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Phan Rang–Tháp Chàm, nestled in the coastal province of Ninh Thuận, Vietnam, occupies a unique geographic position that significantly influences its air quality. Situated at approximately 11.57°N, 108.98°E, the city lies on a relatively flat coastal plain, transitioning rapidly to the rugged foothills of the Chư Đăng Ya range to the west. This terrain creates a funneling effect, particularly during certain weather patterns, which can trap pollutants. The city’s proximity to the South China Sea moderates temperatures but also introduces marine aerosols and salt, impacting atmospheric composition. Ninh Thuận is characterized by a semi-arid climate, with limited rainfall and high evaporation rates, contributing to a drier atmosphere that can exacerbate particulate matter issues. Surrounding Phan Rang are extensive agricultural zones, primarily focused on cashew nuts, grapes, and dragon fruit cultivation. These agricultural practices, including pesticide use and fertilizer application, can contribute to localized air pollution. Further inland, the landscape shifts to drier scrubland and sparsely forested areas. The urban–rural gradient is relatively sharp, with agricultural land quickly giving way to urban development. Industrial activity is present, though less concentrated than in larger Vietnamese cities; however, cement production and processing plants contribute to emissions. The prevailing winds, often originating from the sea, can either disperse pollutants or, under inversion conditions, trap them close to the ground, creating localized air quality challenges. The elevation, averaging around 20-30 meters above sea level, further limits vertical dispersion of pollutants.

Phan Rang–Tháp Chàm experiences a distinct wet and dry season, profoundly impacting its air quality profile. The dry season, typically spanning from November to April, is characterized by minimal rainfall, high temperatures, and persistent sunshine. This period often sees a build-up of particulate matter, particularly PM2.5 and PM10, due to reduced precipitation to wash pollutants from the atmosphere and increased dust from agricultural activities and construction. Temperature inversions, common during the cooler nights of this season, trap pollutants near the ground, worsening air quality. The months of January and February are generally the most challenging for air quality. Conversely, the wet season, from May to October, brings increased rainfall and higher humidity, which naturally cleanses the air and reduces particulate concentrations. Monsoon winds during this period help disperse pollutants, leading to improved air quality. However, heavy rainfall can also lead to increased levels of ozone due to photochemical reactions. Fog, occasionally occurring during the transitional periods between seasons, can also temporarily trap pollutants. Sensitive groups, including children, the elderly, and individuals with respiratory conditions, should exercise caution during the dry season, limiting outdoor activities during peak pollution periods, typically in the mornings. Maintaining indoor air quality through proper ventilation and air purification can also be beneficial. During the wet season, while generally better, vigilance is still advised, particularly during periods of heavy rainfall or intense sunshine, which can trigger ozone formation.