| Particulate |
Website Links For Particulate |
Information AboutParticulate |
| CATEGORIES ABOUT PARTICULATE | |
| particulates | |
| pollutants | |
| visibility | |
| air pollution | |
|
Particulates, alternatively referred to as '''particulate matter (PM), Aerosol s''' or '''fine particles''', are tiny particles of solid or liquid suspended in a gas. They range in size from less than 10 Nanometre s to more than 100 Micrometre s in diameter. The notation PM10 is used to describe particles of 10 micrometres or less and PM2.5 represents particles less than 2.5 micrometres in aerodynamic diameter; other numeric values may also be used. This range of sizes represent scales from a gathering of a few Molecule s to the size where the particles no longer can be carried by the gas. Sources of particulate matter can be anthropogenic or natural. Some particulates occur naturally, originating from Volcano es, Dust Storm s, Forest and Grassland fires, living vegetation, and Sea Spray . Human activities, such as the burning of Fossil Fuel s also generate aerosols. Averaged over the globe, ''anthropogenic'' aerosols—those made by human activities—currently account for about 10 percent of the total amount of aerosols in our atmosphere. Sources ] There are both natural and human sources of atmospheric particulates. The biggest natural sources are Dust , volcanoes, and forest fires. Sea spray is also a large source of particles though most of these fall back to the ocean close to where they were emitted. The biggest human sources of particles are combustion sources, mainly the burning of fuels in Internal Combustion Engine s in Automobile s and Power Plant s, and wind blown dust from Construction sites and other land areas where the water or vegetation has been removed. Some of these particles are emitted directly to the atmosphere (''primary Emissions '') and some are emitted as gases and form particles in the atmosphere (''secondary emissions''). :"In Europe and the United States, particulate emissions from vehicles are expected to decline over the next decade. For example, by 2005, the European Union will introduce more stringent standards for particulate emissions from light duty vehicles of 0.025 grams per kilometer per mile . :The state of California is implementing an even more restrictive standard in 2004, allowing only 0.006 grams per kilometer grams per mile of particulate emissions. Even if the California standard were introduced worldwide, says Jacobson, diesel cars may still warm the climate more than gasoline cars over 13 to 54 years. New particle traps being introduced by some European automobile manufacturers in their diesel cars appear to reduce Black Carbon emissions to 0.003 grams per kilometer per mile , even below the California standard." [http://www.stanford.edu/dept/news/pr/02/jacobsonJGR1023.html] BlueTec is one technology developed to reduce particulate emissions from Diesel engines in order to meet strigent Californian standards. Composition The composition of aerosol particles depends on their source. Wind-blown Mineral Dust {Link without Title} tends to be made of mineral Oxide s and other material blown from the Earth's Crust ; this aerosol is Light-absorbing . Sea salt {Link without Title} 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 , etc. In addition, sea spray aerosols may contains organic compounds, which influence their chemistry. Sea salt does not Absorb . Secondary particles derive from the Oxidation of primary gases such as Sulfur and Nitrogen Oxide s into Sulfuric Acid (liquid) and Nitric Acid (gaseous). The precursors for these aerosols, i.e. the gases from which they originate, may have an anthropogenic origin (from fossil fuel Combustion ) and 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 Acid ic form as sulfuric acid (liquid aerosol droplets) and nitric acid (atmospheric gas). Secondary sulfate and nitrate aerosols are strong Light-scatterers . {Link without Title} This is mainly because the presence of sulphate and nitrate causes the aerosols to increase to a size that scatters light effectively. Organic Matter (OM) can be either primary or secondary, the latter part deriving from the oxidation of VOCs ; organic material in the atmosphere may either be biogenic or Anthropogenic . Organic matter influences the atmospheric Radiation field by both Scattering and Absorption . Another important aerosol type is constitude of Elemental Carbon (EC, also known as '' Black Carbon '', BC): this aerosol type includes strongly light-absorbing material and is thought to yield large positive Radiative Forcing . Organic matter and elemental carbon together constitute the Carbonaceous fraction of aerosols.ii {Link without Title} 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. Removal processes 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 the ground by gravity in a matter of hours whereas the smallest particles (less than 1 micrometer) can stay in the atmosphere for weeks and are mostly removed by Precipitation . RADIATIVE FORCING FROM AEROSOLS Aerosols, natural and es 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 modelling studies that are difficult to verify at the present time'' {Link without Title} . A graphic showing the contributions (at 2000, relative to pre-industrial) and uncertainties of various forcings is available here . Sulphate aerosol Sulphate aerosol has two main effects, direct and indirect. The direct effect, via s attempting to deal with the Attribution Of Recent Climate Change need to include sulfate forcing, which appears to account (at least partly) for the slight drop in global temperature in the middle of the 20th century. The indirect effect (via the aerosol acting as cloud condensation nuclei, CCN , and thereby modifying the cloud properties) is more uncertain but is believed to be a cooling. Black carbon Black Carbon (BC), or Carbon Black, or Elemental Carbon (EC), often called soot, is composed of pure carbon clusters, skeleton balls and Buckyballs , 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. BC from fossil fuels is estimated by the IPCC in the Fourth Assessment Report of the IPCC, TAR, to contribute a global mean radiative forcing of +0.2 W/m&2 (was +0.1 W/m&2 in the Second Assessment Report of the IPCC, SAR), with a range +0.1 to +0.4 W/m&2. All aerosols both Absorb and Scatter Solar and terrestrial Radiation . If a substance absorbs a significant amount of radiation, as well as scattering, we call it absorbing. This is quantified in the ''Single Scattering Albedo'' (SSA), the ratio of scattering alone to scattering plus absorption (''extinction'') of radiation by 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, 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. HEALTH EFFECTS , Germany ]] The effects of inhaling particulate matter has been widely studied in humans and animals and include Asthma , Lung Cancer , cardiovascular issues, and premature Death . The size of the particle is a main determinant of where in the respiratory tract the particle will come to rest when inhaled. Larger particles are generally filtered in the nose and throat and do not cause problems, but particulate matter smaller than about 10 micrometres, referred to as ''PM10'', can settle in the bronchi and Lung s and cause health problems. The 10 micrometer size does not represent a strict boundary between respirable and non-respirable particles, but has been agreed upon for monitoring of airborne particulate matter by most regulatory agencies. Similarly, particles smaller than 2.5 micrometres, ''PM2.5'', tend to penetrate into the gas-exchange regions of the lung, and very small particles (< 100 nanometers) may pass through the lungs to affect other organs. In particular, a study published in the ''Journal of the American Medical Association'' indicates that PM2.5 leads to high plaque deposits in arteries, causing vascular inflammation and atherosclerosis — a hardening of the arteries that reduces elasticity, which can lead to heart attacks and other cardiovascular problems |
|
|