Determination of Polycyclic Aromatic Hydrocarbons (PAH) in Size Fractionated Diesel Particles from a Light Duty Vehicle

A light-duty diesel vehicle with an oxidising catalyst exhaust after-treatment device was fuelled with reference diesel and run in a transient driving cycle (new European Driving Cycle). The particulate emissions were sampled from the diluted exhausts using an Electrical Low Pressure Impactor (ELPI) with separation of the particles according to aerodynamic size into 13-size levels ranging from 30 nm to 10 μm. The particles were collected on glass fibre filters used as substrates in the impactor. The particlulate mass collected for each size level was determined by weighing the filter prior and after sampling. Each filter was extracted in dichloromethane (DCM) in an ultrasonic bath. The obtained raw-extracts were thereafter fractionated in accordance to increasing polarity into two fractions (I-II) using an open tubular silica column. The fractions were chemically characterised using Gas Chromatography-Mass Spectrometry. The compounds in fractions I were tentatively identified as aliphatic material, in fraction II Polycyclic Aromatic Hydrocarbons (PAH) were positively identified and quantified. When comparing PAH emissions by conventional filter sampling to those obtained from the ELPI sampling, the former was found to be larger by a factor of about 3. The highest particle mass was found to be emitted at 100 nm aerodynamic diameter, with 70 % of the total mass in the interval 50 to 400 nm. A co-variation was found between particulate mass and the identified compounds.