The use of methanol as a fuel can have a beneficial impact on exhaust emissions, although results vary by engine type and operating conditions.

In spark-ignition (SI) engines, blending methanol with gasoline generally leads to a reduction in regulated tailpipe emissions. According to a study from AMF Task 44, hydrocarbons (HC), carbon monoxide (CO), and methane emissions tend to decrease as the methanol content in the fuel increases. The same study noted this is often accompanied by a slight increase in nitrogen oxides (NO_x) and no significant change in carbon dioxide (CO₂). However, unregulated emissions, specifically formaldehyde and unburned methanol, typically increase, particularly during cold starts, as noted in the AMF Task 44 study and earlier works by Bromberg and Cheng (2010) and others. The AMF Task 44 report also found that methanol blends reduce emissions of key air toxics like benzene and 1,3-butadiene.

In compression-ignition (CI) engines, which require specialized concepts like dual-fuel systems or ignition enhancers, methanol is also seen as a promising way to reduce emissions. Its chemical structure, which lacks carbon-to-carbon bonds, means it fundamentally produces very low levels of soot and particulate matter (PM) compared to conventional diesel. By enabling advanced combustion strategies like Partially Premixed Combustion (PPC), methanol can also achieve very low NO_x formation while maintaining high engine efficiency, making it an attractive alternative fuel for heavy-duty and marine applications.