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Tonacatepeque, situated in the department of San Salvador, occupies a strategic position within the volcanic highlands of El Salvador. Nestled at an elevation of approximately 650 meters above sea level, the city is characterized by its rolling, rugged terrain typical of the Central American volcanic arc. Its geographical footprint is defined by a transition between the dense, sprawling urbanization of the San Salvador metropolitan area and the verdant agricultural hinterlands that characterize the northern reaches of the department. This urban–rural gradient plays a critical role in the city's atmospheric profile, as the city acts as a gateway between the heavily industrialised capital and the more sparsely populated rural valleys. The surrounding landscape, rich in volcanic soil, supports intensive subsistence and commercial agriculture, which contributes intermittent particulate matter to the local air shed. Because Tonacatepeque is situated on elevated, undulating plateaus, it is subject to complex wind patterns that funnel air through narrow corridors. While the city benefits from the cooling influence of trade winds, its position in a basin-like proximity to the capital means that it often traps stagnant air during the early morning hours. There is a notable absence of large, permanent bodies of water in the immediate vicinity, which limits the moderating effect of humidity on airborne pollutants. Consequently, the city’s air quality is heavily influenced by the interplay between regional vehicular emissions drifting from the south and local dust and smoke generated by agricultural burning and unpaved secondary roads that snake through the surrounding volcanic terrain.

Tonacatepeque experiences a distinct tropical climate defined by a pronounced dry season, spanning from November to April, and a wet season, lasting from May to October. The dry season represents the most challenging period for air quality in the region. During these months, the lack of precipitation removes the natural cleansing mechanism of rainfall, allowing particulate matter from vehicular traffic and regional combustion to linger in the atmosphere. Furthermore, the dry season coincides with traditional agricultural practices, where slash-and-burn clearing of nearby fields significantly increases smoke concentration. Temperature inversions, common during the cool, clear nights of January and February, trap pollutants near the surface, leading to degraded air quality that persists until the morning sun breaks the inversion layer. In contrast, the wet season offers a reprieve, as frequent, heavy convective storms wash atmospheric pollutants from the air, providing clearer skies and improved visibility. However, the wet season can introduce issues related to mold and high humidity, which pose different challenges for sensitive groups. For residents with respiratory sensitivities, the peak months for poor air quality are February and March, when winds are often lighter and biomass burning is at its height. During these periods, outdoor exercise should be restricted to the late afternoon, once the daily thermal mixing has dispersed accumulated pollutants. Conversely, the months of June and July, following the onset of the rains, are the most favorable for outdoor activities, offering the cleanest air and cooler temperatures for the local population.