Abstract
Carbonaceous particulate matter (PM), comprising black carbon (BC), primary organic aerosol (POA) and secondary organic aerosol (SOA, from atmospheric aging of precursors), is a highly toxic vehicle exhaust component. Therefore, understanding vehicle pollution requires knowledge of both primary emissions, and how these emissions age in the atmosphere. We provide a systematic examination of carbonaceous PM emissions and parameterisation of SOA formation from modern diesel and gasoline cars at different temperatures (22, −7 °C) during controlled laboratory experiments. Carbonaceous PM emission and SOA formation is markedly higher from gasoline than diesel particle filter (DPF) and catalyst-equipped diesel cars, more so at −7 °C, contrasting with nitrogen oxides (NOX). Higher SOA formation from gasoline cars and primary emission reductions for diesels implies gasoline cars will increasingly dominate vehicular total carbonaceous PM, though older non-DPF-equipped diesels will continue to dominate the primary fraction for some time. Supported by state-of-the-art source apportionment of ambient fossil fuel derived PM, our results show that whether gasoline or diesel cars are more polluting depends on the pollutant in question, i.e. that diesel cars are not necessarily worse polluters than gasoline cars.
Highlights
Most carbonaceous particulate matter (PM) from passenger cars is SOA1–4, known to contain harmful reactive oxygen species[5] and damage lung tissue[6]
While current EU-average passenger car fleet PM emission factors are much higher for diesel than gasoline[8], these values are skewed by older vehicles and do not reflect the impacts of the latest generation of after-treatment devices
In order to assess the relative merits of different engine technologies and mitigate vehicle pollution, knowledge of the primary emissions and SOA formation from modern passenger cars equipped with the newest after-treatment technologies is required
Summary
In parallel to diluted sampling necessary to fulfil the legislative requirements, we characterised the raw exhaust in real-time (at 1 Hz) during the driving cycles with the same techniques described above Procedures such as preand post-test flushing (30 minutes each) of the transfer lines and dilution tunnel were automatically executed to assure monitored background concentrations below the respective detection limits. Volume data from integrated scanning mobility particle sizer (SMPS, custom built) data from the chamber were transformed into mass concentrations using densities based on the particle chemical composition measured by the HR-ToF-AMS and subtracting BC, to provide a second measurement of the total non-refractory PM mass (i.e. those species quantified in the HR-ToF-AMS) This was used to correct for collection efficiency, CE, which was between 0.5–1.0 throughout all experiments where the non-refractory mass was above detection limit. Where P is the species of interest, ωc the carbon fraction of the fuel and CO2 and CO are in units of carbon mass
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