What Smog Season Looks Like in the Imaging Suite: Reading Air Pollution in Chest Studies

The requests change before the calendar does. Somewhere around the second week of November, the chest X-ray list in a Lahore hospital starts filling with the same three lines: cough for two weeks, shortness of breath, not settling on inhalers. Half the films look almost normal. The patients do not.

Air pollution is now one of the largest respiratory exposures in South Asia, and radiology often sits closer to the front of it than the pulmonologist in Lahore who sees the patient weeks later. Imaging cannot measure what a patient has breathed. It can, over time, show what that exposure has cost. Knowing the difference matters when a report goes back to a clinician who wants a cause, not a description.

How bad is the exposure, in numbers?

Bad enough that the readings stop sounding like weather and start sounding like a dose. On 14 October 2025, IQAir ranked Lahore as the world’s most polluted major city, with an AQI above 200 driven mainly by PM2.5. The city’s 2024 annual average PM2.5 was slightly above 100 micrograms per cubic metre, more than 20 times the WHO guideline level.

The wider picture is no gentler. WHO estimates that ambient air pollution caused about 4.2 million premature deaths worldwide in 2019, and that 99% of the world’s population lives where its air quality guidelines are not met. Of those deaths, WHO attributes 14% to chronic obstructive pulmonary disease and 4% to lung cancer, with 89% occurring in low and middle income countries.

For a radiologist in Punjab, that last figure is not an abstraction. It describes the catchment area.

Why a chest film is not a pollution meter

There is no imaging sign that says “air pollution”. Pollution-related lung injury does not look like a single pattern on a plain film or a CT. It looks like the ordinary findings of airway and parenchymal disease: bronchial wall thickening, air trapping, emphysematous change, sometimes nothing at all.

That is the trap. During smog weeks, clinicians want imaging to confirm a cause they already suspect, and a report that hints at one can end the diagnostic thinking early. A patient with new breathlessness in November can still have heart failure, tuberculosis, interstitial disease, or an undiagnosed asthma phenotype. Smog does not protect anyone from the rest of the differential.

The honest position is narrower and more useful. Imaging describes the burden of disease. Exposure history explains part of where it came from.

Paediatric studies carry the same risk in a sharper form. Children arrive in large numbers through smog season, mostly with wheeze, and the pressure to scan is real because parents are frightened and clinics are full. Most of those children need assessment and a trial of treatment, not a film. Every avoided chest radiograph in a seven-year-old is a small win that nobody records.

What does the imaging evidence actually show?

Quantitative CT has produced the clearest link so far. A 2019 cohort study in JAMA drew on the MESA Air and MESA Lung studies. It followed 7,071 adults aged 45 to 84 across six American metropolitan regions, using more than 15,000 CT scans acquired between 2000 and 2018.

Percent emphysema, defined as the share of lung pixels below minus 950 Hounsfield units, increased by an average of 0.58 percentage points over ten years. Baseline exposure to every pollutant studied was linked to faster progression. For ozone, that was 0.13 percentage points per 10 years for each 3 parts per billion. For PM2.5, it was 0.11 for each 2 micrograms per cubic metre. Ozone exposure was also associated with a faster decline in FEV1.

There is a second lesson buried in that design. The signal only appeared because the same people were scanned repeatedly over nearly two decades. A single CT cannot show emphysema progressing. It can only show how much is there on the day, which is why comparison studies matter more in a polluted city than anywhere else.

Two things are worth holding onto here. The effect sizes are small per unit, and the exposure gradient in that American cohort was a fraction of what Lahore records in a single winter week. The study was not designed to answer what happens at 100 micrograms per cubic metre, and nobody should extrapolate a clean dose curve from it. What it does establish is that emphysema progression on CT tracks with ambient pollution at concentrations far lower than South Asia’s.

Why patients reach imaging late during smog season

By the time a chest study is ordered in December, many patients have already spent six weeks managing symptoms elsewhere. In practice, chronic cough treatment in Pakistan starts at a pharmacy counter far more often than at a chest clinic. There are a few honest reasons for that.

Symptoms get blamed on the season: A winter cough is treated as a fact of life in most Punjabi households. Patients wait for the fog to lift rather than for the cough to.
The pharmacy comes before the clinic: Nebulisation and a course of whatever is on the shelf is cheaper and faster than a consultation. It also delays the first objective measurement of lung function.
Spirometry is scarce, so imaging is asked to do its job: When no baseline lung function exists, clinicians lean harder on radiology to explain symptoms. Imaging is not built for that role.
Exposure is not only outdoors: Biomass cooking fuel, roadside work, brick kilns and unventilated rooms add to the load. None of this reaches the report unless someone asks.
Cost decides the modality: A plain film is affordable, a CT often is not. The scan that would answer the question is frequently not the scan that gets done.

What this means at the reporting console

The practical adjustments are small, and most of them are about restraint rather than new technique.

Describe, then stop: Report the emphysema, the air trapping, the bronchial thickening. Resist writing a cause. “Findings may reflect chronic inhalational exposure” is defensible only when the clinical history supports it.
Ask for the priors: Progression is the signal. A single winter scan says little, while a comparison across two or three years says a great deal about whether a patient is losing lung.
Quantify where the scanner allows: Where quantitative CT tools are available, percent emphysema gives clinicians a number they can follow over time, which is more actionable than an adjective.
Handle nodules by protocol, not by season: Smog does not change nodule management. Apply the follow-up interval the guideline gives, and state it explicitly in the report.
Say who should see the patient next: A report that names the next step gets acted on more often. For patients whose scans show progressive airway disease, review with a chest physician or the nearest pulmonology clinic is worth writing into the impression rather than leaving implied.

The dose question nobody asks in November

Repeat imaging has its own cost, and smog season is when that cost gets forgotten. A patient who has three plain films and a CT between November and February has usually been scanned because each new clinician wanted their own baseline, not because the disease changed.

Two habits help. The first is making prior studies genuinely available rather than technically available, because a scan sitting on a CD in another hospital does not exist for practical purposes. The second is protocolling to the question. Low-dose technique answers most follow-up questions about nodules and emphysema, and it answers them at a fraction of the exposure.

Symptoms that should not wait for the fog to clear

Radiology teams often field questions from family members who see the report before the clinician does. These are the situations where the advice should be prompt and uncomplicated. Seek medical care straight away if a patient has any of the following:

Breathlessness at rest, or difficulty completing a sentence
Chest pain with breathlessness
Coughing up blood
Blue-tinged lips or fingertips
Fever with breathlessness lasting more than three days
Weight loss and a cough lasting more than two weeks, which needs tuberculosis to be ruled out

A realistic way forward

Nobody reporting chest studies in South Asia is going to fix the air. What radiology can do is refuse to let smog become a diagnosis of convenience.

Every winter, a proportion of these patients have something else. Tuberculosis remains common. Heart failure gets missed. Occupational exposure goes unrecorded because nobody asked what the patient does for a living. A report that describes findings precisely, compares them with priors, and points to the right clinic does more good than one that gestures at the season.

The exposure data is now strong enough to take seriously and specific enough to stay honest about. Pollution shortens lungs’ working lives, and imaging can show that happening across years. It cannot tell you which breath did it.

This article is for educational purposes and is not a substitute for medical advice. Imaging findings should be interpreted alongside clinical assessment by a qualified practitioner.

Sources

1. IQAir. (2025). Lahore among the top 10 most polluted cities in the world, 14 October 2025. https://www.iqair.com/newsroom/lahore-among-top-10-most-polluted-cities-in-the-world-10-14-2025

2. World Health Organization. (2024). Ambient (outdoor) air quality and health fact sheet. https://www.who.int/news-room/fact-sheets/detail/ambient-(outdoor)-air-quality-and-health

3. Wang M, Aaron CP, Madrigano J, et al. (2019). Association Between Long-term Exposure to Ambient Air Pollution and Change in Quantitatively Assessed Emphysema and Lung Function. JAMA. https://pubmed.ncbi.nlm.nih.gov/31408135/

4. National Heart, Lung, and Blood Institute. (2019). Study finds link between long-term exposure to air pollution and emphysema. https://www.nhlbi.nih.gov/news/2019/study-finds-link-between-long-term-exposure-air-pollution-and-emphysema

Author Bio

Farwa Hassan is the Web Acquisition Lead at Marham.pk. A homeopath pursuing further studies in psychology, she creates health content that helps patients across Pakistan find reliable information and the right doctors. Reach her at farwa.hassan@marham.pk

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