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Cariús, a municipality nestled in the state of Ceará, Brazil, occupies a position within the semi-arid Sertão region. Located at approximately -6.5369 latitude and -39.4969 longitude, the city’s terrain is characterised by gently undulating hills and flatlands typical of the Brazilian Northeast. The elevation is relatively low, contributing to limited natural dispersion of pollutants. Cariús is not directly coastal, lying inland approximately 120km from the Atlantic Ocean, but its climate is still influenced by maritime air masses, albeit moderated by the distance. The surrounding landscape is dominated by *caatinga* vegetation – a thorny scrub forest adapted to drought conditions. Agriculture, primarily subsistence farming and livestock raising, forms a significant part of the regional economy, with potential for dust emissions from land cultivation. While Cariús isn’t a major industrial hub, smaller-scale processing of agricultural products and construction activities contribute to localised pollution sources. The urban-rural gradient is relatively sharp, with the city centre representing a concentrated area of human activity and associated emissions, quickly transitioning to sparsely populated rural areas. This concentration, coupled with the region’s limited rainfall and prevailing wind patterns, can exacerbate air quality issues, particularly during the dry season. The city’s geographical setting dictates a vulnerability to dust storms and limited atmospheric flushing.

Cariús experiences a distinct wet and dry season, rather than traditional four seasons. Air quality in Cariús is most compromised during the prolonged dry season, typically from August to December. This period sees minimal rainfall, leading to increased dust resuspension from the *caatinga* landscape and agricultural lands. Lower humidity also reduces the natural scavenging of pollutants. The hot, dry air can create temperature inversions, trapping pollutants near the ground. February to May represents the wet season, bringing significant improvements in air quality as rainfall washes away particulate matter and suppresses dust. However, even during the wet season, localised pollution from vehicle emissions and small-scale industries persists. June and July offer a transitional period with moderate air quality. Sensitive groups – children, the elderly, and those with respiratory conditions – should exercise caution during the dry season, limiting strenuous outdoor activity and monitoring their health. The prevailing easterly winds can transport pollutants from agricultural burning further afield, impacting Cariús during certain periods. Fog is infrequent, but when it occurs, it can exacerbate particulate matter concentrations. Avoiding outdoor exertion during peak heat hours in the dry season is advisable.