What Are the Environmental Hazards of Automobile Exhaust?

[LeHazel]

Automobile exhaust contains 150 to 200 different compounds, among which the most harmful to humans are carbon monoxide, hydrocarbons, nitrogen oxides, lead compounds, and carbon particulate matter. These harmful gases diffuse into the air, causing air pollution. Automobile emissions account for 60% to 90% of urban air pollution. The smoke and dust in automobile exhaust contain the strong carcinogen benzo(a)pyrene. Automobile exhaust exacerbates the greenhouse effect: Automobile exhaust contributes to the occurrence of the greenhouse effect. The greenhouse effect originates from greenhouse gases, such as carbon dioxide, which absorb heat and allow sunlight to enter while preventing its reflection, thereby retaining heat and raising temperatures. Other greenhouse gases emitted by human activities and nature include chlorofluorocarbons (CFCs), methane, ground-level ozone, and nitrogen oxides. Many other trace gases also produce greenhouse effects, some of which are even stronger than carbon dioxide. For example, methane absorbs 21 times more heat per molecule than carbon dioxide, and nitrous oxide (N2O) absorbs 270 times more. The greenhouse effect is primarily caused by the excessive burning of coal, oil, and natural gas in modern industrial societies, which releases large amounts of greenhouse gases into the atmosphere. Automobile exhaust contributes to acid rain formation: Automobile exhaust promotes the formation of acid rain. Acid rain refers to precipitation with a pH below 5.6, including rain, snow, or other forms. During their formation and fall, rain and snow absorb and dissolve sulfur dioxide and nitrogen oxides from the air, forming acidic precipitation with a pH below 5.6. Acid rain is mainly caused by the large-scale emission of acidic substances into the atmosphere by human activities. In China, acid rain is primarily formed due to the extensive burning of high-sulfur coal, resulting mostly in sulfuric acid rain and, to a lesser extent, nitric acid rain. Additionally, exhaust emissions from various motor vehicles are a significant contributor to acid rain.