Sampler validated
Particles are discrete and well-dispersed — present but not overloaded. The custom rooftop sampler works.
New result · SEM / EDX
LahoreSmogUndertheMicroscope
First SEM/EDX characterization of particles from Lahore's urban smog — confirming a custom-built rooftop sampler captures fine, PM2.5-range aerosol.
A custom rooftop high-volume air sampler collected Lahore smog onto Teflon filters. Scanning electron microscopy (SEM) and energy-dispersive X-ray analysis (EDX) confirm the sampler captures discrete, PM2.5-dominated particles. About 99% of measured particles are smaller than 2.5 µm, and their chemistry — mineral dust, combustion sulfate, and industrial metals — matches known Lahore pollution sources.
~11,000
particles measured across two SEM fields
99.8%
smaller than 2.5 µm (PM2.5)
0.34 µm
median particle diameter
10 / 15 kV
FEI Nova NanoSEM imaging / EDX
Key findings
Mostly fine (PM2.5)
~99% below 2.5 µm; typical 0.2–0.4 µm, with soot building-blocks down to 15–75 nm. Only rare grains reach 3–5 µm.
Crustal dust dominates
Silicon + Aluminium + Calcium + Oxygen — the signature of mineral / road dust, the fraction most relevant to ice nucleation.
Pollution signatures
Sulfur (sulfate from fuel burning) and a Zinc-rich particle (traffic / industry / waste burning) confirm the urban source mix.
How small are they?
Every particle in two SEM fields was measured against the image scale bar. The distribution is overwhelmingly fine — almost entirely below the 2.5 µm PM2.5 threshold.
Particle-size distribution
11,217 particles · median 0.34 µm · 99.8% below 2.5 µm. Nearly everything sits left of the PM2.5 line — the sampler catches mainly fine aerosol.
Automated sizing from SEM images (scale-bar calibrated). Bin width 0.1 µm; a few grains beyond 3 µm are omitted for clarity. Counts are approximate; the sub-2.5 µm dominance is robust.
What they look like
Secondary-electron images from the FEI Nova NanoSEM. Click any image to enlarge.
Smog particles on the filter
Discrete particulate matter collected from Lahore air — dispersed, countable, and not overloaded.
Near-clean control filter
The bare Teflon fibre network from a low-loading control — the baseline the loaded sample is judged against.
Combustion soot spherules
Spherical combustion particles clustered into aggregates — the nanometre-scale (15–75 nm) building blocks of urban soot.
What they're made of
Energy-dispersive X-ray (EDX) maps colour each element, revealing a mix of crustal dust, construction dust, and industrial metals.
Mineral dust grain
Silicon + Oxygen light up a crustal-dust particle — the dominant, INP-relevant fraction.
Construction / road dust
A silicon-dominated grain — resuspended construction and road dust, ubiquitous in Lahore air.
Industrial zinc particle
A sphere glowing with Zinc — an industrial / traffic / waste-burning signature in the aerosol.
What the elements mean: Silicon, Aluminium, Calcium and Oxygen mark mineral / road dust; Sulfur points to combustion sulfate from fuel burning; Zinc flags an industrial / traffic source. Together they fingerprint Lahore's mixed crustal-plus-combustion aerosol.
Why it matters
The ice-nucleation link
Mineral dust dominates this sample — and dust is among the most effective ice-nucleating particle (INP) types known. So these images physically confirm that the INP-relevant material is present in Lahore's smog, connecting directly to the droplet-freezing results.
See the freezing-spectrum result →Method
- Instrument
- FEI Nova NanoSEM (LUMS Central Lab)
- Imaging
- 10 kV secondary-electron imaging
- EDX
- 15 kV energy-dispersive X-ray analysis
- Sample prep
- Gold-coated Teflon filters; two samples — a loaded field and a near-clean control
A note on the numbers. Particle counts are automated estimates (~11,000 particles across two fields) and are approximate — filter texture can be miscounted as fine particles, so the number runs slightly high. The core conclusion — that the collected aerosol is overwhelmingly sub-2.5 µm — is robust to the counting settings.