Cars: Air Polluters And Their Harmful Emissions

Cars are a significant contributor to air pollution and its associated health consequences. When cars burn gasoline, they emit pollutants such as nitrogen dioxide, carbon dioxide, hydrocarbons, and particulate matter. These emissions have been linked to climate change, environmental issues, and adverse effects on human health. The transportation sector, including cars, trucks, and buses, plays a major role in increasing greenhouse gas emissions. Electric vehicles and improved fuel efficiency offer potential solutions to reduce air pollution from cars. While it is challenging to determine the exact percentage of air pollution attributed to cars, their impact on air quality, particularly in urban areas with high traffic congestion, is significant.

Nitrogen Dioxide (NO2) and Nitrogen Oxides (NOx)

Nitrogen oxides (NOx) are formed when a car engine runs and causes combustion by heating up quickly. This process acts as a catalyst, binding nitrogen and oxygen to form nitric oxide (NO) or nitrogen dioxide (NO2). Both of these gases are described generically as nitrogen oxides (NOx) and are considered by-products of combustion.

In recent years, the negative effects of nitrogen oxides have been well documented, and car manufacturers have been working to reduce their presence in modern vehicles. This is because nitrogen oxides are harmful to human health. They contribute to the production of ozone and fine particulate matter less than 2.5 micrometres in size, called PM2.5. These are two of the most notorious pollutants that can impact human health. When hydrocarbons and NOx combine in sunlight, they produce ozone. While a layer of ozone in the upper atmosphere protects us from the sun's ultraviolet rays, ozone at ground level contributes to smog and causes respiratory problems.

NOx can also directly damage health. It irritates the lungs and weakens the body's defences against respiratory infections such as pneumonia and influenza. The World Health Organization has recognised the problem, concluding that NO2 is a direct hazard to health in its own right. The switch from petrol to diesel vehicles increases the toxicity of NOx discharges from exhaust pipes. When diesel is burned in an engine instead of petrol, more NOx is produced overall, and 70% of the NOx produced is NO2, compared with only 10-15% when petrol is burned.

The transportation sector is responsible for over 55% of NOx total emissions inventory in the US, and vehicles cause nearly 75% of carbon monoxide pollution in the country. Cars, trucks, buses, power plants, and off-road equipment like construction vehicles and boats produce at least half of the hydrocarbons and nitrogen oxides in typical urban areas. Diesel vehicles, in particular, have dominated the emission of NO2 from road vehicles.

To reduce NOx emissions, the Euro emissions standards were introduced in 1992, dictating the maximum number of emissions that a car can legally produce. Carpooling and switching to cleaner transport, such as electric cars and hybrid vehicles, can also help reduce NOx emissions.

Carbon Monoxide (CO)

CO is a significant contributor to air pollution, and its presence in the air can have detrimental effects on both the environment and human health. The Environmental Protection Agency estimates that vehicles cause nearly 75% of carbon monoxide pollution in the United States. This makes the transportation sector a major source of CO emissions.

When CO is inhaled, it blocks oxygen from reaching vital organs such as the brain and heart. Prolonged exposure to high levels of CO can lead to serious health issues, including carbon monoxide poisoning, which is well-documented in the literature. Certain occupations, such as indoor car wash facilities in shopping malls, expose workers to high levels of CO emissions from cars, putting them at risk of carbon monoxide poisoning.

To address this issue, electric cars, trucks, and other heavy-duty vehicles are being introduced to help reduce pollution from passenger vehicles. These zero-emission vehicles have the potential to eliminate tailpipe pollution entirely and promote the development of clean, renewable energy sources.

Additionally, it is important for individuals who work in close proximity to vehicles or combustion engines to be aware of the potential risks and take necessary precautions, such as using personal protective equipment like masks. By understanding the dangers of CO and taking preventive measures, we can help reduce the impact of this harmful pollutant on both the environment and human health.

Carbon Dioxide (CO2)

The average passenger vehicle emits about 400 grams of CO2 per mile, with each gallon of gasoline burned creating about 8,887 grams of CO2. Passenger cars are a major polluter, accounting for 61% of total CO2 emissions from road transport in the EU. In the United States, tailpipe emissions from cars, trucks, and buses account for over one-fifth of the country's total global warming pollution.

To reduce CO2 emissions from cars, two main strategies can be employed: improving vehicle efficiency and transitioning to alternative fuels or electric vehicles. The EU has introduced new CO2 emission targets, aiming for zero emissions from new passenger cars and light commercial vehicles by 2035. Electric vehicles are gaining popularity, with a significant increase in sales since 2017, and are proven to be cleaner than petrol-powered cars.

While electric cars are a step towards reducing carbon dioxide emissions, it is important to consider their entire life cycle. The production and disposal of electric vehicles can have a higher environmental impact than traditional cars with internal combustion engines. However, as the share of electricity generated from renewable sources increases, electric cars will become even more environmentally friendly.

Volatile Organic Compounds (VOCs)

Oxygenated volatile organic compounds (OVOCs) are a significant contributor to VOC emissions from vehicles, especially diesel vehicles, which have higher OVOC fractions in their total VOC emissions compared to gasoline vehicles. The large variability in VOC emissions under different engine activities or driving conditions makes it challenging to characterize vehicular emissions. However, studies have shown that emission factors of VOCs generally decrease with the improvement of emission standards, particularly for gasoline vehicles.

The concentration of VOCs inside vehicles is influenced by various factors, including vehicle model, driving speed, air exchange rate, temperature, and the types of substances with different boiling points inside the vehicles. For example, higher temperatures and exposure to direct sunlight can increase the interior temperature, causing the volatilization of various chemical substances from interior surfaces. Additionally, the use of air conditioning and the composition of cleaning products can affect VOC levels inside a vehicle.

The health risks associated with VOCs are significant. Ground-level ozone, formed by the reaction of VOCs with nitrogen oxides in the presence of sunlight, is a major component of smog. This gas irritates the respiratory system, causing coughing, choking, and reduced lung capacity. Exposure to VOCs can also weaken the body's defenses against respiratory infections such as pneumonia and influenza.

To address the issue of VOC emissions from vehicles, various technologies and strategies are being explored. These include the development of electric vehicles, the use of catalytic degradation to break down VOCs like benzene, and the design of environmentally friendly materials for adsorbing and removing VOCs like toluene.

Sulfur Dioxide (SO2)

SO2 emissions have detrimental effects on both human health and the environment. When released into the atmosphere, SO2 can react with other compounds to form small particles, contributing to particulate matter (PM) pollution. These fine particles can penetrate deeply into the lungs and, in sufficient quantities, can cause or exacerbate respiratory issues, particularly in children, the elderly, and individuals with pre-existing conditions. Additionally, SO2 and its derivatives can lead to the formation of acid rain, which damages trees, inhibits plant growth, and harms sensitive ecosystems and waterways.

Furthermore, SO2 emissions contribute to the formation of thick haze and smog, reducing visibility in many areas, including national parks and wilderness areas. The deposition of SO2 particles can also stain and damage stone and other materials, including culturally significant objects such as statues and monuments.

To mitigate the impact of SO2 pollution, regulatory bodies such as the Environmental Protection Agency (EPA) in the United States have implemented measures to reduce SO2 emissions. These efforts include establishing air quality standards and working with state and local governments to develop plans for improving air quality in areas that do not meet the established standards.

While cars are a significant source of SO2 emissions, it is important to recognize that other human activities also contribute to SO2 pollution. Power plants, industrial processes, and the burning of fuel for heating can all release SO2 into the atmosphere. Additionally, the transportation sector as a whole, including airplanes, trains, and ships, accounts for a significant portion of heat-trapping gas emissions.

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