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Key Biscayne, Florida, a barrier island nestled in Biscayne Bay, presents a unique geographic profile significantly influencing its air quality. Situated just southeast of Miami, its location offers both advantages and vulnerabilities. The island’s terrain is remarkably flat, averaging only a few feet above sea level, limiting vertical mixing of air and potentially trapping pollutants. Surrounded by the expansive waters of Biscayne Bay to the west and the Atlantic Ocean to the east, Key Biscayne benefits from prevailing sea breezes that generally disperse pollutants, but these breezes can also carry marine aerosols and salt, impacting air composition. The island’s urban character is predominantly residential, with luxury homes and resorts dominating the landscape, minimizing industrial emissions directly within Key Biscayne itself. However, its proximity to Miami’s urban core and industrial areas to the north and west means it’s susceptible to pollutants transported from those sources. The urban–rural gradient shifts rapidly; beyond the developed areas, the island features protected natural habitats, including Bill Baggs Cape Florida State Park, which contributes to localized air purification through vegetation. The surrounding landscape is characterized by coastal mangroves, seagrass beds, and coral reefs, all of which play a role in the regional ecosystem and, indirectly, air quality. The lack of significant elevation and the island’s exposure to prevailing winds create a dynamic environment where air quality is heavily influenced by external factors and regional weather patterns.

Key Biscayne’s subtropical climate dictates a distinct seasonal narrative regarding air quality. The wet season, typically from May through October, brings frequent afternoon thunderstorms and increased humidity. While these storms can temporarily cleanse the air by washing away particulate matter, they also contribute to ozone formation due to increased sunlight and stagnant air conditions preceding the storms. The high humidity can exacerbate respiratory issues for sensitive individuals. Conversely, the dry season (November through April) generally offers improved air quality. Cooler temperatures and more consistent trade winds promote better dispersion of pollutants. However, temperature inversions, though less frequent than in colder climates, can occasionally occur, trapping pollutants near the ground, particularly during calmer periods. January and February often see the clearest skies and most favourable conditions for outdoor activities. During the summer months, the combination of heat, humidity, and occasional stagnant air can lead to elevated levels of ground-level ozone, impacting those with asthma or other respiratory sensitivities. Sensitive groups, including children, the elderly, and individuals with pre-existing respiratory conditions, should limit prolonged outdoor exertion during the hotter, more humid periods of the year, especially on days with visible haze. Monitoring local weather forecasts for potential temperature inversions or stagnant air advisories is crucial for informed decision-making regarding outdoor activities.