Quali-quantitative Scanning Electron Microscope elemental analysis of in-cabin particulate matter


  • Davide Campagnolo Department of Science and High Technology, University of Insubria, Como
  • Andrea Cattaneo Department of Science and High Technology, University of Insubria, Como
  • Gabriele Carugati Department of Science and High Technology, University of Insubria, Como
  • Francesca Borghi Department of Science and High Technology, University of Insubria, Como
  • Giacomo Fanti Department of Science and High Technology, University of Insubria, Como
  • Marta Keller Department of Science and High Technology, University of Insubria, Como
  • Sabrina Rovelli Università  degli Studi dell'Insubria, Como
  • Andrea Spinazzè Department of Science and High Technology, University of Insubria, Como
  • Domenico Maria Cavallo Department of Science and High Technology, University of Insubria, Como




Vehicle environment, Particles, Elemental size-distribution, Traffic-related sources, Cabin filtration


The present research is dedicated to the investigation of PM fractions (PM10 and PM2.5), but also including their differential fractions (i.e., PM2.5-10, PM1-2.5, PM0.5-1, PM0.25-0.5, PM0.25) collected inside a vehicle cabin. PM levels were characterized both in terms of concentration levels and chemical elemental composition (percentage composition).

The PM concentrations were measured gravimetrically by means of a personal cascade impactor sampler (PCIS) that was located on the passenger seat with the sampling inlet at the height of a seated passenger’s head. The samplings were carried-out two times per day (outward trip and return trip during morning and evening commuter rush hours, respectively) on a pre-determined route that included several types of main roads during two sampling campaigns. The study vehicle was a Euro 6 petrol-fuelled car. For all the samplings, the in-cabin ventilation settings were set as follows: windows closed, air conditioning off, recirculation fan off, fanned ventilation system on a moderate setting (2 on a scale of 1–4). To reduce any driver-related behavioural effect, the study vehicle was driven by the same operator who was always alone inside the cabin.

In-cabin PM10 and PM2.5 mean concentrations were compared with daily averages measured at two fixed air quality stations located near the sampling route at urban contexts. This comparison was affected by spatial and temporal dissimilarities and, consequently, it was only indicative. The outcomes showed that in-cabin PM10 and PM2.5 levels were up to three times lower than urban concentrations measured at fixed air quality stations. That difference may be probably attributed to cabin protection especially against coarse particles penetration from outdoor environment. Another comparison was also performed on in-cabin PM fractions and it was found that PM0.25 (called quasi-ultrafine fraction) showed the highest concentration levels (from 4 to 20 times higher than the other PM fractions). In this regard, the main explanation could be related to the fact that most of the particles emitted by light-duty vehicles are very small, with median size of the order 100 nm. Moreover, as reported in literature, the cabin filtration efficiency was extremely lower for particles with an aerodynamic diameter between 80 nm and 300 nm.

Four PM fractions (PM2.5-10, PM1-2.5, PM0.5-1, PM0.25-0.5) were also analysed using Scanning Electron Microscope with Energy Dispersive Spectrometer. Several images of the collected particles were captured and quali-quantitative analyses were performed. Based on the quali-quantitative data, the size percentage distribution was built per each element and a preliminary source interpretation suggested the presence of crustal sources, re-suspended sources of local soils, road pavement erosion and other particles previously deposited on the ground and traffic sources from exhaust and non-exhaust emissions. The quali-quantitative results also showed that Sulphur weight percentage was higher in PM0.25-0.5 (i.e., the finest fraction analysed by SEM-EDS) than in the other ones, probably due to secondary sulphates and traffic emissions. In conclusion, this survey highlighted the importance to study the exposure to PM inside vehicle cabins, paying particular attention on PM0.25. It also suggested that future studies should be focused on exposure assessment to PM0.25 of professional drivers, in terms of PM concentration levels, elemental characterization and source identification.


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