Fine ParticlesFine particles are airborne particles which are smaller than coarse particles. They have an aerodynamic diameter of 2.5 µm or less (PM2.5). The fine particles which are smaller than 0.1 µm are referred to as ultrafine particles (PM0.1). Fine particles are largely formed from gases. Ultrafine particles are formed by nucleation, which is the initial stage in which gas becomes a particle. These particles can grow up to a size of 1µm either through condensation, when additional gas condensates on the particles, or through coagulation, when two or more particles combine to form a larger particle. Ultrafine particles (PM0.1) are part of the fine fraction (PM2.5).
FloodA flood is an overflow of water that submerges land which is usually dry. Flooding may occur as an overflow of water from water bodies (river or lake) or it may occur due to an accumulation of rainwater on saturated ground.
Fly ashFinely divided particles of ash in fuel gases resulting from combustion of fuel or other material.
FogIt is a collection of liquid water droplets or ice crystals suspended in the air at or near the Earth's surface. It reduces visibility to less than 1 kilometre (0.62 mi). It forms when the difference between air temperature and dew point is generally less than 2.5 °C or 4 °F.
Fossil FuelsProducts of partial or complete decomposition of plants and animals that occur as crude oil, coal, natural gas or heavy oils as a result of exposure to heat and pressure in the earth’s crust over millions of years.