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Palmilla, nestled within the Libertador General Bernardo O’Higgins Region of Chile, occupies a unique and challenging geographic position. Located at approximately -34.6042 latitude and -71.3583 longitude, the city sits on the western slopes of the Andes Mountains, a mere 10 kilometers from the Pacific Ocean. This proximity to the coast significantly influences its climate and, consequently, its air quality. The terrain is steep and rugged, characterized by terraced hillsides and narrow valleys, a legacy of historical agricultural practices and the city’s gradual expansion. Palmilla’s elevation, averaging around 500 meters above sea level, contributes to the potential for temperature inversions, a key factor in trapping pollutants. The surrounding landscape is a mosaic of vineyards, orchards (particularly citrus), and small-scale agriculture, interspersed with patches of native matorral vegetation. To the east, the imposing Andes rise dramatically, acting as a barrier to prevailing winds and further exacerbating the potential for pollutant accumulation. While not directly adjacent to major industrial belts, Palmilla’s location within the broader Valparaíso Region places it within reach of industrial activity concentrated further north. The urban–rural gradient is relatively sharp; the city transitions quickly into agricultural land and then into the mountainous terrain, limiting the dispersion of pollutants and creating a microclimate susceptible to localized air quality issues. The Pacific Ocean provides a source of moisture and sea breezes, but also introduces marine aerosols that can interact with pollutants.

Palmilla’s air quality follows a distinct seasonal pattern dictated by its Mediterranean climate. The dry summer months (December to February) are typically characterized by clear skies and strong, persistent Pacific winds, which generally provide good ventilation and disperse pollutants. However, during periods of high-pressure systems, these winds can subside, leading to stagnant air and the potential for localized pollution episodes, particularly from agricultural burning practices common in the region. Spring (September to November) sees increasing rainfall and a gradual shift in wind patterns, which can initially trap pollutants but eventually lead to improved air quality as the season progresses. Autumn (March to May) is often the most challenging period. As temperatures cool, the likelihood of temperature inversions increases, trapping pollutants close to the ground. Fog, common during these months, further reduces visibility and exacerbates the issue. The combination of cooler temperatures, reduced wind speeds, and frequent fog creates conditions conducive to pollutant accumulation. Winter (June to August) brings the highest rainfall, which helps to cleanse the atmosphere, but also introduces moisture that can react with pollutants, forming secondary particles. Sensitive groups, including children, the elderly, and individuals with respiratory conditions, should exercise caution during autumn and early spring, limiting outdoor activity during periods of fog or stagnant air. Agricultural workers should be particularly mindful of smoke exposure during the dry season.