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Chittagong, Bangladesh's second-largest city and principal seaport, occupies a dramatic coastal position where the Karnaphuli River meets the Bay of Bengal. Nestled within the Chittagong Hill Tracts to the east and the Chittagong Coastal Plain to the west, the city sprawls across undulating terrain with elevations ranging from sea level to about 60 meters in northern hills, creating natural basins that trap pollutants. Its strategic location as South Asia's busiest port—handling 90% of Bangladesh's maritime trade—makes it the epicenter of a dense industrial belt along the Karnaphuli River, featuring ship-breaking yards, steel mills, cement factories, and chemical plants whose emissions mingle with those from thousands of vessels. The urban–rural gradient sharpens pollution contrasts: the city core suffers intense vehicular and construction emissions, while surrounding agricultural zones add seasonal biomass burning. Proximity to the Bay of Bengal brings sea breezes that occasionally disperse pollutants, but the encircling hills and river valley often act as a topographic bowl, inhibiting ventilation. This geography, combined with explosive urban growth and lax environmental regulations, creates a perfect storm for poor air quality, exacerbated by road dust from unpaved streets and construction dust from hill-clearing projects that destabilize slopes and trigger landslides.

Chittagong's tropical monsoon climate dictates a stark seasonal air quality narrative, with pollution peaking dramatically from November through March. During these dry winter months, northeasterly winds bring cool, stable air that fosters frequent temperature inversions, trapping ship-breaking emissions, industrial pollutants, and vehicle exhaust near the ground. Reduced rainfall allows construction dust and road particulates to accumulate, while morning fog often mixes with smog, creating hazardous visibility and respiratory conditions. Sensitive groups—children, the elderly, and those with asthma or heart conditions—should avoid prolonged outdoor activity in these months, especially near the port and industrial zones. From April to June, pre-monsoon heat increases convection, slightly improving dispersion, but rising temperatures also intensify ozone formation. The monsoon season (July–October) brings salvation: heavy southwest monsoon rains scour the atmosphere, washing away particulates and dramatically clearing the air. However, this period introduces weather hazards like cyclones and flooding that pose different risks. For the health-conscious, late monsoon months (September–October) offer the cleanest air for outdoor activities, while winter requires masks and indoor air purifiers, particularly during morning inversion episodes when pollution concentrations peak.