissions for highway driving.
The measurements were performed in 2015 and 2016 aboard the Tampere University of Technology Mobile measurement unit, a van modified to house a mobile laboratory setup, accommodating high-quality aerosol and trace gas observation setups. The modifications include a lithium battery powered inverter power supply with a supplementary charging generator powered by the van engine allowing continuous measurement instrument operation while driving. In addition, the van is fitted with aerosol and gas sampling lines, instrument installation shelving, a GPS and weatherstation, and a temperature regulation system. The sampling inlets were characterized with polydisperse aerosol and found to have good transmission efficiency for particles in the 1-1000 nm size range.
During the trans-European expeditions the instrumentation aboard the measurement unit consisted of aerosol size distribution instrumentation (Dekati ELPI), aerosol number concentration instrumentation (TSI and Airmodus CPC:s), trace gas detectors (CO2, NOx, O3), and a fast-response oxidation flow tube (OFR) for the simulation the conversion of freshly emitted aerosol to photochemically aged aerosol (TUT Secondary Aerosol Reactor, TSAR). To bring the measured concentrations into the instrument's detection range, we used bridge dilution systems.
Measurements were predominantly performed on highways, with the driving speed over 80 km/h. The aerosol number concentrations were found to be clearly elevated in comparison to background. Motorway median number concentrations exceeded 4·104 cm-3. On all expeditions, we found a significant fraction of particles in the sub-3nm particle size range, in line with recent findings that traffic is a significant source of nanocluster aerosol. Using CO2 data, we estimated average high-speed motorway driving number emission factors. Measurements using the the TSAR OFR showed that concentrations of potential secondary mass clearly exceeded the primary mass emissions, and our measurements also demonstrate that the high time resolution of the TSAR enables on-road emission factor determination of secondary aerosol.