Carbon dioxide (CO₂) is typically not considered a direct air pollutant in the traditional sense, as it does not have immediate harmful effects on human health at ambient concentrations. However, its role as a greenhouse gas makes it a major contributor to global climate change, which indirectly affects human health. High levels of CO₂ in indoor environments can cause discomfort, drowsiness, and reduced cognitive function. The primary health concerns associated with CO₂ are related to its impact on climate change, leading to increased heat waves, air pollution, spread of infectious diseases, and extreme weather events. These indirect effects pose significant risks to public health, emphasizing the need to control CO₂ emissions.

Oxides of nitrogen (NOx), particularly nitrogen dioxide (NO₂) and nitric oxide (NO), contribute to environmental degradation in several ways. They play a crucial role in the formation of ground-level ozone and smog, which negatively affect air quality and harm ecosystems. NOx emissions also lead to acid rain, which can damage forests, soils, and aquatic habitats. Additionally, they contribute to eutrophication in water bodies, leading to excessive growth of algae and depletion of oxygen, harming aquatic life. To reduce NOx emissions, measures such as implementing stricter vehicle emission standards, promoting the use of low-NOx burners in industrial processes, and increasing the use of renewable energy sources can be effective. These measures help in reducing the concentration of NOx in the atmosphere, mitigating its environmental impacts.

Catalytic converters are essential components in modern vehicles, designed to reduce harmful emissions of pollutants like carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx). They function by facilitating chemical reactions that convert these pollutants into less harmful substances. Inside the converter, exhaust gases pass over catalysts, typically platinum, palladium, and rhodium, which catalyze the oxidation of CO and HC into carbon dioxide (CO₂) and water (H₂O), and the reduction of NOx into nitrogen (N₂) and oxygen (O₂). This process significantly reduces the emission of these pollutants, contributing to improved air quality. However, the efficiency of catalytic converters can be compromised by engine malfunctions or the use of leaded petrol, which can poison the catalysts. Regular maintenance and the use of unleaded petrol are therefore essential to ensure the effective functioning of catalytic converters.

Particulate matter (PM), especially fine particles like PM2.5 (particles with a diameter of 2.5 micrometres or smaller), poses serious health risks. When inhaled, these fine particles can penetrate deep into the lungs and even enter the bloodstream, leading to respiratory and cardiovascular issues. Exposure to PM is linked to aggravated asthma, lung cancer, heart attacks, and premature death in people with heart or lung disease. To minimize exposure, individuals can reduce outdoor activities during high pollution days, use air purifiers indoors, and live in areas with lower traffic emissions. Governments and industries can contribute by enforcing stricter emissions standards, promoting cleaner transportation, and implementing policies to reduce industrial emissions. Reducing exposure to PM is vital for public health, particularly in urban areas with high levels of air pollution.

Methane (CH₄) is a potent greenhouse gas, approximately 25 times more effective than carbon dioxide (CO₂) in trapping heat in the Earth's atmosphere over a 100-year period. Its contribution to the greenhouse effect lies in its ability to absorb infrared radiation emitted from the Earth's surface, trapping heat in the atmosphere. This process exacerbates global warming, leading to a rise in global temperatures, melting of polar ice caps, and an increase in extreme weather events. The major sources of methane include agricultural practices, especially livestock farming, landfills, and the extraction of fossil fuels. Methane's high global warming potential, despite its lower concentration compared to CO₂, makes it a significant contributor to climate change. Reducing methane emissions is thus critical in mitigating global warming and its associated impacts on ecosystems, sea levels, and weather patterns.