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Sisophon, located in Banteay Meanchey province, Cambodia, occupies a strategically important position along National Road 5, a major artery connecting Phnom Penh to the Thai border. Its coordinates (13.5839, 102.9736) place it within a relatively flat, alluvial plain characteristic of the Cambodian Northwest. The terrain is gently undulating, primarily composed of fertile agricultural land, supporting rice cultivation and other crops. The city’s urban footprint is modest, exhibiting a clear urban–rural gradient extending outwards into the surrounding countryside. While not directly adjacent to a major river, Sisophon benefits from the proximity of the Sangkae River basin, influencing local humidity and microclimates. The surrounding landscape is dominated by rice paddies, interspersed with cashew plantations and scattered villages, creating a predominantly agrarian setting. The city’s location near the border with Thailand means it experiences some influence from industrial activity in neighboring regions, though direct industrial zones within Sisophon itself are limited. The prevailing winds generally blow from the southwest during the monsoon season, carrying moisture and potential pollutants from across the Tonle Sap lake and beyond. Elevation is low, averaging around 15 meters above sea level, which can exacerbate the trapping of pollutants during periods of temperature inversion, particularly during the drier months. The lack of significant topographical barriers contributes to a relatively open atmospheric circulation, but also means pollutants can spread easily across the region.

Sisophon’s air quality is heavily influenced by its tropical monsoon climate, resulting in distinct seasonal patterns. The wet season (roughly May to October) brings increased rainfall and humidity, generally leading to improved air quality as precipitation washes away particulate matter. However, periods of intense rainfall can also stir up dust and contribute to localized flooding, potentially releasing pollutants from inundated areas. The monsoon winds, typically from the southwest, play a crucial role in dispersing pollutants, though they can also carry them from distant sources. The dry season (November to April) presents a more challenging scenario. Reduced rainfall, lower humidity, and calmer winds often lead to temperature inversions, where cooler air becomes trapped beneath a layer of warmer air, preventing vertical mixing and allowing pollutants to accumulate near ground level. Fog, particularly in the early morning hours during November and December, further exacerbates this issue, trapping pollutants and reducing visibility. Agricultural burning, a common practice for land clearing and crop residue disposal, significantly contributes to particulate matter pollution during the transition months (February-March). Sensitive groups, including children, the elderly, and individuals with respiratory conditions, should exercise caution during these periods, limiting outdoor activity and avoiding areas with visible smoke. The months of January, February, and March often present the most significant air quality challenges due to the combination of temperature inversions, agricultural burning, and reduced rainfall.