On the Morphology and Composition of Particulate Matter in an Urban Environment

Abstract

Particulate matter (PM) plays a vital role in altering air quality, human health, and climate change. There are sparse data relevant to PM characteristics in urban environments of the Middle East, including Peshawar city in Pakistan. This work reports on the morphology and composition of PM in two size fractions (PM_2.5 and PM₁₀) during November 2016 in Peshawar. The 24 hous mass concentration of PM_2.5 varied from 72 μg m^-3 to 500 μg m^-3 with an average value of 286 μg m^-3. The 24 hours PM₁₀ concentration varied from 300 μg m^-3 to 1440 μg m^-3 with an average of 638 μg m^-3. The morphology, size, and elemental composition of PM were measured using Fourier Transform Infra Red (FT-IR) Spectroscopy and Scanning Electron Microscopy (SEM) with Energy Dispersive X-ray (EDX) Spectroscopy. The size of the analyzed particles by EDX ranged from 916 nm to 22 μm. Particles were classified into the following groups based on their elemental composition and morphology: silica (12%), aluminosilicates (23%), calcium rich (3%), chloride (2%), Fe/Ti oxides (3%), carbonaceous (49%), sulfate (5%), biogenic (3%). The major identified sources of PM are vehicular emissions, biomass burning, soil and re-suspended road dust, biological emissions, and construction activities in and around the vicinity of the sampling site.

Keywords: Energy Dispersive X-ray; Fourier Transform Infra Red Spectroscopy; Morphology and elemental composition; Particulate matter; Scanning Electron Microscopy.

Fig. 1

Map of Peshawar showing the sampling site.

Fig. 2

(a–b) Prevailing meteorological conditions of Peshawar city during November 2016.

Fig. 3

MODIS-AQUA satellite images during the study period (November 2016) on various days. The circle in each map indicates the sampling location.

Fig. 4

Daily variation in PM mass concentrations in Peshawar.

Fig. 5

The average percent weight of the various elements in Peshawar city during November 2016.

Fig. 6

Frequency of particle types observed during the study period.

Fig. 7

SEM-EDX spectra: (a) Blank quartz fiber filter; (b) Biotite, a triangular shaped particle having size of 15.05 μm; (c) K-feld Spar, a trapezium shaped particle having a size of 12 μm; (d) Na-feld spar of shape like soap and size of 26 μm; (e) a tablet shape, calcium-magnesium aluminosilicate of size 2.5 μm.

Fig. 7

SEM-EDX spectra: (a) Blank quartz fiber filter; (b) Biotite, a triangular shaped particle having size of 15.05 μm; (c) K-feld Spar, a trapezium shaped particle having a size of 12 μm; (d) Na-feld spar of shape like soap and size of 26 μm; (e) a tablet shape, calcium-magnesium aluminosilicate of size 2.5 μm.

Fig. 8

SEM-EDX spectra: (a) Ca-rich particle having a size of 17.1 μm with a pentagon-like shape; (b) Chloride particles of size 5.6 μm and tablet-like shape; (c) an iron titanium oxide particle with traces of elements such as Ca, K, Mg, Na, Al, and Si having size of 4.8 μm and of spherical morphology.

Fig. 9

SEM-EDX spectra: (a) A single carbon particle with completely spherical morphology dominated by C and O (> 90%) having a size of 6.4 μm; (b) A cluster of carbonaceous particle with traces of soil-related elements; (c) A sulfate particle of capsule-like shape having length of 14 μm and width of 2.8 μm; (d) A spherical particle with smooth texture made up of Al-Si-O (fly ash) of size 14 μm; (e) Spherical particles of biological nature having size of 4.2 μm.

Fig. 9

SEM-EDX spectra: (a) A single carbon particle with completely spherical morphology dominated by C and O (> 90%) having a size of 6.4 μm; (b) A cluster of carbonaceous particle with traces of soil-related elements; (c) A sulfate particle of capsule-like shape having length of 14 μm and width of 2.8 μm; (d) A spherical particle with smooth texture made up of Al-Si-O (fly ash) of size 14 μm; (e) Spherical particles of biological nature having size of 4.2 μm.

Fig. 10

FTIR spectrum of (a) PM_2.5 and (b) PM₁₀ collected at Peshawar during November 2016.