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Lihe is situated within the verdant folds of the Longnan region in Gansu province, a geographic anomaly compared to the arid loess plateaus of the north. Nestled amidst the rugged terrain of the Qinling and Daba mountain ranges, the town is defined by its undulating topography and steep valley slopes. This specific location creates a complex urban character where small-scale residential clusters are interspersed with dense forest cover and terraced agricultural plots. The town sits at a moderate elevation, where the interplay between high ridges and deep basins significantly dictates local atmospheric behavior. Because Lihe is cradled by mountains, it often experiences stagnant air masses, as the surrounding peaks act as physical barriers that inhibit the horizontal dispersion of pollutants. The proximity to small river tributaries provides essential moisture, but also contributes to higher humidity levels that can trap particulate matter near the ground. The urban-rural gradient is narrow, with the transition from the town center to the agricultural hinterland occurring rapidly. This proximity means that seasonal agricultural activities, such as crop residue burning, directly impact the air quality of the residential core. Unlike the industrial belts of eastern China, Lihe's pollution profile is driven more by domestic heating and topographical confinement than by heavy manufacturing. The resulting environment is one of stunning natural beauty but inherent atmospheric vulnerability, where the very mountains that protect the region also concentrate pollutants during periods of low wind. Thus, the forest ecosystem and human settlement create a microclimate that fluctuates with seasons.

Air quality in Lihe follows a rhythmic cycle dictated by the subtropical monsoon and local topography. Spring marks a period of instability, where occasional incursions of dust from the northern Gobi Desert reach the region, though the mountains provide some shielding. This season is often characterized by rising particulate levels as the land dries and wind speeds increase. Summer brings the most pristine air, as the heavy rains of the monsoon season effectively scrub the atmosphere of pollutants, and the lush vegetation maximizes oxygen production. For outdoor activities, July and August are ideal. However, autumn introduces a distinct pollution peak. During the harvest months, the widespread practice of burning agricultural residues creates a thick haze of organic aerosols that lingers in the valley, making September and October challenging for those with respiratory issues. Winter is the most critical period for air quality. As temperatures plummet, the reliance on coal and biomass for domestic heating increases significantly. This coincides with frequent temperature inversions, where a layer of warm air traps cold, polluted air near the surface, preventing vertical dispersion. During December and January, sensitive groups, including children and the elderly, should limit prolonged outdoor exposure to avoid exacerbating asthma or bronchitis. Health guidance emphasizes the use of air purifiers indoors during winter peaks and monitoring local forecasts during the autumn burning season. The transition between these seasons is sharp, reflecting the dramatic shift from monsoon humidity to winter stagnation. Thus, visibility and air clarity vary throughout the calendar year.