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Banjarmasin, the capital of South Kalimantan province in Indonesia, is a unique riverine city situated on the island of Borneo, approximately 25 kilometers inland from the Java Sea. Built across a network of interconnected waterways and canals, it is often called the 'River City' due to its extensive floating markets and houses on stilts, with the Barito River serving as its main aquatic artery. The city lies within the vast, low-lying peat swamp forests of southern Borneo, at an elevation of just 1–5 meters above sea level, making it highly susceptible to tidal flooding. This flat, marshy terrain, combined with its tropical rainforest climate, creates a natural basin that traps air pollutants, exacerbating local air quality issues. Banjarmasin is surrounded by extensive peatland areas to the north and east, which are prone to fires, while to the south and west, it borders agricultural zones and coal mining regions. The city's urban–rural gradient is blurred, with dense settlements along the rivers blending into rural peatland and plantations. Its position along the Barito River facilitates coal barge traffic from upstream mines, contributing directly to emissions, while the lack of significant elevation changes prevents pollutant dispersion, allowing vehicle exhaust, construction dust, and waste burning fumes to accumulate over the urban area.

In Banjarmasin's tropical rainforest climate, seasonal variations are subtle but critical for air quality, driven primarily by rainfall patterns rather than temperature changes. The dry season, from May to October, sees pollution peak, especially from August to October, when reduced precipitation allows pollutants like vehicle exhaust, road dust, and construction emissions to build up. During these months, the southwest monsoon brings drier air from the Australian continent, lowering humidity and increasing the frequency of peat fires in surrounding areas, which produce thick haze that blankets the city. Sensitive groups, such as children, the elderly, and those with respiratory conditions, should limit outdoor activities and use masks during this period. The wet season, from November to April, offers relief as the northwest monsoon delivers heavy rainfall that washes pollutants from the air, though occasional flooding can stir up sediment and waste. Throughout the year, low wind speeds and frequent temperature inversions, common in the early morning, trap pollutants near the ground, creating persistent smog. Fog is rare, but haze from transboundary sources, such as fires in neighboring provinces, can worsen air quality unpredictably. For the best air quality, plan visits during the wet season months of December to February, when rainfall is highest and outdoor activities are safer.