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Casma, a coastal city in the Ancash region of Peru, presents a unique geographic setting influencing its air quality. Situated at coordinates -9.4742, -78.3106, the city lies within a narrow coastal plain between the Pacific Ocean and the towering peaks of the Andes Mountains. This terrain creates a microclimate prone to temperature inversions, trapping pollutants near ground level. Casma’s elevation is relatively low, averaging around 131 meters above sea level, contributing to limited atmospheric dispersion. The city’s urban character is defined by a blend of residential areas, commercial zones focused around the port, and surrounding agricultural lands – primarily dedicated to sugarcane and fruit cultivation. The proximity to the ocean introduces sea salt aerosols into the air, while agricultural activities contribute to particulate matter from dust and potential pesticide drift. The urban-rural gradient is sharp; moving inland quickly transitions from populated areas to arid foothills. The port activity, handling both fishing and cargo, is a significant source of localised emissions. The prevailing winds, generally blowing from the sea, can either disperse or concentrate pollutants depending on atmospheric stability. Understanding this interplay of coastal, mountainous, and agricultural influences is crucial for assessing Casma’s air quality challenges.

Casma experiences a distinct coastal desert climate, characterized by a pronounced dry season and a relatively short, mild wet season. Air quality in Casma generally deteriorates during the dry season (May to November) due to reduced rainfall, which limits the natural scavenging of pollutants. Dust from agricultural activities and the surrounding arid landscape becomes more prevalent, increasing particulate matter concentrations. Temperature inversions are also more frequent during this period, trapping pollutants close to the ground. January to April brings the wet season, offering temporary relief as rainfall washes away accumulated pollutants. However, increased humidity can also promote the formation of secondary pollutants. February and March often see higher levels of coastal fog, which can trap pollutants and reduce visibility. Sensitive groups, including children, the elderly, and those with respiratory conditions, should limit strenuous outdoor activity during the peak of the dry season, particularly in July and August. Monitoring wind patterns is crucial; strong winds can temporarily improve conditions, while calm periods exacerbate pollution. The port’s activity remains a consistent source of emissions year-round, but is less impactful during the wetter months.