An air pollutant can be considered as a substance in the air that, in high enough concentrations, produces a detrimental environmental effect. Air pollutants can be either primary or secondary, depending on how they are formed. Primary pollutants are generated daily and are emitted directly from a source into the air. Examples of primary pollutants include: carbon monoxide, nitrogen dioxide, nitric oxide, sulfur dioxide, particulates and various hydrocarbons, also known as reactive organic compounds. The predominant source of air emissions can be generated by truck diesel emissions. Secondary pollutants are created over time and occur within the atmosphere as chemical and photochemical reactions take place. An example of a secondary pollutant is ozone, which is one of the products formed when reacting with hydrocarbons, in the presence of sunlight. Other secondary pollutants include photochemical aerosols. Secondary pollutants such as oxidants represent major air quality problems. Air pollutant called ozone can affect insects, animals, plants, and people that live in the troposphere. It is the layer where all weather occurs. Ozone occurs naturally at ground-level in low concentrations. The two major sources of natural ground-level ozone are hydrocarbons, which are released by plants and soil, and small amounts of stratospheric ozone, which occasionally migrate down to the earth's surface. Neither of these sources contributes enough ozone to be considered a threat to the health of humans or the environment. But the ozone that is a byproduct of certain human activities does become a problem at ground level and this is what we think of as bad ozone. With increasing populations, more automobiles, and more industry, there's more ozone in the lower atmosphere. Since 1900 the amount of ozone near the earth's surface has more than doubled. Unlike most other air pollutants, ozone is not directly emitted from any one source. Tropospheric ozone is formed by the interaction of sunlight, particularly ultraviolet light, with hydrocarbons and nitrogen oxides, which are emitted by automobiles, gasoline vapors, fossil fuel power plants, refineries, and certain other industries. Given the natural variability of the Earth’s climate, it is difficult to determine the extent of change that humans cause. In computer-based models, rising concentrations of greenhouse gases generally produce an increase in the average temperature of the Earth. Rising temperatures may, in turn, produce changes in weather, sea levels, and land use patterns, commonly referred to as climate change. Assessments generally suggest that the Earth’s climate has warmed over the past century and that human activity affecting the atmosphere is likely an important driving factor. A National Research Council study dated May 2001 stated, “Greenhouse gases are accumulating in Earth’s atmosphere as a result of human activities, causing surface air temperatures and sub-surface ocean temperatures to rise. Temperatures are, in fact, rising. The changes observed over the last several decades are likely mostly due to human activities, but we cannot rule out that some significant part of these changes is also a reflection of natural variability”(Wieman 2009). However, there is uncertainty in how the climate system varies naturally and reacts to emissions of greenhouse gases. Making progress in reducing uncertainties in projections of future climate will require better awareness and understanding of the buildup of greenhouse gases in the atmosphere and the behavior of the climate system. Greenhouse can make an effect in the Earth's atmosphere of animal’s habitats and food sources. The greenhouse effect is causes of global warming like volcanic eruptions, sunspots and burning fossil fuels. Many changes attributed to the greenhouse effect cause a ripple effect, with the impact starting on smaller species and eventually reaching larger species, like humans. A study found “a link between air pollution and increased deaths from cardiovascular and respiratory problems Humans are not the only living creatures affected by toxic air pollutants. Some toxins, like mercury, settle onto plants and into water sources that are then consumed by animals. The health effects of these poisons are then magnified up the food chain. Animals that are at the top of the food chain end up with the largest concentrations of toxins in their bodies” (Wieman 2009). Arsenic is a poisonous substance, which is released both from certain human activities and naturally from the Earth's crust. Humans may be exposed to arsenic mainly through food and water, particularly in certain areas where the groundwater is in contact with arsenic-containing minerals. Mercury is an element in the earth's crust. Humans cannot create or destroy mercury. Pure mercury is a liquid metal, sometimes referred to as quicksilver that volatizes readily. It has traditionally been used to make products like thermometers, switches, and some light bulbs. The effect of poor water quality on humans is waterborne diseases and sicknesses such as respiratory problems, diarrheal, gastroenteritis and cholera. Water pollution can cause heart problems and poor blood circulation, reduce fertility and increase in bone disorder damage to the kidneys. The increased incidence of skin disorders due to contact with pollutants, dangerous effects on growing fetus in pregnant women. It causes a weak immune system. The flora and fauna of the rivers and oceans, pollution will alter the acidity, temperature and conductivity of water. The last thing is tumors and ulcers due to nitrate pollution. These all cause an effect on humans and the environment.