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Macau, nestled in the state of Rio Grande do Norte, Brazil (-5.1150, -36.6339), is a coastal city of approximately 27,369 inhabitants. Its geography is defined by a relatively flat coastal plain, typical of much of Rio Grande do Norte’s shoreline. The city sits close to the Atlantic Ocean, experiencing the moderating influence of marine air masses. The surrounding landscape is a mix of sandy beaches, dunes, and patches of *restinga* – a unique coastal forest ecosystem. Macau isn’t situated near major industrial belts, which is a positive factor for air quality, but it’s surrounded by agricultural zones, primarily focused on fruit cultivation and small-scale farming. These agricultural activities contribute to particulate matter through dust from land preparation and potential burning of agricultural waste. The urban-rural gradient is fairly sharp; Macau itself is a concentrated urban area, quickly transitioning to rural landscapes dominated by agriculture and natural vegetation. The city’s low elevation makes it susceptible to humidity and the effects of sea breezes, which can both disperse and concentrate pollutants depending on atmospheric conditions. The proximity to the ocean also means potential for salt spray contributing to aerosol formation, impacting visibility and potentially influencing cloud formation.

Macau experiences a distinct wet and dry season, rather than traditional four seasons. Air quality generally improves during the wet season (roughly April to August) due to rainfall effectively scavenging pollutants from the atmosphere. The increased humidity, however, can also promote the formation of secondary pollutants. The dry season (September to March) presents the greatest air quality challenges. Lower rainfall means pollutants accumulate, and stronger winds can carry dust from inland agricultural areas towards the city. November and December often see the poorest air quality as agricultural burning peaks following the harvest. Temperature inversions, common during the calmer nights of the dry season, trap pollutants near the ground, exacerbating conditions. Sea breezes offer some relief, but their effectiveness is variable. Sensitive groups – children, the elderly, and those with respiratory conditions – should limit strenuous outdoor activity during the dry season, particularly in November and December. Monitoring wind direction is crucial; winds from the west are more likely to carry agricultural dust. Fog, common in the early mornings, can trap pollutants and reduce visibility, requiring caution for those with respiratory sensitivities.