A System of Air Quality and Weather Forecasting and Research (SAFAR) study termed it as the "first good indicator" of the season and said a "sudden fall in influx of emissions" may explain the fall.
Gufran Beig, Chief Project Scientist of SAFAR, told PTI that PM 2.5, harmful microscopic particles that can penetrate deep into the lungs, have decreased "very significantly" in the last two-three days.
The average level of PM 2.5 has been 129 microgram per cubic metre of late, still "very poor", which at this time last year was 196 with not only the minimum temperature in the same range but also much lesser maximum temperature (16 degrees Celsius as opposed to last year's 24 degrees Celsius).
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PM 2.5 was at 96 micrograms per cubic metre at around 6 PM in Anand Vihar, one of the Delhi's majorly polluted spots. In areas such Punjabi Bagh and Mandir Marg, the corresponding figures were 83 and 22 around the same time.
The safe limits of PM 2.5 and PM 10 are 60 and 100 and anything beyond that poses threat to a healthy respiratory system. They have been consistently high, at times multiple times, in the capital, prompting the government to resort to a host of anti-pollution measures.
"The haze which has contribution of both fog and particulate matter reduces visibility faster and last longer which is not the case so far," he said.
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Hussain said 3,500 violators of waste burning norms were challaned last year while the number stood at 6,500 for construction works violations.