Arese, nestled in the province of Milan, Lombardy, occupies a strategically important position within Italy’s densely populated and industrialized north. Located approximately 10 kilometers northwest of Milan’s city center, its coordinates (45.5500, 9.0783) place it within the Po Valley, a broad alluvial plain characterized by relatively flat terrain. The municipality sits at a modest elevation of around 190 meters above sea level, contributing to a tendency for air stagnation, particularly during periods of stable atmospheric conditions. The surrounding landscape is a mosaic of agricultural fields – primarily maize and soy – interspersed with residential areas and light industrial zones, reflecting the urban–rural gradient typical of the Milan metropolitan area. To the south lies the sprawling urban fabric of Milan, a major economic and industrial hub, while to the north, the landscape gradually transitions to the foothills of the Alps, offering a degree of relief but also a potential pathway for transboundary pollution. The Olona River flows nearby, influencing local microclimates and potentially impacting pollutant dispersion. The proximity to Milan’s industrial belt, including automotive manufacturing and chemical processing, is a significant factor shaping Arese’s air quality profile. The valley’s topography, combined with the prevalence of anthropogenic emissions, creates a complex interplay that can exacerbate pollution episodes. The region’s fertile soil supports intensive agriculture, which, while economically vital, can also contribute to ammonia emissions, a precursor to particulate matter formation.

Arese’s air quality experiences a distinct seasonal cycle heavily influenced by meteorological patterns. Winter months (December-February) typically see the poorest air quality, driven by temperature inversions. Cold, stable air becomes trapped near the ground, preventing vertical mixing and concentrating pollutants released from residential heating (often wood-burning stoves) and industrial sources. Fog, common during this period, further reduces visibility and traps particulate matter. Spring (March-May) brings a gradual improvement as temperatures rise, and wind speeds increase, facilitating pollutant dispersion. However, pollen seasons can trigger respiratory sensitivities. Summer (June-August) generally offers the best air quality, with frequent convective mixing and occasional thunderstorms cleansing the atmosphere. High temperatures can, however, contribute to ozone formation, particularly on stagnant days. Autumn (September-November) presents a transitional period. Initially, conditions can be favorable, but as temperatures drop and wind speeds decrease, a return to winter-like stagnation is possible, often accompanied by agricultural burning practices in surrounding areas. Sensitive groups, including children, the elderly, and individuals with respiratory conditions, should exercise caution during winter and early spring, limiting outdoor activity during periods of heavy fog or noticeable air pollution. During summer, monitor for ozone alerts and avoid strenuous outdoor exercise during peak ozone hours. The agricultural cycle, with its associated fertilizer application and harvesting, can impact air quality throughout the year, requiring vigilance regarding ammonia and particulate matter levels.