Thailand has ordered more than 400 schools in Bangkok to close for the rest of week due to toxic smog.<br />The Thai capital is experiencing some of its worst air pollution with harmful levels of ultra-fine dust particles.<br />The Air Quality Index, or AQI, is used by cities to determine levels of air pollution.<br />AQI levels under 25 are considered safe to breather. <br />The reading in Bangkok on Wednesday evening was 175.<br />The government has tried a slew of measures to try to clear the air.<br />These include sending water-spraying drones and hosing down streets, but they have all had little impact. <br />
