Written by Science Knowledge on 1:19 AM

When you think about pollution, you probably imagine belching smokestacks and clouds of car exhaust. But most of the airborne particles that threaten your lungs are invisible. These silent drifters, called particulate matter, fill the air around you, whether you’re walking outdoors or sitting in the comfort of your home.

In the following sections, you’ll take a closer look at these microscopic particles. You’ll learn how they attack your lungs, and you’ll pick up a few practices to help control the risk. Finally, you’ll consider the very worst substance that humans regularly inhale—cigarette smoke.

The Size of the Problem
Unsurprisingly, particulate matter consists of tiny particles—vanishingly small bits of material formed through chemical reactions (say, burning fossil fuels) or shed from larger objects (like dust, pollen, and mold). Traditionally, environmental scientists distinguish between two broad categories of particulate matter, based on size:

• PM10 (pronounced “pee em 10”). These particles are smaller than 10 microns across, but larger than 2.5 microns. (For comparison, a human hair is about 60 microns thick and the finest beach sand is 90 microns.)

• PM2.5. These particles are the really tiny ones—they’re smaller than 2.5 microns thick.

Particles in these two categories act quite differently. PM2.5 particles are extremely light. They can travel hundreds of miles and stay aloft for weeks. PM10 particles can manage a few miles and a few hours, at best. But the most important distinction is the way these two particle types affect your lungs. When you breathe, you suck in lungfuls of air and particulate matter. Your respiratory system’s natural defenses trap many of these particles. They stick to the mucus-lined airways in your lungs. Once immobilized this way, tiny hairs called cilia slowly brush them back upstream and out of your lungs, so you can cough them out or swallow and destroy them with the digestive acids in your stomach.

But here’s the catch: The tiny PM2.5 particles travel deeper into your lungs. They’re less likely to get stuck in your passageways and more likely to travel all the way to the alveoli, where your blood absorbs oxygen. This poses a problem, because your alveoli aren’t able to sweep out foreign particles like the rest of your lungs can. Instead, the particulate matter can remain lodged in your alveoli indefinitely, eventually damaging lung function and contributing to diseases like emphysema and lung cancer. Furthermore, some substances can pass through the walls of alveoli and directly into your blood. This is another case of seriously bad news, because PM2.5 particles are more likely to include toxic substances like lead.

To take good care of your lungs, you should reduce your exposure to PM2.5 particles as much as possible. If you live in a large city, pay attention to the air-quality index, which soars when the air is thick with certain pollutants (including ozone, carbon dioxide, and particulate matter). When the index is high—often during hot, humid weather—the outside air is most likely to harm your lungs and aggravate medical conditions. On bad air days like these, just stay in. And whatever you do, avoid vigorous exercise when pollution is high. Many air experts believe a morning jog through the smog does more cardiovascular harm than good.

Source of Information : Oreilly - Your Body Missing Manual

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In its broadest sense, science (from the Latin scientia, meaning "knowledge") refers to any systematic knowledge or practice. In its more usual restricted sense, science refers to a system of acquiring knowledge based on scientific method, as well as to the organized body of knowledge gained through such research.

Fields of science are commonly classified along two major lines: natural sciences, which study natural phenomena (including biological life), and social sciences, which study human behavior and societies. These groupings are empirical sciences, which means the knowledge must be based on observable phenomena and capable of being experimented for its validity by other researchers working under the same conditions.

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