Characterization of Airborne Particles Collected from Car Engine Air Filters Using SEM and EDX Techniques

Abstract

Particulate matter accumulated on car engine air-filters (CAFs) was examined in order to investigate the potential use of these devices as efficient samplers for collecting street level air that people are exposed to. The morphology, microstructure, and chemical composition of a variety of particles were studied using scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX). The particulate matter accumulated by the CAFs was studied in two categories; the first was of removed particles by friction, and the second consisted of particles retained on the filters. Larger particles with a diameter of 74-10 µm were observed in the first category. In the second one, the detected particles had a diameter between 16 and 0.7 µm. These particles exhibited different morphologies and composition, indicating mostly a soil origin. The elemental composition revealed the presence of three groups: mineral (clay and asphalt), metallic (mainly Fe), and biological particles (vegetal and animal debris). The palynological analysis showed the presence of pollen grains associated with urban plants. These results suggest that CAFs capture a mixture of atmospheric particles, which can be analyzed in order to monitor urban air. Thus, the continuous availability of large numbers of filters and the retroactivity associated to the car routes suggest that these CAFs are very useful for studying the high traffic zones within a city.

Keywords: SEM microscopy; car air filter; particle; pollen.

Figure 1

Map of Aguascalientes State.

Figure 2

(a) Car air filter collected, (b,c) blends show the dust trapped, (d–f) macroparticles and dust retained.

Figure 3

Mosaic of animal debris collected by the CAFs.

Figure 4

(a–c) Representative metallic and (c–g) inorganic particles observed by reflected light microscopy; (d) Synthetic fibers were also observed. Arrows on f and g indicate small particles.

Figure 5

Distribution of particles removed from CAFs collected.

Figure 6

(a–c) Scanning electron micrographs and EDX spectrum of control filters and (d–f) collected CAFs.

Figure 7

Identification of mineral K-feldspar particles by SEM-EDX (arrow particle <10 µm).

Figure 8

(a) Particles less than 2.5 µm and (b) nucleation and condensation of <2.5 µm particles that were deposited on CAF.

Figure 9

Metallic particles composed of (1) iron and (2) chromium.

Figure 10

Metallic particle that contains platinum was found on CAF (black arrows).

Figure 11

Iron particles with different morphologies. (a) Layer; (b) EDX spectrum; (c) rhomboid and (d) agglomerate.

Figure 12

Pollen grain collected in Aguascalientes by CAFs.

Figure 13

Frequency of elements in the composition of pollens collected by CAFs.

Figure 14

Pollen grain with adherent silicon particles collected by CAFs.