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110-473: The term particle is rather general in meaning, and is refined as needed by various scientific fields. Anything that is composed of particles may be referred to as being particulate. However, the noun particulate is most frequently used to refer to pollutants in the Earth's atmosphere , which are a suspension of unconnected particles, rather than a connected particle aggregation . The concept of particles

220-484: A car accident , or even objects as big as the stars of a galaxy . Another type, microscopic particles usually refers to particles of sizes ranging from atoms to molecules , such as carbon dioxide , nanoparticles , and colloidal particles . These particles are studied in chemistry , as well as atomic and molecular physics . The smallest particles are the subatomic particles , which refer to particles smaller than atoms. These would include particles such as

330-404: A charged lepton while a neutral lepton is called a neutrino . For example, the first generation consists of the electron e with a negative electric charge and the electrically neutral electron neutrino ν e . In the language of quantum field theory, the electromagnetic interaction of the charged leptons is expressed by the fact that the particles interact with

440-520: A diameter of 10 micrometers (μm) or less; fine particles, designated PM 2.5 , 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 (other than ultra-fines ) of air pollution as they can penetrate deep into the lungs and brain from blood streams, causing health problems such as heart disease , lung disease , cancer and preterm birth . There

550-783: A granular material . Particulates Particulates or atmospheric particulate matter (see below for other names) are microscopic particles of solid or liquid matter suspended in the air . The term aerosol refers to the particulate/air mixture , 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 . They have impacts on climate and precipitation that adversely affect human health , in ways additional to direct inhalation. Types of atmospheric particles include suspended particulate matter; thoracic and respirable particles; inhalable coarse particles, designated PM 10 , which are coarse particles with

660-587: A lepton is an elementary particle of half-integer spin ( spin ⁠ 1 / 2 ⁠ ) that does not undergo strong interactions . Two main classes of leptons exist: charged leptons (also known as the electron -like leptons or muons), including the electron , muon , and tauon , and neutral leptons, better known as neutrinos . Charged leptons can combine with other particles to form various composite particles such as atoms and positronium , while neutrinos rarely interact with anything, and are consequently rarely observed. The best known of all leptons

770-401: A muonic number of L μ = 1 , while tau particles and tau neutrinos have a tauonic number of L τ = 1 . The antileptons have their respective generation's leptonic numbers of −1. Conservation of the leptonic numbers means that the number of leptons of the same type remains the same, when particles interact. This implies that leptons and antileptons must be created in pairs of

880-471: A capital R subscript (e.g. a positron e R ). Right-handed neutrinos and left-handed anti-neutrinos have no possible interaction with other particles (see Sterile neutrino ) and so are not a functional part of the Standard Model, although their exclusion is not a strict requirement; they are sometimes listed in particle tables to emphasize that they would have no active role if included in

990-502: A climate feedback) by the IPCC due to the interdependence between it and the hydrological cycle. However, it has previously been classified as a negative radiative forcing. Sulfate aerosols are mostly inorganic sulfur compounds like (SO 4 ),HSO 4 and H 2 SO 4 , which are mainly produced when sulfur dioxide reacts with water vapor to form gaseous sulfuric acid and various salts (often through an oxidation reaction in

1100-522: A completely enclosed system or facility, and fit any vent or exhaust with an effective fabric filter or equivalent air pollution control system or equipment, enclose the scaffolding of the building with dust screens, use impervious sheeting to enclose both material hoist and debris chute, wet debris with water before it is dumped into a debris chute, have water sprayed on the facade surface before and during grinding work, use grinder equipped with vacuum cleaner for facade grinding work, spray water continuously on

1210-627: 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

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1320-410: 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

1430-523: A global mean radiative forcing of +0.2 W/m (was +0.1 W/m in the Second Assessment Report of the IPCC, SAR), with a range +0.1 to +0.4 W/m . A study published in 2013 however, states that "the best estimate for the industrial-era (1750 to 2005) direct radiative forcing of atmospheric black carbon is +0.71 W/m with 90% uncertainty bounds of (+0.08, +1.27) W/m " with "total direct forcing by all-black carbon sources, without subtracting

1540-562: A high sulfur content, primarily coal and certain less-refined fuels, like aviation and bunker fuel , had dominated. By 1990, global human-caused emissions of sulfur into the atmosphere became "at least as large" as all natural emissions of sulfur-containing compounds combined , and were at least 10 times more numerous than the natural aerosols in the most polluted regions of Europe and North America, where they accounted for 25% or more of all air pollution. This led to acid rain , and also contributed to heart and lung conditions and even

1650-562: A mixture of both, monthly. 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,

1760-426: A net negative radiative forcing. The magnitude of the resultant radiative forcing due to the direct effect of an aerosol is dependent on the albedo of the underlying surface, as this affects the net amount of radiation absorbed or scattered to space. For example, if a highly scattering aerosol is above a surface of low albedo it has a greater radiative forcing than if it was above a surface of high albedo. The converse

1870-408: A particle. The SSA tends to unity if scattering dominates, with relatively little absorption, and decreases as absorption increases, becoming zero for infinite absorption. For example, the sea-salt aerosol has an SSA of 1, as a sea-salt particle only scatters, whereas soot has an SSA of 0.23, showing that it is a major atmospheric aerosol absorber. The Indirect aerosol effect consists of any change to

1980-772: A regional scale. The failure of the Indian monsoon has been linked to the suppression of evaporation of water from the Indian Ocean due to the semi-direct effect of anthropogenic aerosol. Recent studies of the Sahel drought and major increases since 1967 in rainfall in Australia over the Northern Territory , Kimberley , Pilbara and around the Nullarbor Plain have led some scientists to conclude that

2090-469: A single generation. For example, the following processes are allowed under conservation of leptonic numbers: but none of these: However, neutrino oscillations are known to violate the conservation of the individual leptonic numbers. Such a violation is considered to be smoking gun evidence for physics beyond the Standard Model . A much stronger conservation law is the conservation of the total number of leptons ( L with no subscript ), conserved even in

2200-503: Is a first order effect and therefore classified as a radiative forcing by the IPCC . An increase in cloud droplet number due to the introduction of aerosol acts to reduce the cloud droplet size, as the same amount of water is divided into more droplets. This has the effect of suppressing precipitation, increasing the cloud lifetime, known as the cloud lifetime aerosol effect, second indirect effect or Albrecht effect. This has been observed as

2310-460: Is a technical property, defined through transformation behaviour under the Poincaré group , that does not change with reference frame. It is contrived to agree with helicity for massless particles, and is still well defined for particles with mass. In many quantum field theories , such as quantum electrodynamics and quantum chromodynamics , left- and right-handed fermions are identical. However,

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2420-428: Is also dependent upon air flow rates and the partial pressure of the gases in the inspired air. The fate of a specific contaminant is dependent upon the form in which it exists (aerosol or particulate). Inhalation also depends upon the breathing rate of the subject. Another complexity not entirely documented is how the shape of PM can affect health, except for the needle-like shape of asbestos fibres which can lodge in

2530-409: Is classified as the direct effect. It encompasses many individual mechanisms, and in general is more poorly defined and understood than the direct and indirect aerosol effects. For instance, if absorbing aerosols are present in a layer aloft in the atmosphere, they can heat surrounding air which inhibits the condensation of water vapour, resulting in less cloud formation. Additionally, heating a layer of

2640-483: Is composed of pure carbon clusters, skeleton balls and fullerenes , and is one of the most important absorbing aerosol species in the atmosphere. It should be distinguished from organic carbon (OC): clustered or aggregated organic molecules on their own or permeating an EC buckyball. Black carbon from fossil fuels is estimated by the IPCC in the Fourth Assessment Report of the IPCC, 4AR, to contribute

2750-462: Is consistent with three generations of leptons, some particle physicists are searching for a fourth generation. The current lower limit on the mass of such a fourth charged lepton is 100.8  GeV/ c , while its associated neutrino would have a mass of at least 45.0  GeV/ c . Leptons are spin   ⁠ 1 / 2 ⁠ particles. The spin-statistics theorem thus implies that they are fermions and thus that they are subject to

2860-474: Is especially useful when modelling nature , as the full treatment of many phenomena can be complex and also involve difficult computation. It can be used to make simplifying assumptions concerning the processes involved. Francis Sears and Mark Zemansky , in University Physics , give the example of calculating the landing location and speed of a baseball thrown in the air. They gradually strip

2970-672: 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. 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 ( cyclonic separators ), fabric filter collectors (baghouses) , electrostatic filters used in facemasks, wet scrubbers , and electrostatic precipitators . Cyclonic separators are useful for removing large, coarse particles and are often employed as

3080-727: Is mainly because the presence of sulfate and nitrate causes the aerosols to increase to a size that scatters light effectively. Organic matter (OM) found in aerosols can be either primary or secondary, the latter part deriving from the oxidation of volatile organic compounds (VOCs); 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 (SOAs) resulting from combustion products of internal combustion engines, have been identified as

3190-429: Is no mixing of the different generations of charged leptons as there is for quarks . The zero mass of neutrino is in close agreement with current direct experimental observations of the mass. However, it is known from indirect experiments—most prominently from observed neutrino oscillations —that neutrinos have to have a nonzero mass, probably less than 2  eV/ c . This implies the existence of physics beyond

3300-851: Is no safe level of particulates. Worldwide, exposure to PM 2.5 contributed to 4.1 million deaths from heart disease, stroke, lung cancer, chronic lung disease, and respiratory infections in 2016. Overall, ambient particulate matter is one of the leading risk factor for premature death globally. Human activities generate significant amounts of particulates. For example: Some types of dust, e.g., ashes , soot , paint , glass , plastic and dust from certain man-made fibres, which are brittle and break easily (can fragment and "proliferate"), can pose greater threats and irritations to humans. Those with sharp edges may be even more problematic. The number, shapes, stickiness, etc. of particulates may also be altered by different meteorological conditions. Human-made (anthropogenic) aerosols account for about 10 percent of

3410-402: Is not currently known whether this is the case. The first charged lepton, the electron, was theorized in the mid-19th century by several scientists and was discovered in 1897 by J. J. Thomson . The next lepton to be observed was the muon , discovered by Carl D. Anderson in 1936, which was classified as a meson at the time. After investigation, it was realized that the muon did not have

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3520-577: Is related to the decay rate by where B ( x → y ) {\displaystyle \;{\mathcal {B}}(x\rightarrow y)\;} denotes the branching ratios and Γ ( x → y ) {\displaystyle \;\Gamma (x\rightarrow y)\;} denotes the resonance width of the process x → y   , {\displaystyle \;x\rightarrow y~,} with x and y replaced by two different particles from " e " or " μ " or " τ ". The ratio of tau and muon lifetime

3630-514: Is some constant, and G F is the Fermi coupling constant . The decay rate of tau particles through the process τ → e + ν e + ν τ is given by an expression of the same form where K 3 is some other constant. Muon–tauon universality implies that K 2 ≈ K 3 . On the other hand, electron–muon universality implies The branching ratios for

3740-424: Is the electron . There are six types of leptons, known as flavours , grouped in three generations . The first-generation leptons, also called electronic leptons , comprise the electron ( e ) and the electron neutrino ( ν e ); the second are the muonic leptons , comprising the muon ( μ ) and the muon neutrino ( ν μ ); and

3850-460: Is thus given by Using values from the 2008 Review of Particle Physics for the branching ratios of the muon and tau yields a lifetime ratio of ~  1.29 × 10 , comparable to the measured lifetime ratio of ~  1.32 × 10 . The difference is due to K 2 and K 3 not actually being constants: They depend slightly on the mass of leptons involved. Recent tests of lepton universality in B meson decays, performed by

3960-445: Is true of absorbing aerosol, with the greatest radiative forcing arising from a highly absorbing aerosol over a surface of high albedo. The direct aerosol effect is a first-order effect and is therefore classified as a radiative forcing by the IPCC . The interaction of an aerosol with radiation is quantified by the single-scattering albedo (SSA), the ratio of scattering alone to scattering plus absorption ( extinction ) of radiation by

4070-499: The LHCb , BaBar , and Belle experiments, have shown consistent deviations from the Standard Model predictions. However the combined statistical and systematic significance is not yet high enough to claim an observation of new physics . In July 2021 results on lepton flavour universality have been published testing W decays, previous measurements by the LEP had given a slight imbalance but

4180-497: The Pauli exclusion principle : no two leptons of the same species can be in the same state at the same time. Furthermore, it means that a lepton can have only two possible spin states, namely up or down. A closely related property is chirality , which in turn is closely related to a more easily visualized property called helicity . The helicity of a particle is the direction of its spin relative to its momentum ; particles with spin in

4290-542: The Standard Model . Electrons are one of the components of atoms , alongside protons and neutrons . Exotic atoms with muons and taus instead of electrons can also be synthesized, as well as lepton–antilepton particles such as positronium . The name lepton comes from the Greek λεπτός leptós , "fine, small, thin" ( neuter nominative/accusative singular form: λεπτόν leptón ); the earliest attested form of

4400-509: The Stanford Linear Collider (SLC) and Large Electron–Positron Collider (LEP) experiments. The decay rate ( Γ {\displaystyle \Gamma } ) of muons through the process μ → e + ν e + ν μ is approximately given by an expression of the form (see muon decay for more details) where K 2

4510-485: The clouds ), which are then thought to experience hygroscopic growth and coagulation and then shrink through evaporation . Some of them are biogenic (typically produced via atmospheric chemical reactions with dimethyl sulfide from mostly marine plankton ) or geological via volcanoes or weather-driven from wildfires and other natural combustion events, but in the recent decades anthropogenic sulfate aerosols produced through combustion of fossil fuels with

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4620-539: The electron or a helium-4 nucleus . The lifetime of stable particles can be either infinite or large enough to hinder attempts to observe such decays. In the latter case, those particles are called " observationally stable ". In general, a particle decays from a high- energy state to a lower-energy state by emitting some form of radiation , such as the emission of photons . In computational physics , N -body simulations (also called N -particle simulations) are simulations of dynamical systems of particles under

4730-539: The muon neutrino, which earned them the 1988 Nobel Prize , although by then the different flavours of neutrino had already been theorized. The tau was first detected in a series of experiments between 1974 and 1977 by Martin Lewis Perl with his colleagues at the SLAC LBL group . Like the electron and the muon, it too was expected to have an associated neutrino. The first evidence for tau neutrinos came from

4840-624: The particle in a box model, including wave–particle duality , and whether particles can be considered distinct or identical is an important question in many situations. Particles can also be classified according to composition. Composite particles refer to particles that have composition – that is particles which are made of other particles. For example, a carbon-14 atom is made of six protons, eight neutrons, and six electrons. By contrast, elementary particles (also called fundamental particles ) refer to particles that are not made of other particles. According to our current understanding of

4950-504: The spinor representation ( T = ⁠ 1  / 2 ⁠ ) of the weak isospin SU(2) gauge symmetry. This means that these particles are eigenstates of the isospin projection T 3 with eigenvalues ⁠+ +  1  / 2 ⁠ and ⁠− +  1  / 2 ⁠ respectively. In the meantime, the right-handed charged lepton transforms as a weak isospin scalar ( T = 0 ) and thus does not participate in

5060-460: The weak interaction , while there is no evidence that a right-handed neutrino exists at all. The Higgs mechanism recombines the gauge fields of the weak isospin SU(2) and the weak hypercharge U(1) symmetries to three massive vector bosons ( W , W , Z ) mediating the weak interaction , and one massless vector boson, the photon (γ), responsible for

5170-452: The 1991 eruption of Mount Pinatubo which caused a global cooling of approximately 0.5 °C lasting several years. Research tracking the effect of light-scattering aerosols in the stratosphere during 2000 and 2010 and comparing its pattern to volcanic activity show a close correlation. Simulations of the effect of anthropogenic particles showed little influence at present levels. Aerosols are also thought to affect weather and climate on

5280-638: The Earth's radiative budget due to the modification of clouds by atmospheric aerosols and consists of several distinct effects. Cloud droplets form onto pre-existing aerosol particles, known as cloud condensation nuclei (CCN). Droplets condensing around human-produced aerosols such as found in particulate pollution tend to be smaller and more numerous than those forming around aerosol particles of natural origin (such as windblown dust ). For any given meteorological conditions, an increase in CCN leads to an increase in

5390-522: The Standard Model . The currently most favoured extension is the so-called seesaw mechanism , which would explain both why the left-handed neutrinos are so light compared to the corresponding charged leptons, and why we have not yet seen any right-handed neutrinos. The members of each generation's weak isospin doublet are assigned leptonic numbers that are conserved under the Standard Model. Electrons and electron neutrinos have an electronic number of L e = 1 , while muons and muon neutrinos have

5500-431: The Standard Model's weak interaction treats left-handed and right-handed fermions differently: only left-handed fermions (and right-handed anti-fermions) participate in the weak interaction. This is an example of parity violation explicitly written into the model. In the literature, left-handed fields are often denoted by a capital L subscript (e.g. the normal electron e L ) and right-handed fields are denoted by

5610-436: The Standard Model. The theoretical and measured values for the electron anomalous magnetic dipole moment are within agreement within eight significant figures. The results for the muon , however, are problematic , hinting at a small, persistent discrepancy between the Standard Model and experiment. In the Standard Model, the left-handed charged lepton and the left-handed neutrino are arranged in doublet that transforms in

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5720-490: The United States alone. Yet, around the same time, research had shown that sulfate aerosols were affecting both the visible light received by the Earth and its surface temperature , and as the so-called global dimming ) began to reverse in the 1990s in line with the reduced anthropogenic sulfate pollution, climate change accelerated. As of 2021, state-of-the-art CMIP6 models estimate that total cooling from

5830-470: The aerosol haze over South and East Asia has been steadily shifting tropical rainfall in both hemispheres southward. The size of particulate matter (PM) is a key determinant of its potential to cause health problems. Particles of different sizes deposit in different regions of the respiratory tract , leading to various health effects. The particles are grouped by sizes: Particles can cause health effects through several mechanisms: inflammation in

5940-711: 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 (land-clearing fires in the Amazon from August–October, for example, or lightning-triggered fires in

6050-479: The atmosphere relative to the surface results in a more stable atmosphere due to the inhibition of atmospheric convection . This inhibits the convective uplift of moisture, which in turn reduces cloud formation. The heating of the atmosphere aloft also leads to a cooling of the surface, resulting in less evaporation of surface water. The effects described here all lead to a reduction in cloud cover i.e. an increase in planetary albedo. The semi-direct effect classified as

6160-723: The baseball of most of its properties, by first idealizing it as a rigid smooth sphere , then by neglecting rotation , buoyancy and friction , ultimately reducing the problem to the ballistics of a classical point particle . The treatment of large numbers of particles is the realm of statistical physics . The term "particle" is usually applied differently to three classes of sizes. The term macroscopic particle , usually refers to particles much larger than atoms and molecules . These are usually abstracted as point-like particles , even though they have volumes, shapes, structures, and etc. Examples of macroscopic particles would include powder , dust , sand , pieces of debris during

6270-440: The burning of living and dead vegetation would be different from those emitted from the burning of joss paper or construction wastes . Particles emitted from fuel combustion are not the same as those emitted from waste combustion. The particulate matter generated from the fire of a recycling yard or a ship full of scrap metal may contain more toxic substances than other types of burning. Lepton In particle physics ,

6380-466: The case of neutrino oscillations, but even it is still violated by a tiny amount by the chiral anomaly . The coupling of leptons to all types of gauge boson are flavour-independent: The interaction between leptons and a gauge boson measures the same for each lepton. This property is called lepton universality and has been tested in measurements of the muon and tau lifetimes and of Z boson partial decay widths , particularly at

6490-451: The climate of the Earth by changing the amount of incoming solar radiation and outgoing terrestrial longwave radiation retained in the Earth's system. This occurs through several distinct mechanisms which are split into direct, indirect and semi-direct aerosol effects. The aerosol climate effects are the biggest source of uncertainty in future climate predictions. The Intergovernmental Panel on Climate Change (IPCC) stated in 2001: While

6600-472: The components of a colloid. A colloid is a substance microscopically dispersed evenly throughout another substance. Such colloidal system can be solid , liquid , or gaseous ; as well as continuous or dispersed. The dispersed-phase particles have a diameter of between approximately 5 and 200 nanometers . Soluble particles smaller than this will form a solution as opposed to a colloid. Colloidal systems (also called colloidal solutions or colloidal suspensions) are

6710-473: 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 (liquid) and nitric acid (gaseous) or from biogenic emissions. The precursors for these aerosols—i.e.

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6820-404: The constituents of atoms – protons , neutrons , and electrons – as well as other types of particles which can only be produced in particle accelerators or cosmic rays . These particles are studied in particle physics . Because of their extremely small size, the study of microscopic and subatomic particles falls in the realm of quantum mechanics . They will exhibit phenomena demonstrated in

6930-457: The cooling from sulfate pollution while minimizing the negative effects on health through deploying in the stratosphere , where only a fraction of the current sulfur pollution would be needed to avoid multiple degrees of warming, but the assessment of costs and benefits remains incomplete, even with hundreds of studies into the subject completed by the early 2020s. Black carbon (BC), or carbon black, or elemental carbon (EC), often called soot,

7040-560: The currently present aerosols is between 0.1 °C (0.18 °F) to 0.7 °C (1.3 °F); the IPCC Sixth Assessment Report uses the best estimate of 0.5 °C (0.90 °F), with the uncertainty mainly caused by contradictory research on the impacts of aerosols of clouds . Some are certain that they cool the planet, though, and this led to solar geoengineering proposals known as stratospheric aerosol injection , which seeks to replicate and enhance

7150-507: The dirty air through a scrubbing solution (usually a mixture of water and other compounds) 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. For general building construction, some places that have acknowledged

7260-466: The early 20th century. The earliest methods included relatively crude Ringelmann charts , which were grey-shaded cards against which emissions from smokestacks could be visually compared, and deposit gauges , which collected the soot deposited in a particular location so it could be weighed. Automated, modern methods of measuring particulates include optical photodetectors , tapered element oscillating microbalances , and Aethalometers . Besides measuring

7370-500: The electromagnetic interaction. The electric charge Q can be calculated from the isospin projection T 3 and weak hypercharge Y W through the Gell-Mann–Nishijima formula , To recover the observed electric charges for all particles, the left-handed weak isospin doublet (ν eL , e L ) must thus have Y W = −1 , while the right-handed isospin scalar e R must have Y W = −2 . The interaction of

7480-461: The electronic mode (17.82%) and muonic (17.39%) mode of tau decay are not equal due to the mass difference of the final state leptons. Universality also accounts for the ratio of muon and tau lifetimes. The lifetime T ℓ {\displaystyle \mathrm {T} _{\ell }} of a lepton ℓ {\displaystyle \ell } (with ℓ {\displaystyle \ell } = " μ " or " τ ")

7590-519: The expected properties of a meson, but rather behaved like an electron, only with higher mass. It took until 1947 for the concept of "leptons" as a family of particles to be proposed. The first neutrino, the electron neutrino, was proposed by Wolfgang Pauli in 1930 to explain certain characteristics of beta decay . It was first observed in the Cowan–Reines neutrino experiment conducted by Clyde Cowan and Frederick Reines in 1956. The muon neutrino

7700-407: The forests of northern Canada in Northern Hemisphere summer) are dominated by smaller aerosols. Human-produced (fossil fuel) 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

7810-562: The gases from which they originate—may have an anthropogenic origin (from biomass and fossil fuel combustion ) 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 (both can be dry or in aqueous solution ); in the absence of ammonia, secondary compounds take an acidic form as sulfuric acid (liquid aerosol droplets) and nitric acid (atmospheric gas). Secondary sulfate and nitrate aerosols are strong light-scatterers . This

7920-607: The ground by gravity in a matter of hours. The smallest particles (less than 1 micrometer) 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

8030-481: The influence of certain conditions, such as being subject to gravity . These simulations are common in cosmology and computational fluid dynamics . N refers to the number of particles considered. As simulations with higher N are more computationally intensive, systems with large numbers of actual particles will often be approximated to a smaller number of particles, and simulation algorithms need to be optimized through various methods . Colloidal particles are

8140-477: The lepton. First-order quantum mechanical approximation predicts that the g  factor is 2 for all leptons. However, higher-order quantum effects caused by loops in Feynman diagrams introduce corrections to this value. These corrections, referred to as the anomalous magnetic dipole moment , are very sensitive to the details of a quantum field theory model, and thus provide the opportunity for precision tests of

8250-456: The leptons with the massive weak interaction vector bosons is shown in the figure on the right. In the Standard Model , each lepton starts out with no intrinsic mass. The charged leptons (i.e. the electron, muon, and tau) obtain an effective mass through interaction with the Higgs field , but the neutrinos remain massless. For technical reasons, the masslessness of the neutrinos implies that there

8360-515: The local council. 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

8470-408: The lungs. Geometrically angular shapes have more surface area than rounder shapes, which in turn affects the binding capacity of the particle to other, possibly more dangerous substances. The table below lists the colours and shapes of some common atmospheric particulates: Composition of particles can vary greatly depending on their sources and how they are produced. For example, dust emitted from

8580-410: The model. Even though electrically charged right-handed particles (electron, muon, or tau) do not engage in the weak interaction specifically, they can still interact electrically, and hence still participate in the combined electroweak force , although with different strengths ( Y W ). One of the most prominent properties of leptons is their electric charge , Q . The electric charge determines

8690-410: The most common charged lepton in the universe , whereas muons and taus can only be produced in high-energy collisions (such as those involving cosmic rays and those carried out in particle accelerators ). Leptons have various intrinsic properties , including electric charge , spin , and mass . Unlike quarks , however, leptons are not subject to the strong interaction , but they are subject to

8800-399: The muon, initially classified as a meson, was reclassified as a lepton in the 1950s. The masses of those particles are small compared to nucleons—the mass of an electron ( 0.511  MeV/ c ) and the mass of a muon (with a value of 105.7 MeV/ c ) are fractions of the mass of the "heavy" proton ( 938.3 MeV/ c ), and the mass of a neutrino is nearly zero. However, the mass of

8910-611: The new measurement by the ATLAS collaboration have twice the precision and give a ratio of R W τ / μ = B ( W → τ ν τ ) / B ( W → μ ν μ ) = 0.992 ± 0.013 {\displaystyle R_{W}^{\tau /\mu }={\mathcal {B}}(W\rightarrow \tau \nu _{\tau })/{\mathcal {B}}(W\rightarrow \mu \nu _{\mu })=0.992\pm 0.013} , which agrees with

9020-408: The number of cloud droplets. This leads to more scattering of shortwave radiation i.e. an increase in the albedo of the cloud, known as the cloud albedo effect, First indirect effect or Twomey effect . Evidence supporting the cloud albedo effect has been observed from the effects of ship exhaust plumes and biomass burning on cloud albedo compared to ambient clouds. The Cloud albedo aerosol effect

9130-510: The observation of "missing" energy and momentum in tau decay, analogous to the "missing" energy and momentum in beta decay leading to the discovery of the electron neutrino. The first detection of tau neutrino interactions was announced in 2000 by the DONUT collaboration at Fermilab , making it the second-to-latest particle of the Standard Model to have been directly observed, with Higgs boson being discovered in 2012. Although all present data

9240-497: The other three fundamental interactions : gravitation , the weak interaction , and to electromagnetism , of which the latter is proportional to charge, and is thus zero for the electrically neutral neutrinos. For every lepton flavor, there is a corresponding type of antiparticle , known as an antilepton, that differs from the lepton only in that some of its properties have equal magnitude but opposite sign . According to certain theories, neutrinos may be their own antiparticle . It

9350-422: 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 (commonly known as Teflon). The excess dust buildup is then cleaned from the bags and removed from the collector. Wet scrubbers pass

9460-430: The pollution control facilities and retain the videos for one month for future inspections. Besides removing particulates from the source of pollution, they may also be cleaned in the open air (e.g. smog tower , moss wall , and water truck), while other control measures employ the use of barriers. Particulates have been measured in increasingly sophisticated ways since air pollution was first systematically studied in

9570-511: The possible health risks of construction dust for decades legally require the relevant contractor to adopt effective dust control measures, although inspections, fines and imprisonments are rare in recent years (for example, two prosecutions with a total fines of HKD$ 6000 in Hong Kong in the year 2021). Some of the mandatory dust control measures include load, unload, handle, transfer, store or dispose of cement or dry pulverized fuel ash in

9680-466: The preindustrial background, is estimated as +0.88 (+0.17, +1.48) W/m ". Volcanoes are a large natural source of aerosol and have been linked to changes in the Earth's climate often with consequences for the human population. Eruptions linked to changes in climate include the 1600 eruption of Huaynaputina which was linked to the Russian famine of 1601–1603 , leading to the deaths of two million, and

9790-465: The presence of sulfur, and SO 2 is converted to sulfate when high humidity and low temperatures are present. This causes reduced visibility and red-orange-yellow colors. Human-produced aerosols such as particle pollution tend to have a smaller radius than aerosol particles of natural origin (such as windblown dust). The false-color maps in the map of distribution of aerosol particles on the right show where there are natural aerosols, human pollution, or

9900-504: 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

10010-399: The quantum of the electromagnetic field, the photon . The Feynman diagram of the electron–photon interaction is shown on the right. Because leptons possess an intrinsic rotation in the form of their spin, charged leptons generate a magnetic field. The size of their magnetic dipole moment μ is given by where m is the mass of the lepton and g is the so-called " g  factor" for

10120-494: The radiative forcing due to greenhouse gases may be determined to a reasonably high degree of accuracy... the uncertainties relating to aerosol radiative forcings remain large, and rely to a large extent on the estimates from global modeling studies that are difficult to verify at the present time. The direct aerosol effect consists of any direct interaction of radiation with atmospheric aerosols, such as absorption or scattering. It affects both short and longwave radiation to produce

10230-856: The respiratory tract oxidative stress via reactive oxygen species, leading to cellular damage, and systemic effects, such as translocation of ultrafine particles into circulation affects organs beyond the lungs. Exposure to particulate matter is linked to various diseases across body systems, such as respiratory system (asthma, chronic obstructive pulmonary disease (COPD), lung cancer, and rhinosinusitis), cardiovascular system (heart attacks, hypertension, arrhythmias, and atherosclerosis), nervous system (cognitive decline and neurodegenerative diseases), metabolic system (diabetes and metabolic syndrome due to inflammatory pathways). The World Health Organization (WHO) provides guidelines to limit exposure: The site and extent of absorption of inhaled gases and vapors are determined by their solubility in water. Absorption

10340-517: The risk of preterm birth and low birth weight . Sulfate pollution also has a complex relationship with NOx pollution and ozone, reducing the also harmful ground-level ozone , yet capable of damaging the stratospheric ozone layer as well. Once the problem became clear, the efforts to remove this pollution through flue-gas desulfurization measures and other pollution controls were largely successful, reducing their prevalence by 53% and causing healthcare savings valued at $ 50 billion annually in

10450-401: The same direction as their momentum are called right-handed and they are otherwise called left-handed . When a particle is massless, the direction of its momentum relative to its spin is the same in every reference frame, whereas for massive particles it is possible to 'overtake' the particle by choosing a faster-moving reference frame ; in the faster frame, the helicity is reversed. Chirality

10560-577: The standard-model prediction of unity. In 2024 a preprint by the ATLAS collaboration has published a new value of R W μ / e = B ( W → μ ν μ ) / B ( W → e ν e ) = 0.9995 ± 0.0045 {\displaystyle R_{W}^{\mu /e}={\mathcal {B}}(W\rightarrow \mu \nu _{\mu })/{\mathcal {B}}(W\rightarrow e\nu _{e})=0.9995\pm 0.0045}

10670-421: The strength of their electromagnetic interactions . It determines the strength of the electric field generated by the particle (see Coulomb's law ) and how strongly the particle reacts to an external electric or magnetic field (see Lorentz force ). Each generation contains one lepton with Q = −1 e and one lepton with zero electric charge. The lepton with electric charge is commonly simply referred to as

10780-438: The subject of interface and colloid science . Suspended solids may be held in a liquid, while solid or liquid particles suspended in a gas together form an aerosol . Particles may also be suspended in the form of atmospheric particulate matter , which may constitute air pollution . Larger particles can similarly form marine debris or space debris . A conglomeration of discrete solid, macroscopic particles may be described as

10890-546: The suppression of drizzle in ship exhaust plume compared to ambient clouds, and inhibited precipitation in biomass burning plumes. This cloud lifetime effect is classified as a climate feedback (rather than a radiative forcing) by the IPCC due to the interdependence between it and the hydrological cycle. However, it has previously been classified as a negative radiative forcing. The Semi-direct effect concerns any radiative effect caused by absorbing atmospheric aerosol such as soot, apart from direct scattering and absorption, which

11000-524: The surface for any pneumatic or power-driven drilling, cutting, polishing or other mechanical breaking operation that causes dust emission, unless there is the operation of an effective dust extraction and filtering device, provide hoarding of not less than 2.4 m in height along the whole length of the site boundary, have hard paving on open area and wash every vehicle that leaves the construction sites. Use of automatic sprinkler equipment, automatic carwash equipment and installation of video surveillance system for

11110-501: The tau (discovered in the mid-1970s) ( 1777 MeV/ c ) is nearly twice that of the proton and 3477 ‍ times that of the electron. The first lepton identified was the electron, discovered by J.J. Thomson and his team of British physicists in 1897. Then in 1930, Wolfgang Pauli postulated the electron neutrino to preserve conservation of energy , conservation of momentum , and conservation of angular momentum in beta decay . Pauli theorized that an undetected particle

11220-409: The third are the tauonic leptons , comprising the tau ( τ ) and the tau neutrino ( ν τ ). Electrons have the least mass of all the charged leptons. The heavier muons and taus will rapidly change into electrons and neutrinos through a process of particle decay : the transformation from a higher mass state to a lower mass state. Thus electrons are stable and

11330-591: The total mass of aerosols in the atmosphere as estimated in 2010. The remaining 90 percent comes from natural sources such as volcanoes , dust storms , forest and grassland fires, living vegetation and sea spray , emitting particulates such as volcanic ash, desert dust, soot and sea salt. In the United Kingdom domestic combustion is the largest single source of PM 2.5 and PM 10 annually, with domestic wood burning in both closed stoves and open fires responsible for 38% of PM 2.5 in 2019. To tackle

11440-422: The total mass of particles per unit volume of air (particle mass concentration), sometimes it is more useful to measure the total number of particles per unit volume of air ( particle number concentration ). This can be done by using a condensation particle counter (CPC). To measure the atomic composition of particulate samples, techniques such as X-ray spectrometry can be used. Atmospheric aerosols affect

11550-441: The way the atmosphere reflects and absorbs visible and infrared light. As shown in this page , an optical thickness of less than 0.1 (palest yellow) indicates a crystal clear sky with maximum visibility, whereas a value of 1 (reddish-brown) indicates very hazy conditions. In general, the smaller and lighter a particle is, the longer it will stay in the air. Larger particles (greater than 10 micrometers in diameter) tend to settle to

11660-564: The word is the Mycenaean Greek 𐀩𐀡𐀵 , re-po-to , written in Linear B syllabic script. Lepton was first used by physicist Léon Rosenfeld in 1948: Following a suggestion of Prof. C. Møller , I adopt—as a pendant to "nucleon"—the denomination "lepton" (from λεπτός, small, thin, delicate) to denote a particle of small mass. Rosenfeld chose the name as the common name for electrons and (then hypothesized) neutrinos. Additionally,

11770-530: The world , only a very small number of these exist, such as leptons , quarks , and gluons . However it is possible that some of these might be composite particles after all , and merely appear to be elementary for the moment. While composite particles can very often be considered point-like , elementary particles are truly punctual . Both elementary (such as muons ) and composite particles (such as uranium nuclei ), are known to undergo particle decay . Those that do not are called stable particles, such as

11880-417: Was carrying away the difference between the energy , momentum , and angular momentum of the initial and observed final particles. The electron neutrino was simply called the neutrino, as it was not yet known that neutrinos came in different flavours (or different "generations"). Nearly 40 years after the discovery of the electron, the muon was discovered by Carl D. Anderson in 1936. Due to its mass, it

11990-576: Was discovered in 1962 by Leon M. Lederman , Melvin Schwartz , and Jack Steinberger , and the tau discovered between 1974 and 1977 by Martin Lewis Perl and his colleagues from the Stanford Linear Accelerator Center and Lawrence Berkeley National Laboratory . The tau neutrino remained elusive until July 2000, when the DONUT collaboration from Fermilab announced its discovery. Leptons are an important part of

12100-496: Was initially categorized as a meson rather than a lepton. It later became clear that the muon was much more similar to the electron than to mesons, as muons do not undergo the strong interaction , and thus the muon was reclassified: electrons, muons, and the (electron) neutrino were grouped into a new group of particles—the leptons. In 1962, Leon M. Lederman , Melvin Schwartz , and Jack Steinberger showed that more than one type of neutrino exists by first detecting interactions of

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