Milan was ranked third among the most polluted cities in the world last Sunday, according to the AQI (Air Quality Index), which combines numerous indicators — small particles PM2.5 and PM10, ozone, nitrogen oxides, and sulfur — and compares cities moment by moment and day by day. The Lombard capital had fallen one position by the evening, being surpassed by Delhi; while Lahore (Pakistan), and Dhaka (Bangladesh), maintained their respective lead positions. But all the sites specialized in air quality, including the European Cams, which uses a similar index called Aqi, mounted by default in many smartphones, agreed that the Po Valley and Central-Northern Italy in general have the unenviable record of being the most polluted area in Europe, ahead of even the eastern areas of the continent that still make extensive use of coal for heating and electricity production. The AQI index is continually changing and does not provide an annual average, but rather a moment-to-moment ranking. The high levels of pollutants these days are caused by four factors: the unfavorable geography of the Po Valley, with poor air circulation; the high pressure that has reigned for weeks and causes the colder air to stagnate with the accumulation of smog; the high density of population, houses, and cars; and the presence of intensive livestock and agricultural crops. In fact, 54% of PM2.5 is caused by residential and livestock heating, with transportation accounting for only 15%.
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