Milan, a prominent European city, faces significant air quality challenges. This issue impacts residents and draws environmental attention. This article explores the primary factors contributing to Milan’s air pollution: its unique geography, prevailing weather patterns, and major human-related emission sources.
Geographic Factors
Milan’s location within the Po Valley is a primary reason for its persistent air quality problems. The valley forms a natural basin, surrounded by the Alps to the north and the Apennine mountains to the south. This unique topography significantly hinders air circulation, trapping pollutants within the valley. The entrapped air prevents contaminant dispersion, leading to their accumulation. This geographical entrapment makes the region particularly vulnerable to air pollution.
Meteorological Conditions
Atmospheric phenomena frequently exacerbate the geographical challenges inherent to the Po Valley. A primary meteorological factor is temperature inversions, where a layer of warm air settles above cooler, denser air closer to the ground. This warmer layer acts like a lid, trapping pollutants below and preventing vertical mixing. Temperature inversions are common in the Po Valley, particularly during the colder winter months, leading to prolonged periods of stagnant air and heightened pollution levels.
The region also experiences consistently low wind speeds, which further impede the horizontal dispersion of pollutants. The average wind speeds in the Po Valley are among the lowest in Europe, especially during winter, averaging around 1.5 meters per second. This atmospheric stability, combined with frequent temperature inversions, creates conditions where airborne contaminants linger close to the ground, significantly worsening air quality.
Dominant Emission Sources
Human activities in Milan and the broader Po Valley contribute substantially to the region’s air pollution. Vehicle traffic is a major source, with Milan having one of Europe’s highest rates of car ownership, despite a majority of trips utilizing public transport. Older diesel vehicles contribute significant amounts of particulate matter (PM2.5) and nitrogen oxides (NOx) to the urban atmosphere. Road transport is a leading contributor to NOx emissions, and traffic restrictions, such as Milan’s Area C congestion charge, aim to reduce these emissions in the city center.
Residential heating systems, especially during colder months, are another substantial source of emissions. The use of older boilers and the burning of biomass, such as wood and pellets, release considerable amounts of fine particulate matter (PM2.5) and black carbon. Domestic and commercial heating accounts for a significant portion of the Po Valley’s air pollution, estimated to contribute around 37% of the total emissions, making it the largest single source of primary PM10. Measures to limit heating temperatures and restrict inefficient wood-burning stoves are implemented to mitigate these emissions.
Industrial activity contributes to air pollution in the densely industrialized Po Valley. Combustion processes within various industries release pollutants, including particulate matter and nitrogen dioxide. Although industrial emissions are often regulated, their cumulative impact in a region with limited air circulation adds to the overall pollution burden.
Agricultural practices in the surrounding Lombardy region also play a considerable role in air quality degradation. Livestock farming is a major producer of ammonia emissions. Ammonia acts as a precursor for the formation of secondary particulate matter, which contributes significantly to PM10 concentrations. Manure spreading, a common agricultural practice, can elevate secondary inorganic aerosol (SIA) levels in urban areas. Studies indicate that agricultural activities, including livestock farming, can account for up to 25% of local pollution exposure in Lombardy.