Air Pollutants: Cars' Harmful Emissions

Cars, trucks, and buses are a significant source of air pollution, emitting a variety of harmful pollutants from their exhausts and through the evaporation of fuel. These pollutants include particulate matter (PM), volatile organic compounds (VOCs), nitrogen oxides, carbon monoxide, and toxic compounds such as benzene and formaldehyde. While newer vehicles tend to emit less pollution, the increasing number of automobiles and traffic congestion in urban areas contribute significantly to air pollution, particularly in communities of color and low-income areas, which are disproportionately exposed to higher pollution levels.

Nitrogen Oxides (NOx)

NOx consists of nitric oxide (NO) and nitrogen dioxide (NO2), which are the most relevant nitrogen oxides for air pollution. These gases play a crucial role in the formation of smog and acid rain. Additionally, they impact tropospheric ozone and contribute to various environmental issues, including climate change, water quality deterioration, air toxics, and particulate matter.

The production of NOx is not limited to human activities. Lightning is a natural source of NOx, and the amount produced depends on the season and geographic location. On average, each flash of lightning turns approximately 7 kilograms of nitrogen into chemically reactive NOx.

Agricultural practices, such as the use of nitrogen fertilizers and nitrogen-fixing plants, also contribute to atmospheric NOx levels. The nitrification process, which involves transforming ammonia into nitrate, plays a role in NOx emissions. Similarly, denitrification, the reverse process of nitrification, releases NOx into the atmosphere.

While individual car emissions may vary, the collective impact of millions of vehicles on the road significantly contributes to air pollution. It is important to recognize that newer vehicles generally emit fewer pollutants and consume less gasoline due to stricter emission standards and improved technology. However, the increasing number of automobiles and traffic congestion in urban areas continue to pose challenges in managing NOx emissions and air quality.

Carbon Monoxide (CO)

In mammalian physiology, carbon monoxide acts as a neurotransmitter (gasotransmitter) at low concentrations. However, at high concentrations, it is toxic and can lead to carbon monoxide poisoning, which is fatal in many cases. The acute effects of carbon monoxide poisoning are due to the formation of carboxyhemoglobin in the blood, which inhibits oxygen intake. Symptoms of carbon monoxide poisoning include headaches, dizziness, weakness, nausea, vomiting, chest pain, and confusion. These symptoms are often described as "flu-like".

Carbon monoxide is a significant air pollutant, with 56% of CO emissions in the United States attributed to on-road vehicles. This percentage increases to up to 95% in cities. The transportation sector's contribution to climate change is primarily through carbon dioxide (CO2) emissions, which are proportional to fuel consumption. However, CO is a more immediate health concern, as it can cause sudden illness and death if inhaled.

To prevent carbon monoxide poisoning, it is recommended to install battery-operated or battery backup CO detectors near sleeping areas. Additionally, it is important to regularly check the batteries and follow the manufacturer's instructions for replacement, which is generally recommended every 5 years. Taking these precautions can help reduce the risk of CO poisoning, which is a serious health hazard associated with the use of automobiles and other fuel-burning sources.

Particulate Matter (PM)

PM is a significant air pollutant, posing risks to both human health and the environment. Its adverse effects on human health have been well documented, particularly in urban areas. On-road vehicles are a major source of fine particulate matter (PM2.5) in cities. High levels of PM2.5 in the air have been linked to various health issues, including respiratory and cardiovascular problems. Studies have shown that air pollutant emissions from on-road vehicles contribute to hundreds of preventable PM2.5-attributable deaths, hospitalizations, and emergency department visits, with a disproportionate impact on high-poverty neighbourhoods.

The combustion of polluting fuels in vehicles contributes to the release of PM into the atmosphere. Incomplete combustion processes and the evaporation of fuel itself are major sources of air pollution from automobiles. Older vehicles tend to emit more pollution and use more gasoline due to the deterioration of emission control technology over time. Additionally, diesel vehicles are recognised emitters of PM.

The health risks associated with particulate matter are extensive. PM can penetrate deep into the lungs and enter the bloodstream, causing cardiovascular issues such as ischaemic heart disease and respiratory problems. It may also contribute to neurological issues by invading the brain via the olfactory route, leading to inflammation and oxidative stress. The inhalation of PM has been linked to impaired cognitive functions and an increased incidence of neurodegenerative diseases such as Alzheimer's.

Furthermore, PM has adverse effects beyond human health. It impacts visibility, soil quality, infrastructure, and climate. The solid fraction of PM, which includes black carbon and organic carbon, has been a particular focus for reduction efforts over the last two decades. Additionally, PM contributes to the formation of smog, which further reduces lung function, aggravates asthma, and increases the likelihood of respiratory illnesses.

Volatile Organic Compounds (VOCs)

VOCs are a significant contributor to air pollution, particularly in urban areas. According to the US Environmental Protection Agency (EPA), cars, buses, trucks, and other vehicles produce at least half of the hydrocarbons and nitrogen oxides in typical urban areas. The EPA also notes that newer vehicles generally emit less pollution and use less gasoline, while older vehicles tend to emit more pollution and consume more fuel.

The health effects of VOCs can vary. Most VOCs are not acutely toxic, but some may have long-term chronic health effects. Certain VOCs, such as benzene, are known or probable human carcinogens, while others can cause respiratory tract irritation, nausea, and headaches. VOCs are also known to have adverse effects on the development of animal fetuses.

To mitigate the impact of VOCs, various regulations and directives have been implemented. For example, the VOC Solvents Emissions Directive sets emission limit values, and the Paints Directive limits the use of organic solvents in decorative paints and varnishes. Additionally, the Occupational Safety and Health Administration (OSHA) regulates VOC exposure in the workplace, and the Pipeline and Hazardous Materials Safety Administration regulates the transportation of VOCs classified as hazardous materials.

In summary, volatile organic compounds (VOCs) are a significant contributor to air pollution, particularly from automobiles and other vehicles. They have various adverse health effects and are regulated by multiple organizations to minimize their impact on human health and the environment.

Lead

In the past, lead emissions came from motor vehicles and industrial sources, specifically from the combustion of fuel with lead. While the phasing out of leaded gasoline has significantly reduced lead emissions from cars, lead is still used in general-aviation gasoline for piston-engine aircraft.

Today, the automobile industry is the largest source of lead pollution. Lead is used in various car components, including lead wheel weights, solder in electronics, and lead-acid batteries. Over a car's lifetime, it releases approximately 16 pounds of lead into the environment through normal vehicle use, manufacturing, and disposal. Lead gets into the air and soil during the production and recycling of lead for car parts, particularly batteries.

The release of lead into the environment from automobiles poses significant health risks, especially to children and pregnant women. Lead exposure can cause behaviour and learning problems, lower IQ, hyperactivity, slowed growth, hearing issues, and anemia in children. For pregnant women, it can lead to reduced fetal growth and premature birth. Adults exposed to lead are at an increased risk of cardiovascular problems, high blood pressure, kidney dysfunction, and reproductive issues.

To mitigate lead pollution from automobiles, there have been calls for the automotive industry to phase out the use of lead in cars, particularly in starter batteries. Ensuring the proper management and recovery of lead used in automotive components is crucial for reducing lead pollution.

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