Particulates are small particles of solid or liquid matter. In the atmosphere, they are often referred to as aerosols, while in water they are called suspended particulates. Particulates can be emitted directly into the air by human activities such as combustion, windblown dust and grinding operations. They can also be produced indirectly when gases react with each other to form new compounds.
Most atmospheric particulates come from natural sources, such as volcanoes, sea spray, forest fires and wind-blown dust from dry land. However, human activities are also a significant source of atmospheric particulate pollution – particularly in urban areas. The main sources of man-made particulate pollution include: road transport (particularly diesel vehicles), power generation (both coal-fired and gas-fired power stations), domestic heating (including wood burning), industry (such as cement production) and agricultural waste burning.
The size of atmospheric particulates varies widely. Some are large enough to be seen with the naked eye (e.g., smoke particles from a fire), while others are so small that they can only be detected using an electron microscope. The smaller the particle, the greater its potential to penetrate deep into the lungs and cause health problems. Inhalation of fine particulates has been linked with respiratory illnesses such as asthma, bronchitis and heart disease; it is also thought to increase the risk of lung cancer.
There are a number of methods for measuring atmospheric particulate levels:
* Gravimetric analysis involves weighing filter paper samples before and after exposure to measured volumes of air;
* Optical microscopy uses light scattering techniques to estimate particle sizes;
* Electrical mobility classification sorts particles according to their electrical charge;
* Mass spectrometry identifies different types of particles present in a sample based on their mass/charge ratio.