Particulates – also known as particulate matter (PM), suspended particulate matter (SPM), respirable suspended particle (RSP; particles with diameter of 10 micrometres or less) fine particles, and soot – are tiny subdivisions of solid matter suspended in a gas or liquid. In contrast, aerosol refers to particles and/or liquid droplets and the gas together. Sources of particulate matter can be man made or natural. Air pollution and water pollution can take the form of solid particulate matter, or be dissolved. Salt is an example of a dissolved contaminant in water, while sand is generally a solid particulate.

To improve water quality, solid particulates can be removed by water filters or settling, and is referred to as insoluble particulate matter. Dissolved contaminants in water are often collected by distilling, allowing the water to evaporate and the contaminants to return to particle form and precipitate.

Some particulates occur naturally, originating from volcanoes, dust storms, forest and grassland fires, living vegetation, and sea spray. Human activities, such as the burning of fossil fuels in vehicles, power plants and various industrial processes also generate significant amounts of particulates. Coal combustion in developing countries is the primary method for heating homes and supplying energy. Because salt spray over the oceans is the overwhelmingly most common form of particulate in the atmosphere, anthropogenic aerosols—those made by human activities—currently account for about 10 percent of the total amount of aerosols in our atmosphere. Increased levels of fine particles in the air are linked to health hazards such as heart disease, altered lung function and lung cancer.