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San Lorenzo, San Marcos, Guatemala, nestled within the western highlands, occupies a geographically significant position at approximately 15.0211° latitude and -91.7378° longitude. The city’s elevation, hovering around 2,100 meters (6,889 feet) above sea level, immediately influences its climate and, consequently, its air quality. San Lorenzo is surrounded by a dramatic landscape of steep, forested slopes and deep valleys, characteristic of the Sierra Madre de Gualmala. This terrain creates localized microclimates and can trap pollutants, particularly during periods of low wind. The surrounding region is predominantly rural, characterized by small-scale agriculture, including coffee and maize cultivation, and interspersed with patches of cloud forest. While San Lorenzo itself is a relatively small urban center with a population of around 14,085, it sits within a broader agricultural zone, and the burning of agricultural waste, a common practice in the region, contributes to seasonal air pollution episodes. The urban–rural gradient is sharp; the city transitions quickly into agricultural land and dense forest. The lack of major industrial belts directly adjacent to San Lorenzo mitigates some industrial pollution risks, but transportation-related emissions from vehicles traveling along regional routes are a factor. The proximity to the Suchitepéquez River, though not directly within the city limits, influences local humidity and can affect the dispersion of particulate matter. The mountainous terrain and prevailing wind patterns significantly impact how pollutants are transported and diluted, creating areas of higher and lower concentration within and around San Lorenzo.

San Lorenzo’s air quality follows a distinct seasonal pattern dictated by Guatemala’s tropical climate, exhibiting a pronounced wet and dry season cycle. The dry season, typically spanning November through April, often brings the poorest air quality. Reduced rainfall leads to lower atmospheric moisture, which inhibits the scavenging of particulate matter. Furthermore, the lack of cloud cover allows for increased solar radiation, promoting photochemical reactions that can form ozone and other secondary pollutants. Temperature inversions, common during the dry season, trap pollutants near the ground, exacerbating the problem. Agricultural burning, prevalent during land clearing and crop residue disposal, peaks during this period, releasing significant amounts of smoke and particulate matter. The wet season, from May to October, generally brings improved air quality due to frequent rainfall that washes pollutants from the atmosphere. Increased cloud cover reduces solar radiation, limiting photochemical smog formation. However, periods of heavy fog, particularly in the early morning, can temporarily trap pollutants close to the ground. November and December often see a gradual deterioration in air quality as the dry season approaches. Sensitive groups, including children, the elderly, and individuals with respiratory conditions, should exercise caution during the dry season, limiting outdoor activities during peak pollution periods, typically mid-morning and early afternoon. Maintaining indoor air quality through ventilation and air purification can also be beneficial. The transition months of May and October can be unpredictable, with occasional periods of poor air quality due to lingering agricultural burning or localized weather patterns.