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Keywords: plants; plant extracts; anti-pollution ingredients; antioxidant
Nowadays air pollution is a global environmental and health problem of growing concern. While some kinds of air pollution are produced naturally (forest fires, volcanic eruptions, dust storms), anthropogenic activities are the main cause of the emission of chemical pollutants into the atmosphere . Most of air chemical pollutants of human origin are produced by the combustion of fossil fuel to produce heat and energy, major industrial processes, exhaust from transportation vehicles (aircraft, cars) and agricultural sources (livestock farms, application of fertilizers, herbicides and pesticides in crop production). Air pollution is composed of a heterogeneous mixture of compounds, categorized into two broad groups: primary and secondary pollutants . Primary pollutants are emitted directly from pollution sources, and include gases (CO2, CO, SO2, NO, NO2), low molecular weight hydrocarbons, persistent organic pollutants (e.g., dioxins), heavy metals (e.g., lead, mercury) and particulate matter (PM). Secondary pollutants are formed in the atmosphere through chemical and photochemical reactions involving primary pollutants; they include ozone (O3), NO2, peroxy acetyl nitrate, hydrogen peroxide and aldehydes . Gaseous pollutants are mainly produced by fuel combustion (CO from incomplete combustion and SO2 from combustion of sulfur-rich fuels), while dioxines are produced when materials containing chlorine are burned. Airborne particulate matter (PM) is a major concern especially in the air of densely populated urban areas; it consists of mixtures of particles of different size and composition. Depending on their aerodynamic diameter, they are commonly referred to as PM10(<10 μm), PM2.5–10 (coarse particles, 2.5–10 μm), PM2.5 (fine particles, <2.5 μm) and ultrafine particles (UFP, <100 nm) . The composition of PM varies, because they can absorb and carry on their surface a great variety of pollutants, such as gases, heavy metals, organic compounds, polyaromatic hydrocarbons, directly related to their toxicity. In countries such as Northern India and China, particularly high levels of PM2.5 are detectable (annual average over 50 μg/m3), subject to seasonal fluctuations and higher than the World Health Organization (WHO) recommendations
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