The Bangkok Metropolitan Administration (BMA) announced on 30 October that the permissible opacity of diesel vehicle emissions will be reduced from 30 per cent to 20 per cent, under a new standard formalised in the Royal Gazette, the official journal of the Thai government used to publish laws, regulations and official announcements for public information.
Officials said the rule targets soot and particulate matter released by older diesel engines, particularly those predating Euro 5 standards, which are among the city’s biggest sources of PM2.5 pollution.
PM2.5 pollution refers to fine airborne particles smaller than 2.5 micrometres that can penetrate deep into the lungs and bloodstream, posing serious health and environmental risks.
“This revision is intended to curb traffic-related pollution, a leading source of PM2.5 caused by incomplete fuel combustion,” the BMA’s Environment Department said in a statement. “Don’t let your vehicle exceed the smoke standard!”
Under the new regulation, vehicles emitting smoke above the 20 per cent threshold will be issued a “Temporary Ban on Use” sticker and ordered to make repairs within 30 days. Offenders also face fines of up to THB 4,000 (US$123). Vehicles that fail to comply or continue to violate the standard after re-inspection will be barred from use for 30 days.
The city government is urging motorists to service their engines regularly and follow basic maintenance routines – such as cleaning exhaust pipes, replacing oil and air filters, and calibrating fuel injectors – to meet the new standard.
The new measure follows a series of severe smog episodes earlier this year that forced the Thai capital to take emergency action.
In late January 2025, the BMA ordered the temporary closure of more than 350 schools and urged residents to work from home as PM2.5 concentrations reached hazardous levels. The city government also introduced free public transport to discourage private vehicle use and deployed street-spraying trucks to suppress dust particles.
At the time, Bangkok briefly ranked as the most polluted city in the world, according to global air-quality trackers, with fine-dust levels more than ten times the World Health Organization’s safe limit.
Public frustration over recurring smog crises and growing pressure on authorities to address vehicle emissions helped pave the way for the latest crackdown on diesel exhaust.
In Thailand, electric vehicles (EVs) now account for only a small share of the light-vehicle market, estimated at around 13 per cent of new car sales in 2024.
The government is offering a range of incentives to boost uptake, including excise-tax reductions, import-duty exemptions and cash subsidies under its EV3.0 and EV3.5 programmes – phased schemes that reward both EV buyers and automakers committed to local production. The latest phase extends support through 2027.
Officials say the stricter limits will complement other long-term measures, including efforts to expand public transport, promote electric vehicles and enforce industrial-emission standards more rigorously.
The stricter vehicle-emission rule also dovetails with Thailand’s broader climate ambitions.
The Thai government is finalising its first-ever Climate Change Act, which is expected to create a legal framework for greenhouse gas reduction, a national climate fund and mechanisms such as carbon trading and a future carbon tax.
The draft law supports Thailand’s pledge to reach carbon neutrality by 2050 and net zero emissions by 2065.
While the national legislation focuses on long-term climate targets, Bangkok’s diesel crackdown represents a tangible, immediate move to clean up urban air.
Officials said the 2025 deadline gives vehicle owners sufficient time to adjust, but enforcement will be strict once the rule takes effect.
