Particulate matter
Particulate matter or particulates are microscopic particles of solid or liquid matter suspended in the air. An aerosol is a mixture of particulates and air, as opposed to the particulate matter alone, though it is sometimes defined as a subset of aerosol terminology. Sources of particulate matter can be natural or anthropogenic. Particulates have impacts on climate and precipitation that adversely affect human health.
Types of atmospheric particles include suspended particulate matter; thoracic and respirable particles; inhalable coarse particles, designated PM, which are coarse particles with a diameter of 10 micrometers or less; fine particles, designated PM, with a diameter of 2.5 μm or less; ultrafine particles, with a diameter of 100 nm or less; and soot.
Airborne particulate matter is a Group 1 carcinogen. Particulates are the most harmful form of air pollution as they can penetrate deep into the lungs and brain from blood streams, causing health problems such as stroke, heart disease, lung disease, cancer and preterm birth. There is no safe level of particulates. Worldwide, exposure to PM contributed to 7.8 million deaths in 2021, and of which 4.7 million from outdoor air pollution and the remainder from household air pollution. Overall, ambient particulate matter is one of the leading risk factor for premature death globally.
Domestic combustion and wood smoke
In the United Kingdom domestic combustion is the largest single source of PM and PM annually, with domestic wood burning in both closed stoves and open fires responsible for 38% of PM in 2019. To tackle the problem [|some new laws] were introduced since 2021. In some towns and cities in New South Wales wood smoke may be responsible for 60% of fine particle air pollution in the winter.There are a few ways to reduce wood smoke, e.g., buying the right wood heater and maintaining it well, choosing the right firewood and burning it the right way. There are also regulations in some countries where people can report smoke pollution to the local council.
Composition
The composition and toxicity of aerosols, including particles, depends on their source and atmospheric chemistry and varies widely.Wind-blown mineral dust tends to be made of mineral oxides and other material blown from the Earth's crust; this particulate is light-absorbing. Sea salt is considered the second-largest contributor in the global aerosol budget, and consists mainly of sodium chloride originated from sea spray; other constituents of atmospheric sea salt reflect the composition of sea water, and thus include magnesium, sulfate, calcium, potassium, and others. In addition, sea spray aerosols may contain organic compounds like fatty acids and sugars, which influence their chemistry.
Some secondary particles derive from the oxidation of primary gases such as sulfur and nitrogen oxides into sulfuric acid and nitric acid or from biogenic emissions. The precursors for these aerosols—i.e. the gases from which they originate—may have an anthropogenic origin as well as a natural biogenic origin. In the presence of ammonia, secondary aerosols often take the form of ammonium salts; i.e. ammonium sulfate and ammonium nitrate ; in the absence of ammonia, secondary compounds take an acidic form as sulfuric acid and nitric acid.
Secondary sulfate and nitrate aerosols are strong light-scatterers. This is mainly because the presence of sulfate and nitrate causes the aerosols to increase to a size that scatters light effectively.
Organic matter found in aerosols can be either primary or secondary, the latter part deriving from the oxidation of volatile organic compounds ; organic material in the atmosphere may either be biogenic or anthropogenic. Organic matter influences the atmospheric radiation field by both scattering and absorption. Some aerosols are predicted to include strongly light-absorbing material and are thought to yield large positive radiative forcing. Some secondary organic aerosols resulting from combustion products of internal combustion engines, have been identified as a danger to health. Particulate toxicity has been found to vary by region and source contribution which affects the particles chemical composition.
The chemical composition of the aerosol directly affects how it interacts with solar radiation. The chemical constituents within the aerosol change the overall refractive index. The refractive index will determine how much light is scattered and absorbed.
The composition of particulate matter that generally causes visual effects, haze, consists of sulfur dioxide, nitrogen oxides, carbon monoxide, mineral dust, and organic matter. The particles are hygroscopic due to the presence of sulfur, and SO is converted to sulfate when high humidity and low temperatures are present. This causes reduced visibility and red-orange-yellow colors.
Size distribution
Human-produced aerosols such as particle pollution tend to have a smaller radius than aerosol particles of natural origin. The false-color maps in the map of distribution of aerosol particles on the right show where there are natural aerosols, human pollution, or a mixture of both, monthly.Smaller aerosols in the North
The size distribution time series shows that in the planet's most southerly latitudes, nearly all the aerosols are large, but in the high northern latitudes, smaller aerosols are very abundant. Most of the Southern Hemisphere is covered by the ocean, where the largest source of aerosols is natural sea salt from dried sea spray. Because the land is concentrated in the Northern Hemisphere, the amount of small aerosols from fires and human activities is greater there than in the Southern Hemisphere. Overland, patches of large-radius aerosols appear over deserts and arid regions, most prominently, the Sahara Desert in North Africa and the Arabian Peninsula, where dust storms are common. Places where human-triggered or natural fire activity is common are dominated by smaller aerosols. Human-produced pollution is largely responsible for the areas of small aerosols over developed areas such as the eastern United States and Europe, especially in their summer.Satellite measurements of aerosols, called aerosol optical thickness, are based on the fact that the particles change the way the atmosphere reflects and absorbs visible and infrared light. As shown in this page, an optical thickness of less than 0.1 indicates a crystal clear sky with maximum visibility, whereas a value of 1 indicates very hazy conditions.
Deposition processes
In general, the smaller and lighter a particle is, the longer it will stay in the air. Larger particles tend to settle to the ground by gravity in a matter of hours. The smallest particles can stay in the atmosphere for weeks and are mostly removed by precipitation. There are evidence that aerosols can "travel across the ocean". For example, in September 2017 wildfires burning across the western United States and Canada, and the smoke was found to have arrived over the United Kingdom and northern France in three days, as shown by satellite images. Diesel particulate matter is highest near the source of emission. Any information regarding DPM and the atmosphere, flora, height, and distance from major sources is useful to determine health effects.Control
Technologies
Particulate matter emissions are highly regulated in most industrialized countries. Due to environmental concerns, most industries are required to operate some kind of dust collection system. These systems include inertial collectors, fabric filter collectors, electrostatic filters used in facemasks, wet scrubbers, and electrostatic precipitators.Cyclonic separators are useful for removing large, coarse particles and are often employed as a first step or "pre-cleaner" to other more efficient collectors. Well-designed cyclonic separators can be very efficient in removing even fine particulates, and may be operated continuously without requiring frequent shutdowns for maintenance.
Fabric filters or baghouses are the most commonly employed in general industry. They work by forcing dust-laden air through a bag-shaped fabric filter leaving the particulate to collect on the outer surface of the bag and allowing the now clean air to pass through to either be exhausted into the atmosphere or in some cases recirculated into the facility. Common fabrics include polyester and fiberglass and common fabric coatings include PTFE. The excess dust buildup is then cleaned from the bags and removed from the collector.
File:Construction dust emitted and rising up during the building rehabilitation of Treasure Garden, Tai Po, Hong Kong.webm|thumb|Substantial amount of construction dust emitted and rising up from a building under rehabilitation on a Saturday afternoon, Treasure Garden, Tai Po, Hong Kong. The rehabilitation scheme is subsidised by the government and contract like this can worth up to a hundred million. People are living inside the building throughout the whole period of the renovation work, which usually lasts for over a year, and it can be foretold that the residents' exposure to construction dust is even more serious than the occupational exposure of the workers. The possible presence of asbestos and lead paint dust is also worth worrying. This type of rehabilitation works are very common, especially in some older districts. With such a large amount of dust emitted, it was obvious that neither water was being sprayed nor dust extraction device was in use, which was a violation of the local law.
Wet scrubbers pass the dirty air through a scrubbing solution allowing the particulate to attach to the liquid molecules. Electrostatic precipitators electrically charge the dirty air as it passes through. The now charged air then passes through large electrostatic plates which attract the charged particle in the airstream collecting them and leaving the now clean air to be exhausted or recirculated.