Modernization and progress have led to various activities which release substance in the air and water and cause immense problems for humans, plants, and animals. Also human-created noise, human-created excessive and obtrusive lights disrupt the ecosystem, cause adverse health effects and affect the quality of lives on earth. These activities which pollute the air we breathe in, spoil the planet’s water and disrupt the environment with obtrusive light and deafening noise are commonly called pollution – of air, water, sound and light.
 Pollution at Home
Air pollution can exist inside your homes too. As most people spend maximum time indoor it is said that they get affected more by indoor than outdoor pollution. Sources of indoor pollution are tobacco smoke, cooking and heating appliances, and vapors from building materials, paints, furniture, etc. cause pollution inside buildings.
According to some studies indoor pollutants such as allergies can be 2.5 times higher than outdoor pollutants. Simple tasks like cooking, heating the home or bathing can cause pollutants such as dust, mold and spores, pollen, pet dander, smoke and fumes. Exposure to high levels of indoor pollution causes headaches, tiredness, dizziness, nausea, itchy nose, and scratchy throat. Higher levels of exposure can cause asthma and breathing disorder
Here are some simple steps to reduce indoor pollution:
• Install furnace filters and air conditioner filters in your heating or cooling system. For details on filters and installation instructions see here 
• To maintain the humidity level you prefer install humidifiers in your heating or cooling system. Find room and house humidifier details here 
• If certain areas of your house have high humidity, use dehumidifiers to maintain humidity levels between 30 and 50 percent.
• You can considerably reduce indoor pollution with home ventilation. Find out benefits of home ventilation here 
• Change the chemical you use at home to natural products that contain fewer toxic chemicals.
• Try to keep doors and windows open as much as possible. With closed doors and windows indoor toxins get sealed inside.
• Adding plants to your home can help remove the indoor toxins from home
Also see What Are Household Allergies? 
 Air Pollution
The main types of air pollutions include smog, acid rain, the greenhouse effect, and "holes" in the ozone layer. Each of these seriously affects human as well as environmental well being. The industrial revolution and the development of the internal combustion engine brought with them black carbon pollution which are tiny particles released in the air from burning fuel or energy. It is also believed that burning of wood and charcoal in fireplaces and barbeques can release significant quantities of soot into the air.
Fossil fuel burning (petroleum products, coal, and natural gas) has become so commonplace that the sum total of all combustion-related emissions now constitutes a serious and widespread problem, not only to human health, but also to the entire global environment.
Another type of pollution is the release of noxious gases, such as sulfur dioxide, carbon monoxide, nitrogen oxides, and chemical vapors which can take part in further chemical reactions once they are in the atmosphere, forming smog and acid rain.
Pollution can take different dimensions in different cities depending on their geographical location, wind and weather factors, temperature etc. When the air close to the earth is cooler than the air above it, a temperature inversion occurs wherein the pollution cannot rise and get dispersed. Winter inversions are likely to cause particulate and carbon monoxide pollution. Summer inversions are more likely to create smog.
Acid rain is formed when a pollutant, such as sulfuric acid combines with droplets of water in the air becomes acidified.
 How Air Pollution Affects Our Health
Different people are affected differently by air pollution. Some individuals are much more sensitive to pollutants than others. Children and elderly people and those with health problems such as asthma, heart and lung disease suffer more from pollution. The extent of harm, however, varies from people to people who are affected according to their exposure to the damaging chemicals, i.e., the duration of exposure and the concentration of the chemicals.
Short-term exposure may cause irritation to the eyes, nose and throat, and upper respiratory infections such as bronchitis and pneumonia. There are other symptoms like headaches, nausea, and allergic reactions. Long-term health effects can include heart disease, lung cancer, chronic respiratory disease, and even damage to the kidneys, livers, nerves and brain. Continual exposure to air pollution affects the lungs of growing children and may aggravate or complicate medical conditions in the elderly.
Air Quality Guide for Ozone  will help you determine ways to protect your family's health when ozone levels reach the unhealthy range. Here you can also find ways you can help reduce ozone air pollution.
 What We Can Do To Help Prevent Air Pollution
• Opt for a carpool.
• Walk or ride a bicycle.
• Combine your errands into one trip.
• Your car should always be tuned
• At the gas pumps don’t top off
• Replace the air filter of your car.
• Select water-based products or those with low volatile organic compounds (VOCs).
• Use a brush, not a sprayer for painting
• Use air-tight containers to store solvents
• Use fluorescent lighting incandescent lights
• Avoid air conditioning and use fans as much as possible
• Use microwave oven to heat small meals
• Insulate your water heater.
 Water Pollution
Water pollution is caused when toxic substances enter lakes, streams, rivers, oceans, and other water bodies and either lie suspended in water or get dissolved on the bed. With water pollution the quality of water gets deteriorated and the aquatic ecosystem is affected.
How Water Gets Polluted
The biggest cause of water pollution is human activities. There are direct and indirect sources of water contamination. Direct sources include city sewages and industrial waste dumped into the river from factories, refineries, waste treatment plants etc. Indirect sources include contaminants that enter the water supply from soils/groundwater systems and from the atmosphere via rain water. Soils and ground waters contain the residue of fertilizers, pesticides, etc.
Water pollution also occurs when rain water runoff from urban and industrial areas and from agricultural land and mining operations makes its way back to receiving waters like river, lake or ocean and into the ground.
Wastes from households
Wastes from households include a variety of dissolved and suspended impurities such as food, vegetable waste and plant nutrient. These are generally from chemical soaps, washing powders, etc. Many homes dump their garbage containing cans, bottles, plastics, and other household products into streams, lakes, rivers, and seas. Various substances containing harmful chemicals that we use at home and dump in the waters, also add to the pollution.
How Water Pollution Affects Us
Water pollution creates poisonous drinking water, poisonous food animals, unbalanced river and lake ecosystems that can no longer support full biological diversity, deforestation from acid rain, and many other effects. These effects are, of course, specific to the various contaminants.
 What We Can Do To Help Prevent Water Pollution
• Remember to turn off taps after use. This will cut down on the amount of contaminated water that needs treatment and help prevent water shortages.
• Avoid throwing paints, oils or other forms of litter down the drain.
• Use environment-friendly products, such as washing powder, household cleaning agents and toiletries in the household.
• Avoid overuse of pesticides and fertilizers.
• Add more plants in your garden. This will prevent fertilizer, pesticides and contaminated water from running off into nearby water sources.
• Don’t throw litter into rivers, lakes or oceans. Help clean up any litter you see on beaches or in rivers and lakes. Visit Water Pollution Guide  for ready reference
 Light Pollution
Until recently light pollution was of little consequence to us. But now it has increased to such an extent that it interferes with our view of star-filled night sky. It also disturbs the feeding, mating, and migratory habits of many forms of nocturnal wildlife. View the On-line Star Sky Map  and browse through to find objects in the sky.
Excessive obtrusive light created by humans causes light pollution which disrupts ecosystems, obscures stars to city dwellers, interferes with astronomical observatories and produces adverse health effects.
There are two types of light pollution:
(a) annoying light that intrudes on an otherwise natural or low light setting
(b) excessive light, generally indoors, that leads to worker discomfort and adverse health effects.
 Light Pollution Sources
Light pollution is an offshoot of industrialization. Lighting, advertising, commercial properties, offices, factories, streetlights, and illuminated sporting venues are some of the sources of light pollution. This form of pollution is most severe in highly industrialized, densely populated areas of North America, Europe, and Japan, but even relatively small amounts of light are enough to cause discomfort and problems.
Light pollution is probably best described as artificial light that is allowed to illuminate, or pollute, areas not intended to be lit.
This is when over-bright or poorly directed lights enter a neighborhood and affect the neighbors’ right to enjoy their own property. An ill-directed security light directed into a bedroom window and a bright advertising signage. These are some of the examples of intrusive light.
Skyglow is the orange glow seen over towns and roads from upward light. This poses a serious problem for astronomers as the artificial brightness of the sky overpowers distant stars, especially those low in the night sky.
Inconsiderate or incorrectly set lighting can produce a glare which obstructs a person’s vision with its over-brightness. Such lighting can also impact on the ecology and wildlife of an area, and affect the behavioral patterns of mammals, birds, insects and fish.
 What We Can Do to Help Prevent Light Pollution
• Before installing lights the following questions should be asked
• Is this lighting at all necessary?
• If the lighting is for security, can some other possible method, such as segregating or screening of an area, be adopted?
• Are the lights required on all night? For example, over advertising hoardings; the exterior of buildings or empty car parks.
• If lighting is the best option then only the right amount of light for the task should be installed. Lighting will then only become a problem if it is poorly designed or incorrectly installed.
• Adjust the lights correctly so that they only illuminate the intended surface and do overflow onto neighboring property.
• Security lights should be correctly adjusted so that they only pick up the movement of persons in the area intended and not beyond
• Do not install equipment which spreads light above horizontal levels.
 Noise Pollution
Noise pollution is created when unpleasant human or machine sound disturbs the environment. Primarily this comes from motor vehicle transport but also includes aircraft and rail noise. Poor urban planning by way of juxtaposition of industrial to residential land uses may also cause noise pollution.
Other major sources of noise pollution are office equipment, factory machinery, appliances, power tools, lighting hum and audio entertainment systems. Even digital audio player devices, played on full volume can cause harmful effects. Construction equipment also creates noise pollution.
 How We are Affected by Noise Pollution
Noise pollution can severely damage physiological and psychological health. It can cause annoyance and aggression, hypertension, high stress levels, hearing loss, and other harmful effects depending on the level of sound.
Exposure to noise during pregnancy may increase the risk of high-frequency hearing loss in the newborn, shortened gestation, prematurity, and intrauterine growth retardation.
High noise levels may adversely affect animals, including their feeding behavior, breeding rituals and migration paths. Noise is responsible for the systematic reduction of usable wildlife habitat and the death of certain species of beached whales.
 What We Can Do To Help Prevent Noise Pollution
• Keep music volume down and windows closed
• Use manual lawnmowers instead of electric or gas powered ones.
• Commute by bike rather than a loud, polluting car.
• Keep the noise level at parties down.
• Especially don't make noise at night.
 Thermal Pollution
Thermal pollution is a temperature change in natural water bodies caused by human influence. The main cause of thermal pollution is the use of water as a coolant, especially in power plants. Water used as a coolant is returned to the natural environment at a higher temperature. Removing trees and vegetation that shade streams also cause thermal pollution.
Species living in water get accustomed to certain temperature. When the temperature rises, they move if they can, and those who can’t move, such as rooted plants and shellfish, die.
What are the Effects
Many industrial processes, mainly nuclear and power stations, produce heat and hot water which once rejected into the marine medium, has harmful effects on marine animal life. Hotter the rejected water is the more harmful effects it produces.
The greatest source of thermal loading is the steam-electric industry. Both fossil-fueled and nuclear-fueled plants use water as a coolant as because of its high specific heat; air will not function nearly as well.
Water temperature increase can adversely affect aquatic organisms by
(a) decreasing oxygen supply
(b) killing fish juveniles which are vulnerable to small increases in temperature
(c) affecting the composition of the ecosystem
Lowers Oxygen Levels
Thermal pollution decreases the dissolved oxygen level in the water which harms aquatic animals such as fish, amphibians and copepods. The metabolic rate of aquatic animals also increases with thermal pollution. As a result these organisms consume more food in a shorter period than in a normal environment. An increased metabolic rate may also cause shortage of food source, thereby drastically decreasing the population. Organisms may migrate due to change in environment to a more suitable environment. There are also possibilities of in-migration of organisms that normally only live in warmer waters in other areas.