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Nestled in southeastern Michigan's Washtenaw County, Ann Arbor occupies a distinctive position within the Great Lakes Basin, approximately 35 miles west of Detroit and 45 miles north of Toledo, Ohio. The city's geography is characterized by the Huron River, which meanders through its heart, creating a valley that influences local microclimates and air movement. Situated at an elevation of about 850 feet above sea level, Ann Arbor lies within the transition zone between the flat agricultural plains to the west and the more rolling terrain of the Irish Hills to the east. This urban-rural gradient is pronounced, with the city core giving way to suburban developments and then to farmland and natural areas, including the expansive Waterloo and Pinckney recreation areas to the northwest. Proximity to the Detroit-Windsor industrial corridor, part of the Rust Belt, means Ann Arbor can experience transported pollutants from heavy industry and vehicle emissions, particularly under prevailing westerly winds. However, its location away from immediate major industrial centers and surrounded by green spaces like the University of Michigan's Matthaei Botanical Gardens helps moderate air quality. The Huron River and nearby lakes, such as Ford Lake, can contribute to localized humidity and fog, occasionally trapping pollutants. Ann Arbor's position in a temperate continental climate zone, with cold winters and warm summers, combined with its terrain, creates conditions where temperature inversions in valleys can lead to episodic air stagnation, especially in winter, affecting particulate matter and ozone levels.

Ann Arbor's air quality follows a seasonal rhythm shaped by its continental climate and urban activities. In winter, from December to February, cold temperatures and frequent temperature inversions trap pollutants near the ground, leading to peaks in particulate matter from heating sources and vehicle emissions; sensitive groups like those with asthma should limit prolonged outdoor exertion during these months. Spring, from March to May, brings variable conditions: melting snow and increased wind can disperse pollutants, but pollen from trees like oak and maple adds to respiratory irritants, making late spring a better time for outdoor activities. Summer, from June to August, sees higher ozone levels due to intense sunlight reacting with vehicle and industrial emissions, often peaking in July and August; heatwaves can exacerbate this, so early mornings or evenings are preferable for exercise, especially for children and the elderly. Autumn, from September to November, generally offers the cleanest air, with cooler temperatures, reduced ozone formation, and falling leaves minimizing dust, though occasional wildfires from northern regions can bring smoke. Throughout the year, weather hazards like lake-effect snow from Lake Michigan rarely impact air quality directly, but fog and stagnant air in the Huron River valley can cause short-term pollution buildups. Monitoring local forecasts and avoiding high-traffic areas during rush hours can help residents manage exposure.