Air Quality in Santiago: Geographic and Meteorological Impacts

Air Pollution in the Metropolitan Area of Santiago

Geographical Location and Meteorological Factors

The geographic location of Santiago, coupled with meteorological factors, is one of the features that most affect the deterioration of air quality in the city.

The Metropolitan Area of Santiago (AMS) is located in the Maipo River basin, at an altitude ranging from 400m to 900m above sea level. This basin is bounded by:

• East: The foothills of the Andes mountain range, which exceeds 3,200m.
• West: The foothills of the Coastal Range, with elevations not exceeding 1,500m.
• South: The Cantillana hill, with heights exceeding 2,000m.
• North: The Chacabuco hills, which close the basin.

The city only opens to the southwest via the Maipo River valley.

Ventilation and Wind Patterns

The presence of this group of hills surrounding Santiago limits the ventilation of the city and the removal of pollutants. Additional adverse factors include:

• Horizontal movement: Speed and direction of wind.
• Vertical propagation: Restrictions caused by the inversion effect.

During the day, pollutants emitted in the central and southwest sectors are transported to the northeastern sector. At night, the flow is reversed, with cleaner air descending from the Andean foothills and bringing polluted air toward the downtown area and the west of the city.

Vertical Dispersion and Temperature Inversion

The vertical dispersion of pollutants usually occurs in a layer between the surface and a height determined by thermodynamic factors. This mixing height is variable, depending on the time of day and the seasons. In Santiago, the height of the mixed layer varies significantly by month, dropping to 300m in winter and rising to 1,000m in summer.

This layer height is heavily affected by temperature inversion. While air temperature normally decreases with height, a common situation in Santiago is an inversion layer that causes primary gas stagnation, facilitating the formation of secondary gases in the atmosphere. This phenomenon is accentuated during the winter months due to the cooling of the earth's surface.