Delhi has been enveloped in a haze of smog since Monday night, as air quality across most parts of the national capital deteriorated to ‘severe’ levels. On Thursday, the air quality index (AQI) at 7:30 am was recorded at 468, which was worse than Tuesday’s average AQI of 448. Experts warned that light speed winds, high moisture levels and a drop in temperature leading to shallow fog early morning ensured that the cloud of smog wouldn’t be entirely dispersed through the week. The choking cloud of smog brought back memories of similar conditions in November last year. Conditions improved a little by Saturday morning. Delhi’s smog led to the Indian Medical Association declaring a ‘public health emergency’. Here is what happened since Tuesday: The smog descendsDelhi woke up to a blanket of smog on Tuesday, as visibility fell to 900 metres. Monitoring stations across the national capital recorded air quality as “very poor” and experts warned that the conditions would persist through the week. According to the System of Air Quality and Weather Forecasting And Research (Safar), the levels of airborne particulate matter PM 10 was 289 micrograms per cubic metre (µg/m3) and PM 2.5 171 µg/m3 on Tuesday morning. The Central Pollution Control Board (CPCB) considers 100 µg/m3 for PM 10 and 60 µg/m3 for PM 2.5 the safe limit.Accidents, pileups, delaysThe cloud of thick smog persisted on Wednesday, as the hazy conditions and poor visibility lead to accidents and delays. Six people were injured when 13 vehicles were caught in a pile-up on the Yamuna Expressway in Greater Noida’s Dankaur area due to low visibility. Dense smog on National Highway-9, which connects Haryana and its neighbouring Punjab with the national capital, affected the schedule of long-distance trains and state roadways buses. A senior railway official said the schedule of nearly 120 trains has been affected while flights on the Chandigarh-Delhi route got delayed for 30 minutes to two-and-half hours. PTIDamaged vehicles at the accident site after 18 vehicles slammed into each other, due to poor visibiliy owing to dense smog at the Yamuna Expressway near Mathura . ‘Public health emergency’As the air quality index (AQI) – a measure of the level of pollutants in the air – shot past 400 in many places in Delhi on Tuesday, the Indian Medical Association (IMA) issued a stern warning on potential health hazards, describing Delhi as a “public health emergency state” and asking authorities to shut schools as a precautionary measure.Chief minister Arvind Kejriwal tweeted that Delhi had become a ‘gas chamber’ and requested education minister Manish Sisodia to ‘consider closing schools for a few days’. <blockquote class=”twitter-tweet” data-lang=”en”><p lang=”en” dir=”ltr”>Delhi has become a gas chamber. Every year this happens during this part of year. We have to find a soln to crop burning in adjoining states</p>&mdash; Arvind Kejriwal (@ArvindKejriwal) <a href=”https://twitter.com/ArvindKejriwal/status/927785134803136512?ref_src=twsrc%5Etfw”>November 7, 2017</a></blockquote><script async src=”https://platform.twitter.com/widgets.js” charset=”utf-8”></script>Schools closedThe Delhi government ordered all schools to be closed till Sunday in view of deteriorating air quality. Deputy chief minister Manish Sisodia said on Twitter that the order will apply to “all classes and all private and government schools will remain shut for the period”.Odd-even flip flopOn Thursday, the Arvind Kejriwal government announced the return of the odd-even plan from November 13 to 17 as a measure to curb alarming pollution levels. The National Green Tribunal, on Friday, put a brake on the Delhi government’s plans, calling the measure a “farce” and questioning the exemptions given to women and two-wheelers. “Odd-even won’t be implemented without a green signal from us. We are not stopping it yet. Hearing on Saturday,” the tribunal ordered.On Saturday, the NGT gave the go-ahead for the scheme, without any exemptions for women, two-wheelers and government servants. In an emergency meeting called at Kejriwal’s residence, the Delhi government decided to call off the odd-even plan. Delhi transport minister Kailash Gahlot said the government can’t conduct the drive without exemptions. Gahlot said that the government would go back to the NGT on Monday and file a review petition, asking the tribunal to reconsider their decision regarding exemptions. Other emergency measures As pollutions levels spiked, the Supreme Court-appointed Environment Pollution and Control Authority (Epca) ordered a four-time hike in parking fee and a cut in Metro fare during off-peak hours in a series of emergency measures. Announcing these measures, the Epca said the Capital was facing a “crisis situation”, which was likely to persist for the next few days. The parking fee hike came into effect on Thursday. Other measures included a temporary ban on civil construction and banning the entry of heavy and medium sized vehicles in Delhi, except for those carrying essential commodities, till further orders.