Night-time pollution level in Delhi

Delhi, the capital city of India and home to about 18 million people, recently took a brave move to curve its air pollution level. The city started a 15 days long pilot to test the effectiveness of the odd-even formula for the cars.  The move is to cut the pollution from vehicles The city has been in the news for the past 2 years as it tops the list of most polluted cities of the world according to a study by WHO.

The initiative will keep millions of cars off the road on any given day and the expectation is the reduction in pollution level in the Delhi City. The initiative has been greatly appreciated by air pollution experts but at the same time criticized due to various reasons. Delhi govt. making pollution measurements at various locations throughout the day to observe the impact. Its only about 2 days and govt., media and experts started discussing the success and failure of the scheme.

Here in the simple analysis, we are trying to show the complex the diurnal variability of fine particulate matter in Delhi city using measurements from past years.

Day and night time average PM2.5 mass concentration for the first five days of January for the years 2003, 2014 and 2015. All the years show night-time concentrations are higher than day-time. But, it is also important to note that reduction in day time pollution level will also reduce night time pollution.

Diurnal variations in fine particulate matter (PM2.5) in Delhi during Jan 1-5. The three series represents last three years of data as measured by US embassy in New Delhi. The simple analysis clearly shows that the diurnal cycle of PM2.5 over Delhi is highly variable over three different years. The one common observation among three years is higher night time concentration than day time. This is most likely due to the typical winter time boundary layer meteorology. During winter due to low inversion in the night time, most of pollution is trapped near the surface and during the day assun heats up the atmosphere, inversion breaks and pollution diluted due to vertical mixing. The huge variability in day-night is mostly controlled by meteorology but also depends on different day/night sources. Transport from surrounding regions do contribute significantly to the Delhi’s pollution and serious research efforts should be made to quantify it.