Nepal, April 2 -- Kathmandu consistently ranks on top of one chart that I would rather have it not be a part of at all - that of the most polluted cities in the world regarding its air quality. In 2023, Kathmandu was ranked the 11th most polluted city, and Nepal was ranked the 8th most polluted country in the world, with regard to the weighted average concentration of PM2.5. Particulate matter, PM, is the mixture of solid particles and aerosols that pollute the air. PM2.5 are fine inhalable particles that are 2.5 microns in diameter. For comparison, the average human hair is 70 microns thick. So, the largest PM2.5 is 30 times smaller than the average thickness of a human hair. Scientists use a color-coded index called the Air Quality Inde...