Which country has the worst air quality in the world?

Which country has the worst air quality in the world varies by year and measurement, but according to recent World Air Quality Report by IQAir which measures PM2.5 fine particulate matter, Bangladesh, Pakistan, and India consistently rank as countries with worst air quality. In recent reports, Bangladesh often ranks number one worst for average PM2.5 concentration, with Dhaka being heavily polluted due to brick kilns, vehicle emissions, and industrial pollution, with PM2.5 levels many times above WHO guidelines. Pakistan, particularly cities like Lahore and Karachi, also ranks near worst due to similar causes and crop burning. India, with cities like Delhi, which frequently has world's worst city air quality, ranks near worst due to vehicle emissions, industrial emissions, crop burning, and dust. Other countries with very poor air quality include Chad, Iraq, and Nepal. Air quality changes seasonally, with winter months often worse in South Asia due to temperature inversions trapping pollution. Factors include rapid industrialization, large populations, reliance on coal and biomass fuels, and limited environmental regulations. For city-level worst air, Delhi, Lahore, and Dhaka often compete for highest PM2.5. So Bangladesh, Pakistan, and India are generally considered to have worst air quality in world by average PM2.5 measurements.