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Kajang is a rapidly urbanising city located approximately 20 kilometres southeast of Kuala Lumpur in Malaysia's Selangor state, positioned within the Klang Valley conurbation that forms the nation's economic heartland. Situated at coordinates 2.9927°N, 101.7909°E, the city lies at an elevation of approximately 40 metres above sea level, nestled within undulating terrain characterised by low hills and river valleys that influence local air circulation patterns. The Langat River flows through Kajang, providing a natural corridor but also creating microclimates that can trap pollutants under certain conditions. Geographically, Kajang occupies a transitional zone between Kuala Lumpur's dense urban core to the northwest and more rural agricultural areas to the southeast, creating an urban-rural gradient that affects pollution dispersion. The city's location within the Klang Valley places it downwind of major industrial zones in Shah Alam and Petaling Jaya during prevailing winds, while also receiving transboundary haze from Sumatra and Kalimantan during southwest monsoon periods. Surrounding landscapes include oil palm plantations, rubber estates, and limestone hills that contribute biogenic emissions, while urban expansion has replaced much agricultural land with residential and commercial developments. Proximity to the Kuala Lumpur International Airport and major highways like the Kajang-Seremban Highway adds mobile emission sources, creating a complex air quality environment where local emissions mix with regional pollution transported through the valley's topographic funnel.

Kajang experiences consistent tropical weather year-round with distinct monsoon seasons that dramatically influence air quality patterns. During the southwest monsoon from May to September, prevailing winds from the southwest transport smoke and haze from agricultural burning in Sumatra, Indonesia, creating the year's worst pollution episodes typically peaking in August and September when visibility can drop significantly and particulate matter concentrations surge. The northeast monsoon from November to March brings cleaner maritime air from the South China Sea, resulting in generally better air quality from December to February, though occasional haze may still occur from local sources. Inter-monsoon periods in April-May and October-November feature light winds and increased rainfall that help cleanse the atmosphere, though temperature inversions can develop overnight, trapping pollutants near the surface. Sensitive groups including asthmatics, children, and elderly residents should avoid strenuous outdoor activities during haze episodes, particularly in late summer months, and monitor air quality indices regularly. The city's location in a valley can exacerbate pollution during dry periods when atmospheric mixing is limited, while afternoon thunderstorms during inter-monsoon months provide natural cleansing. For optimal outdoor activities, the months of December through February offer the cleanest air, while August and September should be approached with caution, especially for those with respiratory conditions who may need to use air purifiers indoors during peak haze events.