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Andacollo, nestled within the Coquimbo Region of Chile, occupies a geographically complex position significantly influencing its air quality. Located at approximately -30.2303° latitude and -71.0858° longitude, the city sits at an elevation of roughly 450 meters above sea level, placing it within a transitional zone between the coastal plains and the foothills of the Andes Mountains. This location creates a unique interplay of maritime and continental influences. The Pacific Ocean lies a relatively short distance to the west, moderating temperatures and providing a source of moisture, but also introducing marine aerosols. To the east, the Andes rise dramatically, creating a rain shadow effect that contributes to the region's arid climate. Andacollo’s urban character is that of a developing municipality, transitioning from a primarily agricultural base to a more diversified economy. Surrounding the city are extensive agricultural lands, particularly vineyards and fruit orchards, which, while vital to the regional economy, can contribute to localized air pollution through pesticide application and biomass burning during harvest seasons. Further inland, industrial activity, including mining operations in the broader Coquimbo region, can transport pollutants via prevailing winds. The urban–rural gradient is relatively sharp, with agricultural fields quickly giving way to more rugged terrain. Topography plays a crucial role; the valley setting can trap pollutants, especially during periods of calm winds and temperature inversions, exacerbating air quality challenges. The proximity to the Elqui River also influences local humidity and potential for fog formation, which can further impact pollutant dispersion.

Andacollo’s air quality experiences a distinct seasonal pattern dictated by its Mediterranean climate. The dry season, spanning roughly from November to April, typically sees the poorest air quality. During these months, high temperatures and minimal rainfall create conditions conducive to the accumulation of pollutants. Temperature inversions, a common meteorological phenomenon in this region, frequently occur, trapping emissions close to the ground. These inversions are particularly prevalent during the early morning hours, leading to a build-up of particulate matter and other pollutants. Agricultural burning, often practiced during this period for land clearing and crop residue disposal, significantly contributes to the problem. The wet season, from May to October, brings cooler temperatures and increased precipitation, which naturally helps to cleanse the atmosphere. Rainfall effectively washes pollutants from the air, leading to improved air quality. However, fog events, which are more common during the transition months (May and October), can temporarily reduce visibility and trap pollutants in localized areas. Wind patterns also play a crucial role; stronger winds, more frequent during the wet season, help to disperse pollutants. Sensitive groups, including children, the elderly, and individuals with respiratory conditions, should exercise caution during the dry season, particularly during periods of agricultural burning or when temperature inversions are predicted. Outdoor activities are generally more favorable during the wet season, although fog can still pose a visibility hazard.