Automobile exhaust pollution: a moving environmental concern

With the continuous growth of the number of motor vehicles, automobile exhaust has become one of the main sources of urban air pollution. Tail gas contains harmful substances such as carbon monoxide (CO), nitrogen oxides (NOx), hydrocarbons (HC) and fine particulate matter (PM2.5). Carbon monoxide has a binding capacity with human hemoglobin that is 200 times that of oxygen, causing tissue hypoxia; nitrogen oxides cause photochemical smog under light, irritate the respiratory tract and induce asthma; particles with a diameter of less than 2.5 microns can directly penetrate the alveoli and enter the blood, increasing the risk of cardiovascular disease and lung cancer. These pollutants not only destroy the ecological balance, but also directly threaten human health. Tail gas treatment is urgent.
Multiple technologies: a governance system from source to end

1. Catalytic conversion technology: pollution elimination by chemical reaction

Catalytic conversion is currently the most widely used end-of-pipe treatment technology. The core device uses precious metals (platinum, palladium, rhodium) or non-precious metal catalysts to promote redox reactions of pollutants under high temperature conditions: carbon monoxide reacts with oxygen to produce carbon dioxide (2CO + O₂ → 2CO₂), nitrogen oxides react with carbon monoxide to produce nitrogen and carbon dioxide (2NO + 2CO → N₂ + 2CO₂), and hydrocarbons are oxidized to water and carbon dioxide (CxHy + (x+y/4) O₂ → xCO₂ + y/2H₂O). The three-way catalytic converter can treat three major pollutants at the same time, increasing the conversion rate to more than 90%, becoming a standard technology for gasoline vehicle exhaust treatment.
2. Exhaust Gas Recirculation System (EGR): Source Control of the Combustion Process
For the formation mechanism of nitrogen oxides (nitrogen reacts with oxygen in a high-temperature oxygen-rich environment), the exhaust gas recirculation system cools part of the exhaust gas and introduces it into the combustion chamber, reducing the combustion temperature (from more than 2000℃ to about 1600℃) and diluting the oxygen concentration, thereby inhibiting the formation of NOx from the source. This technology is particularly suitable for diesel engines. By adjusting the exhaust gas reflow ratio, nitrogen oxide emissions can be reduced by 30%-50% without significantly affecting the power performance.
3. Particle Capture Technology: Precise Purification by Physical Interception
For the black smoke emitted by diesel vehicles (mainly composed of soot particles), the particle collector (DPF) uses porous ceramic or metal fiber filters to intercept particles with a diameter greater than 0.1 microns like an "air filter". When the filter is clogged, the system temporarily increases the exhaust temperature (above 600°C) to burn particulate matter into carbon dioxide (C + O₂ → CO₂) to complete filter regeneration. This technology can remove more than 90% of visible particulate matter and effectively improve PM2.5 pollution in smog weather.
4. Fuel optimization and combustion improvement: the underlying innovation of clean power
In addition to end-of-pipe treatment, optimizing fuel quality and engine combustion efficiency is a more fundamental way to reduce emissions. High-purity fuel (such as National VI standard gasoline) reduces impurities such as sulfur and benzene, and reduces the generation of harmful substances; direct injection technology (GDI) can make combustion more complete by precisely controlling the fuel injection amount and atomization effect, and can reduce hydrocarbon emissions by 20%-30% compared to traditional intake manifold injection. The popularization of hybrid and electric technologies completely avoids exhaust emissions from the power source level, representing the ultimate emission reduction direction of the automotive industry.
Cooperative governance: technology iteration and policy escort
Automobile exhaust treatment is a complex system engineering, which requires the dual drive of technological innovation and policy supervision. Countries have forced automakers to upgrade their technology through strict emission standards (such as the EU's Euro 7 and China's National VI b), and at the same time, they have accelerated the reduction of pollution sources by eliminating old vehicles and subsidizing new energy. From the micro-control of chemical reactions to the macro-improvement of the atmospheric environment, every technological advancement is contributing to the goal of "carbon neutrality" - when the jumping molecules in the catalyst complete oxidation and reduction, and when the collector intercepts the last particle of carbon smoke, humans are using the power of science and technology to repair the rift between industrial civilization and natural ecology.