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St. John's, the capital of Antigua and Barbuda, occupies a strategic position on the northwest coast of Antigua in the Caribbean Sea. The city's geography is defined by its coastal setting within a natural deep-water harbour, surrounded by rolling hills and low-lying terrain that rarely exceeds 50 meters in elevation. This urban centre functions as the primary commercial and administrative hub for the nation, with a compact urban core that transitions rapidly into suburban and rural areas toward the island's interior. The city's location directly on the Caribbean Sea exposes it to consistent maritime influences, while its position within the Lesser Antilles archipelago places it downwind of prevailing easterly trade winds. These geographic factors significantly impact air quality: the harbour area concentrates emissions from cruise ships and marine vessels, while the city's bowl-like topography can trap pollutants when winds are light. Road dust becomes particularly problematic along the urban-rural gradient where paved surfaces give way to unpaved roads. The absence of major industrial belts means pollution sources remain localized to transportation, construction, and occasional agricultural burning in surrounding areas. Proximity to the ocean typically provides natural ventilation, but during certain meteorological conditions, pollutants can accumulate over the urban area before dispersing seaward.

St. John's experiences relatively stable tropical temperatures year-round, but air quality follows distinct seasonal patterns influenced by the tropical monsoon climate. During the dry season from February to April, pollution peaks occur due to reduced rainfall, increased construction activity, and more frequent agricultural burning in surrounding areas. These months see the highest concentrations of particulate matter from road dust and combustion sources, with light winds occasionally allowing pollutants to accumulate. Sensitive groups should limit prolonged outdoor exertion during this period, particularly on days with visible haze. The wet season from May to November brings relief through frequent rainfall that scrubs pollutants from the air, though hurricane season from June to November introduces different air quality challenges from storm-related debris and post-storm mold. December and January represent the most favourable period for outdoor activities, with moderate rainfall and consistent trade winds providing good ventilation. Throughout the year, morning hours typically offer better air quality before daytime traffic increases emissions. The absence of temperature inversions common in temperate cities is replaced by rainfall patterns as the primary meteorological factor affecting pollution dispersion. Marine breezes generally provide natural air cleansing, but during peak pollution months, these can be insufficient to clear locally generated emissions.