What Causes Excessive NO Emissions in Exhaust?

[LeWilliam]

Excessive NO emissions in exhaust can be attributed to the following reasons: 1. Incomplete combustion in the engine combustion chamber leading to an overly rich air-fuel mixture. 2. Accumulation of a large amount of carbon deposits in the intake system and engine combustion chamber. 3. Excessive combustion chamber temperature causing the exhaust emissions to exceed standards. More information about NO emissions is as follows: 1. NO emissions refer to nitrogen oxides, a type of brown, pungent-smelling exhaust gas that is produced in large quantities when the engine is under certain loads. 2. When the engine exhaust is first emitted, the NO present in the gas is less toxic, but it is easily oxidized into more toxic nitrogen oxides such as NO2. Once NOx enters the alveoli, it can form nitrous acid and nitric acid, causing severe irritation to lung tissue.

[DelCorey]

Regarding the issue of excessive NO in exhaust emissions, I usually pay more attention to car maintenance. Common causes include low engine combustion efficiency. For example, an imbalanced air-fuel ratio leads to a lean mixture, resulting in excess oxygen in the engine, which makes nitrogen oxides (NOx) more likely to exceed standards. When spark plugs are aged or severely carbon-fouled, ignition becomes unstable, combustion is incomplete, and emissions worsen. The three-way catalytic converter is a key component in controlling NOx. If it becomes clogged, fails, or wears out, its conversion function is significantly reduced. Another easily overlooked issue is when the oxygen sensor malfunctions, sending incorrect signals to the ECU, leading to improper adjustments. Additionally, frequent short-distance driving prevents the engine from reaching optimal operating temperature, reducing catalytic converter efficiency and increasing NOx emissions. Low-quality gasoline with high impurity levels can also exacerbate the problem. As vehicles age, components deteriorate, so regular inspections of these systems can prevent excessive emissions. Don’t wait until the annual inspection fails to take action—getting a test at a 4S shop is a safer approach.

[OTalia]

Last time I failed the annual inspection due to excessive NO emissions in the tailpipe test. The main reasons were poor vehicle maintenance - the air filter was clogged for almost a year without replacement, causing insufficient engine airflow and incorrect air-fuel mixture ratio. The catalytic converter, used for over six years, had aged and failed with poor conversion efficiency. The oxygen sensor's connector was loose, preventing the ECU from accurately determining air intake and leading to uncontrolled emissions. My bad driving habits also contributed - commuting with short trips of just a few minutes meant the engine never properly warmed up, resulting in higher NOx emissions. After replacing the filter and sensor, everything returned to normal. Low-quality fuel was another issue - using substandard gasoline worsened emissions. I advise car owners not to underestimate these factors. Regular maintenance of components and avoiding repeated short-trip cold starts can significantly reduce the risk of exceeding standards. Periodic self-checks or professional diagnostics are cost-effective solutions that provide peace of mind.

[SanElle]

Excessive NO emissions not only make vehicles fail to meet environmental standards but also pose health risks. High nitrogen oxide levels easily form smog particles, which irritate the respiratory system when inhaled. Engine design issues are the most common cause, as excessive combustion temperatures or too much oxygen increase NO production. A key reason is the aging or failure of the catalytic converter, which acts like an air purifier—its conversion efficiency drops as it deteriorates. Ignoring faulty sensors or improper air-fuel ratio adjustments worsens emissions. During short trips with cold engine starts, NO emissions rise significantly. Using low-quality gasoline accelerates pollutant buildup. Paying attention to these factors in daily driving ensures optimal vehicle performance. Regular maintenance can prevent excessive emissions, protecting both the environment and public health.