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Longjiang is a county-level city situated in the southeastern coastal region of Zhejiang Province, China, positioned at coordinates 27.5819°N, 120.5489°E. Nestled within the Wenzhou metropolitan area, it lies approximately 30 kilometers inland from the East China Sea, creating a distinctive urban-rural gradient that transitions from dense urban cores to agricultural peripheries. The city's terrain is characterized by the rolling hills and low mountains typical of southeastern China's coastal ranges, with elevations generally ranging from 50 to 300 meters above sea level, which influences local air circulation patterns. Longjiang is part of the economically vibrant Yangtze River Delta region, though it sits at its southern periphery, blending industrial activity with agricultural zones producing tea, citrus fruits, and rice. The Ou River flows nearby, providing some atmospheric moisture but limited pollution dispersion benefits due to the city's inland position. This geographic setting creates a complex air quality dynamic: industrial emissions from urban manufacturing combine with agricultural burning residues, while the surrounding hills can trap pollutants during stable atmospheric conditions. The city's location away from major coastal breezes means it lacks the natural ventilation of coastal cities, making it susceptible to pollutant accumulation, particularly when regional winds carry industrial emissions from neighboring urban centers in the Wenzhou area.

Longjiang experiences distinct seasonal air quality patterns shaped by the East Asian monsoon system and local topography. During winter (December-February), cold, stable air masses from the north often lead to temperature inversions, trapping pollutants near the ground and creating peak pollution periods, particularly in January and February; sensitive groups should limit outdoor activities during these months. Spring (March-May) brings transitional weather with increasing rainfall from the southeast monsoon, which helps wash out particulate matter, making April and May relatively favorable for outdoor pursuits. Summer (June-August) features high humidity and southerly winds from the ocean, dispersing pollutants effectively, though occasional stagnant conditions during heatwaves can cause brief deteriorations; this season generally offers the cleanest air. Autumn (September-November) sees decreasing rainfall and shifting wind patterns, with October often experiencing moderate pollution as agricultural burning coincides with reduced atmospheric mixing. Throughout the year, fog formation in low-lying areas during calm mornings can temporarily worsen air quality by trapping local emissions. Residents with respiratory conditions should monitor daily forecasts closely during winter inversions and autumn transition periods, while planning outdoor activities for late spring and summer when maritime influences prevail.