Unusually high levels of smog worsened by weather patterns have caused alarm across Asia.
Authorities in the Thai capital Bangkok are handing out face masks and stepping up enforcement of pollution controls.
A combination of construction dust, car exhaust and other pollutants lingering over the city due to prevailing weather patterns has taken air quality to unhealthy levels in recent days.
City officials are handing out some 10,000 face masks, spraying water to help settle dust and tightening controls on when big trucks can use the main streets.
The Thai Pollution Control Department said about half of the high levels of PM 2.5 – tiny particulate matter that can dangerously clog lungs – was due to diesel engine emissions.
In South Korea, unusually high PM 2.5 levels prompted emergency measures to reduce the health hazard.
The country’s National Institute of Environmental Research said the daily average of 120 micrograms per cubic metre was the worst since it began monitoring for PM 2.5 in 2015.
Over the years, South Korea has suffered repeated spells when silt and pollution-laden winds have swept over from northern China. Vehicle emissions are also a problem.
South Korea has been fighting an acute rise in air pollution that experts link to emissions from the country’s increasing number of cars and also to China’s massive industrial activity.
Thailand’s air pollution problem tends to wax and wane, partly depending on the season.
As in much of the rest of Asia, the burning of fields after harvests can cause severe smog at certain times of the year.
The spring smog has come early to Bangkok.
“There are a lot of factories and now that the pollution score is higher we have to be more careful,” said Oranart Phongpreecha, 55, a housewife who lives just outside of the city.
“It’s not that I get sick more often. But when I go outside, I have a sore throat and I can’t see clearly … I’m afraid that polluted air is going into my lungs so I have to protect myself.”
Pralong Dumrongthai, head of the Thai pollution control department, said long term solutions would include switching to electric vehicles and bringing in better quality petrol.
He said the weather patterns suggest Bangkok might be stuck with bad air for up to three months.
“I ask for public understanding when your vehicles are being checked, especially those that emit black smoke or big trucks,” he said. “We need your cooperation.”
Pollution generally is out of control by the time countries take action. India’s cities are among the world’s smoggiest and it is just starting to tackle the problem.
The Indian government has announced a five-year programme to cut air pollution by up to 30% from 2017 levels in the country’s 102 worst-affected cities.
Key targets include reducing the burning of field waste, firewood and charcoal, cleaning up thermal power and car emissions and heavily polluting brick production, as well as controlling dust from construction.
Critics say the plan lacks details on enforcement and funding.