Green Bay Air Quality Index (AQI)

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Green Bay, Wisconsin, is strategically positioned on the southwestern shore of Lake Michigan’s Green Bay, a significant arm of the larger lake. This location profoundly influences its air quality. The city itself sits on relatively flat terrain, part of the broader glacial plains of the Midwest, with an average elevation around 680 feet above sea level. Surrounding Green Bay is a mix of agricultural land – primarily dairy farming and crop production – and pockets of forested areas. To the west lies a more intensely farmed landscape, while to the north and east, the terrain becomes increasingly rural and wooded. The lake exerts a moderating influence on temperatures, but also contributes to localized weather patterns like lake-effect snow and fog, which can trap pollutants. Historically, Green Bay developed as a port city, initially focused on timber and then paper production. While heavy industry has declined, remnants of these activities, alongside transportation corridors (rail and highway), contribute to localized emissions. The urban-rural gradient is relatively sharp, with agricultural operations immediately bordering the city limits. This proximity means pollutants from farming – ammonia, particulate matter from soil erosion – can readily impact air quality, particularly during planting and harvesting seasons. The prevailing winds, generally from the west-southwest, carry pollutants across the agricultural heartland towards the city.

Green Bay’s air quality follows a distinct seasonal pattern. Winter, from December to February, often sees poorer air quality due to temperature inversions. Cold, dense air becomes trapped beneath a layer of warmer air, preventing vertical mixing and concentrating pollutants from home heating (primarily wood burning) and vehicle emissions. Snow cover also reflects sunlight, increasing ground-level ozone formation even in cold temperatures. Spring (March-May) brings increased agricultural activity, leading to higher levels of particulate matter from tilling and fertilizer application. Rainfall helps to cleanse the air, but can also mobilize pollutants. Summer (June-August) generally offers the best air quality, with prevailing winds dispersing pollutants and higher temperatures promoting ozone formation, though this is usually moderate. However, stagnant air masses can still lead to localized ozone issues. Autumn (September-November) sees a return to cooler temperatures and increased wood burning, alongside harvest activities. Fog, common over the bay, can trap pollutants, reducing visibility and impacting respiratory health. Sensitive groups – children, the elderly, and those with respiratory conditions – should limit strenuous outdoor activity during winter inversions and periods of high pollen counts in spring. Monitoring conditions and adjusting activity levels accordingly is crucial.