<P> Low visibility has resulted in accidents across the city, notably a 24 vehicle pile - up on the Yamuna Expressway . </P> <P> "The Great Smog" also led to cancellation and delay of public transport, primarily trains and flights, causing much hindrance to the people . </P> <P> The current majority of analysis sources are hinting towards colder weather, stagnant winds trapping the various sources of smoke . The primary sources of smoke are stubble burning, lit garbage, road dust, power plants, factories, and vehicles . </P> <P> Air quality can be measured by the amount of PM 2.5 and PM 10 particulates suspended in air . On Nov 7, 2017 the PM 2.5 levels in Delhi shot up to 999, much above the recommended 60 micrograms . At the same time PM 10 shot to 999 (the maximum level for the monitors), instead of the recommended limit of 100 . </P>

Explain the causes for smog in new delhi
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