The oxygen content in car exhaust varies depending on the type of engine and its operating conditions. Typically, car exhaust from a gasoline engine contains about 0.5% to 2% oxygen. This percentage can change based on factors such as the air-fuel mixture, engine efficiency, and whether the vehicle is equipped with emissions control technologies like catalytic converters.

In more detail:

• Lean Burn Conditions: When the engine runs with excess air (lean mixture), the oxygen content can be higher, potentially up to 5% or more.
• Stoichiometric Conditions: Under ideal air-fuel mixture conditions (stoichiometric ratio), the oxygen content is typically around 1-2%.
• Rich Burn Conditions: When the engine runs with less air (rich mixture), the oxygen content is lower, sometimes close to 0%.

Diesel engines, which often operate with lean mixtures, can have higher oxygen content in their exhaust, typically ranging from 3% to 10%.

Emissions control systems, such as catalytic converters and oxygen sensors, help regulate and reduce harmful emissions, which can also impact the oxygen levels in the exhaust.

1. Carbon Monoxide (CO): A colorless, odorless gas that can cause harmful health effects by reducing the amount of oxygen that can be transported in the bloodstream to critical parts of the body.
2. Nitrogen Oxides (NOx): Gases that can irritate the respiratory system, aggravate lung diseases, and contribute to the formation of ground-level ozone and smog.
3. Particulate Matter (PM): Tiny particles that can penetrate deep into the lungs and even enter the bloodstream, causing cardiovascular and respiratory issues, including lung cancer.
4. Volatile Organic Compounds (VOCs): Organic chemicals that can cause respiratory, allergic, or immune effects and contribute to ground-level ozone formation.
5. Carbon Dioxide (CO2): A greenhouse gas that contributes to global warming and climate change.
6. Sulfur Dioxide (SO2): A gas that can cause acid rain, which can harm ecosystems, and respiratory problems.

Health Impacts

• Short-term Exposure: Can cause headaches, dizziness, eye irritation, and exacerbation of asthma and other respiratory conditions.
• Long-term Exposure: Can lead to chronic respiratory diseases, cardiovascular diseases, lung cancer, and adverse effects on the nervous system.

Environmental Impacts

• Air Pollution: Contributes to smog and ground-level ozone formation, which harm both human health and the environment.
• Acid Rain: Resulting from NOx and SO2 emissions, which can damage forests, soils, and aquatic ecosystems.
• Climate Change: CO2 and other greenhouse gases from car exhaust contribute significantly to global warming.

Efforts to mitigate these harms include the implementation of stricter emissions standards, the use of cleaner fuels, advancements in vehicle technology (such as electric and hybrid vehicles), and promoting public transportation and alternative modes of transport.