page_title: Air pollution
section_title: Air quality
hierarchical_section_title: Air pollution / Air quality
caption_attribution_description: English: On May 18, 1980, at 8:32 a.m. Pacific Daylight Time, a magnitude 5.1 earthquake shook Mount St. Helens. The bulge and surrounding area slid away in a gigantic rockslide and debris avalanche, releasing pressure, and triggering a major pumice and ash eruption of the volcano. Thirteen-hundred feet (400 meters) of the peak collapsed or blew outwards. As a result, 24 square miles (62 square kilometers) of valley was filled by a debris avalanche, 250 square miles (650 square kilometers) of recreation, timber, and private lands were damaged by a lateral blast, and an estimated 200 million cubic yards (150 million cubic meters) of material was deposited directly by lahars (volcanic mudflows) into the river channels. Sixty-one people were killed or are still missing. USGS Photograph taken on May 18, 1980, by Austin Post. Català: El 18 de maig, a les 8:32 a. m. Temps del Pacífic, un terratrèmol de una magnitud de 5,1 va fer trontollar la muntanya St. Helens. La protuberància l'àrea circumdant relliscà en una gegantina esllavissada de roques i un allau de rocam, alliberant la pressió, desencadenà una erupció de pedra tosca i cendra del volcà. 400 metres del puig van col·lapsar o van sortir volant. Com a resultat 62 quilometres quadrats de la vall van ser emplenats per la runa, 650 quilometres quadrats de llocs d'esbarjo, bosc, i finques privades van ser damnificades per una ràfega lateral, i una quantitat estimada en 150 milions de metres cúbics de material van ser dipositats per corrents de fang volcànic en els canals del riu. Cinquanta set persones van morir o han desaparegut (18 de Maig de 1980, Austin Post, USGS) Español: Erupción del Monte Santa Helena Français&#160;: Le 18 mai 1980, à 8h32 minutes (heure du Pacifique), un tremblement de terre de 5,1 sur l'échelle de Richter secoue le Mont Saint Helens, marquant le début de l'éruption du mont Saint Helens en 1980.
context_page_description: Air pollution is a type of environmental pollution that affects the air and is usually caused by smoke or other harmful gases, mainly oxides of carbon, sulphur and nitrogen.
  In other words, air pollution is the contamination of air due to the presence or introduction of a substance which has a poisonous effect.
  Many of the world's large cities today have polluted air or low air quality.
  Even 2,000 years ago, the Romans were complaining about the polluted air in their cities. At that time, the air was thick with smoke from fires and the smell of sewers. Air pollution has been classified as a danger to human health and Earth's many ecosystems for a long time.
context_section_description: Pollution can be gas or liquid or solid. It can also be classified chemically, such as:- oxide, hydrocarbon, acid or other kinds. Pollution can also be classified by what makes it.
  Many pollutants go into the air from natural sources. These pollutants include dust, sea salt, volcanic ashes and gases, smoke from forest fires, pollen, and many other materials. In fact, there are many more natural pollutants than pollutants that humans make. However, humans and other living things have adapted to most of these natural pollutants.
  Air pollution is usually described as either primary pollutants or secondary pollutants.Primary pollutants are pollutants that are put directly into the air by humans or natural sources. Examples of primary pollutants are exhaust fumes (gas) from cars, soot from smoke, dust storms and ash from volcanic eruptions (as seen in the picture on the left).
  Secondary pollutants are pollutants that are made from chemical reactions when pollutants mix with other primary pollutants or natural substances like water vapor. Many secondary pollutants are made when a primary pollutant reacts with sunlight. Ozone and smog are secondary pollutants. Ozone is a gas that stops harmful ultraviolet rays from the sun.  When it is near the ground, though, it can poison people and other organisms.
  Human-made air pollution comes from many things. Most air pollution made by humans today is because of transportation. Automobiles , for instance, make about 60% of the human-made air pollution. The gases inside car exhaust, like nitrogen oxide, make smog and acid rain.
  Farmlands and forests sometimes burn in wildfires producing soot (a black powder composed mainly of carbon, produced when coal, grasses, wood etc. is burned) from smoke. Soot can affect people and other life. People start many of those fires.
caption: Ash from volcanic eruptions is an example of primary pollutants
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